St. Tu et al., DESIGN AGAINST CREEP FAILURE FOR WELDMENTS IN 0.5CR0.5MO0.25V PIPE, International journal of pressure vessels and piping, 58(3), 1994, pp. 345-354
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.