Cause Analysis on Corrosion of an L80 Tube Threaded Joint

Corrosion failure occurred to an L80 tube threaded joint in a well only after six months of use. Means such as macroscopic analysis, metallographic analysis, chemical composition analysis, and corrosion surface micro-morphology and corrosion product analysis were used to test and analyze the corrosion tube sample in the field. The corrosion behavior of the tube material was studied by high temperature and high pressure working condition simulated corrosion test. The results show that the corrosion products on the surface of the tube threaded joint were mainly FeCO₃. The local concentration of corrosion was mainly due to the thread gluing phenomenon of the tube thread part when it went down the well, which resulted in a decrease in sealing performance of the threaded joint. So high salinity formation water and corrosive medium such as CO₂ infiltrated into the threaded joint and crevice corrosion happened.