Abstract: By the analysis of the chemical composition, mechanical properties, microstructure and fracture morphology of the automatic welding butt girth weld of two X80M steel spiral submerged arc welded pipes in a natural gas transmission pipeline, the causes of buried cracks in the girth weld were discussed. The results show that the cracks in the girth welds were located at the fusion line of the groove on the left and right sides of the filler weld. During filler welding, the contact between the copper contact tube and the weld groove led to short circuit; the high temperature generated by the short-circuit current resulted in the melting of the contact part between the contact tube and the groove; the metal copper fused at the groove was fused into the filler metal of the girth weld with the welding wire, and diffused along the base metal and weld grain boundary to form a copper enrichment zone, which finally led to the molten copper cracking of the girth weld.