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Loss of Fatigue and Impact Strength (1.8)

Criticality: High
Progress: Not Addressed
Score: 40
DOT Relevance: §192.501 – §192.517

Description of Key Area

Hydrogen attack can lead to increased crack propagation susceptibility, which degrades properties such as ductility and fracture toughness. Subpart J of 49 CFR 192 prescribes the minimum leak test and strength test requirements for pipelines.

Discussion of Criticality

This area is critical because loss of mechanical properties in the pipe can lead to pipe failure.

Discussion of Progress

ASME has identified a research need for hydrogen testing requirements. This need was presented during the Materials and Components for the Hydrogen Economy Codes and Standards Workshop in Augusta, Georgia on August 29^th to 30^th, 2005. The research need identified was the following: “Testing is needed of all commonly used piping and pipeline materials for loss of fatigue and impact strength in a high pressure hydrogen environment. Research of the effects of pressure cycling on mechanical properties is needed.”

SNL is conducting hydrogen compatible materials studies. The focus is on material data for applications that involve the storage, distribution, and consumption of high-pressure hydrogen gas. Pertinent data include hydrogen-affected mechanical properties (yield, tensile strength, ductility, fracture toughness, threshold stress-intensity factor, fatigue crack growth rate, fatigue crack growth threshold, and impact fracture energy).

Work underway at UIUC has indicated that fatigue cracking appears to be more of prevalent in low cycle rate, low stress situations than in high cycle rate, higher stress situations.

Recommendations

The ASME B31.12 hydrogen task group is considering the addition of cautionary statements on fatigue in hydrogen pipelines and piping. Appropriate tests for hydrogen pipe should be devised including pressure cycling. Once this research has been completed, current standards should be amended based on this research and these amendments incorporated by reference into the federal code.