CO₂ Corrosion Resistance of Amorphous Nickel-Tungsten Alloy Coated Tubing

Nickel-tungsten (Ni-W) alloy coating was prepared on the surface of ordinary N80 tubing by electrodeposition technology. The morphology, composition and corrosion resistance of the Ni-W alloy coating in condition of high salinity formation and high carbon dioxide content were studied through corrosion immersion test at high temperature and high pressure, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and field test. The results show that the Ni-W alloy coating was dense and uniform with an amorphous structure. In corrosion immersion test, the corrosion rate of N80 tubing was beyond 0.25 mm/a, and the corrosion rate of the Ni-W alloy coating was less than the limit of standard (0.076 mm/a), exhibiting better corrosion resistance. After service in field for 240 d, the Ni-W alloy coating was corroded slightly, showing silver-white metallic luster, smooth surface, no cracking or peeling observed on the coating, and the pitting corrosion rate was 0.028 mm/a, while the N80 tubing was corroded heavily with pitting corrosion rate of 0.717 mm/a which was 25.7 times of Ni-W alloy coating corrosion rate. So the amorphous Ni-W alloy coating has good resistance to uniform corrosion and pitting in CO₂ environment.