Abstract

ASME B31.12 provides piping and pipeline design and construction standards specific for H2 service. Due to the material degradation mechanisms in presence of high-pressure hydrogen, B31.12 imposes a significant reduction in allowable stresses by applying materials performance factors (Hf and Mf) in thickness and design pressure calculations. The reduction factor is as much as 54% for high strength piping and pipeline materials at high hydrogen pressures. The application of the materials performance factors significantly penalizes the use of high strength piping and pipeline materials. In the light of recent developments in understanding hydrogen degradation mechanisms, it is recognized that alternative design and fabrication technologies can be employed to mitigate the risk of hydrogen embrittlement without such penalties. Using fracture mechanics approaches, it has been demonstrated that the materials performance factors can be relaxed by implementing additional requirements in non-destructive examination (NDE) and heat treatment. A B31.12 Code Case has been developed to provide alternative rules to relax the materials performance factors. This Code Case has been approved by ASME B31 Committee and Board on Pressure Technology Codes and Standards, and is ready to be used by code users. This paper reviews the background on Materials Performance Factors in current code, and documents the technical justifications of eliminating these factors.

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