Abstract
A longitudinal crack was found in the welding seam during the X-ray inspection of a newly built L245NS gas transmission pipeline in China western oilfield. The crack causes were analyzed by the nondestructive tester (NDT), direct-reading spectrometer, tensile strength test machine, impact test machine, Vickers hardness tester, optical microscope (OM), macroscopic fracture morphology, scanning electron microscopy (SEM) and energy spectrum analysis(EDS) in this paper. The results show that the crack is caused by the original defect. First, the fracture surface of the crack is characterized by multi-source cracking, and the origin of the crack is containing foreign matters. Second, the surface of crack fracture is blue, which indicates that the crack fracture has experienced high-temperature burning, so the crack may be formed before heat treatment. The main reason for steel pipe crack is the low stress cracking at the pipe end by the “slag inclusion” formed in the pipe body when the pipe is processing.
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