Research on the Corrosion Behaviors of L245 Steel and Ni-W Alloy Coating in Alkaline Sodium Sulfide Solution

During the exploitation and transportation of natural gas and petroleum, the sulfur content in the precipitated water is getting higher and higher, which could cause severe corrosion of the carbon steel joints in the gathering pipeline. In order to improve the corrosion resistance of steel substrate and extend the service life of connector, a Ni-W coating was prepared on the carbon steel connecting piece by electroplating method for improving the corrosion resistance of the carbon steel connecting piece. The corrosion behavior of Ni-W coating and L245 steel in the environment containing Na2S simulated production water was studied by immersion method and electrochemical method. Furthermore, the surface morphology, composition and structure of the corrosion products of Ni-W coating and L245 steel were compared and analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results showed that the sulfur ions could accelerate the corrosion of L245 steel, and the Ni-W alloy coating would effectively improve the corrosion resistance of L245 steel in a sulfur-containing solution. When the sulfur ion concentration was 0.005 0 mol/L, the OH- generated from the sulfur ion hydrolysis reaction was adsorbed on the surface of the passivation film, which reduced the corrosion of the Ni-W coating.