Abstract: Corrosion perforation failure occurred around the girth weld of a water-mixing pipeline in an oilfield in north China. Methods including macro-morphology examination, material property testing, corrosion product analysis, and fluid simulation were employed to determine the cause of the pipeline failure. The results show that both the base metal and the weld met the standard requirements in terms of physicochemical properties, and the corrosion products at the failure site were identified as FeOOH. Simulation results indicated that in the presence of weld reinforcement, deposition preferentially occurred on the base metal behind the weld. Once scaling formed, the base metal rapidly perforated due to the combined effects of oxygen corrosion and under-deposit corrosion. It is recommended that internal coating at the girth weld should be repaired, and the weld profile should be kept as smooth as possible to reduce solid particles in the solution.