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Standard for Visual Inspection 1.1��Basic Requirements

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BS EN 970 - Non-destructive examination of fusion welds - Visual examination

Welding Inspection Personnel should:

be familiar with relevant standards, rules and specifications applicable to the fabrication work to be undertaken
be informed about the welding procedures to be used
have good vision (which should be checked every 12 months)

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Welding Inspection 1.2

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Conditions for Visual Inspection (to BS EN 970)

Illumination:

350 lux minimum required
(recommends 500 lux - normal shop or office lighting)

Vision Access:

eye should be within 600mm of the surface
viewing angle (line from eye to surface) to be not less than 30°

30°

600mm

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Welding Inspection 1.3

Aids to Visual Inspection (to BS EN 970)

When access is restricted may use:

a mirrored boroscope
a fibre optic viewing system

Other aids:

welding gauges (for checking bevel angles, weld profile, fillet sizing, undercut depth)
dedicated weld-gap gauges and linear misalignment (high-low) gauges
straight edges and measuring tapes
magnifying lens (if magnification lens used it should have magnification between X2 to X5)

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usually by agreement

}

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Welding Inspectors Equipment 1.3

Measuring devices:

flexible tape, steel rule
Temperature indicating crayons
Welding gauges
Voltmeter
Ammeter
Magnifying glass
Torch / flash light
Gas flow-meter

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Welding Inspectors Gauges 1.3

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TWI Multi-purpose Welding Gauge

Misalignment Gauges

Hi-Lo Gauge

Fillet Weld Gauges

G.A.L.

S.T.D.

10mm

12mm

16mm

3mm

6mm

9mm

5mm

4mm

G.A.L.

S.T.D.

10mm

12mm

16mm

3mm

6mm

9mm

5mm

4mm

1/4

1/2

3/4

1/2

HI-LO Single Purpose Welding Gauge

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Welding Inspectors Equipment 1.3

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Tong Tester

Ammeter

Voltmeter

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Welding Inspection 1.3

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Stages of Visual Inspection (to BS EN 970)

Extent of examination and when required should be defined in the application standard or by agreement between the contracting parties

For high integrity fabrications inspection required throughout the fabrication process:

Before welding

(Before assemble & After assembly)

During welding

After welding

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Typical Duties of a Welding Inspector 1.5

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Before Welding

Preparation:

Familiarisation with relevant ‘documents’…

Application Standard/Code - for visual acceptance requirements
Drawings - item details and positions/tolerances etc
Quality Control Procedures - for activities such as material handling, documentation control, storage & issue of welding consumables
Quality Plan/Inspection & Test Plan/Inspection Checklist - details of inspection requirements, inspection procedures & records required

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Typical Duties of a Welding Inspector 1.5

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Before Welding

Welding Procedures:

are applicable to joints to be welded & approved
are available to welders & inspectors

Welder Qualifications:

list of available qualified welders related to WPS’s
certificates are valid and ‘in-date’

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Typical Duties of a Welding Inspector 1.5

Before Welding

Equipment:

all inspection equipment is in good condition & calibrated as necessary
all safety requirements are understood & necessary equipment available

Materials:

can be identified & related to test certificates, traceability !
are of correct dimensions
are in suitable condition (no damage/contamination)

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Typical Duties of a Welding Inspector 1.5

Before Welding

Consumables:

in accordance with WPS’s
are being controlled in accordance with Procedure

Weld Preparations:

comply with WPS/drawing
free from defects & contamination

Welding Equipment:

in good order & calibrated as required by Procedure

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Typical Duties of a Welding Inspector 1.5

Before Welding

Fit-up

complies with WPS
Number / size of tack welds to Code / good workmanship

Pre-heat

if specified
minimum temperature complies with WPS

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Typical Duties of a Welding Inspector 1.5

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During Welding

Weather conditions

suitable if site / field welding

Welding Process(es)

in accordance with WPS

Welder

is approved to weld the joint

Pre-heat (if required)

minimum temperature as specified by WPS
maximum interpass temperature as WPS

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Typical Duties of a Welding Inspector 1.6

During Welding

Welding consumables

in accordance with WPS
in suitable condition
controlled issue and handling

Welding Parameters

current, voltage & travel speed – as WPS

Root runs

if possible, visually inspect root before single-sided welds are filled up

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Typical Duties of a Welding Inspector 1.6

During Welding

Inter-run cleaning

in accordance with an approved method (& back gouging) to good workmanship standard

Distortion control

welding is balanced & over-welding is avoided

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Typical Duties of a Welding Inspector 1.6

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After Welding

Weld Identification

identified/numbered as required
is marked with welder’s identity

Visual Inspection

ensure weld is suitable for all NDT
visually inspect & ‘sentence’ to Code requirements

Dimensional Survey

ensure dimensions comply with Code/drawing

Other NDT

ensure all NDT is completed & reports available

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Typical Duties of a Welding Inspector 1.6

After Welding

Repairs

monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed
PWHT
monitor for compliance with Procedure
check chart records confirm Procedure compliance

Pressure / Load Test

ensure test equipment is suitably calibrated
monitor to ensure compliance with Procedure
ensure all records are available

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Typical Duties of a Welding Inspector 1.6

After Welding

Documentation

ensure any modifications are on ‘as-built’ drawings
ensure all required documents are available
Collate / file documents for manufacturing records
Sign all documentation and forward it to QC department.

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Summary of Duties

A Welding Inspector must:

Observe

To observe all relevant actions related to weld quality throughout production.

Record

To record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections

Compare

To compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard

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It is the duty of a Welding Inspector to ensure all the welding and associated actions are carried out in accordance with the specification and any applicable procedures.

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Welding Inspector

Terms & Definitions

Section 2

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Welding Terminology & Definitions 2.1

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What is a Weld?

A localised coalescence of metals or non-metals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone (AWS)

A permanent union between materials caused by heat, and or pressure (BS499)

An Autogenous weld:

A weld made with out the use of a filler material and can only be made by TIG or Oxy-Gas Welding

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Welding Terminology & Definitions 2.1

What is a Joint?

The junction of members or the edges of members that are to be joined or have been joined (AWS)

A configuration of members (BS499)

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Joint Terminology 2.2

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Edge

Open & Closed Corner

Lap

Tee

Butt

Cruciform

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Welded Butt Joints 2.2

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A_________Welded butt joint

Butt

A_________Welded butt joint

Fillet

A____________Welded butt joint

Compound

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Welded Tee Joints 2.2

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A_________Welded T joint

Fillet

A_________Welded T joint

Butt

A____________Welded T joint

Compound

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Weld Terminology 2.3

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Compound weld

Fillet weld

Butt weld

Edge weld

Spot weld

Plug weld

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Butt Preparations – Sizes 2.4

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Full Penetration Butt Weld

Partial Penetration Butt Weld

Design Throat

Thickness

Design Throat

Thickness

Actual Throat

Thickness

Actual Throat

Thickness

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Weld Zone Terminology 2.5

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Weld Boundary

Heat Affected Zone

Root

Weld metal

A, B, C & D = Weld Toes

Face

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Weld Zone Terminology 2.5

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Excess Root Penetration

Excess

Cap height

or Weld Reinforcement

Weld cap width

Design Throat Thickness

Actual Throat Thickness

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Heat Affected Zone (HAZ) 2.5

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tempered zone

grain growth zone

recrystallised zone

partially transformed zone

Maximum Temperature

solid-liquid Boundary

solid weld metal

unaffected base

material

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Joint Preparation Terminology 2.7

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Included angle

Root Gap

Root Face

Angle of

bevel

Root Face

Root Gap

Included angle

Root

Radius

Single-V Butt

Single-U Butt

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Joint Preparation Terminology 2.8 & 2.9

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Root Gap

Root Face

Root Gap

Root

Radius

Single Bevel Butt

Single-J Butt

Angle of bevel

Land

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Single Sided Butt Preparations 2.10

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Single Bevel

Single Vee

Single-J

Single-U

Single sided preparations are normally made on thinner materials, or when access form both sides is restricted

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Double Sided Butt Preparations 2.11

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Double sided preparations are normally made on thicker materials, or when access form both sides is unrestricted

-Vee

Double

-Bevel

Double

- J

Double

- U

Double

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Weld Preparation

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Terminology & Typical Dimensions: V-Joints

bevel angle

root face

root gap

included angle

Typical Dimensions

bevel angle 30 to 35°

root face ~1.5 to ~2.5mm

root gap ~2 to ~4mm

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Butt Weld - Toe Blend

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6 mm

80°

Poor Weld Toe Blend Angle

Improved Weld Toe Blend Angle

20°

3 mm

Most codes quote the weld toes shall blend smoothly
This statement is not quantitative and therefore open to individual interpretation
The higher the toe blend angle the greater the amount of stress concentration
The toe blend angle ideally should be between 20^o-30^o

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Fillet Weld Features 2.13

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Design

Throat

Vertical

Leg Length

Horizontal leg Length

Excess

Weld Metal

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Fillet Weld Throat Thickness 2.13

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b = Actual Throat Thickness

a = Design Throat Thickness

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Deep Penetration Fillet Weld Features 2.13

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b = Actual Throat Thickness

a = Design Throat Thickness

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Fillet Weld Sizes 2.14

Calculating Throat Thickness from a known Leg Length:

Design Throat Thickness = Leg Length x 0.7

Question: The Leg length is 14mm.

What is the Design Throat?

Answer: 14mm x 0.7 = 10mm Throat Thickness

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Fillet Weld Sizes 2.14

Calculating Leg Length from a known Design Throat Thickness:

Leg Length = Design Throat Thickness x 1.4

Question: The Design Throat is 10mm.

What is the Leg length?

Answer: 10mm x 1.4 = 14mm Leg Length

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Features to Consider 2 2.14

Importance of Fillet Weld Leg Length Size

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Approximately the same weld volume in both Fillet Welds, but the effective throat thickness has been altered, reducing considerably the strength of weld B

2mm

(b)

4mm

8mm

(a)

4mm

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Fillet Weld Sizes 2.14

Importance of Fillet weld leg length Size

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Area = 4 x 4 = 8mm²

Area = 6 x 6 = 18mm²

The c.s.a. of (b) is over double the area of (a) without the extra excess weld metal being added

4mm

6mm

(a)

(b)

4mm

6mm

(a)

(b)

Excess

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Fillet Weld Profiles 2.15

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Mitre Fillet

Convex Fillet

Concave Fillet

A concave profile is preferred for joints subjected to fatigue loading

Fillet welds - Shape

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EFFECTIVE THROAT THICKNESS

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“s” = Effective throat thickness

“a” = Nominal throat thickness

Deep penetration fillet welds from high heat input welding process MAG, FCAW & SAW etc

Fillet Features to Consider 2.15

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Welding Positions 2.17

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PA	1G / 1F	Flat / Downhand
PB	2F	Horizontal-Vertical
PC	2G	Horizontal
PD	4F	Horizontal-Vertical (Overhead)
PE	4G	Overhead
PF	3G / 5G	Vertical-Up
PG	3G / 5G	Vertical-Down
H-L045	6G	Inclined Pipe (Upwards)
J-L045	6G	Inclined Pipe (Downwards)

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Welding Positions 2.17

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ISO

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Welding position designation 2.17

Butt welds in plate (see ISO 6947)

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Flat - PA

Overhead - PE

Vertical up - PF

Vertical down - PG

Horizontal - PC

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Welding position designation 2.17

Butt welds in pipe (see ISO 6947)

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Flat - PA

axis: horizontal pipe: rotated

H-L045

axis: inclined at 45° pipe: fixed

Horizontal - PC

axis: vertical pipe: fixed

Vertical up - PF

axis: horizontal pipe: fixed

Vertical down - PG

axis: horizontal pipe: fixed

J-L045

axis: inclined at 45° pipe: fixed

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Welding position designation 2.17

Fillet welds on plate (see ISO 6947)

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Flat - PA

Overhead - PD

Vertical up - PF

Vertical down - PG

Horizontal - PB

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Welding position designation 2.17

Fillet welds on pipe (see ISO 6947)

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Flat - PA axis: inclined at 45° pipe: rotated

Overhead - PD axis: vertical pipe: fixed

Vertical up - PF axis: horizontal pipe: fixed

Vertical down - PG axis: horizontal pipe: fixed

Horizontal - PB axis: vertical pipe: fixed

Horizontal - PB axis: horizontal pipe: rotated

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Plate/Fillet Weld Positions 2.17

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PA / 1G

PA / 1F

PC / 2G

PB / 2F

PD / 4F

PE / 4G

PG / 3G

PF / 3G

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Pipe Welding Positions 2.17

Weld: Flat

Pipe: rotated

Axis: Horizontal

PA / 1G

Weld: Vertical Downwards

Pipe: Fixed

Axis: Horizontal

PG / 5G

Weld: Vertical upwards

Pipe: Fixed

Axis: Horizontal

PF / 5G

Weld: Upwards

Pipe: Fixed

Axis: Inclined

Weld: Horizontal

Pipe: Fixed

Axis: Vertical

PC / 2G

45^o

Weld: Downwards

Pipe: Fixed

Axis: Inclined

J-LO 45 / 6G

45^o

H-LO 45 / 6G

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Travel Speed Measurement 2.18

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Definition: the rate of weld progression

measured in case of mechanised and automatic welding processes
in case of MMA can be determined using ROL and arc time

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Welding Inspector

Welding Imperfections

Section 3

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Welding Imperfections 3.1

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All welds have imperfections

Imperfections are classed as defects when they are of a type, or size, not allowed by the Acceptance Standard

A defect is an unacceptable imperfection

A weld imperfection may be allowed by one Acceptance Standard but be classed as a defect by another Standard and require removal/rectification

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Welding Imperfections 3.1

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Standards for Welding Imperfections

BS EN ISO 6520-1(1998) Welding and allied processes – Classification of geometric imperfections in metallic materials - Part 1: Fusion welding

Imperfections are classified into 6 groups, namely:

1 Cracks 2 Cavities 3 Solid inclusions 4 Lack of fusion and penetration 5 Imperfect shape and dimensions 6 Miscellaneous imperfections

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Welding Imperfections 3.1

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Standards for Welding Imperfections

EN ISO 5817 (2003) Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) - Quality levels for imperfections

This main imperfections given in EN ISO 6520-1 are listed in EN ISO 5817 with acceptance criteria at 3 levels, namely

Level B (highest)

Level C (intermediate)

Level D (general)

This Standard is ‘directly applicable to visual testing of welds’ ...(weld surfaces & macro examination)

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Welding imperfections 3.1�classification

Cracks

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Cracks 3.1

Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position.

Note: Cracks are classed as Planar Defects.

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Classified by Shape

Longitudinal
Transverse
Chevron
Lamellar Tear

Classified by Position

HAZ
Centerline
Crater
Fusion zone
Parent metal

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Cracks 3.1

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Longitudinal parent metal

Longitudinal weld metal

Lamellar tearing

Transverse weld metal

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Cracks 3.1

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Transverse crack

Longitudinal crack

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Cracks 3.2

Main Crack Types

Solidification Cracks
Hydrogen Induced Cracks
Lamellar Tearing
Reheat cracks

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Cracks 3.2

Solidification Cracking

Occurs during weld solidification process
Steels with high sulphur impurities content (low ductility at elevated temperature)
Requires high tensile stress
Occur longitudinally down centre of weld

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Cracks 3.3

Hydrogen Induced Cold Cracking

Requires susceptible hard grain structure, stress, low temperature and hydrogen
Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation
Hydrogen diffuses out into parent metal on cooling
Cracking developing most likely in HAZ

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Lamellar Tearing 3.5

Location: Parent metal
Steel Type: Any steel type possible
Susceptible Microstructure: Poor through thickness ductility
Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses
Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing
It forms when the welding stresses act in the short transverse direction of the material (through thickness direction)

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Gas Cavities 3.6

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Root piping

Cluster porosity

Gas pore

Blow hole

Herringbone porosity

Gas pore <1.5mm

Blow hole.>1.6mm

Causes:

Loss of gas shield
Damp electrodes
Contamination
Arc length too large
Damaged electrode flux
Moisture on parent material
Welding current too low

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Gas Cavities 3.7

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Root piping

Porosity

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Gas Cavities 3.8

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Cluster porosity

Herringbone porosity

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Crater pipe

Weld crater

Crater Pipe 3.9

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Crater pipe is a shrinkage defect and not a gas defect, it has the appearance of a gas pore in the weld crater

Causes:

Too fast a cooling rate
Deoxidization reactions and liquid to solid volume change
Contamination

Crater cracks

(Star cracks)

Crater pipe

Crater Pipe 3.9

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Solid Inclusions 3.10

Slag inclusions are defined as a non-metallic inclusion caused by some welding process

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Causes:

Slag originates from welding flux
MAG and TIG welding process produce silica inclusions
Slag is caused by inadequate cleaning
Other inclusions include tungsten and copper inclusions from the TIG and MAG welding process

Slag inclusions

Parallel slag lines

Lack of sidewall fusion with associated slag

Lack of interun fusion + slag

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Solid Inclusions 3.11

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Elongated slag lines

Interpass slag inclusions

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Welding Imperfections 3.13

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Typical Causes of Lack of Fusion:

welding current too low
bevel angle too steep
root face too large (single-sided weld)
root gap too small (single-sided weld)
incorrect electrode angle
linear misalignment
welding speed too high
welding process related – particularly dip-transfer GMAW
flooding the joint with too much weld metal (blocking Out)

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Lack of Fusion 3.13

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Incomplete filled groove + Lack of sidewall fusion

Lack of sidewall fusion
Lack of inter-run fusion

Causes:

Poor welder skill
Incorrect electrode manipulation
Arc blow
Incorrect welding current/voltage
Incorrect travel speed
Incorrect inter-run cleaning

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Lack of sidewall fusion + incomplete filled groove

Lack of Fusion 3.13

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Weld Root Imperfections 3.15

Lack of Root Fusion

Lack of Root Penetration

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Cap Undercut 3.18

Intermittent Cap Undercut

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Undercut 3.18

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Cap undercut

Root undercut

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Surface and Profile 3.19

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Incomplete filled groove

Poor cap profile

Excessive cap height

Poor cap profiles and excessive cap reinforcements may lead to stress concentration points at the weld toes and will also contribute to overall poor toe blend

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Surface and Profile 3.19

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Incomplete filled groove

Excess cap reinforcement

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Excessive root penetration

Weld Root Imperfections 3.20

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Overlap 3.21

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An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it

Causes:

Contamination
Slow travel speed
Incorrect welding technique
Current too low

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Overlap 3.21

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Toe Overlap

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Set-Up Irregularities 3.22

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Plate/pipe Linear Misalignment

(Hi-Lo)

Angular Misalignment

Linear misalignment is measured from the lowest plate to the highest point.

Angular misalignment is measured in degrees

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Set-Up Irregularities 3.22

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Linear Misalignment

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Set-Up Irregularities 3.22

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Linear Misalignment

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Lack of sidewall fusion + incomplete filled groove

Incomplete Groove 3.23

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Concave Root

Causes:

Excessive back purge pressure during TIG welding
Excessive root bead grinding before the application of the second pass
welding current too high for 2nd pass overhead welding
root gap too large - excessive ‘weaving’

A shallow groove, which may occur in the root of a butt weld

Weld Root Imperfections 3.24

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Concave Root

Weld Root Imperfections 3.24

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Weld Root Imperfections 3.24

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Concave root

Excess root penetration

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Causes:

High Amps/volts
Small Root face
Large Root Gap
Slow Travel Speed

Burn through

A localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run

Weld Root Imperfections 3.25

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Weld Root Imperfections 3.25

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Burn Through

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Causes:

Loss or insufficient back purging gas (TIG)
Most commonly occurs when welding stainless steels
Purging gases include argon, helium and occasionally nitrogen

Oxidized Root (Root Coking)

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Miscellaneous Imperfections 3.26

Arc strike

Causes:

Accidental striking of the arc onto the parent material
Faulty electrode holder
Poor cable insulation
Poor return lead clamping

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Miscellaneous Imperfections 3.27

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Causes:

Excessive current
Damp electrodes
Contamination
Incorrect wire feed speed when welding with the MAG welding process
Arc blow

Spatter

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Mechanical Damage 3.28

Mechanical damage can be defined as any surface material

damage cause during the manufacturing process.

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Grinding
Hammering
Chiselling
Chipping
Breaking off welded attachments (torn surfaces)
Using needle guns to compress weld capping runs

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Mechanical Damage 3.28

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Mechanical Damage/Grinding Mark

Chipping Marks

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Welding Inspector

Destructive Testing

Section 4

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Quantitative and Qualitative Tests 4.1

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Quantitative Tests:

For measuring a ‘quantity’ ( a mechanical property )

Mechanical tests - tensile test

- hardness test

- Charpy V-notch test (& CTOD)

Qualitative Tests:

For assessing joint ‘quality’ (good fusion & free from defects)

Qualitative tests - bend tests

- macro examination

- fillet fracture & nick-break tests

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Qualitative and Quantitative Tests 4.1

The following mechanical tests have units and are termed

quantitative tests to measure Mechanical Properties

Tensile tests (Transverse Welded Joint, All Weld Metal)
Toughness testing (Charpy, Izod, CTOD)
Hardness tests (Brinell, Rockwell, Vickers)

The following mechanical tests have no units and are termed

qualitative tests for assessing joint quality

Macro testing
Bend testing
Fillet weld fracture testing
Butt weld nick-break testing

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Mechanical Test Samples 4.1

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Tensile Specimens

Fracture Fillet

Specimen

CTOD Specimen

Charpy Specimen

Bend Test

Specimen

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Destructive Testing 4.1

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Typical Positions for Test Pieces

Specimen Type Position

Macro + Hardness 5
Transverse Tensile 2, 4
Bend Tests 2, 4
Charpy Impact Tests 3
Additional Tests 3

WELDING PROCEDURE QUALIFICATION TESTING

top of fixed pipe

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Definitions

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Malleability
Ductility
Toughness
Hardness
Tensile Strength

Ability of a material to withstand deformation under static compressive loading without rupture

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

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Definitions

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Malleability
Ductility
Toughness
Hardness
Tensile Strength

Ability of a material undergo plastic deformation under static tensile loading without rupture. Measurable elongation and reduction in cross section area

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

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Definitions

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Malleability
Ductility
Toughness
Hardness
Tensile Strength

Ability of a material to withstand bending or the application of shear stresses by impact loading without fracture.

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

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Definitions

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Malleability
Ductility
Toughness
Hardness
Tensile Strength

Measurement of a materials surface resistance to indentation from another material by static load

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

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Definitions

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Malleability
Ductility
Toughness
Hardness
Tensile Strength

Measurement of the maximum force required to fracture a materials bar of unit cross-sectional area in tension

Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

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Transverse Joint Tensile Test 4.2

Weld on plate

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Multiple cross joint specimens

Weld on pipe

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Tensile Test 4.3

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All-Weld Metal Tensile Specimen

Transverse Tensile Specimen

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STRA (Short Transverse Reduction Area)�For materials that may be subject to Lamellar Tearing�

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UTS Tensile test 4.4

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Charpy V-Notch Impact Test 4.5

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Objectives:

measuring impact strength in different weld joint areas
assessing resistance toward brittle fracture

Information to be supplied on the test report:

Material type
Notch type
Specimen size
Test temperature
Notch location
Impact Strength Value

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Ductile / Brittle Transition Curve 4.6

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- 50

- 20

- 10

- 40

- 30

Ductile fracture

Ductile/Brittle

transition point

47 Joules

28 Joules

Testing temperature - Degrees Centigrade

Temperature range

Transition range

Brittle fracture

Three specimens are normally tested at each temperature

Energy absorbed

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Comparison Charpy Impact Test Results 4.6

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Impact Energy Joules

Room Temperature

-20^oC Temperature

1. 197 Joules

2. 191 Joules

3. 186 Joules

1. 49 Joules

2. 53 Joules

3. 51 Joules

Average = 191 Joules

Average = 51 Joules

The test results show the specimens carried out at room temperature absorb more energy than the specimens carried out at -20^oC

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Charpy V-notch impact test specimen 4.7

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Specimen dimensions according ASTM E23

ASTM: American Society of Testing Materials

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Charpy V-Notch Impact Test 4.8

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Specimen

Pendulum

(striker)

Anvil (support)

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Charpy Impact Test 4.9

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10 mm

8 mm

2 mm

22.5^o

Machined notch

100% Ductile

Machined notch

Large reduction in area, shear lips

Fracture surface 100% bright crystalline brittle fracture

Randomly torn, dull gray fracture surface

100% Brittle

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Hardness Testing 4.10

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Definition

Measurement of resistance of a material against penetration of an indenter under a constant load
There is a direct correlation between UTS and hardness

Hardness tests:

Brinell
Vickers
Rockwell

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Hardness Testing 4.10

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Objectives:

measuring hardness in different areas of a welded joint
assessing resistance toward brittle fracture, cold cracking and corrosion sensitivity within a H₂S (Hydrogen Sulphide) environment.

Information to be supplied on the test report:

material type
location of indentation
type of hardness test and load applied on the indenter
hardness value

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Vickers Hardness Test 4.11

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Vickers hardness tests:

indentation body is a square based diamond pyramid (136º included angle)
the average diagonal (d) of the impression is converted to a hardness number from a table
it is measured in HV5, HV10 or HV025

Adjustable shutters

Indentation

Diamond indentor

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Vickers Hardness Test Machine 4.11

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Brinell Hardness Test 4.11

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Hardened steel ball of given diameter is subjected for a given time to a given load
Load divided by area of indentation gives Brinell hardness in kg/mm²
More suitable for on site hardness testing

30KN

Ø=10mm steel ball

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Rockwell Hardness Test

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1KN

Ø=1.6mm steel ball

Rockwell B

Rockwell C

1.5KN

120°Diamond Cone

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Hardness Testing 4.12

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Hardness Test Methods Typical Designations

Vickers 240 HV10

Rockwell Rc 22

Brinell 200 BHN-W

usually the hardest region

1.5 to 3mm

HAZ

fusion line or fusion boundary

Hardness specimens can also be used for CTOD samples

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Crack Tip Opening Displacement testing 4.12

Test is for fracture toughness
Square bar machined with a notch placed in the centre.
Tested below ambient temperature at a specified temperature.
Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch
Normally 3 samples

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Fatigue Fracture 4.13

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Location: Any stress concentration area

Steel Type: All steel types

Susceptible Microstructure: All grain structures

Test for Fracture Toughness is CTOD

(Crack Tip Opening Displacement)

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Fatigue Fracture 4.13

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Fatigue cracks occur under cyclic stress conditions
Fracture normally occurs at a change in section, notch and weld defects i.e stress concentration area
All materials are susceptible to fatigue cracking
Fatigue cracking starts at a specific point referred to as a initiation point
The fracture surface is smooth in appearance sometimes displaying beach markings
The final mode of failure may be brittle or ductile or a combination of both

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Fatigue Fracture

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Toe grinding, profile grinding.
The elimination of poor profiles
The elimination of partial penetration welds and weld defects
Operating conditions under the materials endurance limits
The elimination of notch effects e.g. mechanical damage cap/root undercut
The selection of the correct material for the service conditions of the component

Precautions against Fatigue Cracks

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Fatigue Fracture

Fatigue fracture occurs in structures subject to repeated application of tensile stress.

Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure).

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Fatigue Fracture

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Initiation points / weld defects

Fatigue fracture surface

smooth in appearance

Secondary mode of failure ductile fracture rough fibrous appearance

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Fatigue Fracture

Crack growth is slow
It initiate from stress concentration points
load is considerably below the design or yield stress level
The surface is smooth
The surface is bounded by a curve
Bands may sometimes be seen on the smooth surface –”beachmarks”. They show the progress of the crack front from the point of origin
The surface is 90° to the load
Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!)
Fatigue crack need initiation + propagation periods

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Fatigue fracture distinguish features:

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Bend Tests 4.15

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Object of test:

To determine the soundness of the weld zone. Bend testing can also be used to give an assessment of weld zone ductility.
There are three ways to perform a bend test:

Root bend

Face bend

Side bend

Side bend tests are normally carried out on welds over 12mm in thickness

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Bending test 4.16

Types of bend test for welds (acc. BS EN 910):

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Thickness of material - “t”

“t” up to 12 mm

“t” over 12 mm

Root / face bend

Side bend

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Fillet Weld Fracture Tests 4.17

Object of test:

To break open the joint through the weld to permit examination of the fracture surfaces
Specimens are cut to the required length
A saw cut approximately 2mm in depth is applied along the fillet welds length
Fracture is usually made by striking the specimen with a single hammer blow
Visual inspection for defects

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Fillet Weld Fracture Tests 4.17

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Fracture should break weld saw cut to root

2mm Notch

Hammer

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Fillet Weld Fracture Tests 4.17

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This fracture indicates lack of fusion

This fracture has occurred saw cut to root

Lack of Penetration

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Nick-Break Test 4.18

Object of test:

To permit evaluation of any weld defects across the fracture surface of a butt weld.
Specimens are cut transverse to the weld
A saw cut approximately 2mm in depth is applied along the welds root and cap
Fracture is usually made by striking the specimen with a single hammer blow
Visual inspection for defects

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Nick-Break Test 4.18

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Approximately 230 mm

19 mm

2 mm

Notch cut by hacksaw

Weld reinforcement may or may not be removed

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Nick Break Test 4.18

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Inclusions on fracture line

Lack of root penetration or fusion

Alternative nick-break test specimen, notch applied all way around the specimen

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We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint

We divide tests into Qualitative & Quantitative methods:

Qualitative: (Have no units/numbers)

For assessing joint quality

Macro tests

Bend tests

Fillet weld fracture tests

Butt Nick break tests

Quantitative: (Have units/numbers)

To measure mechanical properties

Hardness (VPN & BHN)

Toughness (Joules & ft.lbs)

Strength (N/mm² & PSI, MPa)

Ductility / Elongation (E%)

Summary of Mechanical Testing 4.19

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Welding Inspector

WPS – Welder Qualifications

Section 5

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Welding Procedure Qualification 5.1

Question:

What is the main reason for carrying out a Welding Procedure Qualification Test ?

(What is the test trying to show ?)

Answer:

To show that the welded joint has the properties* that satisfy the design requirements (fit for purpose)

* properties

mechanical properties are the main interest - always strength but toughness & hardness may be important for some applications
test also demonstrates that the weld can be made without defects

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Welding Procedures 5.1

Producing a welding procedure involves:

Planning the tasks
Collecting the data
Writing a procedure for use of for trial
Making a test welds
Evaluating the results
Approving the procedure
Preparing the documentation

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Welding Procedures 5.2

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In most codes reference is made to how the procedure are to

be devised and whether approval of these procedures is

required.

The approach used for procedure approval depends on the

code:

Example codes:

AWS D.1.1: Structural Steel Welding Code
BS 2633: Class 1 welding of Steel Pipe Work
API 1104: Welding of Pipelines
BS 4515: Welding of Pipelines over 7 Bar

Other codes may not specifically deal with the requirement of

a procedure but may contain information that may be used in

writing a weld procedure

EN 1011Process of Arc Welding Steels

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The welding engineer writes qualified Welding Procedure Specifications (WPS) for production welding

Welding Procedure Qualification 5.3

Production welding conditions must remain within the range of qualification allowed by the WPQR

(according to EN ISO 15614)

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Welding Procedure Qualification 5.3

(according to EN Standards)

welding conditions are called welding variables

welding variables are classified by the EN ISO Standard as:

Essential variables
Non-essential variables
Additional variables

Note: additional variables = ASME supplementary essential

The range of qualification for production welding is based on the limits that the EN ISO Standard specifies for essential variables*

(* and when applicable - the additional variables)

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Welding Procedure Qualification 5.3

(according to EN Standards)

WELDING ESSENTIAL VARIABLES

Question:

Why are some welding variables classified as essential ?

Answer:

A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the properties* of the joint

* particularly joint strength and ductility

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Welding Procedure Qualification 5.3

(according to EN Standards)

SOME TYPICAL ESSENTIAL VARIABLES

Welding Process
Post Weld Heat Treatment (PWHT)
Material Type
Electrode Type, Filler Wire Type (Classification)
Material Thickness
Polarity (AC, DC+ve / DC-ve)
Pre-Heat Temperature
Heat Input
Welding Position

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Welding Procedures 5.3

Components of a welding procedure

Parent material

Type (Grouping)
Thickness
Diameter (Pipes)
Surface condition)

Welding process

Type of process (MMA, MAG, TIG, SAW etc)
Equipment parameters
Amps, Volts, Travel speed

Welding Consumables

Type of consumable/diameter of consumable
Brand/classification
Heat treatments/ storage

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Welding Procedures 5.3

Components of a welding procedure

Joint design

Edge preparation
Root gap, root face
Jigging and tacking
Type of baking

Welding Position

Location, shop or site
Welding position e.g. 1G, 2G, 3G etc
Any weather precaution

Thermal heat treatments

Preheat, temps
Post weld heat treatments e.g. stress relieving

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Welding Procedures 5.3

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Object of a welding procedure test

To give maximum confidence that the welds mechanical and metallurgical properties meet the requirements of the applicable code/specification.

Each welding procedure will show a range to which the procedure is approved (extent of approval)

If a customer queries the approval evidence can be supplied to prove its validity

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Welding Procedures

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Summary of designations:

pWPS: Preliminary Welding Procedure Specification

(Before procedure approval)

WPAR (WPQR): Welding Procedure Approval Record

(Welding procedure Qualification record)

WPS: Welding Procedure Specification

(After procedure approval)

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Example:

Welding Procedure Specification (WPS)

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Welder Qualification 5.4

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Numerous codes and standards deal with welder qualification, e.g. BS EN 287.

Once the content of the procedure is approved the next stage is to approve the welders to the approved procedure.
A welders test know as a Welders Qualification Test (WQT).

Object of a welding qualification test:

To give maximum confidence that the welder meets the quality requirements of the approved procedure (WPS).
The test weld should be carried out on the same material and same conditions as for the production welds.

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Welder Qualification 5.4 & 5.5

(according to EN Standards)

Question:

What is the main reason for qualifying a welder ?

Answer:

To show that he has the skill to be able to make production welds that are free from defects

Note: when welding in accordance with a Qualified WPS

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The welder is allowed to make production welds within the range of qualification shown on the Certificate

The range of qualification allowed for production welding is based on the limits that the EN Standard specifies for the welder qualification essential variables

Welder Qualification 5.5

(according to EN 287 )

A Certificate may be withdrawn by the Employer if there is reason to doubt the ability of the welder, for example

a high repair rate
not working in accordance with a qualified WPS

The qualification shall remain valid for 2 years provided there is certified confirmation of welding to the WPS in that time.

A Welder’s Qualification Certificate automatically expires if the welder has not used the welding process for 6 months or longer.

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Welding Engineer writes a preliminary Welding Procedure Specification (pWPS) for each test weld to be made

A welder makes a test weld in accordance with the pWPS

A welding inspector records all the welding conditions used for the test weld (referred to as the ‘as-run’ conditions)

An Independent Examiner/ Examining Body/ Third Party inspector may be requested to monitor the qualification process

Welding Procedure Qualification 5.7

(according to EN ISO 15614)

The finished test weld is subjected to NDT in accordance with the methods specified by the EN ISO Standard - Visual, MT or PT & RT or UT

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Welding Procedure Qualification 5.7

Test weld is subjected to destructive testing (tensile, bend, macro)

The Application Standard, or Client, may require additional tests such as impact tests, hardness tests (and for some materials - corrosion tests)

(according to EN ISO 15614)

A Welding Procedure Qualification Record (WPQR) is prepared giving details of: -

The welding conditions used for the test weld
Results of the NDT
Results of the destructive tests
The welding conditions that the test weld allows for production welding

The Third Party may be requested to sign the WPQR as a true record

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Welder Qualification 5.9

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(according to EN 287 )

An approved WPS should be available covering the range of qualification required for the welder approval.

The welder qualifies in accordance with an approved WPS

A welding inspector monitors the welding to make sure that the welder uses the conditions specified by the WPS

EN Welding Standard states that an Independent Examiner, Examining Body or Third Party Inspector may be required to monitor the qualification process

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The finished test weld is subjected to NDT by the methods specified by the EN Standard - Visual, MT or PT & RT or UT

The test weld may need to be destructively tested - for certain materials and/or welding processes specified by the EN Standard or the Client Specification

Welder Qualification 5.9

(according to EN 287 )

A Welder’s Qualification Certificate is prepared showing the conditions used for the test weld and the range of qualification allowed by the EN Standard for production welding
The Qualification Certificate is usually endorsed by a Third Party Inspector as a true record of the test

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Welder Qualification 5.10

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Information that should be included on a welders test certificate are, which the welder should have or have access to a copy of !

Welders name and identification number
Date of test and expiry date of certificate
Standard/code e.g. BS EN 287
Test piece details
Welding process.
Welding parameters, amps, volts
Consumables, flux type and filler classification details
Sketch of run sequence
Welding positions
Joint configuration details
Material type qualified, pipe diameter etc
Test results, remarks
Test location and witnessed by
Extent (range) of approval

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Welder Qualification

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Tests methods required for welder qualification (BS EN 287)

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Welding Inspector

Materials Inspection

Section 6

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Material Inspection

One of the most important items to consider is Traceability.

The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client.

All materials arriving on site should be inspected for:

Size / dimensions
Condition
Type / specification

In addition other elements may need to be considered depending on the materials form or shape

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Pipe Inspection

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We inspect the condition (Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)

Specification

Welded seam

Size

LP5

Other checks may need to be made such as: distortion tolerance, number of plates and storage.

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Plate Inspection

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Size

We inspect the condition

(Corrosion, Mechanical damage, Laps, Bands & Laminations)

Specification

Other checks may need to be made such as: distortion tolerance, number of plates and storage.

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Parent Material Imperfections

Lamination

Mechanical damage

Lap

Segregation line

Laminations are caused in the parent plate by the steel making process, originating from ingot casting defects.

Segregation bands occur in the centre of the plate and are low melting point impurities such as sulphur and phosphorous.

Laps are caused during rolling when overlapping metal does not fuse to the base material.

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Lapping

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Lamination

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Laminations

Plate Lamination

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Welding Inspector

Codes & Standards

Section 7

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Codes & Standards

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The 3 agencies generally identified in a code or standard:

The customer, or client

The manufacturer, or contractor

The 3^rd party inspection, or clients representative

Codes often do not contain all relevant data, but may refer to other standards

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Standard/Codes/Specifications

STANDARDS

SPECIFICATIONS

CODES

Examples

plate, pipe

forgings, castings

valves

electrodes

Examples

pressure vessels

bridges

pipelines

tanks

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Welding Inspector

Welding Symbols

Section 8

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Weld symbols on drawings

Advantages of symbolic representation:

simple and quick plotting on the drawing
does not over-burden the drawing
no need for additional view
gives all necessary indications regarding the specific joint to be obtained

Disadvantages of symbolic representation:

used only for usual joints
requires training for properly understanding of symbols

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Weld symbols on drawings

The symbolic representation includes:

an arrow line
a reference line
an elementary symbol

The elementary symbol may be completed by:

a supplementary symbol
a means of showing dimensions
some complementary indications

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Dimensions

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In most standards the cross sectional dimensions are given to the left side of the symbol, and all linear dimensions are give on the right side

Convention of dimensions

a = Design throat thickness

s = Depth of Penetration, Throat thickness

z = Leg length (min material thickness)

BS EN ISO 22553

AWS A2.4

In a fillet weld, the size of the weld is the leg length
In a butt weld, the size of the weld is based on the depth of the joint preparation

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A method of transferring information from the design office to the workshop is:

The above information does not tell us much about the wishes of the designer. We obviously need some sort of code which would be understood by everyone.

Most countries have their own standards for symbols.

Some of them are AWS A2.4 & BS EN 22553 (ISO 2553)

Please weld here

Weld symbols on drawings

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Joints in drawings may be indicated:

by detailed sketches, showing every dimension

by symbolic representation

Weld symbols on drawings

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Elementary Welding Symbols

(BS EN ISO 22553 & AWS A2.4)

Convention of the elementary symbols:

Various categories of joints are characterised by an elementary symbol.

The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side.

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Square edge

butt weld

Weld type

Sketch

Symbol

Single-v

butt weld

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Elementary Welding Symbols

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Single-V butt weld with broad root face

Weld type

Sketch

Symbol

Single bevel butt weld

Single bevel butt weld with broad root face

Backing run

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Elementary Welding Symbols

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Single-U

butt weld

Weld type

Sketch

Symbol

Single-J

butt weld

Fillet weld

Surfacing

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ISO 2553 / BS EN 22553

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Plug weld

Resistance spot weld

Resistance seam weld

Square Butt weld

Steep flanked Single-V Butt

Surfacing

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Arrow Line

(BS EN ISO 22553 & AWS A2.4):

Convention of the arrow line:

Shall touch the joint intersection
Shall not be parallel to the drawing
Shall point towards a single plate preparation (when only one plate has preparation)

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(AWS A2.4)

Convention of the reference line:

Shall touch the arrow line

Shall be parallel to the bottom of the drawing

Reference Line

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Reference Line

(BS EN ISO 22553)

Convention of the reference line:

Shall touch the arrow line
Shall be parallel to the bottom of the drawing
There shall be a further broken identification line above or beneath the reference line (Not necessary where the weld is symmetrical!)

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(BS EN ISO 22553 & AWS A2.4)

Convention of the double side weld symbols:

Representation of welds done from both sides of the joint intersection, touched by the arrow head

Fillet weld

Double V

Double bevel

Double U

Double J

Double side weld symbols

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ISO 2553 / BS EN 22553

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Arrow line

Reference lines

Arrow side

Other side

Arrow side

Other side

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ISO 2553 / BS EN 22553

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Single-V Butt flush cap

Single-U Butt with sealing run

Single-V Butt with permanent backing strip

Single-U Butt with removable backing strip

M R

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ISO 2553 / BS EN 22553

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Single-bevel butt

Double-bevel butt

Single-bevel butt

Single-J butt

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ISO 2553 / BS EN 22553

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Partial penetration single-V butt

‘S’ indicates the depth of penetration

s10

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ISO 2553 / BS EN 22553

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a = Design throat thickness

s = Depth of Penetration, Throat thickness

z = Leg length(min material thickness)

a = (0.7 x z)

a 4

4mm Design throat

z 6

6mm leg

s 6

6mm Actual throat

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ISO 2553 / BS EN 22553

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Arrow side

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ISO 2553 / BS EN 22553

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Other side

6mm fillet weld

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ISO 2553 / BS EN 22553

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n = number of weld elements

l = length of each weld element

(e) = distance between each weld element

n x l (e)

Welds to be staggered

Process

2 x 40 (50)

3 x 40 (50)

111

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ISO 2553 / BS EN 22553

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3 x 80 (90)

All dimensions in mm

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ISO 2553 / BS EN 22553

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All dimensions in mm

3 x 80 (90)

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Supplementary symbols

Concave or Convex

Toes to be ground smoothly (BS EN only)

Site Weld

Weld all round

(BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbols

Supplementary information such as welding process, weld profile, NDT and any special instructions

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Supplementary symbols

Further supplementary information, such as WPS number, or NDT may be placed in the fish tail

Ground flush

111

Welding process numerical BS EN

Removable backing strip

Permanent backing strip

(BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbols

Supplementary information such as welding process, weld profile, NDT and any special instructions

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ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

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Convex

Mitre

Toes shall be blended

Concave

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ISO 2553 / BS EN 22553

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a = Design throat thickness

s = Depth of Penetration, Throat thickness

z = Leg length(min material thickness)

a = (0.7 x z)

a 4

4mm Design throat

z 6

6mm leg

s 6

6mm Actual throat

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ISO 2553 / BS EN 22553�Complimentary Symbols

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Field weld (site weld)

The component requires NDT inspection

WPS

Additional information, the reference document is included in the box

Welding to be carried out all round component (peripheral weld)

NDT

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ISO 2553 / BS EN 22553

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Numerical Values for Welding Processes:

111: MMA welding with covered electrode

121: Sub-arc welding with wire electrode

131: MIG welding with inert gas shield

135: MAG welding with non-inert gas shield

136: Flux core arc welding

141: TIG welding

311: Oxy-acetylene welding

72: Electro-slag welding

15: Plasma arc welding

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AWS A2.4 Welding Symbols

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AWS Welding Symbols

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(1-1/8)

60^o

1/8

Depth of Bevel

Effective Throat

Root Opening

Groove Angle

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AWS Welding Symbols

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(1-1/8)

60^o

1/8

GSFCAW

Welding Process

GMAW

GTAW

SAW

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AWS Welding Symbols

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3 – 10

Welds to be staggered

SMAW

Process

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AWS Welding Symbols

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(1-1/8)

60^o

1/8

FCAW

Sequence of Operations

1st Operation

2nd Operation

3rd Operation

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AWS Welding Symbols

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(1-1/8)

60^o

1/8

FCAW

Sequence of Operations

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AWS Welding Symbols

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Dimensions- Leg Length

6/8

6 leg on member A

Member A

Member B

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Welds “on arrow side” of joint go underneath the reference line while welds “the other side” of the joint, go on top of the reference line

Symbols with a vertical line component must be drawn with the vertical line to the left side of the symbol

All CSA dimensions are shown to the left of the symbol

All linear dimensions are shown on the right of the symbol i.e. number of welds, length of welds, length of any spaces

Included angle and root opening are shown on top of the symbol

AWS A 2.4 rules

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3 x 50 (70)

AWS A 2.4 rules-example

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5 x 8

Fillet weld dimensions according AWS A 2.4

Fillet welds

5 leg on vertical member

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Intermittent fillet welds

Chain intermittent fillet weld

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length (l)

pitch (e)

l - e

Symbol to AWS A2.4

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Intermittent fillet welds

Staggered intermittent fillet weld

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length (l)

pitch (e)

l - e

Symbol to AWS A2.4

e/2

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Welding Inspector

Intro To Welding Processes

Section 9

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Welding Processes

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Welding is regarded as a joining process in which the work pieces are in atomic contact

Pressure welding

Forge welding
Friction welding
Resistance Welding

Fusion welding

Oxy-acetylene
MMA (SMAW)
MIG/MAG (GMAW)
TIG (GTAW)
Sub-arc (SAW)
Electro-slag (ESW)
Laser Beam (LBW)
Electron-Beam (EBW)

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Welding Processes

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The four essential factors for fusion welding:

Fusion is achieved by melting using a high intensity heat source
The welding process must be capable of removing any oxide and contamination from the joint
Atmosphere contamination must be avoided
The welded joint must possess the mechanical properties required by the specification being adapted

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Process

Electrical characteristic

Electrode current type

MMA

Drooping / constant current

DC+ve, DC-ve, AC

TIG

Drooping / constant current

DC-ve, AC

MIG/MAG

Flat / constant voltage

DC+ve,

MAG FCAW

Flat / constant voltage

DC+ve, DC-ve,

Sub-arc

DC+ve, DC-ve, AC

Electro-slag

Flat / constant voltage

DC+ve,

Drooping / constant current >1000amp

Flat / constant voltage <1000amp

Welding Process Comparison

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130

140

120

100

180

160

200

100

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length)

Small amperage change resulting in virtually constant current e.g. + 5A.

Voltage

Amperage

Required for: MMA, TIG, Plasma arc and SAW > 1000 AMPS

O.C.V. Striking voltage (typical) for arc initiation

Constant Current Power Source� (Drooping Characteristic)

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage = large change in amperage

The self adjusting arc.

Large arc gap

Small arc gap

Large & momentary change in current due to arc gap

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Monitoring Heat Input

Heat Input:

The amount of heat generated in the

welding arc per unit length of weld.

Expressed in kilo Joules per millimetre

length of weld (kJ/mm).

Heat Input (kJ/mm)= Volts x Amps

Travel speed(mm/s) x 1000

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Monitoring Heat Input

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Weld and weld pool temperatures

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Monitoring Heat Input

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Monitoring Heat Input

Monitoring Heat Input As Required by
BS EN ISO 15614-1:2004
In accordance with EN 1011-1:1998

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When impact requirements and/or hardness requirements are specified, impact test shall be taken from the weld in the highest heat input position and hardness tests shall be taken from the weld in the lowest heat input position in order to qualify for all positions

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Welding Inspector

MMA Welding

Section 10

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Manual Metal Arc Introduction

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The MMA welding Process was first developed in the late 19^th century using bare wire consumables.

MMA is a simple process in terms of equipment
The process can by used in AC, DC+ or DC-
The process is a manual process and demands a high skill from the welder.
The process is widely used throughout the welding industry both for shop and site working conditions

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MMA - Principle of operation

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MMA welding

Main features:

Shielding provided by decomposition of flux covering
Electrode consumable
Manual process

Welder controls:

Arc length
Angle of electrode
Speed of travel
Amperage settings

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Manual Metal Arc Basic Equipment

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Power source

Holding oven

Inverter power source

Electrode holder

Power cables

Welding visor filter glass

Return lead

Electrodes

Electrode oven

Control panel (amps, volts)

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MMA Welding Plant

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Transformer:

Changes mains supply voltage to a voltage suitable for welding. Has no moving parts and is often termed static plant.

Rectifier:

Changes a.c. to d.c., can be mechanically or statically achieved.

Generator:

Produces welding current. The generator consists of an armature rotating in a magnetic field, the armature must be rotated at a constant speed either by a motor unit or, in the absence of electrical power, by an internal combustion engine.

Inverter:

An inverter changes d.c. to a.c. at a higher frequency.

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MMA Welding Variables

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Voltage

The arc voltage in the MMA process is measured as close to the arc as possible. It is variable with a change in arc length

O.C.V.

The open circuit voltage is the voltage required to initiate, or re-ignite the electrical arc and will change with the type of electrode being used e.g 70-90 volts

Current

The current used will be determined by the choice of electrode, electrode diameter and material type and thickness. Current has the most effect on penetration.

Polarity

Polarity is generally determined by operation and electrode type e.g DC +ve, DC –ve or AC

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MMA Welding Checks

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OCV open circuit volts

A check should be made to ensure that the equipment can produce the OCV required by the consumable and that any voltage selector has been moved to the correct position

Current & polarity

A check should be made to ensure the current type and range is as detailed on the WPS

Other variables

Checks should be made for correct electrode angle, arc gap and travel speed

Safety

Check should be made on the current carrying capacity, or duty cycle of the equipment and all electrical insulation is sound and in place. Correct extraction systems should be in use to avoid exposure to toxic fume.

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130

140

120

100

180

160

200

100

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length)

Small amperage change resulting in virtually constant current e.g. + 5A.

Voltage

Amperage

O.C.V. Striking voltage (typical) for arc initiation

Constant Current Power Source� (Drooping Characteristic)

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MMA welding parameters

Travel speed

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Travel speed

Too high

Too low

wide weld bead contour
lack of penetration
burn-through

lack of root fusion
incomplete root penetration
undercut
poor bead profile, difficult slag removal

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MMA welding parameters

Type of current:

voltage drop in welding cables is lower with AC
inductive looses can appear with AC if cables are coiled
cheaper power source for AC
no problems with arc blow with AC
DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications
welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties
DC provides a smoother metal transfer, less spatter

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MMA welding parameters

Welding current

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approx. 35 A/mm of diameter
governed by thickness, type of joint and welding position

Welding current

Too high

Too low

poor starting
slag inclusions
weld bead contour too high
lack of fusion/penetration

spatter
excess penetration
undercut
burn-through

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MMA welding parameters

Arc length = arc voltage

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Arc voltage

Too high

Too low

arc can be extinguished
“stubbing”

spatter
porosity
excess penetration
undercut
burn-through

Polarity: DCEP generally gives deeper penetration

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MMA - Troubleshooting

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MMA quality (left to right)

current, arc length and travel speed normal;

current too low;

current too high;

arc length too short;

arc length too long;

travel speed too slow;

travel speed too high

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MMA electrode holder

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Collet or twist type

“Tongs” type with spring-loaded jaws

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MMA Welding Consumables

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The three main electrode covering types used in MMA welding

Cellulosic - deep penetration/fusion
Rutile - general purpose
Basic - low hydrogen

(Covered in more detail in Section 14)

MMA Covered Electrodes

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Most welding defects in MMA are caused by a lack of welder skill (not an easily controlled process), the incorrect settings of the equipment, or the incorrect use, and treatment of electrodes

Typical Welding Defects:

Slag inclusions
Arc strikes
Porosity
Undercut
Shape defects (overlap, excessive root penetration, etc.)

MMA welding typical defects

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Manual Metal Arc Welding (MMA)

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Advantages:

Field or shop use
Range of consumables
All positions
Portable
Simple equipment

Disadvantages:

High welder skill required
High levels of fume
Hydrogen control (flux)
Stop/start problems
Comparatively uneconomic when compared with some other processes i.e MAG, SAW and FCAW

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Welding Inspector

TIG Welding

Section 11

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Tungsten Inert Gas Welding

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The TIG welding process was first developed in the USA during the 2^nd world war for the welding of aluminum alloys

The process uses a non-consumable tungsten electrode
The process requires a high level of welder skill
The process produces very high quality welds.
The TIG process is considered as a slow process compared to other arc welding processes
The arc may be initiated by a high frequency to avoid scratch starting, which could cause contamination of the tungsten and weld

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TIG - Principle of operation

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Tungsten Inert Gas Welding

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USA: GTAW

Gas Shield

Arc

Weld Pool

Ceramic Nozzle

Tungsten Electrode

Filler Wire

Contact Tube

Welding Torch

Current Conductor

Shielding gas

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TIG Welding Variables

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Gas type and flow rate

Generally two types of gases are used in TIG welding, argon and helium, though nitrogen may be considered for welding copper and hydrogen may be added for the welding of austenitic stainless steels.

The gas flow rate is also important.

Argon (Ar) Inert

Suitable for welding carbon steel,stainless steel, aluminium and magnesium
Lower cost, lower flow rates
More suitable for thinner materials and positional welding

Helium Argon mixes
Suitable for welding carbon steel, stainless steel, copper, aluminium and magnesium
High cost, high flow rates
More suitable for thicker materials and materials of high thermal conductivity.

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TIG Welding Variables

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Voltage

The voltage of the TIG welding process is variable only by the type of gas being used, and changes in the arc length

Current

The current is adjusted proportionally to the tungsten electrodes diameter being used. The higher the current the deeper the penetration and fusion

Polarity

The polarity used for steels is always DC –ve as most of the heat is concentrated at the +ve pole, this is required to keep the tungsten electrode at the cool end of the arc. When welding aluminium and its alloys AC current is used

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TIG power source

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Types of current

can be DCEN or DCEP
DCEN gives deep penetration

requires special power source
low frequency - up to 20 pulses/sec (thermal pulsing)
better weld pool control
weld pool partially solidifies between pulses

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Type of welding current

can be sine or square wave
requires a HF current (continuos or periodical)
provide cleaning action

Pulsed current

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Choosing the proper electrode

Current type influence

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Electrode capacity

Current type & polarity

Heat balance

Oxide cleaning action

Penetration

DCEN

DCEP

AC (balanced)

70% at work 30% at electrode

50% at work 50% at electrode

35% at work 65% at electrode

Deep, narrow

Medium

Shallow, wide

Yes - every half cycle

Yes

Excellent (e.g. 3,2 mm/400A)

Good (e.g. 3,2 mm/225A)

Poor (e.g. 6,4 mm/120A)

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Current/Amperage Characteristic

Large change in voltage = Smaller change in amperage

Welding Voltage

Large arc gap

Small arc gap

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TIG - arc initiation methods

simple method
tungsten electrode is in contact with the workpiece!
high initial arc current due to the short circuit
impractical to set arc length in advance
electrode should tap the workpiece - no scratch!
ineffective in case of AC
used when a high quality is not essential

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Arc initiation method

Lift arc

HF start

need a HF generator (spark-gap oscillator) that generates a high voltage AC output (radio frequency)  costly
reliable method  required on both DC (for start) and AC (to re-ignite the arc)
can be used remotely
HF produce interference
requires superior insulation

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Pulsed current

usually peak current is 2-10 times background current
useful on metals sensitive to high heat input
reduced distortions
in case of dissimilar thicknesses equal penetration can be achieved

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Time

Current (A)

Pulse time

Cycle time

Peak current

Background current

Average current

one set of variables can be used in all positions
used for bridging gaps in open root joints
require special power source

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Choosing the proper electrode

Polarity Influence – cathodic cleaning effect

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Tungsten Electrodes

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Old types: (Slightly Radioactive)

Thoriated: DC electrode -ve - steels and most metals
1% thoriated + tungsten for higher current values
2% thoriated for lower current values
Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

Cerium: DC electrode -ve - steels and most metals
Lanthanum: AC - Aluminum alloys and magnesium

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TIG torch set-up

Electrode extension

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Electrode extension

Stickout

2-3 times electrode diameter

Electrode extension

Low electron emission  Unstable arc

Too small

Overheating  Tungsten inclusions

Too large

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Choosing the correct electrode

Polarity Influence – cathodic cleaning effect

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Tungsten Electrodes

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Old types: (Slightly Radioactive)

Thoriated: DC electrode -ve - steels and most metals
1% thoriated + tungsten for higher current values
2% thoriated for lower current values
Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive)

Cerium: DC electrode -ve - steels and most metals
Lanthanum: AC - Aluminum alloys and magnesium

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Tungsten electrode types

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Pure tungsten electrodes:

colour code - green
no alloy additions
low current carrying capacity
maintains a clean balled end
can be used for AC welding of Al and Mg alloys
poor arc initiation and arc stability with AC compared with other electrode types
used on less critical applications
low cost

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Tungsten electrode types

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Thoriated tungsten electrodes:

colour code - yellow/red/violet
20% higher current carrying capacity compared to pure tungsten electrodes
longer life - greater resistance to contamination
thermionic - easy arc initiation, more stable arc
maintain a sharpened tip
recommended for DCEN, seldom used on AC (difficult to maintain a balled tip)
This slightly radioactive

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Tungsten electrode types

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Ceriated tungsten electrodes:

colour code - grey (orange acc. AWS A-5.12)
operate successfully with AC or DC
Ce not radioactive - replacement for thoriated types

Lanthaniated tungsten electrodes:

colour code - black/gold/blue
operating characteristics similar with ceriated electrode

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Tungsten electrode types

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Zirconiated tungsten electrodes:

colour code - brown/white
operating characteristics fall between those of pure and thoriated electrodes
retains a balled end during welding - good for AC welding
high resistance to contamination
preferred for radiographic quality welds

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Electrode tip for DCEN

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Electrode tip prepared for low current welding

Electrode tip prepared for high current welding

Vertex angle

Penetration increase

Increase

Bead width increase

Decrease

2-2,5 times electrode diameter

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Electrode tip for AC

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Electrode tip ground

Electrode tip ground and then conditioned

DC -ve

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TIG Welding Variables

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Tungsten electrodes

The electrode diameter, type and vertex angle are all critical factors considered as essential variables. The vertex angle is as shown

Vetex angle

Note: when welding aluminium with AC current, the tungsten end is chamfered and forms a ball end when welding

DC -ve

Note: too fine an angle will promote melting of the electrodes tip

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Choosing the proper electrode

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Unstable arc

Tungsten inclusions

Welding current

Electrode tip not properly heated

Excessive melting or volatilisation

Too low

Too high

Factors to be considered:

Penetration

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TIG Welding Gases

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Gas type and flow rate

Generally two types of gases are used in TIG welding, argon and helium, though nitrogen may be considered for welding copper and hydrogen may be added for the welding of austenitic stainless steels.

The gas flow rate is also important.

Argon (Ar) Inert

Suitable for welding carbon steel,stainless steel, aluminium and magnesium
Lower cost, lower flow rates
More suitable for thinner materials and positional welding

Helium Argon mixes
Suitable for welding carbon steel, stainless steel, copper, aluminium and magnesium
High cost, high flow rates
More suitable for thicker materials and materials of high thermal conductivity.

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Shielding gas requirements

Preflow and postflow

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Preflow

Postflow

Shielding gas flow

Welding current

Flow rate too low

Flow rate too high

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Special shielding methods

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Pipe root run shielding – Back Purging to prevent excessive oxidation during welding, normally argon.

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TIG torch set-up

Electrode extension

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Electrode extension

Stickout

2-3 times electrode diameter

Electrode extension

Low electron emission  Unstable arc

Too small

Overheating  Tungsten inclusions

Too large

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TIG Welding Consumables

Welding consumables for TIG:

Filler wires, Shielding gases, tungsten electrodes (non-consumable).
Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification
Steel Filler wires of very high quality, with copper coating to resist corrosion.
shielding gases mainly Argon and Helium, usually of highest purity (99.9%).

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Tungsten Inclusion

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A Tungsten Inclusion always shows up as

bright white on a radiograph

May be caused by Thermal Shock of heating to fast and small fragments break off and enter the weld pool, so a “slope up” device is normally fitted to prevent this could be caused by touch down also.

Most TIG sets these days have slope-up devices that brings the current to the set level over a short period of time so the tungsten is heated more slowly and gently

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Most welding defects with TIG are caused by a lack of welder skill, or incorrect setting of the equipment. i.e. current, torch manipulation, welding speed, gas flow rate, etc.

Tungsten inclusions (low skill or wrong vertex angle)
Surface porosity (loss of gas shield mainly on site)
Crater pipes (bad weld finish technique i.e. slope out)
Oxidation of S/S weld bead, or root by poor gas cover
Root concavity (excess purge pressure in pipe)
Lack of penetration/fusion (widely on root runs)

TIG typical defects

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Tungsten Inert Gas Welding

Advantages

High quality
Good control
All positions
Lowest H₂ process
Minimal cleaning
Autogenous welding

(No filler material)

Can be automated

Disadvantages

High skill factor required
Low deposition rate
Small consumable range
High protection required
Complex equipment
Low productivity
High ozone levels +HF

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Welding Inspector

MIG/MAG Welding

Section 12

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Gas Metal Arc Welding

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The MIG/MAG welding process was initially developed in the USA in the late 1940s for the welding of aluminum alloys.

The latest EN Welding Standards now refer the process by the American term GMAW (Gas Metal Arc Welding)

The process uses a continuously fed wire electrode
The weld pool is protected by a separately supplied shielding gas
The process is classified as a semi-automatic welding process but may be fully automated
The wire electrode can be either bare/solid wire or flux cored hollow wire

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MIG/MAG - Principle of operation

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Gas Metal Arc Welding

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Advantages

Disadvantages

High productivity
Easily automated
All positional (dip & pulse)
Material thickness

range

Continuous electrode
Wide range of application

Lack of fusion (dip)
Small range of consumables
Protection on site
Complex equipment
Not so portable

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MIG/MAG process variables

Welding current

Polarity

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Increasing welding current
Increase in depth and width
Increase in deposition rate

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MIG/MAG process variables

Arc voltage

Travel speed

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Increasing travel speed
Reduced penetration and width, undercut

Increasing arc voltage
Reduced penetration, increased width
Excessive voltage can cause porosity, spatter and undercut

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Shielding Gases:

The gasses used in MIG/MAG welding can be either 100% CO₂or Argon + CO₂mixes.

100% CO₂: Can not sustain true spray transfer, but gives very good penetration. The arc is unstable which produces a lot of spatter and a coarse weld profile.
Argon + CO₂ mixes: Argon can sustain spray transfer above 24 volts, and gives a very stable arc with a reduction in spatter. Argon being a cooler gas produces less penetration than CO₂. Argon in normally mixed with CO₂ at a mixture of between 5-25%

MAG Welding Variable Parameters

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Gas Metal Arc Welding

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Types of Shielding Gas

MIG (Metal Inert Gas)

Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni)
Most common inert gas is Argon
Argon + Helium used to give a ‘hotter’ arc - better for thicker joints and alloys with higher thermal conductivity

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MIG/MAG – shielding gases

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Type of material

Shielding gas

Carbon steel

Stainless steel

Aluminium

CO₂ , Ar+(5-20)%CO₂

Ar+2%O₂

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MIG/MAG shielding gases

Argon (Ar):

higher density than air; low thermal conductivity  the arc has a high energy inner cone; good wetting at the toes; low ionisation potential

Helium (He):

lower density than air; high thermal conductivity  uniformly distributed arc energy; parabolic profile; high ionisation potential

Carbon Dioxide (CO₂):

cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter

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Ar-He

CO₂

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MIG/MAG shielding gases

Gases for dip transfer:

CO₂: carbon steels only: deep penetration; fast welding speed; high spatter levels
Ar + up to 25% CO₂: carbon and low alloy steels: minimum spatter; good wetting and bead contour
90% He + 7.5% Ar + 2.5% CO₂:stainless steels: minimises undercut; small HAZ
Ar: Al, Mg, Cu, Ni and their alloys on thin sections
Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm)

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MIG/MAG shielding gases

Gases for spray transfer

Ar + (5-18)% CO₂: carbon steels: minimum spatter; good wetting and bead contour
Ar + 2% O₂: low alloy steels: minimise undercut; provides good toughness
Ar + 2% O₂ or CO₂: stainless steels: improved arc stability; provides good fusion
Ar: Al, Mg, Cu, Ni, Ti and their alloys
Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation
Ar + (25-30)% N₂: Cu alloys: greater heat input

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Gas Metal Arc Welding

Types of Shielding Gas

MAG (Metal Active Gas)

Active gases used are Oxygen and Carbon Dioxide
Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool
Typical active gases are

Ar + 20% CO₂ for C-Mn & low alloy steels

Ar + 2% O₂ for stainless steels

100% CO₂ can be used for C - steels

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MIG/MAG Gas Metal Arc Welding

Electrode orientation

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Penetration Deep Moderate Shallow

Excess weld metal Maximum Moderate Minimum

Undercut Severe Moderate Minimum

Electrode extension

Increased extension

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MIG / MAG - self-regulating arc

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Stable condition

Sudden change in gun position

19 mm

25 mm

L’

Arc length L = 6,4 mm

Arc voltage = 24V

Welding current = 250A

WFS = 6,4 m/min

Melt off rate = 6,4 m/min

Arc length L’ = 12,7 mm

Arc voltage = 29V

Welding current = 220A

WFS = 6,4 m/min

Melt off rate = 5,6 m/min

Current (A)

Voltage (V)

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MIG/MAG - self-regulating arc

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Sudden change in gun position

25 mm

L’

Arc length L’ = 12,7 mm

Arc voltage = 29V

Welding current = 220A

WFS = 6,4 m/min

Melt off rate = 5,6 m/min

Current (A)

Voltage (V)

Re-established stable condition

25 mm

Arc length L = 6,4 mm

Arc voltage = 24V

Welding current = 250A

WFS = 6,4 m/min

Melt off rate = 6,4 m/min

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Terminating the arc

Burnback time

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delayed current cut-off to prevent wire freeze in the weld end crater
depends on WFS (set as short as possible!)

Contact tip

Workpiece

Burnback time

0.05 sec

0.10 sec

0.15 sec

14 mm

8 mm

3 mm

Current - 250A

Voltage - 27V

WFS - 7,8 m/min

Wire diam. - 1,2 mm

Shielding gas - Ar+18%CO₂

Insulating slag

Crater fill

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MIG/MAG - metal transfer modes

Set-up for dip transfer

Set-up for spray transfer

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Electrode extension 19-25 mm

Contact tip recessed (3-5 mm)

Contact tip extension (0-3,2 mm)

Electrode extension 6-13 mm

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Gas Metal Arc Welding

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MODES OF METAL TRANSFER

The current and voltage settings determine the way molten droplets of weld metal transfer from the tip of the wire to the weld pool

There are 3 principle modes of droplet transfer, namely

dip transfer (short-circuiting)
spray transfer
pulsed transfer

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MIG/MAG - metal transfer modes

Current/voltage conditions

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Current

Voltage

Dip transfer

Spray transfer

Globular transfer

Electrode diameter = 1,2 mm

WFS = 3,2 m/min

Current = 145 A

Voltage = 18-20V

Electrode diameter = 1,2 mm

WFS = 8,3 m/min

Current = 295 A

Voltage = 28V

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Gas Metal Arc Welding

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Dip Transfer

Dip transfer occurs when current & voltage settings are low (typically < ~ 200amps & ~ 22volts)
There is just enough energy to give an arc and cause fusion at the tip of the wire
A droplet grows to a size larger than the wire diameter and eventually extinguishes the arc - causing a short-circuit
The short circuit causes the current rises very quickly giving energy to violently ‘pinch-off’ the droplet
This is akin to ‘blowing a fuse’ and causes spatter
When the droplet detaches, the arc is re-established and the current falls
This cycle occurs at up to ~ 200 times per second

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MIG/MAG-methods of metal transfer

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Dip transfer

Transfer occur due to short circuits between wire and weld pool, high level of spatter, need inductance control to limit current raise
Can use pure CO₂ or Ar- CO₂ mixtures as shielding gas
Metal transfer occur when arc is extinguished
Requires low welding current/arc voltage, a low heat input process. Resulting in low residual stress and distortion
Used for thin materials and all position welds

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Gas Metal Arc Welding

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Dip Transfer

Transfer-mode advantages

The low energy conditions allow welding in all positions
It can be used for putting in the root run on single-sided welds
It can be used for welding thin materials

Transfer-mode disadvantages

It frequently gives lack of fusion and may not be allowed in semi-automatic mode for high-integrity applications
It tends to give spatter (this can be reduced/controlled by having an ‘inductance’ control on the power source)

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Gas Metal Arc Welding

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Spray Transfer

When current & voltage are raised together higher energy is available for fusion (typically > ~ 25 volts & ~ 250 amps)

This causes a fine droplets of weld metal to be ‘sprayed’ from the tip of the wire into the weld pool

Transfer-mode advantages

High energy gives good fusion
High rates of weld metal deposition are given
These characteristics make it suitable for welding thicker joints
Transfer-mode disadvantages
It cannot be used for positional welding

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MIG/MAG-methods of metal transfer

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Spray transfer

Transfer occur due to pinch effect NO contact between wire and weld pool!
Requires argon-rich shielding gas
Metal transfer occur in small droplets, a large volume weld pool
Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion
Used for thick materials and flat/horizontal position welds

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MIG/MAG-methods of metal transfer

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Pulsed transfer

Controlled metal transfer, one droplet per pulse,
No transfer between droplet and weld pool!
Requires special power sources
Metal transfer occur in small droplets (diameter equal to that of electrode)
Requires moderate welding current/arc voltage, a reduced heat input . Resulting in smaller residual stress and distortion compared to spray transfer
Pulse frequency controls the volume of weld pool, used for root runs and out of position welds

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MIG/MAG - metal transfer modes

Pulsed transfer

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Controlled metal transfer. one droplet per pulse. NO transfer during background current!
Requires special power sources
Metal transfer occur in small droplets (diameter equal to that of electrode)

Requires moderate welding current/arc voltage, reduced heat input’ smaller residual stress and distortions compared to spray transfer
Pulse frequency controls the volume of weld pool, used for root runs and out of position welds

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Gas Metal Arc Welding

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Pulsed Transfer

Transfer-mode advantages

Good fusion
Small weld pool allows all-position welding

Transfer-mode disadvantages

More complex & expensive power source
Difficult to set parameters - requires power source manufacturer to provide pulse programmes to suit wire type, dia. and type of gas

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MIG/MAG-methods of metal transfer

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Globular transfer

Transfer occur due to gravity or short circuits between drops and weld pool
Requires CO₂ shielding gas
Metal transfer occur in large drops (diameter larger than that of electrode) hence severe spatter
Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion
Non desired mode of transfer!

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Dip Transfer: (Voltage < 22) / (Amperage < 200)

Thin materials positional welding

Globular Transfer: Between Dip & Spray Transfer

Limited commercial, Used only in some mechanized MAG process using CO₂shielding gas

Spray Transfer: (Voltage > 27) / (Amperage > 220)

Thicker materials, limited to flat welding positions, high deposition

Pulse Transfer: Both spray and dip transfer in

one mode of operation, frequency range 50-300 pulses/second
Positional welding and root runs

Gas Metal Arc Welding

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Inductance:

Applicable to MIG/MAG process in dip transfer mode.
The electrode is fed slowly through the arc until it touches the weld pool, at this point the output from the power supply is short circuited and a very high current flows through the electrode. If this was allowed to continue, the wire would melt and eject excessive amounts of spatter.
The inclusion or the choke in the welding circuit controls the rate at which the current rises so that the electrode tip is melted uniformly without excessive spatter

MAG Welding Variable Parameters

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The effect of inductance

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Maximum inductance

Minimum inductance

Hotter arc, more penetration
reduced spatter
More fluid weld pool, flatter and smoother weld
Recommended on thicker materials and stainless steels

Colder arc, used only for arc stability when welding wide gaps
Convex weld, more spatter
Improved weld pool control
Recommended on thin materials

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage = large change in amperage

The self adjusting arc.

Large arc gap

Small arc gap

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O.C.V. Arc Voltage Virtually no Change.

Voltage

Flat or Constant Voltage Characteristic Used With

MIG/MAG, ESW & SAW < 1000 amps

100

200

300

Large Current Change

Small Voltage Change.

Amperage

Flat or Constant Voltage Characteristic

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MIG/MAG welding gun assembly

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Contact tip

Gas diffuser

Handle

Gas nozzle

Trigger

WFS remote control potentiometer

Union nut

The Push-Pull gun

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Wire feed speed:

Increasing the wire feed speed automatically increases the current in the wire

Voltage:

The voltage is the most important setting in the spray transfer mode, as it controls the arc length. In dip transfer it controls the rise in current

Current:

The current is automatically increased as the wire feed is increased. Current mainly affects penetration

MAG Welding Variable Parameters

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Gas Metal Arc Welding

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PROCESS CHARACTERISTICS

Requires a constant voltage power source, gas supply, wire feeder, welding torch/gun and ‘hose package’
Wire is fed continuously through the conduit and is burnt-off at a rate that maintains a constant arc length/arc voltage
Wire feed speed is directly related to burn-off rate
Wire burn-off rate is directly related to current
When the welder holds the welding gun the process is said to be a semi-automatic process
The process can be mechanised and also automated
In Europe the process is usually called MIG or MAG

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Gas Metal Arc Welding

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Types of Filler Wire

Filler wires have similar composition to the base material
Wires can be solid, flux cored or metal cored
Flux cored wires are designed to run in spray mode and therefore they give good fusion
Flux cored wires cannot be used for root runs on unbacked joints
The slag formed from flux cored wire enables welding to be done in all-positions
Most flux cored wires have a folded seam that can allow moisture to get into the flux
Controlled storage & handling is required for ‘seamed’ wires
Metal cored wires have the same general characteristics as solid wires - they can be operated in dip or spray mode
Some flux cored wires do not require a gas shield (Innershield)

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The welding equipment

A visual check should be made on the equipment to ensure it is in good working order

The electrodes

The diameter, specification and the quality of the wire are essential for inspection. The level of deoxidisation in the wire, single, double or triple de-oxidised. The quality of the wire winding and the copper coating should also be inspected to minimize wire feed problems.

Checks when MAG Welding

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Wire liner

Check that the liner is the correct type and size for the wire being used. Steel liners for steel and Teflon liners for aluminium.

Contact tips

Check the tip is the correct size for the wire being used and check the amount of wear. Excessive wear will affect wire speed and electrical current pick-up

Gas and gas flow-rates

Type of gas and the flow rate need to be checked to ensure they comply with the WPS

Other welding variables

Check WFS, amps, volts and travel speed

Checks when MAG Welding

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Most welding imperfections in MIG/MAG are caused by lack of welder skill, or incorrect settings of the equipment

Worn contact tips will cause poor power pick up, or transfer
Bad power connections will cause a loss of voltage in the arc
Silica inclusions (in Fe steels) due to poor inter-run cleaning
Lack of fusion (primarily with dip transfer)
Porosity (from loss of gas shield on site etc)
Solidification problems (cracking, centerline pipes, crater pipes) especially on deep narrow welds

MIG/MAG typical defects

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WELDING PROCESS

Flux Core Arc Welding

(Not In The Training Manual)

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Flux cored arc welding

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FCAW methods

With gas shielding - “Outershield”

Without gas shielding - “Innershield”

With metal powder - “Metal core”

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“Outershield” - principle of operation

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“Innershield” - principle of operation

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage = large change in amperage

The self adjusting arc.

Large arc gap

Small arc gap

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Insulated extension nozzle

Current carrying guild tube

Flux cored hollow wire

Flux powder

Arc shield composed of vaporized and slag forming compounds

Metal droplets covered with thin slag coating

Molten weld pool

Solidified weld metal and slag

Flux core

Wire joint

Flux core wires

Flux Core Arc Welding (FCAW)

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Flux cored arc welding

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FCAW methods

With gas shielding - “Outershield”

Without gas shielding - “Innershield” (114)

With metal powder - “Metal core”

With active gas shielding (136)

With inert gas shielding (137)

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FCAW - differences from MIG/MAG

usually operates in DCEP but some “Innershield” wires operates in DCEN
power sources need to be more powerful due to the higher currents
doesn't work in deep transfer mode
require knurled feed rolls

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“Innershield” wires use a different type of welding gun

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Backhand (“drag”) technique

Advantages

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preferred method for flat or horizontal position
slower progression of the weld
deeper penetration
weld stays hot longer, easy to remove dissolved gasses

Disadvantages

produce a higher weld profile
difficult to follow the weld joint
can lead to burn-through on thin sheet plates

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Forehand (“push”) technique

Advantages

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preferred method for vertical up or overhead position
arc is directed towards the unwelded joint , preheat effect
easy to follow the weld joint and control the penetration

Disadvantages

produce a low weld profile, with coarser ripples
fast weld progression, shallower depth of penetration
the amount of spatter can increase

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FCAW advantages

less sensitive to lack of fusion
requires smaller included angle compared to MMA
high productivity
all positional
smooth bead surface, less danger of undercut
basic types produce excellent toughness properties
good control of the weld pool in positional welding especially with rutile wires
seamless wires have no torsional strain, twist free
ease of varying the alloying constituents
no need for shielding gas

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FCAW disadvantages

limited to steels and Ni-base alloys
slag covering must be removed
FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels)
for gas shielded process, the gaseous shield may be affected by winds and drafts
more smoke and fumes are generated compared with MIG/MAG
in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire)

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Advantages:

1) Field or shop use

2) High productivity

3) All positional

4) Slag supports and shapes the weld Bead

5) No need for shielding gas

Disadvantages:

1) High skill factor

2) Slag inclusions

3) Cored wire is Expensive

4) High level of fume (Inner-shield)

5) Limited to steels and nickel alloys

FCAW advantages/disadvantages

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Welding Inspector

Submerged Arc Welding

Section 13

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Submerged arc welding was developed in the Soviet Union during the 2^nd world war for the welding of thick section steel.
The process is normally mechanized.
The process uses amps in the range of 100 to over 2000, which gives a very high current density in the wire producing deep penetration and high dilution welds.
A flux is supplied separately via a flux hopper in the form of either fused or agglomerated.
The arc is not visible as it is submerged beneath the flux layer and no eye protection is required.

Submerged Arc Welding Introduction

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SAW Principle of operation

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Principles of operation

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Factors that determine whether to use SAW chemical composition and mechanical properties required for the weld deposit

thickness of base metal to be welded
joint accessibility
position in which the weld is to be made
frequency or volume of welding to be performed

SAW methods

Semiautomatic

Mechanised

Automatic

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Submerged Arc Welding

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Power supply

Filler wire spool

Flux hopper

Wire electrode

Flux

Slide rail

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SAW process variables

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welding current
current type and polarity
welding voltage
travel speed
electrode size
electrode extension
width and depth of the layer of flux

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SAW process variables

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Welding current

controls depth of penetration and the amount of base metal melted & dilution

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SAW operating variables

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Current type and polarity

Usually DCEP, deep penetration, better resistance to porosity
DCEN increase deposition rate but reduce penetration (surfacing)
AC used to avoid arc blow; can give unstable arc

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SAW Consumables�(Covered in detail in Section 14)

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Fused fluxes advantages:

good chemical homogeneity
easy removal of fines without affecting flux composition
normally not hygroscopic & easy storage and handling
readily recycled without significant change in particle size or composition

Fused fluxes disadvantages:

difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss)
high temperatures needed to melt ingredients limit the range of flux compositions

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SAW Consumables

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Agglomerated fluxes advantages:

easy addition of deoxidizers and alloying elements
usable with thicker layer of flux when welding
colour identification

Agglomerated fluxes disadvantages:

tendency to absorb moisture
possible gas evolution from the molten slag leading to porosity
possible change in flux composition due to segregation or removal of fine mesh particles

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SAW equipment

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Power sources can be:

transformers for AC
transformer-rectifiers for DC

Static characteristic can be:

Constant Voltage (flat) - most of the power sources
Constant Current (drooping)

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SAW equipment

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Constant Voltage (Flat Characteristic) power sources:

most commonly used supplies for SAW
can be used for both semiautomatic and automatic welding
self-regulating arc
simple wire feed speed control
wire feed speed controls the current and power supply controls the voltage
applications for DC are limited to 1000A due to severe arc blow (also thin wires!)

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ARC CHARACTERISTICS

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Volts

Amps

OCV

Constant Voltage Characteristic

Small change in voltage = large change in amperage

The self adjusting arc.

Large arc gap

Small arc gap

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SAW equipment

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Constant Current (Drooping Characteristic) power sources:

Over 1000A - very fast speed required - control of burn off rate and stick out length
can be used for both semiautomatic and automatic welding
not self-regulating arc
must be used with a voltage-sensing variable wire feed speed control
more expensive due to more complex wire feed speed control
arc voltage depends upon wire feed speed whilst the power source controls the current
cannot be used for high-speed welding of thin steel

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SAW equipment

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Welding heads can be mounted on a:

Tractor type carriage

provides travel along straight or gently curved joints
can ride on tracks set up along the joint (with grooved wheels) or on the workpiece itself
can use guide wheels as tracking device
due to their portability, are used in field welding or where the piece cannot be moved

Courtesy of ESAB AB

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SAW operating variables

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Welding current

too high current: excessive excess weld metal (waste of electrode), increase weld shrinkage and causes greater distortions
excessively high current: digging arc, undercut, burn through; also a high and narrow bead & solidification cracking

too low current: incomplete fusion or inadequate penetration
excessively low current: unstable arc

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SAW operating variables

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Welding voltage

welding voltage controls arc length

an increased voltage can increase pick-up of alloying elements from an alloy flux

increase in voltage produce a flatter and wider bead
increase in voltage increase flux consumption
increase in voltage tend to reduce porosity
an increased voltage may help bridging an excessive root gap

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SAW operating variables

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Welding voltage

low voltage produce a “stiffer” arc & improves penetration in a deep weld groove and resists arc blow

excessive low voltage produce a high narrow bead & difficult slag removal

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SAW operating variables

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Welding voltage

excessively high voltage produce a “hat-shaped” bead & tendency to crack

excessively high voltage increase undercut & make slag removal difficult in groove welds

excessively high voltage produce a concave fillet weld that is subject to cracking

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SAW operating variables

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Travel speed

increase in travel speed: decrease heat input & less filler metal applied per unit of length, less excess weld metal & weld bead becomes smaller

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SAW operating variables

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Travel speed

excessively high speed lead to undercut, arc blow and porosity

excessively low speed produce “hat-shaped” beads  danger of cracking

excessively low speed produce rough beads and lead to slag inclusions

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SAW operating variables

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Electrode size

at the same current, small electrodes have higher current density & higher deposition rates

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SAW operating variables

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Electrode extension

increased electrode extension adds resistance in the welding circuit I increase in deposition rate, decrease in penetration and bead width

to keep a proper weld shape, when electrode extension is increased, voltage must also be increased
when burn-through is a problem (e.g. thin gauge), increase electrode extension
excessive electrode extension: it is more difficult to maintain the electrode tip in the correct position

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SAW operating variables

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Depth of flux

depth of flux layer influence the appearance of weld
usually, depth of flux is 25-30 mm
if flux layer is to deep the arc is too confined, result is a rough ropelike appearing weld
if flux layer is to deep the gases cannot escape & the surface of molten weld metal becomes irregularly distorted
if flux layer is too shallow, flashing and spattering will occur, give a poor appearance and porous weld

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SAW

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SAW

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SAW

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SAW technological variables

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Travel angle effect - Butt weld on plates

Penetration Deep Moderate Shallow

Excess weld metal Maximum Moderate Minimum

Tendency to undercut Severe Moderate Minimum

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SAW technological variables

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Earth position

Direction of travel

welding towards earth produces backward arc blow
deep penetration
convex weld profile

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SAW technological variables

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Earth position

Direction of travel

welding away earth produces forward arc blow
normal penetration depth
smooth, even weld profile

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Weld backing

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Backing strip

Backing weld

Copper backing

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Starting/finishing the weld

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SAW variants

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Twin wire SAW welding

two electrodes are feed into the same weld pool
wire diameter usually 1,6 to 3,2 mm
electrodes are connected to a single power source & a single arc is established
normally operate with DCEP
offers increased deposition rate by up to 80% compared to single wire SAW

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SAW variants

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Wires can be oriented for maximum or minimum penetration

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SAW variants

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Tandem arc SAW process

usually DCEP on lead and AC on trail to reduce arc blow
requires two separate power sources
the electrodes are active in the same puddle BUT there are 2 separate arcs
increased deposition rate by up to 100% compared with single wire SAW

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SAW variants

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SAW tandem arc with two wires

Courtesy of ESAB AB

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SAW variants

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Single pool - highest deposition rate

Twin pool - travel speed limited by undercut; very resistant to porosity and cracks

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SAW variants

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Tandem arc SAW process - multiple wires

only for welding thick sections (>30 mm)
not suitable for use in narrow weld preparations (root passes)
one 4 mm wire at 600 A, 6.8 kg/hr
tandem two 4 mm wires at 600 A, 13.6 kg/hr

Courtesy of ESAB AB

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SAW variants

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Strip cladding needs a

special welding head

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SAW variants

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Narrow gap welding

for welding thick materials
less filler metal required
requires special groove preparation and special welding head
requires special fluxes, otherwise problems with slag removal
defect removal is very difficult

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SAW variants

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Cold wire welding

the cold wire is not connected to power source
increase deposition rates up to 75%
high deposition rate at fixed heat input results in lower penetration!

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SAW variants

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Hot wire welding

the hot wire is connected to power source & much more efficient than cold wire (current is used entirely to heat the wire!)

increase deposition rates up to 100%
requires additional welding equipment, additional control of variables, considerable set-up time and closer operator attention

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SAW variants

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SAW with metal powder addition

increased deposition rates up to 70%; increased welding speed
gives smooth fusion, improved bead appearance, reduced penetration and dilution from parent metal & higher impact strength
metal powders can modify chemical composition of final weld deposit
does not increase risk of cracking
do not require additional arc energy
metal powder can be added ahead or directly into the weld pool

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SAW variants

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SAW with metal powder addition

magnetic attachment of powder

SAW with metal cored wires

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SAW variants

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Storage tank SAW of circular welds

Courtesy of ESAB AB

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Submerged arc welds are difficult to predict as the weld is made up of three elements. The dilution may be as much as 60% resulting in a high susceptibility to solidification cracking

Submerged Arc Welding Process (SAW)

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Advantages of SAW

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high current density, high deposition rates (up to 10 times those for MMA), high productivity
deep penetration allowing the use of small welding grooves
fast travel speed, less distortion
deslagging is easier
uniform bead appearance with good surface finish and good fatigue properties
can be easily performed mechanised, giving a higher duty cycle and low skill level required
provide consistent quality when performed automatic or mechanised
Virtually assured radiographically sound welds
arc is not visible
little smoke/fumes are developed

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Disadvantages of SAW

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limited mainly between flat and horizontal positions
limited to carbon, low alloy, creep resisting, stainless steels and nickel alloys
due to the high heat input, impact strength of weld metal/HAZ may be low; also high dilution
slag must be cleared away after welding due to the danger of slag inclusions
need flux storage, handling and recirculation control
difficult to apply on-site due to complicated equipment
high capital costs
weld line must be regular (straight or circumferential seams only) with accurate fit-up

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Advantages

Low weld-metal cost
Easily automated
Low levels of ozone
High productivity
No visible arc light
Minimum cleaning

Disadvantages

Restricted welding positions
Arc blow on DC current
Shrinkage defects
Difficult penetration control
Limited joints

Submerged Arc Welding

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Welding Inspector

Welding Consumables

Section 14

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BS EN 499 MMA Covered Electrodes

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Covered Electrode

Toughness

Yield Strength N/mm²

Chemical composition

Flux Covering

Weld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

2Ni

H10

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Welding consumables are any products that are used up in the production of a weld

Welding consumables may be:

Covered electrodes, filler wires and electrode wires.
Shielding or oxy-fuel gases.
Separately supplied fluxes.
Fusible inserts.

Welding consumables

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Welding Consumable Standards

MMA (SMAW)

BS EN 499: Steel electrodes
AWS A5.1 Non-alloyed steel electrodes
AWS A5.4 Chromium electrodes
AWS A5.5 Alloyed steel electrodes

MIG/MAG (GMAW) TIG (GTAW)

BS 2901: Filler wires
BS EN 440: Wire electrodes
AWS A5.9: Filler wires
BS EN 439: Shielding gases

SAW

BS 4165: Wire and fluxes
BS EN 756: Wire electrodes
BS EN 760: Fluxes
AWS A5.17: Wires and fluxes

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Welding Consumable Gases

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welding gases

GMAW, FCAW, TIG, Oxy- Fuel
Supplied in cylinders or storage tanks for large quantities
Colour coded cylinders to minimise wrong use
Subject to regulations concerned handling, quantities and positioning of storage areas
Moisture content is limited to avoid cold cracking
Dew point (the temperature at which the vapour begins to condense) must be checked

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Welding Consumables

Each consumable is critical in respect to:

Size, (diameter and length)
Classification / Supplier
Condition
Treatments e.g. baking / drying
Handling and storage is critical for consumable control
Handling and storage of gases is critical for safety

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Quality Assurance

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Welding Consumables:

filler material must be stored in an area with controlled temperature and humidity
poor handling and incorrect stacking may damage coatings, rendering the electrodes unusable
there should be an issue and return policy for welding consumables (system procedure)
control systems for electrode treatment must be checked and calibrated; those operations must be recorded
filler material suppliers must be approved before purchasing any material

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MMA Welding Consumables

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The three main electrode covering types used in MMA welding

Cellulosic - deep penetration/fusion
Rutile - general purpose
Basic - low hydrogen

MMA Covered Electrodes

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MMA Welding Consumables

Welding consumables for MMA:

Consist of a core wire typically between 350-450mm in length and from 2.5mm - 6mm in diameter
The wire is covered with an extruded flux coating
The core wire is generally of a low quality rimming steel
The weld quality is refined by the addition of alloying and refining agents in the flux coating
The flux coating contains many elements and compounds that all have a variety of functions during welding

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MMA Welding Consumables

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Function of the Electrode Covering:

To facilitate arc ignition and give arc stability
To generate gas for shielding the arc & molten metal from air contamination
To de-oxidise the weld metal and flux impurities into the slag
To form a protective slag blanket over the solidifying and cooling weld metal
To provide alloying elements to give the required weld metal properties
To aid positional welding (slag design to have suitable freezing temperature to support the molten weld metal)
To control hydrogen contents in the weld (basic type)

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1: Electrode size (diameter and length)

2: Covering condition: adherence, cracks, chips and concentricity

3: Electrode designation

EN 499-E 51 3 B

Arc ignition enhancing materials (optional!)

See BS EN ISO 544 for further information

Covered electrode inspection

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MMA Welding Consumables

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Plastic foil sealed cardboard box

rutile electrodes
general purpose basic electrodes

Tin can

cellulosic electrodes

Vacuum sealed pack

extra low hydrogen electrodes

Courtesy of Lincoln Electric

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MMA Welding Consumables

Cellulosic electrodes:

covering contains cellulose (organic material).
produce a gas shield high in hydrogen raising the arc voltage.
Deep penetration / fusion characteristics enables welding at high speed without risk of lack of fusion.
generates high level of fumes and H2 cold cracking.
Forms a thin slag layer with coarse weld profile.
not require baking or drying (excessive heat will damage electrode covering!).
Mainly used for stove pipe welding
hydrogen content is 80-90 ml/100 g of weld metal.

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MMA Welding Consumables

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Cellulosic Electrodes

Disadvantages:

weld beads have high hydrogen
risk of cracking (need to keep joint hot during welding to allow H to escape)
not suitable for higher strength steels - cracking risk too high (may not be allowed for Grades stronger than X70)
not suitable for very thick sections (may not be used on thicknesses > ~ 35mm)
not suitable when low temperature toughness is required (impact toughness satisfactory down to ~ -20°C)

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MMA Welding Consumables

Advantages:

Deep penetration/fusion
Suitable for welding in all positions
Fast travel speeds
Large volumes of shielding gas
Low control

Disadvantages:

High in hydrogen
High crack tendency
Rough weld appearance
High spatter contents
Low deposition rates

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Cellulosic Electrodes

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MMA Welding Consumables

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Rutile electrodes:

covering contains TiO₂ slag former and arc stabiliser.
easy to strike arc, less spatter, excellent for positional welding.
stable, easy-to-use arc can operate in both DC and AC.
slag easy to detach, smooth profile.
Reasonably good strength weld metal.
Used mainly on general purpose work.
Low pressure pipework, support brackets.
electrodes can be dried to lower H2 content but cannot be baked as it will destroy the coating.
hydrogen content is 25-30 ml/100 g of weld metal.

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MMA Welding Consumables

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Rutile electrodes

Disadvantages:

they cannot be made with a low hydrogen content
cannot be used on high strength steels or thick joints - cracking risk too high
they do not give good toughness at low temperatures
these limitations mean that they are only suitable for general engineering - low strength, thin steel

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MMA Welding Consumables

Advantages:

Easy to use
Low cost / control
Smooth weld profiles
Slag easily detachable
High deposition possible with the addition of iron powder

Disadvantages:

High in hydrogen
High crack tendency
Low strength
Low toughness values

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Rutile Electrodes

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MMA Welding Consumables�Rutile Variants

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High Recovery Rutile Electrodes

Characteristics:

coating is ‘bulked out’ with iron powder
iron powder gives the electrode ‘high recovery’
extra weld metal from the iron powder can mean that weld deposit from a single electrode can be as high as 180% of the core wire weight
give good productivity
large weld beads with smooth profile can look very similar to SAW welds

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MMA Welding Consumables

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High Recovery Rutile Electrodes

Disadvantages:

Same as standard rutile electrodes with respect to hydrogen control
large weld beads produced cannot be used for all-positional welding
the very high recovery types usually limited to PA & PB positions
more moderate recovery may allow PC use

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MMA Welding Consumables

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Basic covering:

Produce convex weld profile and difficult to detach slag.
Very suitable for for high pressure work, thick section steel and for high strength steels.
Prior to use electrodes should be baked, typically 350°C for 2 hour plus to reduce moisture to very low levels and achieve low hydrogen potential status.
Contain calcium fluoride and calcium carbonate compounds.
cannot be re-baked indefinitely!
low hydrogen potential gives weld metal very good toughness and YS.
have the lowest level of hydrogen (less than 5 ml/100 g of weld metal).

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MMA Welding Consumables

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Basic Electrodes

Disadvantages:

Careful control of baking and/or issuing of electrodes is essential to maintain low hydrogen status and avoid risk of cracking
Typical baking temperature 350°C for 1 to 2hours.
Holding temperature 120 to 150°C.
Issue in heated quivers typically 70°C.
Welders need to take more care / require greater skill.
Weld profile usually more convex.
Deslagging requires more effort than for other types.

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Basic Electrodes

Advantages

High toughness values
Low hydrogen contents
Low crack tendency

Disadvantages

High cost
High control
High welder skill required
Convex weld profiles
Poor stop / start properties

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MMA Welding Consumables

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BS EN 499 MMA Covered Electrodes

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Covered Electrode

Toughness

Yield Strength N/mm²

Chemical composition

Flux Covering

Weld Metal Recovery

and Current Type

Welding Position

Hydrogen Content

2Ni

H10

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BS EN 499 MMA Covered Electrodes

Electrodes classified as follows:

E 35 - Minimum yield strength 350 N/mm²

Tensile strength 440 - 570 N/mm²

E 38 - Minimum yield strength 380 N/mm²

Tensile strength 470 - 600 N/mm²

E 42 - Minimum yield strength 420 N/mm²

Tensile strength 500 - 640 N/mm²

E 46 - Minimum yield strength 460 N/mm²

Tensile strength 530 - 680 N/mm²

E 50 - Minimum yield strength 500 N/mm²

Tensile strength 560 - 720 N/mm²

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BS EN 499 electrode designation

Recovery and type of current designation

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Symbol

Weld metal recovery (%)

Type of current

>105 ≤125

>125 ≤160

>160

≤105

AC/DC

Welding position designation

Symbol

Welding position

Flat butt/fillet, horizontal fillet

Flat butt/fillet

All positions

All positions except vertical down

Flat butt/fillet, horizontal fillet, vertical down

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AWS A5.1 Alloyed Electrodes

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Covered Electrode

Tensile Strength (p.s.i)

Welding Position

Flux Covering

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AWS A5.5 Alloyed Electrodes

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Covered Electrode

Tensile Strength (p.s.i)

Welding Position

Flux Covering

Moisture Control

Alloy Content

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MMA Welding Consumables

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TYPES OF ELECTRODES

(for C, C-Mn Steels)

BS EN 499 AWS A5.1

Cellulosic E XX X C EXX10 EXX11
Rutile E XX X R EXX12 EXX13
Rutile Heavy Coated E XX X RR EXX24
Basic E XX X B EXX15 EXX16 EXX18

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Electrode efficiency

75-90% for usual electrodes

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up to 180% for iron powder electrodes

Mass of weld metal deposited

Electrode Eficiency =

Mass of core wire melted

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Covered electrode treatment

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Cellulosic electrodes

Rutile electrodes

Use straight from the box - No baking/drying!

If necessary, dry up to 120°C- No baking!

Vacuum packed basic electrodes

Use straight from the pack within 4 hours - No rebaking!

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Covered electrode treatment

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After baking, maintain in oven at 150°C

Basic electrodes

Baking in oven 2 hours at 350°C!

Use from quivers at 75°C

If not used within 4 hours, return to oven and rebake!

Weld

Limited number of rebakes!

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TIG Consumables

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Welding Consumables

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TIG Welding Consumables

Welding consumables for TIG:

Filler wires, Shielding gases, tungsten electrodes (non-consumable).
Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification
Steel Filler wires of very high quality, with copper coating to resist corrosion.
shielding gases mainly Argon and Helium, usually of highest purity (99.9%).

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TIG Welding Consumables

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Welding rods:

supplied in cardboard/plastic tubes

must be kept clean and free from oil and dust
might require degreasing

Courtesy of Lincoln Electric

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Fusible Inserts

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Before Welding

Pre-placed filler material

After Welding

Other terms used include:

EB inserts (Electric Boat Company)
Consumable socket rings (CSR)

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Fusible Inserts

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Consumable inserts:

used for root runs on pipes
used in conjunction with TIG welding
available for carbon steel, Cr-Mo steel, austenitic stainless steel, nickel and copper-nickel alloys
different shapes to suit application

Radius

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Fusible Inserts

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Application of consumable inserts

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Shielding gases for TIG welding

Argon

low cost and greater availability
heavier than air - lower flow rates than Helium
low thermal conductivity - wide top bead profile
low ionisation potential - easier arc starting, better arc stability with AC, cleaning effect
for the same arc current produce less heat than helium - reduced penetration, wider HAZ
to obtain the same arc arc power, argon requires a higher current - increased undercut

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Shielding gases for TIG welding

Helium

costly and lower availability than Argon
lighter than air - requires a higher flow rate compared with argon (2-3 times)
higher ionisation potential - poor arc stability with AC, less forgiving for manual welding
for the same arc current produce more heat than argon - increased penetration, welding of metals with high melting point or thermal conductivity
to obtain the same arc arc power, helium requires a lower current - no undercut

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Shielding gases for TIG welding

Hydrogen

not an inert gas - not used as a primary shielding gas
increase the heat input - faster travel speed and increased penetration
better wetting action - improved bead profile
produce a cleaner weld bead surface
added to argon (up to 5%) - only for austenitic stainless steels and nickel alloys
flammable and explosive

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Shielding gases for TIG welding

Nitrogen

not an inert gas
high availability - cheap
added to argon (up to 5%) - only for back purge for duplex stainless, austenitic stainless steels and copper alloys
not used for mild steels (age embritlement)
strictly prohibited in case of Ni and Ni alloys (porosity)

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MIG / MAG Consumables�(Gases Covered previously)

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Welding Consumables

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MIG/MAG Welding Consumables

Welding consumables for MIG/MAG

Spools of Continuous electrode wires and shielding gases
variable spool size (1-15Kg) and Wire diameter (0.6-1.6mm) supplied in random or orderly layers
Basic Selection of different materials and their alloys as electrode wires.
Some Steel Electrode wires copper coating purpose is corrosion resistance and electrical pick-up
Gases can be pure CO₂, CO₂+Argon mixes and Argon+2%O₂ mixes (stainless steels).

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MIG/MAG Welding Consumables

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Welding wires:

carbon and low alloy wires may be copper coated
stainless steel wires are not coated

wires must be kept clean and free from oil and dust
flux cored wires does not require baking or drying

Courtesy of Lincoln Electric

Courtesy of ESAB AB

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MIG/MAG Welding Consumables

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Wire designation acc. BS EN 440:

EN 440 - G 46 3 M G3Si1

Standard number

Weld deposit produced by gas shielded metal arc welding

Tensile properties

Impact properties

Type of shielding gas

Type of wire electrode

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MIG/MAG Welding Consumables

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Wire designation acc. AWS A-5.18:

Minimum UTS of weld metal (ksi)

Chemical composition of the solid wire or of the weld metal in case of composite electrodes

AWS A-5.18 ER 70 S-6

Standard number

Designate an electrode/rod (ER) or only an electrode (E)

Solid (S) or composite (C) wire

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MIG/MAG shielding gases

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Gas shielded metal arc welding

MIG process (131)

MAG process (135)

BS EN 439

Group “I” - Ar, He and Ar-He mixtures

Group “R” - Ar + H₂ (<35%)

Group “M” - Ar + CO₂/O₂ (<50/15%)

Group “C” - CO₂, CO₂ + O₂ (<30%)

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Flux Core Wire Consumables�(Not in training manual)

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Welding Consumables

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Flux Core Wire Consumables

Functions of metallic sheath:

Function of the filling powder:

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provide form stability to the wire
serves as current transfer during welding

stabilise the arc
add alloy elements
produce gaseous shield
produce slag
add iron powder

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Types of cored wire

not sensitive to moisture pick-up
can be copper coated, better current transfer
thick sheath, good form stability, 2 roll drive feeding possible
difficult to manufacture

good resistance to moisture pick-up
can be copper coated
thick sheath
difficult to seal the sheath

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Seamless cored wire

Butt joint cored wire

Overlapping cored wire

sensitive to moisture pick-up
cannot be copper coated
thin sheath
easy to manufacture

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Core elements and their function

Aluminium - deoxidize & denitrify

Calcium - provide shielding & form slag

Carbon - increase hardness & strength

Manganese - deoxidize & increase strength and toughness

Molybdenum - increase hardness & strength

Nickel - improve hardness, strength, toughness & corrosion resistance

Potassium - stabilize the arc & form slag

Silicon - deoxidize & form slag

Sodium - stabilize arc & form slag

Titanium - deoxidize, denitrify & form slag

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SAW Consumables

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Welding Consumables

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SAW Consumables

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Welding fluxes:

are granular mineral compounds mixed according to various formulations
shield the molten weld pool from the atmosphere
clean the molten weld pool
can modify the chemical composition of the weld metal
prevents rapid escape of heat from welding zone
influence the shape of the weld bead (wetting action)
can be fused, agglomerated or mixed
must be kept warm and dry to avoid porosity

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SAW Consumables

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Fused fluxes are normally not hygroscopic but particles can hold surface moisture so only drying
Agglomerated fluxes contain chemically bonded water. Similar treatment as basic electrodes
If flux is too fine it will pack and not feed properly. It cannot be recycled indefinitely

Welding flux:

might be fused or agglomerated
supplied in bags
must be kept warm and dry
handling and stacking requires care

Courtesy of Lincoln Electric

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SAW Consumables

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Welding flux:

supplied in bags/pails (approx. 25 kg) or bulk bags (approx. 1200 kg)
might be fused, agglomerated or mixed

Courtesy of Lincoln Electric

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SAW Consumables

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Fused Flux:

Baked at high temperature, glossy, hard and black in colour, cannot add ferro-manganese, non moisture absorbent and tends to be of the acidic type

Fused Flux

Flaky appearance
Lower weld quality
Low moisture intake
Low dust tendency
Good re-cycling
Very smooth weld profile

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SAW Consumables

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TYPES OF FLUX

FUSED (ACID TYPE)

name indicates method of manufacture
minerals are fused (melted) and granules produced by allowing to cool to a solid mass and then crushing or by spraying the molten flux into water
flux tends to be ‘glass-like’ (high in Silica)
granules are hard and may appear shiny
granules do not absorb moisture
granules do not tend break down into powder when being re-circulated
are effectively a low hydrogen flux
welds do not tend to give good toughness at low temperatures

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SAW Consumables

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Fused fluxes advantages:

good chemical homogeneity
easy removal of fines without affecting flux composition
normally not hygroscopic  easy storage and handling
readily recycled without significant change in particle size or composition

Fused fluxes disadvantages:

difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss)
high temperatures needed to melt ingredients limit the range of flux compositions

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SAW Consumables

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Agglomerated Flux:

Baked at a lower temperature, dull, irregularly shaped, friable, (easily crushed) can easily add alloying elements, moisture absorbent and tend to be of the basic type

Agglomerated Flux

Granulated appearance
High weld quality
Addition of alloys
Lower consumption
Easy slag removal
Smooth weld profile

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SAW Consumables

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Agglomerated fluxes advantages:

easy addition of deoxidizers and alloying elements
usable with thicker layer of flux when welding
colour identification

Agglomerated fluxes disadvantages:

tendency to absorb moisture
possible gas evolution from the molten slag leading to porosity
possible change in flux composition due to segregation or removal of fine mesh particles

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SAW Consumables

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TYPES OF FLUX

AGGLOMERATED (BASIC TYPE)

name indicates method of manufacture
basic minerals are used in powder form and are mixed with a binder to form individual granules
granules are soft and easily crushed to powder
granules will absorb moisture and it is necessary to protect the flux from moisture pick-up - usually by holding in a heated silo
granules tend to break down into powder when being re-circulated
are a low hydrogen flux - if correctly controlled
welds give good toughness at low temperatures

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SAW Consumables

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Mixed fluxes advantages:

several commercial fluxes may be mixed for highly critical or proprietary welding operations

Mixed fluxes disadvantages:

segregation of the combined fluxes during shipment, storage and handling
segregation occurring in the feeding and recovery systems during welding
inconsistency in the combined flux from mix to mix

Mixed fluxes - two or more fused or bonded fluxes are mixed in any ratio necessary to yield the desired results

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SAW filler material

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Welding wires can be used to weld:

carbon steels
low alloy steels
creep resisting steels
stainless steels
nickel-base alloys
special alloys for surfacing applications

Welding wires can be:

solid wires
metal-cored wires

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SAW filler material

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Welding wires:

carbon and low alloy wires are copper coated

wires must be kept clean and free from oil and dust

stainless steel wires are not coated

Courtesy of Lincoln Electric

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SAW filler material

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Copper coating functions:

to assure a good electric contact between wire and contact tip
to assure a smooth feed of the wire through the guide tube, feed rolls and contact tip (decrease contact tube wear)
to provide protection against corrosion

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Ceramic Backing

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Ceramic backing:

used to support the weld pool on root runs
usually fitted on an aluminium self adhesive tape

allow increased welding current without danger of burn-through, increased productivity, consistent quality
different profiles to suit different applications
no backing/drying required

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Welding Inspector

Non Destructive Testing

Section 15

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Non-Destructive Testing

A welding inspector should have a working knowledge of NDT methods and their applications, advantages and disadvantages.

Four basic NDT methods

Radiographic inspection (RT)
Ultrasonic inspection (UT)
Magnetic particle inspection (MT)
Dye penetrant inspection (PT)

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Non-Destructive Testing

Surface Crack Detection

Liquid Penetrant (PT or Dye-Penetrant)
Magnetic Particle Inspection (MT or MPI)

Volumetric & Planar Inspection

Ultrasonics (UT)
Radiography (RT)

Each technique has advantages & disadvantages with respect to:

Technical Capability and Cost

Note: The choice of NDT techniques is based on consideration of these advantages and disadvantages

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Radiographic Testing (RT)

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Radiographic Testing

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The principles of radiography

X or Gamma radiation is imposed upon a test object
Radiation is transmitted to varying degrees dependant upon the density of the material through which it is travelling
Thinner areas and materials of a less density show as darker areas on the radiograph
Thicker areas and materials of a greater density show as lighter areas on a radiograph
Applicable to metals,non-metals and composites

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Radiographic Testing

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X – Rays

Electrically generated

Gamma Rays

Generated by the decay of unstable atoms

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Radiographic Testing

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Source

Radiation beam

Image quality indicator

Radiographic film with latent image after exposure

10fe16

Test specimen

10fe16

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Radiographic Testing

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Density - relates to the degree of darkness

Contrast - relates to the degree of difference

Definition - relates to the degree of sharpness

Sensitivity - relates to the overall quality of the radiograph

Densitometer

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Radiographic Sensitivity

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7FE12

Step / Hole type IQI

Wire type IQI

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Radiographic Sensitivity

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Wire Type IQI

Step/Hole Type IQI

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Radiographic Techniques

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Single Wall Single Image (SWSI)

film inside, source outside

Single Wall Single Image (SWSI) panoramic

film outside, source inside (internal exposure)

Double Wall Single Image (DWSI)

film outside, source outside (external exposure)

Double Wall Double Image (DWDI)

film outside, source outside (elliptical exposure)

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Single Wall Single Image (SWSI)

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IQI’s should be placed source side

Film

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Single Wall Single Image Panoramic

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IQI’s are placed on the film side
Source inside film outside (single exposure)

Film

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Double Wall Single Image (DWSI)

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IQI’s are placed on the film side
Source outside film outside (multiple exposure)
This technique is intended for pipe diameters over 100mm

Film

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Double Wall Single Image (DWSI)

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Radiograph

Identification

ID MR11

Unique identification

EN W10

IQI placing

Pitch marks indicating readable film length

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Double Wall Single Image (DWSI)

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Radiograph

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Double Wall Double Image (DWDI)

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Film

IQI’s are placed on the source or film side
Source outside film outside (multiple exposure)
A minimum of two exposures
This technique is intended for pipe diameters less than 100mm

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Double Wall Double Image (DWDI)

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Shot A Radiograph

Identification

ID MR12

Unique identification

EN W10

IQI placing

Pitch marks indicating readable film length

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Double Wall Double Image (DWDI)

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Elliptical Radiograph

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Radiography

PENETRATING POWER

Question:

What determines the penetrating power of an X-ray ?

the kilo-voltage applied (between anode & cathode)

Question:

What determines the penetrating power of a gamma ray ?

the type of isotope (the wavelength of the gamma rays)

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Radiography

GAMMA SOURCES

Isotope Typical Thickness Range

Iridium 192 10 to 50 mm (mostly used)
Cobalt 60 > 50 mm
Ytterbium < 10 mm
Thulium < 10 mm
Cesium < 10 mm

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Radiographic Testing

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Advantages

Permanent record
Little surface preparation
Defect identification
No material type limitation
Not so reliant upon operator skill
Thin materials

Disadvantages

Expensive consumables
Bulky equipment
Harmful radiation
Defect require significant depth in relation to the radiation beam (not good for planar defects)
Slow results
Very little indication of depths
Access to both sides required

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Radiographic Testing

Comparison with Ultrasonic Examination

ADVANTAGES

good for non-planar defects

good for thin sections

gives permanent record

easier for 2nd party interpretation

can use on all material types

high productivity

direct image of imperfections

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Radiographic Testing

Comparison with Ultrasonic Examination

DISADVANTAGES

health & safety hazard
not good for thick sections
high capital and relatively high running costs
not good for planar defects
X-ray sets not very portable
requires access to both sides of weld
frequent replacement of gamma source needed (half life)

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Ultrasonic Testing (UT)

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Ultrasonic Testing

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Main Features:

Surface and sub-surface detection
This detection method uses high frequency sound waves, typically above 2MHz to pass through a material
A probe is used which contains a piezo electric crystal to transmit and receive ultrasonic pulses and display the signals on a cathode ray tube or digital display
The actual display relates to the time taken for the ultrasonic pulses to travel the distance to the interface and back
An interface could be the back of a plate material or a defect
For ultrasound to enter a material a couplant must be introduced between the probe and specimen

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Ultrasonic Testing

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Digital

UT Set,

Pulse echo signals

A scan Display

Compression probe

checking the material Thickness

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Ultrasonic Testing

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defect

defect echo

Back wall echo

CRT Display

Compression Probe

Material Thk

initial pulse

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Ultrasonic Testing

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Angle Probe

UT Set

A Scan Display

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Ultrasonic Testing

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initial pulse

defect echo

defect

CRT Display

initial pulse

defect echo

CRT Display

½ Skip

Full Skip

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Ultrasonic Testing

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Advantages

Rapid results
Both surface and

sub-surface detection

Safe
Capable of measuring the depth of defects
May be battery powered
Portable

Disadvantages

Trained and skilled operator required
Requires high operator skill
Good surface finish required
Defect identification
Couplant may contaminate
No permanent record
Calibration Required
Ferritic Material (Mostly)

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Ultrasonic Testing

Comparison with Radiography

ADVANTAGES

good for planar defects
good for thick sections
instant results
can use on complex joints
can automate
very portable
no safety problems (‘parallel’ working is possible)
low capital & running costs

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Ultrasonic Testing

Comparison with Radiography

DISADVANTAGES

no permanent record (with standard equipment)
not suitable for very thin joints <8mm
reliant on operator interpretation
not good for sizing Porosity
good/smooth surface profile needed
not suitable for coarse grain materials (e.g., castings)
Ferritic Materials (with standard equipment)

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Magnetic Particle testing (MT)

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Magnetic Particle Testing

Main features:

Surface and slight sub-surface detection
Relies on magnetization of component being tested
Only Ferro-magnetic materials can be tested
A magnetic field is introduced into a specimen being tested
Methods of applying a magnetic field, yoke, permanent magnet, prods and flexible cables.
Fine particles of iron powder are applied to the test area
Any defect which interrupts the magnetic field, will create a leakage field, which attracts the particles
Any defect will show up as either a dark indication or in the case of fluorescent particles under UV-A light a green/yellow indication

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Magnetic Particle Testing

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Electro-magnet (yoke) DC or AC

Prods DC or AC

Collection of ink particles due to leakage field

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Magnetic Particle Testing

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A crack like indication

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Magnetic Particle Testing

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Alternatively to contrast inks, fluorescent inks may be used for greater sensitivity. These inks require a UV-A light source and a darkened viewing area to inspect the component

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Magnetic Particle Testing

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Typical sequence of operations to inspect a weld

Clean area to be tested
Apply contrast paint
Apply magnetisism to the component
Apply ferro-magnetic ink to the component during magnatising
Iterpret the test area
Post clean and de-magnatise if required

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Magnetic Particle Testing

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Advantages

Simple to use
Inexpensive
Rapid results
Little surface preparation required
Possible to inspect through thin coatings

Disadvantages

Surface or slight sub-surface detection only
Magnetic materials only
No indication of defects depths
Only suitable for linear defects
Detection is required in two directions

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Magnetic Particle Testing

Comparison with Penetrant Testing

ADVANTAGES

much quicker than PT
instant results
can detect near-surface imperfections (by current flow technique)
less surface preparation needed

DISADVANTAGES

only suitable for ferromagnetic materials
electrical power for most techniques
may need to de-magnetise (machine components)

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Penetrant Testing (PT)

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Penetrant Testing

Main features:

Detection of surface breaking defects only.
This test method uses the forces of capillary action
Applicable on any material type, as long they are non porous.
Penetrants are available in many different types:

Water washable contrast
Solvent removable contrast
Water washable fluorescent
Solvent removable fluorescent
Post-emulsifiable fluorescent

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Penetrant Testing

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Step 1. Pre-Cleaning

Ensure surface is very Clean normally with the use of a solvent

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Penetrant Testing

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Step 2. Apply penetrant

After the application, the penetrant is normally left on the components surface for approximately 15-20 minutes (dwell time).

The penetrant enters any defects that may be present by capillary action.

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Step 3. Clean off penetrant

the penetrant is removed after sufficient penetration time (dwell time).

Care must be taken not to wash any penetrant out off any defects present

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Step 3. Apply developer

After the penetrant has be cleaned sufficiently, a thin layer of developer is applied.

The developer acts as a contrast against the penetrant and allows for reverse capillary action to take place.

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Penetrant Testing

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Step 4. Inspection / development time

Inspection should take place immediately after the developer has been applied.

any defects present will show as a bleed out during development time.

After full inspection has been carried out post cleaning is generally required.

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Penetrant Testing

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Colour contrast Penetrant

Fluorescent Penetrant

Bleed out viewed under a UV-A light source

Bleed out viewed under white light

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Penetrant Testing

Advantages

Simple to use
Inexpensive
Quick results
Can be used on any non-porous material
Portability
Low operator skill required

Disadvantages

Surface breaking defect only
little indication of depths
Penetrant may contaminate component
Surface preparation critical
Post cleaning required
Potentially hazardous chemicals
Can not test unlimited times
Temperature dependant

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Penetrant Testing

Comparison with Magnetic Particle Inspection

ADVANTAGES

easy to interpret results
no power requirements
relatively little training required
can use on all materials

DISADVANTAGES

good surface finish needed
relatively slow
chemicals - health & safety issue

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Welding Inspector

Weld Repairs

Section 16

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Weld Repairs

Weld repairs can be divided into 2 specific areas:

Production repairs
In service repairs

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Weld Repairs

A weld repair can be a relatively straight forward activity, but in many instances it is quite complex, and various engineering disciplines may need to be involved to ensure a successful outcome.

Analysis of the defect types may be carried out by the Q/C department to discover the likely reason for their occurrence, (Material/Process or Skill related).

In general terms, a welding repair involves What!

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Weld Repairs

A weld repair may be used to improve weld profiles or extensive metal removal:

Repairs to fabrication defects are generally easier than repairs to service failures because the repair procedure may be followed
The main problem with repairing a weld is the maintenance of mechanical properties
During the inspection of the removed area prior to welding the inspector must ensure that the defects have been totally removed and the original joint profile has been maintained as close as possible

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Weld Repairs

In the event of repair, it is required:

Authorization and procedure for repair
Removal of material and preparation for repair
Monitoring of repair Weld
Testing of repair - visual and NDT

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Weld Repairs

There are a number of key factors that need to be considered before undertaking any repair:

The most important - is it financially worthwhile?
Can structural integrity be achieved if the item is repaired?
Are there any alternatives to welding?
What caused the defect and is it likely to happen again?
How is the defect to be removed and what welding process is to be used?
What NDE is required to ensure complete removal of the defect?
Will the welding procedures require approval/re-approval?

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Weld Repairs

Cleaning the repair area, (removal of paint, grease, etc)
A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub surface NDE method.
Once established the excavation site must be clearly identified and marked out.
An excavation procedure may be required (method used i.e. grinding, arc-air gouging, preheat requirements etc).
NDE should be used to locate the defect and confirm its removal.
A welding repair procedure/method statement with the appropriate welding process, consumable, technique, controlled heat input and interpass temperatures etc will need to be approved.

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Weld Repairs

Use of approved welders.
Dressing the weld and final visual.
A NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired.
Any post repair heat treatment requirements.
Final NDT procedure/technique prepared and carried out after heat treatment requirements.
Applying protective treatments (painting etc as required).
(*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations)

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Weld Repairs

What will be the effect of welding distortion and residual stress?
Will heat treatment be required?
What NDE is required and how can acceptability of the repair be demonstrated?
Will approval of the repair be required – if yes, how and by whom?

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Production Weld Repairs

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Before the repair can commence, a number of elements need to be fulfilled:

If the defect is surface breaking and has occurred at the fusion face the problem could be cracking or lack of sidewall fusion.

If the defect is found to be cracking the cause may be associated with the material or the welding procedure

If the defect is lack of sidewall fusion this can be apportioned to the lack of skill of the welder.

In this particular case as the defect is open to the surface, MPI or DYE-PEN may be used to gauge the length of the defect and U/T inspection used to gauge the depth.

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Weld Repairs

The specification or procedure will govern how the defective areas are to be removed. The method of removal may be:

Grinding
Chipping
Machining
Filing
Oxy-Gas gouging
Arc air gouging

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Defect Excavation

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Arc-air gouging

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Arc-air gouging features

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Operate ONLY on DCEP
Special gouging copper coated carbon electrode
Can be used on carbon and low alloy steels, austenitic stainless steels and non-ferrous materials
Requires CLEAN/DRY compressed air supply

Provides fast rate of metal removal
Can remove complex shape defects
After gouging, grinding of carbured layer is mandatory
Gouging doesn’t require a qualified welder!

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Production Weld Repairs

Production Repairs

are usually identified during production inspection
evaluation of the reports is usually carried out by the Welding Inspector, or NDT operator

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Production Weld Repairs

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Plan View of defect

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Production Weld Repairs

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Side View of defect excavation

Side View of repair welding

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In Service Weld Repairs

In service repairs

Can be of a very complex nature, as the component is very likely to be in a different welding position and condition than it was during production
It may also have been in contact with toxic, or combustible fluids hence a permit to work will need to be sought prior to any work being carried out
The repair welding procedure may look very different to the original production procedure due to changes in these elements.

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In Service Weld Repairs

Other factors to be taken into consideration:

Effect of heat on any surrounding areas of the component i.e. electrical components, or materials that may become damaged by the repair procedure.

This may also include difficulty in carrying out any required pre or post welding heat treatments and a possible restriction of access to the area to be repaired.

For large fabrications it is likely that the repair must also take place on site and without a shut down of operations, which may bring other elements that need to be considered.

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Weld Repairs

Is welding the best method of repair?
Is the repair really like earlier repairs?
What is the composition and weldability of the base metal?
What strength is required from the repair?
Can preheat be tolerated?
Can softening or hardening of the HAZ be tolerated?
Is PWHT necessary and practicable?
Will the fatigue resistance of the repair be adequate?
Will the repair resist its environment?
Can the repair be inspected and tested?

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Weld repair related problems

heat from welding may affect dimensional stability and/or mechanical properties of repaired assembly
due to heat from welding, YS goes down, danger of collapse
filler materials used on dissimilar welds may lead to galvanic corrosion
local preheat may induce residual stresses
cost of weld metal deposited during a weld joint repair can reach up to 10 times the original weld metal cost!

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Welding Inspector

Residual Stress & Distortion

Section 17

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Residual stress

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Residual stresses are undesirable because:

they lead to distortion
they affect dimensional stability of the welded assembly
they enhance the risk of brittle fracture
they can facilitate certain types of corrosion

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Residual Stresses

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The heating and subsequent cooling from welding produces expansion and contractions which affect the weld metal and adjacent material.

If this contraction is prevented or inhibited residual stress will develop.

The tendency to develop residual stresses increases when the heating and cooling is localised.

Residual stresses are very difficult to measure with any real accuracy.

Residual stresses are self balancing internal forces and not stresses induced whilst applying external load

Stresses are more concentrated at the surface of the component.

The removal of residual stresses is termed stress relieving.

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Stresses

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Normal Stress

Stress arising from a force perpendicular to the cross sectional area

Compression

Tension

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Stresses

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Shear Stress

Stress arising from forces which are parallel to, and lie in the plane of the cross sectional area.

Shear Stress

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Stresses

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Hoop Stress

Internal stress acting on the wall a pipe or cylinder due to internal pressure.

Hoop Stress

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Residual Stresses

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Longitudinal

Along the weld – longitudinal residual stresses

Transverse

Across the weld – transverse residual stresses

Short Transverse

Through the weld – short transverse residual stresses

Residual stresses occur in welds in the following directions

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Residual stress

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Heating and cooling causes expansion and contraction

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Residual stress

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In case of a heated bar, the resistance of the surrounding material to the expansion and contraction leads to formation of residual stress

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Summary

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Residual stresses are locked in elastic strain, which is caused by local expansion and contraction in the weld area.
Residual stresses should be removed from structures after welding.
The amount of contraction is controlled by, the volume of weld metal in the joint, the thickness, heat input, joint design and the materials properties
Offsetting may be used to finalise the position of the joint.
If plates or pipes are prevented from moving by tacking, clamping or jigging etc (restraint), then the amount of residual stresses that remain will be higher.

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Summary

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The movement caused by welding related stresses is called distortion.
The directions of contractional stresses and distortion is very complex, as is the amount and type of final distortion, however we can say that there are three directions:

a. Longitudinal b. Transverse c. Short transverse

A high percentage of residual stresses can be removed by heat treatments.
The peening of weld faces will only redistribute the residual stress, and place the weld face in compression.

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Types of distortion

Angular distortion

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Distortion

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Angular Distortion

Bowing Distortion

Longitudinal Distortion

Transverse Distortion

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Distortion

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Factors which affect distortion

Material properties and condition
Heat input
The amount of restrain
The amount of weld metal deposited

Control of distortion my be achieved in the following way:

The used of a different joint design
Presetting the joints to be welded – so that the metal distorts into the required position.
The use of a balanced welding technique
The use of clamps, jigs and fixtures.

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Distortion

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Distortion will occur in all welded joints if the material are free to move i.e. not restrained
Restrained materials result in low distortion but high residual stress
More than one type of distortion may occur at one time
Highly restrained joints also have a higher crack tendency than joints of a low restraint
The action of residual stress in welded joints is to cause distortion

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Distortion

Factors affecting distortion:

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parent material properties
amount of restrain
joint design
fit-up
welding sequence

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Factors affecting distortion

Parent material properties:

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thermal expansion coefficient - the greater the value, the greater the residual stress
yield strength - the greater the value, the greater the residual stress
Young’s modulus - the greater the value (increase in stiffness), the greater the residual stress
thermal conductivity - the higher the value, the lower the residual stress
transformation temperature - during phase transformation, expansion/contraction takes place. The lower the transformation temperature, the lower the residual stress

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Factors affecting distortion

Joint design:

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weld metal volume
type of joint - butt vs. fillet, single vs. double side

Amount of restrain:

thickness - as thickness increase, so do the stresses
high level of restrain lead to high stresses
preheat may increase the level of stresses (pipe welding!)

Fit-up:

misalignment may reduce stresses in some cases
root gap - increase in root gap increases shrinkage

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Factors affecting distortion

Welding sequence:

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number of passes - every pass adds to the total contraction
heat input - the higher the heat input, the greater the shrinkage
travel speed - the faster the welding speed, the less the stress
build-up sequence

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Distortion prevention

Distortion prevention by pre-setting

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a) pre-setting of fillet joint to prevent angular distortion

b) pre-setting of butt joint to prevent angular distortion

c) tapered gap to prevent closure

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Distortion

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Pre-set or Offsetting:

The amount of offsetting required is generally a function of trial and error.

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Distortion prevention

Distortion prevention by pre-bending using strongbacks and wedges

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Distortion

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Clamping and jigging:

The materials to be welded are prevented from moving by the clamp or jig the main advantage of using a jig is that the elements in a fabrication can be precisely located in the position to be welded. Main disadvantage of jigging is high restraint and high levels of residual stresses.

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Distortion prevention

Distortion prevention by restraint techniques

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a) use of welding jigs

b) use of flexible clamps

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Distortion prevention

Distortion prevention by restraint techniques

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c) use of strongbacks with wedges

d) use of fully welded strongbacks

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Distortion prevention

Distortion prevention by design

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Consider eliminating the welding!!

a) by forming the plate

b) by use of rolled or extruded sections

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Distortion prevention

Distortion prevention by design

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consider weld placement

reduce weld metal volume and/or number of runs

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Distortion prevention

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The volume of weld metal in a joint will affect the amount of local expansion and contraction, hence the more weld deposited the higher amount of distortion

Preparation angle 60^o

Preparation angle 40^o

Preparation angle 0^o

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Distortion prevention

Distortion prevention by design

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use of balanced welding

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Distortion prevention

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- Transverse Shrinkage

Fillet Welds 0.8mm per weld where the leg length does not exceed 3/4 plate thickness
Butt weld 1.5 to 3mm per weld for 60° V joint, depending on number of runs

- Longitudinal Shrinkage

Fillet Welds 0.8mm per 3m of weld
Butt Welds 3mm per 3m of weld

Allowances to cover shrinkage

Distortions prevention by design

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Distortion prevention

Distortion prevention by fabrication techniques

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tack welding

a) tack weld straight through to end of joint

b) tack weld one end, then use back-step technique for tacking the rest of the joint

c) tack weld the centre, then complete the tack welding by the back-step technique

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Distortion prevention

Distortion prevention by fabrication techniques

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back to back assembly

a) assemblies tacked together before welding

b) use of wedges for components that distort on separation after welding

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Distortion prevention

Distortion prevention by fabrication techniques

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use of stiffeners

control welding process by:

- deposit the weld metal as quickly as possible

- use the least number of runs to fill the joint

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Distortion prevention

Distortion prevention by welding procedure

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reduce the number of runs required to make a weld (e.g. angular distortion as a function of number of runs for a 10 mm leg length weld)

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Distortion prevention

Distortion prevention by welding procedure

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control welding techniques by use balanced welding about the neutral axis
control welding techniques by keeping the time between runs to a minimum

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Distortion prevention

Distortion prevention by welding procedure

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control welding techniques by

a) Back-step welding

b) Skip welding

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Distortion prevention

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Back-skip welding technique

Back-step welding technique

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Distortion prevention

Distortion - Best practice for fabrication corrective techniques

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using tack welds to set up and maintain the joint gap
identical components welded back to back so welding can be balanced about the neutral axis
attachment of longitudinal stiffeners to prevent longitudinal bowing in butt welds of thin plate structures
where there is choice of welding procedure, process and technique should aim to deposit the weld metal as quickly as possible; MIG in preference to MMA or gas welding and mechanised rather than manual welding
in long runs, the whole weld should not be completed in one direction; back-step or skip welding techniques should be used

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Distortion corrective techniques

Distortion - mechanical corrective techniques

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Use of press to correct bowing in T butt joint

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Distortion corrective techniques

Distortion - Best practice for mechanical corrective techniques

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Use packing pieces which will over correct the distortion so that spring-back will return the component to the correct shape
Check that the component is adequately supported during pressing to prevent buckling
Use a former (or rolling) to achieve a straight component or produce a curvature
As unsecured packing pieces may fly out from the press, the following safe practice must be adopted:

- bolt the packing pieces to the platen

- place a metal plate of adequate thickness to intercept the 'missile'

- clear personnel from the hazard area

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Distortion corrective techniques

Distortion - thermal corrective techniques

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Localised heating to correct distortion

Spot heating for correcting buckling

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Distortion corrective techniques

Distortion - thermal corrective techniques

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Line heating to correct angular distortion in a fillet weld

Use of wedge shaped heating to straighten plate

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Distortion corrective techniques

Distortion - thermal corrective techniques

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Wedge shaped heating to correct distortion

a) standard rolled steel section

b) buckled edge of plate

c) box fabrication

General guidelines:

Length of wedge = two-thirds of the plate width
Width of wedge (base) = one sixth of its length (base to apex)

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Distortion corrective techniques

Distortion - thermal corrective techniques

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use spot heating to remove buckling in thin sheet structures
other than in spot heating of thin panels, use a wedge-shaped heating technique
use line heating to correct angular distortion in plate
restrict the area of heating to avoid over-shrinking the component
limit the temperature to 60° to 650°C (dull red heat) in steels to prevent metallurgical damage
in wedge heating, heat from the base to the apex of the wedge, penetrate evenly through the plate thickness and maintain an even temperature

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Welding Inspector

Heat Treatment

Section 18

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Heat Treatment

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Why?

Improve mechanical properties
Change microstructure
Reduce residual stress level
Change chemical composition

How?

Flame oven
Electric oven/electric heating blankets
induction/HF heating elements

Where?

Local

Global

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Heat Treatments

Many metals must be given heat treatment before and after welding.

The inspector’s function is to ensure that the treatment is given correctly in accordance with the specification or as per the details supplied.

Types of heat treatment available:

Preheat
Annealing
Normalising
Quench Hardening
Temper
Stress Relief

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Heat Treatments

Pre-heat treatments

are used to increase weldability, by reducing sudden reduction of temperature, and control expansion and contraction forces during welding

Post weld heat treatments

are used to change the properties of the weld metal, controlling the formation of crystalline structures

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Post Weld -Heat Treatments

Post Hydrogen Release (according to BS EN1011-2)

Temperature: Approximately 250°C hold up to 3 hours

Cooling: Slow cool in air

Result: Relieves residual hydrogen

Procedure: Maintaining pre-heat / interpass temperature after completion of welding for 2 to 3 hours.

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Post Weld Heat Treatments

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(A) Normalised

(B) Fully Annealed

(D) Water-quenched & tempered

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Post Weld Heat Treatments

The inspector, in general, should ensure that:

Equipment is as specified
Temperature control equipment is in good condition
Procedures as specified, is being used e.g.

Method of application
Rate of heating and cooling
Maximum temperature
Soak time
Temperature measurement (and calibration)

DOCUMENTATION AND RECORDS

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Post Weld Heat Treatment

PWHT Procedures - Basic Requirements

Maximum Heating Rate

Usually from 300 or 400°C - need to avoid large temperature gradients that may cause distortion/cracking

Maximum rate depends on thickness but typically up to ~ 200°C/h

‘Soak’ Temperature depends on steel type - usually specified by Code (~550 to ~750 °C )

Minimum ‘Soak’ Time

need to make sure and whole item/full thickness reaches specified temp.

Codes typically specify 1h per 25mm related to max. joint thickness

Maximum Cooling Rate

usually down to 400 or 300°C - for same reasons as controlled heating rate

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Post Weld Heat Treatment Cycle

Time

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Temperature

SoakingTemperature and time at the attained temperature

Heating

Soaking

Cooling

heating rate

Cooling rate

Variables for heat treatment process must be carefully controlled

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Post Weld Heat Treatment

Removal of Residual Stress

Temperature (°C)

100

200

300

400

500

600

700

Yield Strength (N/mm²)

100

200

300

400

500

Cr-Mo steel - typical

C-Mn steel - typical

At PWHT temp. the yield strength of steel reduced so that it it is not strong enough to give restraint.
Residual stress reduced to very low level by straining (typically < ~ 0.5% strain)

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Heat Treatment

Recommendations

Provide adequate support (low YS at high temperature!)
Control heating rate to avoid uneven thermal expansions
Control soak time to equalise temperatures
Control temperature gradients - NO direct flame impingement!
Control furnace atmosphere to reduce scaling
Control cooling rate to avoid brittle structure formation

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Post Weld Heat Treatment Methods

Gas furnace heat treatment

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Advantages:

Easy to set up
Good portability
repeatability and temperature uniformity

Disadvantages:

Limited to size of parts

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Post Weld Heat Treatment Methods

HF (Induction) local heat treatment

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Advantages:

High heating rates
Ability to heat a narrow band

Disadvantages:

High equipment cost
Large equipment, less portable

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Post Weld Heat Treatment Methods

Local heat treatment using electric heating blankets

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Advantages:

Ability to vary heat
Ability to continuously maintain heat

Disadvantages:

Elements may burn out or arcing during heating

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Welding Inspector

Cutting Processes

Section 19

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Use of gas flame

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Welding

Gouging

Brazing

Heating

Straightening

Cutting

Blasting

Spraying

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Regulators

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Oxygen regulator

Fuel gas regulator

Regulator type

Single stage

Two stage

used when slight rise in delivery pressure from full to empty cylinder condition can be tolerated

used when a constant delivery pressure from full to empty cylinder condition is required

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Flashback arrestors

Flashback - recession of the flame into or back of the mixing chamber

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Flashback flame quenched at the flashback barrier

Flame barrier

Built-in check valve

Normal flow

Reverse flow

Flashback

Built-in check valve stops reverse flow

SAFETY SAFETY SAFETY

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A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to produce the oxide Fe₃O₄by exothermic reaction.This oxide is then blown through the material by the velocity of the oxygen stream

Different types of fuel gases may be used for the pre-heating flame in oxy fuel gas cutting: i.e. acetylene, hydrogen, propane. etc

By adding iron powder to the flame we are able to cut most metals - “Iron Powder Injection”

The high intensity of heat and rapid cooling will cause hardening in low alloy and medium/high C steels  they are thus pre-heated to avoid the hardening effect

Oxyfuel gas cutting process

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Oxyfuel gas cutting equipment

The cutting torch

Neutral cutting flame

Neutral cutting flame with oxygen cutting stream

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Oxyfuel gas cutting related terms

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Oxyfuel gas cutting quality

Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge

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Cut too fast - pronounced break in the drag line, irregular cut edge

Cut too slow - top edge is melted, deep groves in the lower portion, heavy scaling, rough bottom edge

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Oxyfuel gas cutting quality

Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge

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Preheat flame too high - top edge is melted, irregular cut, excess of adherent dross

Preheat flame too low - deep groves in the lower part of the cut face

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Oxyfuel gas cutting quality

Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge

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Irregular travel speed - uneven space between drag lines, irregular bottom with adherent oxide

Nozzle is too high above the works - excessive melting of the top edge, much oxide

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Mechanised oxyfuel cutting

can use portable carriages or gantry type machines and obtain high productivity
accurate cutting for complicate shapes

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OFW/C advantages/disadvantages

Disadvantages:

1) High skill factor

2) Wide HAZ

4) Slow process

5) Limited range of consumables

3) Safety issues

Advantages:

1) No need for power supply, portable

3) Low equipment cost

4) Can cut carbon and low alloy steels

5) Good on thin materials

2) Versatile: preheat, brazing, surfacing, repair, straightening

6) Not suitable for reactive & refractory metals

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Special oxyfuel operations

Gouging

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Rivet cutting

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Special oxyfuel operations

Thin sheet cutting

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Rivet washing

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Cutting Processes

Plasma arc cutting

Uses high velocity jet of ionised gas through a constricted nozzle to remove the molten metal
Uses a tungsten electrode and water cooled nozzle
High quality cutting
High intensity and UV radiation – EYES !

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Cutting Processes�Air-arc for cutting or gouging

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Air-arc gouging features

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Operate ONLY on DCEP
Special gouging copper coated carbon electrode
Can be used on carbon and low alloy steels, austenitic stainless steels and non-ferrous materials
Requires CLEAN/DRY compressed air supply

Provides fast rate of metal removal
Can remove complex shape defects
After gouging, grinding of carbured layer is mandatory
Gouging doesn’t require a qualified welder!

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Welding Inspector

Arc Welding Safety

Please discuss

Section 20

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Safety

Electrical safety
Heat & Light

Visible light
UV radiation - effects on skin and eyes

Fumes & Explosive Gasses
Noise levels
Fire Hazards
Scaffolding & Staging
Slips, trips and falls
Protection of others from exposure

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Welding Inspector

Weldability Of Steels

Section 21

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Weldability of Steels

Definition

It relates to the ability of the metal (or alloy) to be welded with mechanical soundness by most of the common welding processes, and the resulting welded joint retain the properties for which it has been designed.

is a function of many inter-related factors but these may be summarised as:

Composition of parent material
Joint design and size
Process and technique
Access

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Weldability of Steels

The weldability of steel is mainly dependant on carbon & other alloying elements content.

If a material has limited weldability, we need to take special measures to ensure the maintenance of the properties required

Poor weldability normally results in the occurrence of cracking

A steel is considered to have poor weldability when:

an acceptable joint can only be made by using very narrow range of welding conditions
great precautions to avoid cracking are essential (e.g., high pre-heat etc)

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The Effect of Alloying on Steels

Elements may be added to steels to produce the properties required to make it useful for an application.

Most elements can have many effects on the properties of steels.

Other factors which affect material properties are:

The temperature reached before and during welding
Heat input
The cooling rate after welding and or PWHT

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Steel Alloying Elements

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Iron (Fe): Main steel constituent. On its own, is relatively soft, ductile, with low strength.

Carbon (C): Major alloying element in steels, a strengthening element with major influence on HAZ hardness. Decreases weldability.

typically < ~ 0.25%

Manganese (Mn): Secondary only to carbon for strength, toughness and ductility, secondary de-oxidiser and also reacts with sulphur to form manganese sulphide.

< ~0.8% is residual from steel de-oxidation

up to ~1.6% (in C-Mn steels) improves strength & toughness

Silicon (Si): Residual element from steel de-oxidation.

typically to ~0.35%

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Steel Alloying Elements

Phosphorus (P): Residual element from steel-making minerals. difficult to reduce below < ~ 0.015% brittleness

Sulphur (S): Residual element from steel-making minerals

< ~ 0.015% in modern steels

< ~ 0.003% in very clean steels

Aluminium (Al): De-oxidant and grain size control

typically ~ 0.02 to ~ 0.05%

Chromium (Cr): For creep resistance & oxidation (scaling) resistance for elevated temperature service. Widely used in stainless steels for corrosion resistance, increases hardness and strength but reduces ductility.

typically ~ 1 to 9% in low alloy steels

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Nickel (Ni): Used in stainless steels, high resistance to corrosion from acids, increases strength and toughness

Molybdenum (Mo): Affects hardenability. Steels containing molybdenum are less susceptible to temper brittleness than other alloy steels. Increases the high temperature tensile and creep strengths of steel. typically ~ 0.5 to 1.0%

Niobium (Nb): a grain refiner, typically~ 0.05%

Vanadium (V): a grain refiner, typically ~ 0.05%

Titanium (Ti): a grain refiner, typically ~ 0.05%

Copper (Cu): present as a residual, (typically < ~ 0.30%)

added to ‘weathering steels’ (~ 0.6%) to give better resistance to atmospheric corrosion

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Steel Alloying Elements

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Classification of Steels

Mild steel (CE < 0.4)

Readily weldable, preheat generally not required if low hydrogen processes or electrodes are used
Preheat may be required when welding thick section material, high restraint and with higher levels of hydrogen being generated

C-Mn, medium carbon, low alloy steels (CE 0.4 to 0.5)

Thin sections can be welded without preheat but thicker sections will require low preheat levels and low hydrogen processes or electrodes should be used

Higher carbon and alloyed steels (CE > 0.5)

Preheat, low hydrogen processes or electrodes, post weld heating and slow cooling may be required

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Process Cracks

Hydrogen Induced HAZ Cracking (C/Mn steels)
Hydrogen Induced Weld Metal Cracking (HSLA steels).
Solidification or Hot Cracking (All steels)
Lamellar Tearing (All steels)
Re-heat Cracking (All steels, very susceptible Cr/Mo/V steels)
Inter-Crystalline Corrosion or Weld Decay (stainless steels)

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Cracking

When considering any type of cracking mechanism, three elements must always be present:

Stress

Residual stress is always present in a weldment, through unbalanced local expansion and contraction

Restraint

Restraint may be a local restriction, or through plates being welded to each other

Susceptible microstructure

The microstructure may be made susceptible to cracking by the process of welding

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Cracks

Hydrogen Induced Cold Cracking

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Hydrogen Induced Cold Cracking

May occur:

up to 48 hrs after completion
In weld metal, HAZ, parent metal.
At weld toes
Under weld beads
At stress raisers.

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Also know as:

Cold Cracking, happens when the welds cool down.

HAZ cracking, normally occurs in the HAZ.

Delayed cracking, as it takes time for the hydrogen to migrate. 48 Hours normally but up to 72,

Under-bead cracking, normally happens in the HAZ under a weld bead

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Hydrogen Induced Cold Cracking

There is a risk of hydrogen cracking when all of the 4 factors occur together:

Hydrogen More than 15ml/100g of weld metal
Stress More than ½ the yield stress
Temperature Below 300^oC
Hardness Greater than 400HV Vickers

Susceptible Microstructure (Martensite)

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Hydrogen Induced Cold Cracking

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Hydrogen Induced Cold Cracking

Precautions for controlling hydrogen cracking

Pre heat, removes moisture from the joint preparations, and slows down the cooling rate
Ensure joint preparations are clean and free from contamination
The use of a low hydrogen welding process and correct arc length
Ensure all welding is carried out is carried out under controlled environmental conditions
Ensure good fit-up as to reduced stress
The use of a PWHT
Avoid poor weld profiles

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Hydrogen Induced Cold Cracking

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Hydrogen is the smallest atom known
Hydrogen enters the weld via the arc
Source of hydrogen mainly from moisture pick-up on the electrodes coating, welding fluxes or from the consumable gas

H₂

Moisture on the electrode or grease on the wire

Water vapour in the air or in the shielding gas

Oxide or grease on the plate

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Hydrogen absorbed in a long, or unstable arc

Hydrogen introduced in weld from consumable, oils, or paint on plate

Cellulosic electrodes produce hydrogen as a shielding gas

Hydrogen crack

Martensite forms from γ

H₂ diffuses to γ in HAZ

H₂

Hydrogen Induced Cold Cracking

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Hydrogen Induced Cold Cracking

Susceptible Microstructure:

Hard brittle structure – MARTENSITE Promoted by:

A) High Carbon Content, Carbon Equivalent (CE)

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Heat input (Kj/mm) = Amps x Volts x arc time

Run out length x 10³(1000)

CEV = %C + Mn + Cr+Mo+V + Ni+Cu

6 5 15

B) high alloy content

C) fast cooling rate: Inadequate Pre-Heating

Cold Material

Thick Material

Low Heat Input.

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Hydrogen Induced Cold Cracking

Typical locations for Cold Cracking

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HSLA or Micro-Alloyed Steels are high strength steels (800MPa/N/mm2) that derive their high strength from small percentage alloying (over-alloyed Weld metal to match the strength of parent metal)
Typically the level of alloying is in the elements such as vanadium molybdenum and titanium, nickel and chromium Strength. are used. It would be impossible to match this micro alloying in the electrode due to the effect of losses across an electric arc (Ti burn in the arc)
It is however important to match the strength of the weld to the strength of the plate, Mn 1.6 Cr Ni Mo

HICC in HSLA steels

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Transverse Weld Cracks in HSLA Steels*

Longitudinal contractional strain

Low ductility weld metal

H₂ HAZ Cracks in Alloy steels*

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Hydrogen Scales

List of hydrogen scales from BS EN 1011:part 2.

Hydrogen content related to 100 grams of weld metal deposited.

Scale A High: >15 ml
Scale B Medium: 10 ml - 15 ml
Scale C Low: 5 ml - 10 ml
Scale D Very low: 3 ml - 5 ml
Scale E Ultra-low: < 3 ml

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Potential Hydrogen Level Processes

list of welding processes in order of potential lowest hydrogen content with regards to 100g of deposited weld metal.

TIG < 3 ml
MIG < 5 ml
ESW < 5 ml
MMA (Basic Electrodes) < 5 ml
SAW < 10ml
FCAW < 15 ml

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Weldability

Solidification Cracking

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Solidification Cracking

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Usually Occurs in Weld Centerline

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Solidification Cracking

Also referred as

Hot Cracking: Occurring at high temperatures while the weld is hot

Centerline cracking: cracks appear down the centre line of the bead.

Crater cracking: Small cracks in weld centers are solidification cracks

Crack type: Solidification cracking

Location: Weld centreline (longitudinal)

Steel types: High sulphur & phosphor concentration in steels.

Susceptible Microstructure: Columnar grains In direction of solidification

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Solidification Cracking

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Factors for solidification cracking

Columnar grain growth with impurities in weld metal (sulphur, phosphor and carbon)
The amount of stress/restraint
Joint design high depth to width ratios
Liquid iron sulphides are formed around solidifying grains.
High contractional strains are present
High dilution processes are being used.
There is a high carbon content in the weld metal
Most commonly occurring in sub-arc welded joints

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Solidification Cracking

Sulphur in the parent material may dilute in the weld metal to form iron sulphides (low strength, low melting point compounds)
During weld metal solidification, columnar crystals push still liquid iron sulphides in front to the last place of solidification, weld centerline.
The bonding between the grains which are themselves under great stress and may now be very poor to maintain cohesion and a crack will result, weld centerline.

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Solidification Cracking�Avoidance

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Deep, narrower weld bead

On solidification the bonding between the grains may now be very poor to maintain cohesion and a crack may result

Shallow, wider weld bead

On solidification the bonding between the grains may be adequate to maintain cohesion and a crack is unlikely to occur

HAZ

Intergranular liquid film

Columnar grains

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Solidification Cracking

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Precautions for controlling solidification cracking

The first steps in eliminating this problem would be to choose a low dilution process, and change the joint design

Grind and seal in any lamination and avoid further dilution????

Add Manganese to the electrode to form spherical Mn/S which form between the grain and maintain grain cohesion

As carbon increases the Mn/S ratio required increases exponentially and is a major factor. Carbon content % should be a minimised by careful control in electrode and dilution

Limit the heat input, hence low contraction, & minimise restraint

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Solidification Cracking

Precautions for controlling solidification cracking

The use of high manganese and low carbon content fillers
Minimise the amount of stress / restraint acting on the joint during welding
The use of high quality parent materials, low levels of impurities (Phosphor & sulphur)
Clean joint preparations contaminants (oil, grease, paints and any other sulphur containing product)
Joint design selection depth to width ratios

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Solidification Cracking

Solidification cracking in Austenitic Stainless Steel

particularly prone to solidification cracking
large grain size gives rise to a reduction in grain boundary area with high concentration of impurities
Austenitic structure very intolerant to contaminants (sulphur, phosphorous and other impurities).
High coefficient of thermal expansion /Low coefficient of thermal conductivity, with high resultant residual stress
same precautions against cracking as for plain carbon steels with extra emphasis on thorough cleaning and high dilution controls.

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Cracks

Lamellar Tearing

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Lamellar Tearing

Factors for lamellar tearing to occur

Cracks only occur in the rolled plate !

Close to or just outside the HAZ !

Cracks lay parallel to the plate surface and the fusion boundary of the weld and has a stepped aspect.

Low quality parent materials, high levels of impurities
Joint design, direction of stress
The amount of stress acting across the joint during welding
Note: very susceptible joints may form lamellar tearing under very low levels of stress

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Lamellar Tearing

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Tee fillet weld

Tee butt weld (double-bevel)

Corner butt weld

(single-bevel)

Susceptible joint types combined with susceptible rolled plate used to make a joint.

High stresses act in the through thickness direction of the plate (know as the short transverse direction).

T, K & Y joints normally end up with a tensile residual stress component in the through thickness direction.

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Lamellar Tearing

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Critical area

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Lamellar Tearing

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Modifying a corner joint to avoid lamellar tearing

Susceptible

Non-Susceptible

Prior welding both plates may be grooved to avoid lamellar tearing

An open corner joint may be selected to avoid lamellar tearing

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Lamellar Tearing

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Precautions for controlling lamellar tearing

The use of high quality parent materials, low levels of impurities
The use of buttering runs
A gap can be left between the horizontal and vertical members enabling the contraction movement to take place
Joint design selection
Minimise the amount of stress / restraint acting on the joint during welding
Hydrogen precautions

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Lamellar Tearing

Crack type: Lamellar tearing

Location: Below weld HAZ

Steel types: High sulphur & phosphorous steels

Microstructure: Lamination & Segregation

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Occurs when:

High contractional strains are through the short transverse direction. There is a high sulfur content in the base metal.
There is low through thickness ductility in the base metal.
There is high restraint on the work

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Short Tensile (Through Thickness) Test

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The short tensile test or through thickness test is a test to determine a materials susceptibility to lamellar tearing

Friction Welded Caps

Short Tensile Specimen

Through Thickness Ductility

Sample of Parent Material

The results are given as a STRA value

Short Transverse Reduction in Area

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High contractional strains

Lamellar tear

Restraint

Lamellar Tearing

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Welding Inspector

Practical Visual Inspection

Section 22

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Leg Length Gauge

G.A.L.

S.T.D.

10mm

12mm

16mm

3mm

6mm

9mm

5mm

4mm

Throat Thickness Gauge

G.A.L.

S.T.D.

10mm

12mm

16mm

3mm

6mm

9mm

5mm

4mm

Fillet Weld Gauges

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HI-LO Single Purpose Welding Gauge

Root gap dimension

Internal alignment

HI-LO Welding Gauge

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Plate / Pipe Inspection

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Remember in the CSWIP 3.1 Welding Inspectors examination your are required to conduct a practical examination of a plate test weld, complete a thumb print sketch and a final report on your findings

Time allowed 1 hour and 15 minutes
The code is provided

Plate Inspection Examination

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Use a pencil for the arrow lines, but make all written comments and measurements in ink only

3) Do not forget to compare and sentence your report

2) Report everything that you can observe

4) Do not forget to date & sign your report

5) Make any observations, such as recommendations for further investigation for crack-like imperfections.

Plate Inspection Points

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After you have observed an imperfection and determined its type, you must be able to take measurements and complete the thumb print report sketch

The first thumb print report sketch should be in the form of a repair map of the weld. (i.e. All observations are Identified Sized and Located)

The thumb print report sketch used in CSWIP exam will look like the following example.

Plate Thumb Print Report

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After you have completed your thumb print report sketch of your test plate the next step is to complete your final report again the report must be completed in ink (no pencil).

The report must be completed to your thumb print sketch, do not leave any boxes empty, every box must be completed or dashed out. You must also make any comments you feel are necessary regarding any defects observed.

The report form used in CSWIP will look like the following example.

Plate Inspection Final Report

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Remember in the CSWIP 3.1 Welding Inspectors examination your are required to conduct a practical examination of a pipe test weld, complete a thumb print sketch and a final report on your findings

Time allowed 1 hour and 45 minutes
The code is nominated e.g API 1104

Pipe Inspection

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Application & Control of Pre heat

Section 23

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Welding Temperatures

Definitions

Preheat temperature

is the temperature of the workpiece in the weld zone immediately before any welding operation (including tack welding!)
normally expressed as a minimum Interpass temperature

is the temperature in a multi-run weld and adjacent parent metal immediately prior to the application of the next run
normally expressed as a maximum

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Minimum interpass temperature = Preheat temperature

Pre heat maintenance temperature = the minimum temperature in the weld zone which shall be maintained if welding is interrupted and shall be monitored during the interruption.

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Pre-heat Application

Furnace - Heating entire component - best

Electrical elements -Controllable; Portable; Site use; Clean; Component cannot be moved.

Gas burners - direct flame impingement; Possible local overheating; Less controllable;Portable; Manual operation possible; Component can be moved.

Radiant gas heaters - capable of automatic control; No flame impingement; No contact with component; Portable.

Induction heating - controllable; Rapid heating (mins not hours); Large power supply; Expensive equipment

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Measuring pre heat in Welding

Parameters to be measured:

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welding current
arc voltage
travel speed
shielding gas flow rate

The purposes of measuring

Demonstration of conformance to specified requirements

preheat/interpass temperature
force/pressure
humidity

Welding process control

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Pre-heat Application

Application Of Preheat

Heat either side of joint
Measure temp 2 mins after heat removal
Always best to heat complete component rather than local if possible to avoid distortion
Preheat always higher for fillet than butt welds due to different combined thicknesses and chill effect factors.

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Pre-Heat Application

Manual Gas Operation

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Electrical Heated Elements

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Welding Temperatures

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Point of Measurement

BS EN ISO 13916
t < 50 mm
A = 4 x t but max. 50 mm
the temperature shall be measured on the surface of the workpiece facing the welder

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Welding Temperatures

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Point of Measurement

BS EN ISO 13916
t > 50mm
A = 75mm minimum
the temperature shall be measured on the face opposite to that being heated
allow 2 min per every 25 mm of parent metal thickness for temperature equalisation

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Combined Thickness

The Chilling Effect of the Joint

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Combined Thickness

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The Chilling Effect of the Joint

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Combined Thickness

Combined chilling effect of joint type and thickness.

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The Chill Effect of the Material

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Heating Temperature Control

TEMPILSTICKS - crayons, melt at set temps. Will not measure max temp.
Pyrometers - contact or remote, measure actual temp.
Thermocouples - contact or attached, very accurate, measure actual temp.

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Temperature Test Equipment

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Temperature sensitive materials:

crayons, paints and pills
cheap
convenient, easy to use
doesn’t measure the actual temperature!

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Temperature Test Equipment

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Contact thermometer

Accurate
Easy to use
Gives the actual temperature
Requires calibration
suitable for moderate temperatures

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Temperature Test Equipment

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Thermocouple

based on measuring the thermoelectric potential difference between a hot junction (on weld) and a cold junction
accurate method
measures over a wide range of temperatures
gives the actual temperature
need calibration

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Temperature Test Equipment

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Thermistors

temperature-sensitive resistors whose resistance varies inversely with temperature
used when high sensitivity is required
gives the actual temperature
need calibration
can be used up to 999°C

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Temperature test equipment

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Devices for contactless measurement

IR radiation and optical pyrometer
measure the radiant energy emitted by the hot body
contactless method, can be used for remote measurements
very complex
for measuring high temperatures

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Welding Inspector

Calibration

Section 24

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Calibration, validation and monitoring

Definitions:

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Measurement = set of operations for determining a value of a quantity
Repeatability = closeness between successive measuring results of the same instrument carried out under the same conditions
Accuracy class = class of measuring instruments that are intended to keep the errors within specified limits
Calibration = checking the errors in a meter or measuring device
Validation = checking the control knobs and switches provide the same level of accuracy when returned to a pre-determined point
Monitoring = checking the welding parameters (and other items) are in accordance with the procedure or specification

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Calibration and validation

Frequency - When it is required?

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once a year unless otherwise specified
whenever there are indications that the instrument does not register properly
whenever the equipment has been damaged, misused or subject to severe stress
whenever the equipment has been rebuild or repaired

See BS EN ISO 17662 for details!

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Welding parameter calibration/validation

Which parameters need calibration/validation?

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depends on the welding process
see BS EN ISO 17662 and BS 7570 for details

How accurate?

depends on the application
welding current - ±2,5%
arc voltage - ±5%
wire feed speed - ±2,5%
gas flow rate - ±20% (±25% for backing gas flow rate)
temperature (thermocouple) - ±5%

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PAMS (Portable Arc Monitor System)

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What does a PAMS measure?

Welding current (Hall effect device)

Arc voltage (connection leads)

Temperature (thermocouple)

Wire feed speed (tachometer)

Gas flow rate (heating element sensor)

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PAMS (Portable Arc Monitor System)

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The purposes of a PAMS

For calibrating and validating the welding equipment

For measuring and recording the welding parameters

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Use of PAMS

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Wire feed speed monitoring

Incorporated pair of rolls connected to a tachogenerator

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Use of PAMS

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Shielding gas flow rate monitoring

Heating element sensor

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Summary

a welding power source can only be calibrated if it has meters fitted

the inspector should check for calibration stickers, dates etc.

a welding power source without meters can only be validated that the control knobs provide repeatability

the main role is to carryout “in process monitoring” to ensure that the welding requirements are met during production

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Welding Inspector

Macro/Micro Examination

Section 25

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Macro Preparation

Purpose

To examine the weld cross-section to give assurance that: -

The weld has been made in accordance with the WPS
The weld is free from defects

Specimen Preparation

Full thickness slice taken from the weld (typically ~10mm thick)
Width of slice sufficient to show all the weld and HAZ on both sides plus some unaffected base material
One face ground to a progressively fine finish (grit sizes 120 to ~ 400)
Prepared face heavily etched to show all weld runs & all HAZ
Prepared face examined at up to x10 (& usually photographed for records)
Prepared face may also be used for a hardness survey

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Micro Preparation

Purpose

To examine a particular region of the weld or HAZ in order to:-

To examine the microstructure
Identify the nature of a crack or other imperfection

Specimen Preparation

A small piece is cut from the region of interest (typically up to ~ 20mm x 20mm)
The piece is mounted in plastic mould and the surface of interest prepared by progressive grinding (to grit size 600 or 800)
Surface polished on diamond impregnated cloths to a mirror finish
Prepared face may be examined in as-polished condition & then lightly etched
Prepared face examined under the microscope at up to ~ x 600

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Macro / Micro Examination

Object:

Macro / microscopic examinations are used to give a visual evaluation of a cross-section of a welded joint
Carried out on full thickness specimens
The width of the specimen should include HAZ, weld and parent plate
They maybe cut from a stop/start area on a welders approval test

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Macro / Micro Examination

Will Reveal:

Weld soundness
Distribution of inclusions
Number of weld passes
Metallurgical structure of weld, fusion zone and HAZ
Location and depth of penetration of weld
Fillet weld leg and throat dimensions

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Visual examination for defects
Cut transverse from the weld
Ground & polished P400 grit paper
Acid etch using 5-10% nitric acid solution
Wash and dry
Visual evaluation under 5x magnification
Report on results

Visual examination for defects & grain structure
Cut transverse from a weld
Ground & polished P1200 grit paper, 1µm paste
Acid etch using 1-5% nitric acid solution
Wash and dry
Visual evaluation under 100-1000x magnification
Report on results

Macro

Micro