Preparation of Electroless Ni-Fe-P Coating and Evaluation of Its Corrosion Resistance under Corrosive Environments of Carbon Dioxide and Hydrogen Sulfide/Carbon Dioxide

Electroless Ni-Fe-P coating was prepared on the surface of N80 steel from an electroless plating bath without Fe2+ so as to improve the corrosion resistance of the oil casing pipes in CO2- and H2S/CO2-containing corrosive fluids of petroleum and natural gas industries. The morphology, composition and phase structure of as-obtained electroless Ni-Fe-P coating were analyzed by means of scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The corrosion resistance of electroless Ni-Fe-P coating in simulated oilfield extracted water (saturated with CO2) and in corrosive fluid containing H2S/CO2 was evaluated with a static high temperature and high pressure kettle. The effects of CO2, Cl- and pH value on the corrosion resistance of electroless Ni-Fe-P coating were studied. Results show that as-prepared electroless Ni-Fe-P coating is amorphous and contains a high content of P. Besides, electroless Ni-Fe-P coating has good resistance against corrosion induced by CO2; and its corrosion rate in the corrosiove fluid containing H2S is accelerated upon the addition of CO2. Moreover, in the corrosive fluid containing H2S/CO2, Cl- leads to accelerated destruction of the passivation film on electroless Ni-Fe-P coating.