Corrosion Behavior of Ni–P Alloy Coated Carbon Steel Tubing in Water Injection Wells

The cause of severe local corrosion on N80 carbon steel tubing with Ni–P plating after 23 months of service has been analyzed in the present work. Measurements and inspection were performed on the chemical composition and metallographic structure of the tubing. The morphology and composition of the corrosion products were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray power diffraction (XRD). The results indicated that serious scaling and heavy Ni–P plating spalling occurred on the internal surface of the tubing; corrosion failure at the end of the threaded joint was obvious. The Ni–P plating failure was mainly attributed to the poor pretreatment technique and the too thin thickness of the Ni–P plating. The poor protective Ni–P plating gradually failed and flaked off with the effect of the corrosive media and therefore the N80 carbon steel tubing was largely corrupted. The corrosion mechanisms were mainly corrosion under scale, galvanic corrosion, and corrosion induced by dissolved oxygen, Cl− and CO2.