Evaluation of strength and microstructure of welded pipes with wall lamination

Abstract The reported research has been carried out to study the causes of a crack developing along a factory-produced girth weld fabricated with electrical resistance welding using high frequency currents. The crack appeared in an underground main gas pipeline. The study included visual and dimensional inspection of the object, ultrasonic pipe wall thickness tests, chemical analysis, optical and electron-microscopic investigation, weld and heat-affected zone microhardness measurement, tests for static tension and fractographic analysis. The research revealed that the metal of one of the welded pipes had laminations. The structure and morphology of the weld and those of the metal in the adjacent pipe parts were examined, and the effect of inclusions on the weld structure was analyzed. An important outcome of the study was that the laminations were heterogeneous, had a multilayer structure and were formed due to a number of production factors. Their combined effect resulted in substandard production of the weld and furthered crack development when in service. Neither the crack nor the lamination in the pipe wall was detected during the inline inspection with a magnetic flaw detector.