Longitudinally welded 22Cr duplex pipes were delivered to a development project in the North Sea. The pipes were manufactured by ordinary U&O process, and welded using submerged arc welding (SAW). After welding, the pipes were soaked at 1050–1100°C. Final non destructive examination (NDE) of the longitudinal weld seam included 100% radiography and dye penetrant inspection (DPI).

Due to oval original pipe body, quite heavy dimensional calibration was performed after cutting, before girth weld groove preparation. No NDE was done after the last dimensional calibration. The piping system was then welded together and installed in the production facility. By final NDE of the girth welds, also defects in the longitudinal weld seam were detected, in the weld cap inside the pipe.

The cracking was presumably caused by a combination of weakness in the weld metal, and heavy stresses/restrained conditions during dimensional calibration of the thick-walled pipe. The weakness in the weld metal could be caused by welding condition and parameters. Further investigation also revealed internal cracks, not extending to the surface. No hot cracks were observed. Hydrogen induced effects, however, could not be disregarded as a contribution to the cracking.

Extended repair was performed, including disassembling of the pipes, before inside grinding and weld repair using the gas tungsten arc welding (GTAW) process.