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gas pipeline steel is 800 MPa . The properties of welds are carefully controlled to preclude hydrogen embrittlement .
As hydrogen pipelines are operated at near constant pressure , cracking due to hydrogen embrittlement must
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be driven by static mechanical forces . Cyclic loading , which can drive fatigue crack propagation aided by hydrogen embrittlement , has not been a concern for hydrogen gas transmission pipelines . |
Experience from the petroleum industry , however , has demonstrated that hydrogen-assisted fatigue is possible with hydrogen piping . Defects can form on the inner and outer surfaces of steel pipelines from several sources , including welds , corrosion , and third-party damage . Welds are of particular concern since steel pipelines can require two different welds : longitudinal ( seam ) welds to manufacture sections of pipeline , and girth welds to assemble the pipeline system . These welds are inspected to detect the presence of defects in pipeline walls that intensify stresses locally , creating more severe mechanical conditions for crack extension and concentrating atomic hydrogen in the steel . |
ceed the limit in current applications .
Data consistently shows that steels are more susceptible to hydrogen embrittlement at higher gas pressures . As operating pressures increase , designs will demand materials with higher strength . Most data indicate that steels are more vulnerable to hydrogen embrittlement when strength increases . The effects of other variables , such as gas impurities , welds , and mechanical loading on hydrogen embrittlement of steel vessels and pipelines in the hydrogen economy are not as certain . Hydrogen embrittlement resistance of steels could be improved through production of lowmanganese and low-silicon steels .
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Conclusion |
Although hydrogen embrittlement is |
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Experience with steel vessels and pipelines in the industrial gas and petroleum industries demonstrates that these structures can be operated safely with hydrogen . The use of this gas is however limited to certain ranges of material , the environment , and mechanical variables . Gas pressures in valves , vessels , and pipelines for the hydrogen economy are certain to ex- |
more severe at high gas pressures and in high strength steels , structures can still be designed with steels under these conditions by using fracture mechanics . Provided material data is available for steels in high-pressure hydrogen gas , the limiting crack depth , wall stress , and structure dimensions can be defined using fracture mechanics . |