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Study on Alloys for �Storage and Transportation �of Liquid Hydrogen

Rutvik Patel

MENG, Mechanical Engineering

Meet Chanchapara

MENG, Mechanical Engineering

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Introduction

Hindenburg disaster:

On 6th May 1937, the Airship Zeppelin inflated with 200,000 m3 of H2 ignited in less than a minute resulting in the death of 35 out of the 97 passengers, in Manchester Township, New Jersey, United States.

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Introduction

Liquid Hydrogen is widely used in many applications:

- as main fuel for rockets

- as a clean energy

- in civil and industrial applications

470 tons/day worldwide
Hydrogen has the highest energy per mass of any fuel; however, its low ambient temperature density results in a low energy per unit volume, therefore requiring the development of advanced storage methods that have potential for higher energy density.

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Introduction

Hydrogen can be stored in a two ways :-
As a compressed gas
Liquid H₂

_{Due to the low temperature of liquid hydrogen (20 K), special requirements have been put forward for the selection of materials for storage and transportation containers.}
_{Therefore, it is important to develop appropriate alloy for Cryogenic vessels, for the safe storage and transportation of liquid hydrogen.}

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Challenges in Storage and Transportation

Hydrogen : a light weight compound (High tendency to leak)
Hydrogen’s extreme flammability and low ignition energy
Degradation of metals and alloys by hydrogen
Cryogenic hydrogen is stored in liquid form at -253 °C

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Properties of importance

Physical properties :
Coefficient of linear expansion
Young’s modulus
Thermal conductivity

Mechanical Properties :
Hydrogen Embrittlement
Tensile strength
Yield strength
Ductility
Impact toughness
Weldability

Service Properties :
Corrosion resistance
Welding performance
Cost of the materials

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Hydrogen Embrittlement :

Hydrogen embrittlement refers to the phenomenon of material crack initiation and fracture caused by the diffusion of hydrogen molecules into the material.
Due to the serious damage of hydrogen embrittlement to the structure, especially in a hydrogen environment, it needs special attention.
When the material is loaded in the hydrogen environment, hydrogen molecules will gather at the internal stress concentration of the material, resulting in crack initiation, propagation, and fracture.

Hydrogen Blistering 2. Hydrogen Embrittlement 3. Hydrogen Stress Cracking

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Materials / Options :

Advantages :-
Excellent hydrogen brittleness resistance
Good low temperature performance
Weldability
Corrosion resistance

Disadvantages :-
the low-temperature mechanical properties of materials under specific environmental requirements need to be further improved.

For example,the combination of corrosion resistance and low-temperature properties of storage tanks.

1. Stainless steel

Application :

Especially used in the ground liquid hydrogen storage and transportation.

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Chemical composition of austenite stainless steel commonly used in cryogenic temperature

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2. Titanium Alloy

Advantages :-
Good corrosion resistance
High specific strength
High temperature resistance
Low thermal conductivity
Small coefficient of expansion

Disadvantages :-
Impact toughness, and fracture toughness decrease with the decrease in temperature.
Cost is relatively high

Application :-

Widely used in the aerospace field. In 1981, the Apollo space rocket launched by NASA used titanium and titanium alloys as liquid helium and liquid hydrogen containers and structural pipes.

Alloys :

Ti-2Al- 2.5Zr, Ti-3Al-2.5Zr, CT20

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3. Aluminum Alloy

Advantages :-
Excellent formability
Lightweight
Low sensitivity to hydrogen embrittlement
Welding performance
Good corrosion resistance

Disadvantages :-
The corrosion resistance and stress corrosion characteristics of the welding parts are aspects of aluminum alloy tanks that need to be concerned.

Application :-

Have been widely used in liquid hydrogen storage tanks for space launches both domestically and internationally

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Chemical composition of aluminum alloys commonly used in cryogenic temperatures

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Al-based Alloys – Crystal Structure

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Al-based Alloys – Effect of different alloying elements

Cu
Mg
Ag
Li
Mn
Ti, V, Zr
Fe

Cu & Mg: increases the yield and ultimate strengths by a factor of 4 to 6

Ag: increases the strength of heat-treated and aged Aluminium-copper-magnesium alloys

Li: density is decreased, the young modulus is increased, and the fatigue crack growth resistance is increased

Mn: tensile strength increases. and the yield strength also increases, but to a lesser extent.

Additions of manganese and magnesium decrease the fabricating characteristics of the aluminum-copper alloys, and manganese also causes a loss in ductility; hence, the concentration of this element does not exceed about 1% in commercial alloys.

Alloy containing small amount of Ti, Vanadium, Zr is known to raise the recrystallization temperature. An alloy of this nature retains its properties well at elevated temperatures, fabricates readily, and has good casting and welding characteristics.

Iron is the most common impurity found in aluminum. It has a high solubility in molten aluminum and is therefore easily dissolved at all molten stages of production. Iron reduces the grain size in wrought products. The solubility of iron in the solid state is very low (~0.05%); therefore, most of the iron present in aluminum over this amount appears as an intermetallic second phase in combination with aluminum and often other elements.

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Proposed Solution - Challenges

Yield strength and UTS
Weight of the material
Fatigue crack resistance
Formability
Strength and toughness at Cryogenic temperatures

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Proposed Solution - Options

AA 2219

Alloying elements: Cu 6.3; Mn 0.3; Ti 0.06; V 0.1; Zr 0.18

AA 2195

Alloying elements: Cu 4.0; Mn 0.5; Mg 0.45; Li 1.0; Ag 0.4; Zr 0.12

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Proposed Solution - Solution

AA 2195
Reason for the selection of alloying elements

Cu
Mg
Li
Mn

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Ternary diagram of Al-4% Cu-1% Li

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Equilibrium Solidification

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Improvement in manufacturing of LH2�storage vessel using Cryogenic Forming

Cryogenic forming
Friction stir welding

LH2 storage vessels are made using forming process. Cryogenic forming generally refers to the process of forming at the temperature of liquid nitrogen (77 K).

Aluminum alloys have been proven to not change from toughness to brittleness at cryogenic temperatures. On the contrary, aluminum alloys tend to increase plasticity and toughness at cryogenic temperatures.

Cryogenic forming can significantly improve the strength and plasticity of aluminum alloy materials simultaneously, which is expected to become a revolutionary processing technology.

Jin Zhang et al. studied cryogenic deformation behavior and microstructural characteristics of 2195 Alloy and found that the deformation temperature had a significant effect on tensile properties of the alloy. The strength and elongation of the alloys increased with the decrease in deformation temperature. Therefore this method of forming with friction stir welding (FSW) can be used to produce better pressure vessels for storage of liquid hydrogen.

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Fitness for service

Evaluation of mechanical properties of storage vessel material
Evaluation of safety, reliability and structural integrity of the storage vessel

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Fitness for service�(1) Evaluation of mechanical properties of storage vessel material �

Cryogenic Toughness
Tensile strength, yield strength, elastic modulus, plasticity index

The impact toughness is closely related to the crystal structure of the material. The face centered cubic crystal has better impact resistance at low temperature, while the body centered cubic crystal has worse impact resistance, The plasticity of materials at low temperature depends on the ductile brittle transition characteristics of materials.
For materials with low-temperature brittle transition, the plasticity decreases sharply at low temperature, and cannot be applied to a low-temperature environment.
Checking the impact toughness of weld is also necessary with the testing of storage tank material. Because the performance of the welded parts is usually significantly worse than that of main material.
There are many test methods for testing the toughness. But most widely used test is the cryogenic Charpy impact toughness test. For doing this test 294 N-m Charpy test machine, liquid helium Dewar, and a vacuum insulated transfer tube is required. In the impact test, the pressure inside the Dewar is maintained to 3-4MPa by supplying helium gas.
The materials which easily fracture due to brittleness cannot be used at cryogenic temperature. The significant decrease in the plasticity at low temperature will induce brittle brittle crack initiation and fracture risk.
From tensile test, the tensile strength, yield strength, elastic modulus, and plasticity index all can be evaluated. For performing tensile testing, the electronic universal testing machine can be used at low temperatures. In this testing process, the apparatus pulls on each end of the material until it fractures.

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Fitness for service�(2) Evaluation of safety, reliability and structural integrity of the storage vessel�

Safety and reliability

API 579-1

Structural integrity of pressure vessel and related equipment

API 510 (Pressure Vessel Inspection Code)
API 570 (Piping Inspection Code
API 653 (Tank inspection, Repair, Alteration, and Reconstruction)
NB-23 (National Board Inspection Code)

Liquid hydrogen is stored at high pressure and very low temperature in the insulated vessel. When stored, the LH2 is accompanied by a certain amount of gaseous hydrogen. Hydrogen is easily ignited; its minimum ignition energy is very low around 19μJ. In practice hydrogen venting or leaking to atmosphere, particularly from a pressure source can ignite due to electrostatic or self-igniting impurities in the hydrogen. Hydrogen is flammable and therefore presents a possible explosion hazard.
For these reason the safety and reliability of liquid hydrogen storage vessel must be checked before use. For that purpose, API 579-1/ASME FFS-1 is used.
API 579-1 describes several fitness-for-service (FFS) assessment techniques that help ensure the safe and reliable operation of pressurized equipment used in oil & gas, petrochemical, and chemical facilities. This standard contains numerous sections on assessment procedures for calculating the impact of damage mechanisms such as brittle fracture, general metal loss and local metal loss, pitting corrosion, blisters and laminations, weld misalignment and shell distortion, crack-like flaws, creep damage, and fire damage.
Fitness-for-service evaluations performed in accordance with API 579-1 Standard are recognized and referenced by API 510 (“Pressure Vessel Inspection Code”), API 570 (“Piping Inspection Code”), API 653 (“Tank Inspection, Repair, Alteration, and Reconstruction”), and by NB-23 (“National Board Inspection Code”) as suitable for evaluating the structural integrity of pressure vessels and related equipment.
When it comes to inspections, most pressure vessels should be examined once before being placed into service and again every 5 years after every alteration or major repair.

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Thank You.

Questions?