Abstract: After six months of service, perforation occurred on the surface of a 316L stainless steel heat exchanger coil.Macroscopic observation, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), metallographic examination, and chemical composition analysis were used to characterize the morphology of the inner and outer walls at the perforation, corrosion products, microstructure, and chemical composition of the tube wall.The results show that abnormal carbides existed in the coil.These carbides reduced the corrosion resistance of the coil, and their spalling provided sites for the deposition of corrosive media outside the tube.Under the action of external environmental media, pitting corrosion initiated at the pits formed by carbide spalling.Combined with continuous scouring by the external fluid and intergranular corrosion during the corrosion process, the corrosion gradually propagated through the tube wall to the inner surface, eventually leading to corrosion perforation.