DESIGN AGAINST CREEP FAILURE FOR WELDMENTS IN 0.5CR0.5MO0.25V PIPE

The present paper studies design principles for weldments against cree p failure in terms of failure experiences. Constitutive equations are developed for simulation of the creep behaviour of postservice materia ls. Numerical simulations of damage development in the weldment are th en carried out. The damage state is well predicted by the presented pr ocedure. Microcracking or severe cavitation is predicted to occur in t he weld metal and the heat affected zone, which is in good agreement w ith the observations of the damage distribution through the wall thick ness. It is found that, in the normal operating condition, the creep l ifetime can be reduced by a factor of 3 due to the presence of the wel d. Weldment reduction factors are then developed for design considerat ions. A stress reduction factor of about 0.9 or a strain reduction fac tor of 0.33 is required for the weldment design. The strain reduction factor is smaller than 0.5, which implies that the rule for the weldme nt design in the ASME CC-N47 might not be sufficiently conservative.