Study on Electroless-plated Ni-P Anti-corrosion Coating on Internal Surface of Carbon Steel Pipe

In order to prepare Ni-P electroless-plated coating on the internal surface of the Q235 steel pipe for the purpose of improving the corrosion resistance of ordinary carbon steel pipes, the formula of the electroless plating solution is obtained by the orthogonal testing method.And the chemical composition and corrosion resistance in salt water of the obtained electroless-plated coating are also tested.The study result reveals that the optimal formula of the said Ni-P electroless-plated coating consists 7.6×10^-2mol/L nickel sulfate, 0.17 mol/L sodium hypophosphite, 3.4×10^-2mol/L sodium citrate and 1.32×10^-5mol/L thiourea.Its plating rate is 25.4 μm/h, and the coating hardness is 747 HV.The mass ratios of the three elements(P, Ni and Fe)in the coating are respectively 13.48 wt.%, 85.63 wt.%and 0.89 wt.%.The selfcorrosion potential of the coating in the 3.5 wt.%NaCl solution is-0.62 V(SCE), while its self-corrosion current density is 5.82×10^-6A/cm², being about 98.1%reduction than that of the neat Q235 steel.