<p>Many researchers are developing mechanistic approaches describing High Temperature Hydrogen Attack (HTHA) damage. Although there are a variety of approaches, all of them make use of describing HTHA as a time and temperature dependent phenomena that is sensitive to methane pressure where the methane pressure results from diffusion of hydrogen into cavities along grain boundaries which reacts with carbon from the steel forming methane.&nbsp;A lot of HTHA research shows the damage process is a phenomenon that is very similar to creep damage which has an exponential relationship to the applied stress and temperature.&nbsp; Also, past research has shown that the equilibrium Methane partial pressures can be&nbsp;orders of magnitude than the Hydrogen partial pressure and that Methane partial pressure increases with decreasing temperature. However, due to fact that the research work draws heavily from creep damage concepts, they are able to show that the HTHA damage is lower at the lower temperatures due to the low creep damage rates at the lower temperatures. Based on these observations, the authors propose an HTHA damage assessment procedure that uses the Larson Miller Parameter (LMP) approach and employs the Linear Life Fraction Rule for evaluating operating condition variations of hydrogen partial pressure and temperature.&nbsp;</p>

Simplified HTHA Evaluation Using Larson Miller Parameter Concepts

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

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