Abstract: A 316L stainless steel pipe cracked, and the crack direction was perpendicular to the weld. The causes of the cracks were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the copper element was enriched on the fracture surface and exhibited intergranular distribution characteristics. Copper contamination occurred during the welding of stainless steel welded pipe. In the subsequent heat treatment process, low melting point copper liquefied and penetrated along the grain boundary, making the grain boundary brittle. Under the action of cooling tensile stress, copper contamination cracks were generated, resulting in cracking of the steel pipe.