Damage Reason of Tubing with Ni-P Plating in Water Injection Wells of an Oilfield

Morphology, composition and structure of the corrosion products on the surface of Ni-P plated oil pipes used in water injection wells for 23 to 65 months were analyzed by means of SEM, EDS and XRD, and the failure causes and corrosion mechanisms of Ni-P coatings and basic steel were discussed. The results show that the Ni-P coating on the surface of the oil pipe suffered various degrees of damage after the service, and corrosion also occurred in the steel pipe substrate. 64.2% of the Ni-P plated oil pipes had a thinner wall thickness due to corrosion than the standard requirement (The defect depth should less than 12.5% of the nominal wall thickness of the pipe body). The thickness of the Ni-P coating was too thin, the pretreatment process of the tubing was not up to standard, and the corrosion caused by Cl^- was the main reason for the failure of the Ni-P coating. After the failure of the Ni-P coating, corrosive medium directly contacted the steel substrate of the pipe, dissolved oxygen corrosion, carbon dioxide corrosion, and subscale corrosion occurred.