HTHA Model Advancements

As described in the first edition of E²G Industry Insights, the Applied Research and Development group at E²G has already developed the most sophisticated model for predicting HTHA life to date, considering both volumetric and crack-like HTHA damage accumulation. These procedures were first developed during the work of the ongoing HTHA JIP, but progress has continued at a rapid pace since, and many improvements have been made. The time-dependent model accounts for many contributing factors to damage accumulation, such as variable operating conditions, the transient diffusion of hydrogen, kinetic rates of methane formation, non-ideal gas behavior, and stress effects including both primary and residual stresses. This model was shown to be fairly predictive and matched all the observed trends very well, including a prediction of the general shape and location of the Nelson curves that appear in API 941.