Pressure and Temperature Interactions (1.5)

Criticality: High
Progress: Not Addressed
Score: 40
DOT Relevance: §192.51 – §192.65

Description of Key Area

Pressure and temperature interactions are addressed under Subpart B (Materials) of 49 CFR 192. Per the Code, Subpart B on materials prescribes the minimum requirements for the selection and qualification of pipe and components for use in pipelines.

Discussion of Criticality

This area is critical because loss of mechanical properties in the pipe due to pressure and temperature interactions can lead to pipe failure.

Discussion of Progress

During a presentation at the Materials and Components for the Hydrogen Economy Codes and Standards Workshop in Augusta, Georgia on August 29^th to 30^th, 2005, ASME identified the following knowledge gap: is there a correlation between pressure and temperature with the loss of mechanical properties of common pipe materials?

SNL is conducting hydrogen material compatibility 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).

The ASME B31.12 hydrogen task group has undertaken a literature search which indicates that embrittlement seems to be most pronounced in carbon steels at about 20°C (68°F) and begins to become less of an issue starting at about 150°C (302°F). Above this temperature hydrogen attack becomes the primary problem. Hydrogen pipelines are not expected to operate above 150°C (302°F).

Recommendations

The ASME B31.12 hydrogen task group is considering adding cautionary statements about embrittlement and requires research data to provide more substantial guidance to code users. The work underway at Sandia needs to reflect the data needs of the ASME B31.12 hydrogen task group. Hydrogen standards for materials compatibility should be established and incorporated by reference into the federal code.