In the present study, simple J-integral estimations of welded pipes with a circumferential through-wall crack (TWC) in weld zone were proposed based on the failure assessment diagram (FAD) concept using scaling factor that is defined as a ratio of plastic limit load of welded pipe to that of base metal pipe. For this purpose, the detailed 3-dimensional (3-D) finite element (FE) limit analyses for welded pipes with a circumferential TWC have been systematically carried out considering various thickness of pipe, circumferential crack lengths, strength mismatches between base and weld metal, widths of weldment and locations of TWC (weld center and interface between the weld metal and the base metal). As for loading conditions, axial tension and global bending were considered in the FE analyses.
Based on the present FE results, numerical expressions on scaling factors representing the ratio of plastic limit loads of welded pipes to those of base metal pipes were derived. Finally, the new FAD-based J-estimations based on option 1 concept was proposed to predict J-integrals of welded pipes incorporating the present scaling factors, i.e. ratio of plastic limit load. Moreover, the proposed J estimations were validated by comparing with FE results using actual properties.