Fracture surface investigations of API pipes welded with parameters determined by Taguchi method

Abstract

In this study, SEM images of the samples taken from welded nick break tests of API 5L X65 pipe joints,whose welding parameters were determined by Taguchi method, were examined. As a result of theinvestigations, the elongations and orientations exhibited by the grains showed that ductile and brittlefractures were observed in the welded joints. As it was observed from equiaxed, honeycomb like imagesthat the fractures exhibited a ductile behavior. Brittle fractures that occurred due to cleavage breaks in someregions were detected. An apparent effect of welding direction was observed in fracture behavior. It wasdetected from the SEM images that a ductile fracture structure had occurred in all joints that were performedfrom bottom to top, while it was observed in the joints performed from top to bottom that generally cleavageplanes had developed along with fibrous structures in places, therefore brittle fractures had occurred.