Abstract
The marked decrease in creep ductility that can be caused by internal pressure in grain boundary pores is modelled to treat the interaction between boundary diffusion, power law creep, and bubble pressure. The application to 2.25 Cr−1 Mo steel in high pressure hydrogen is treated numerically using a computer program since here the internal methane pressure in pores is known, and kinetic data exists. Reasonable agreement is obtained between the predictions and the observed loss in ductility in the presence of 21 MPa of hydrogen. With methane pressurized bubbles, the model suggests intergranular fracture is powerlaw creep limited at essentially all temperatures and stresses. Thus one predicts the hydrogen attack resistance in service to be strongly influenced by the creep strength of the alloy. In the absence of hydrogen (methane), intergranular fracture should be limited by diffusion creep and thus much more sensitive to pore density and boundary diffusion rate than strength. Possible application to recent high temperature steamline failures in welded pipe and to helium effects in nuclear reactor materials are also indicated.
Published Version
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