Thickness and multi-axial stress creep rupture criteria of the Type IV component of a ferritic steel weld

The paper summarizes previously derived constitutive parameters for temperatures of 575, 590, 600, 620 and 640 degrees C. Values of the multi-axial stress rupture parameter, P, are reviewed and recorded. This constitutive parameter set is used to determine the thickness of the Type IV material zone (0.7 mm). Values of Type IV multi-axial stress rupture parameter v are determined for a wide range of butt-welded pipe and cross-welded uni-axial specimens, and an interpolation equation is derived in terms of temperatures and stress level. Finally, continuum damage mechanics (CDM) analyses are performed for pipes and cross-welded testpieces, which include a coarse-grained heat-affected zone (CG-HAZ). It is shown that the constitutive parameter set, which corresponds to a minimum creep rate ratio of 1/2.5, with respect to the parent material, gives accurate predictions of lifetimes and damage distributions.