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 29th to 30th,
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.
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