An assessment of primary system stresses on the creep behaviour of high temperature steam piping systems

The effects of creep on the primary system loadings sustained by high temperature steam piping layouts are ignored in design. A detailed evaluation of the consequences of this omission is presented from both the theoretical and practical viewpoints. Piping analyses show that $systems are not supported correctly this can give rise to enhanced primary stresses. In these circumstances if the creep strength of any part of weldments is signgcantly less than the average rupture strength of the parent material circum-ferential cracking may occur in the design lifetime. A feature of the results obtained from creep analyses is that over-stressed systems tend to sink with time. I t is proposed that this characteristic can be used to help decide which piping systems should have their welds examined. NOTATION basic characteristic of a Drimarv stress is that it is no