Simplified Methods for High Temperature Weld Design and Assessment for Steady and Cyclic Loading

摘要

Simplified or reference stress techniques are described and demonstrated for high temperature weld design and life assessment. The objective is the determination of weld life under steady and cyclic loading in boiler headers and piping systems. The analysis deals with the effect of cyclic loading, constraint and multiaxiality in a heterogeneous joint. A common thread that runs through most high temperature weld reports and failure analyses is the existence of a relatively creep-weak zone somewhere in the joint. This paper starts with the assumption that the size and creep strength of this zone are known, in addition to parent metal properties. Life prediction requires an efficient analysis technique (such as the reference stress method), which separates the structural and material problems, and does not require complex constitutive models. The approach is illustrated with a simple example of an IN617 main steam girth weld, which could be present in an advanced plant concept with 700°C steam temperature.