Analyses of Cracking Failure on a P110 EU Tubing Coupling

Longitudinal cracking was found on nine tubing couplings in a water injection well, and different degrees of corrosion pits were found on the outer surface of these couplings. Mechanical and chemical properties were tested to clarify the reasons for cracking. Metallographic, SEM, EDS, XRD and other methods were used to analyze the corrosion products on the fracture surface. The results showed that the reason of cracking was mainly sulfide stress corrosion cracking which was caused by stress concentration at the mechanical clip marks of the outer wall, and the corrosion product mainly consisted of FeS.