Cause Analysis of Corrosion Perforation of C110 Tubing in a Water/Gas Injection Well

In order to find out the reasons for corrosion perforation of C110 tubing in a water/gas injection well, the observation of macrograph and microstructure, testing of chemical composition, mechanical properties and composition of corrosion products were carried out, combined with the investigation of working condition. The results indicate that the material properties of failed C110 tubing met the requirements of API SPEC 5CT-2011 standard. Oxygen corrosion happened on the inner surface of failed tubing, so the corrosion products were composed of Fe₃O₄ and Fe₂O₃. And O₂-CO₂-H₂S corrosion happened on the outer surface of failed tubing, so corrosion products were composed of FeCO₃, Fe₃O₄, FeOOH and FeS. Compared with the working condition of single O₂ for the inner surface, the O₂-CO₂-H₂S working condition for the outer surface had lower pH value and produced porous corrosion products, which resulted in O₂-CO₂-H₂S corrosion perforation happening on the outer surface of tubing.