Decarbonisation Technology - August 2023 Issue

Form of hydrogen

Material

Gas

Liquid

Notes

Aluminium and aluminium alloys

Acceptable

–

Austenitic stainless steels with >7% nickel (304, 304L, 308, 316, 321, 347)

Acceptable

Beware of martensitic conversion at low temperature if stressed above yield point

Carbon steels

Acceptable Acceptable

Not acceptable

Too brittle for cryogenic service

Copper and copper alloys (brass, bronze

Acceptable

–

and copper-nickel) Gray, ductile, or cast iron

Not acceptable Not acceptable

Not permitted for hydrogen service Too brittle for cryogenic service Beware of susceptibility to hydrogen

Low-alloy steels

Acceptable

Not acceptable

Nickel and nickel alloys (e.g. Inconel and Monel)

Not acceptable

Acceptable

embrittlement

Nickel steels (2.25%, 3.5%, 5%, and 9% NI)

Not acceptable Not acceptable

Beware of ductility loss

Titanium and titanium alloys

Acceptable

–

Table 2 Summary of materials compatible with hydrogen service ( Reproduced from Table A-2-1 of ASME B31.12 )

as a general starting point and the performance of the Acceptable materials can vary greatly depending on the particular grade (for example, 316 vs 316L) and metal chemistry controls (for example, nickel content). There is currently no formal methodology for determining whether a material is compatible with hydrogen. However, the basic parameters

that should be considered for determining risk-based material compatibility are the environment in which the equipment will operate, the loads applied during operation, and the material’s sensitivity or susceptibility to hydrogen damage. These parameters are highlighted in Figure 4 . Beyond the basic material selection, damage mechanisms unique to hydrogen service must be taken into consideration. One of the most impactful damage mechanisms is hydrogen embrittlement (HE) or hydrogen-assisted fatigue and fracture. HE is the loss of strength, ductility, and/or fracture toughness of susceptible materials due to the penetration and diffusion of atomic hydrogen. Essentially, the hydrogen dissolves into the metal and changes the mechanical response of the metal when stress is applied. HE can lead to brittle cracking, with high-strength steels being particularly susceptible. In metallic equipment used for hydrogen production, storage, and transportation, even small amounts of hydrogen may accelerate fracture/cracking by a factor of 10. Figure 5 shows the significant increase in crack growth rates for some common pipeline steels compared to similar materials only exposed to air. The chart shows da/dN, which

Applied loads Magnitude of stress Cyclic loading

Environment Pressure/ temperature Hydrogen purity

Potentially compatible material

Material sensitivity Physical/mechanical properties Material microstructure Surface conditions

Figure 4 Material compatibility considerations