Analysis of Causes for Fracture of Specimen for Side-bend Test to Drill Pipe Weld

The weld gray spot acts as a key factor affecting performance consistency of the drill pipe weld.The fracture of the side-bend test specimen of the friction-welded drill pipe is analyzed.As a result,it is identified that both the specimen fracture and the impact fracture obviously present as the brittle fracture morphology.Accordingly the causes are analyzed,and the main cause is found,i.e.,the large amount of inclusions as existing in the end section of the blank pipe which have not been extruded out of the weld during the friction welding process,and then turn into defects as the gray spots locally distributed in the area of the weld,which reduces the strength of the welding joint face.Therefore it is suggested to fully clean up any dirt on the welding end faces of the pipe body and the joint for assuring of the cleanness of the base metals of the ends to be welded,and to properly increase the top section pressure during the friction welding for assuring of the weld axial shortening amount so as to get the oxidized metal excluded out of the weld in the form of fin as far as possibly in a bid to reduce the occurrence of the micro-gray spot in the welding area.