Limit Loads of Surface and Embedded Flaws in Plate with Weld Strength Mismatch

Strength mismatching between weld metal and parent material is common in pressure vessel industry. To carry out the fracture assessment of weld defects, it is required to accurately estimate the reference stress or limit load for the flawed section. Weld strength mismatch introduces complexity in determination of the limit load. Although it is acceptable to use the weaker material properties in the assessment, it can be overly conservative. Industrial standards R6 and BS7910:2013 provide the methods for weld strength mismatch, but no limit load ratio solutions are available for semi-elliptical surface and embedded flaws which are the most common cracks in pressure vessels and pipework. It is useful to understand whether the existing limit load ratio solutions in R6 and BS7910 can be used for surface and embedded flaws. This paper reviews the assumptions used in the existing reference stress solutions and discusses its suitability for mismatch conditions. The effects of weld strength mismatch on limit loads of the surface and embedded flaws are studied using 3D elastic-plastic finite element analyses. The results are compared with the R6 and BS7910 solutions. The validity of the handbook solutions of through-wall flaws for surface and embedded flaws in plate and the mismatch effect on limit loads are discussed.