scope:

This WRC Bulletin presents several new insights into creep crack growth problems:

(1) the potential for stress concentrations resulting from the mismatch of creep properties between weld and base metals;

(2) a creep crack growth model that includes the effects of stress triaxiality; and

(3) a crack initiation model based on the statistical distribution of inclusion size and spacing. Longitudinally welded piping is used extensively in the power industry for high temperature applications. Finite element analysis of a typical symmetric, double-V longitudinal weld showed that a material stress concentration will develop in 1 to 2 years if creep properties of the weld and base metals are different and that differences in material properties have a significant effect on the stress field after a crack has formed. Observations based on a literature review and microscopic studies of welds in low chromium alloy steels indicated that crack initiation and growth models could be developed based solely on the growth and coalescence of cavities emanating from the fusion line inclusions. The models developed agree well with industry experience, accurately predicting two recent piping failures in the power industry. This document should be viewed with the perspective of the events reported in WRC Bulletin 354, Failure Analysis of a Service-Exposed Hot Reheat Steam Line in a Utility Steam Plant and The Influence of Flux Composition of the Elevated Temperature Properties of Cr-Mo Submerged Arc Weldments. Publication of this document - WRC Bulletin No. 390 was sponsored by the WRC