Insight into the corrosion susceptibility and failure mechanism of Cu-Ni alloy pipeline welded joints in simulated marine environment

In this work, the corrosion behavior of Cu-Ni alloy pipeline welded joints is investigated in a simulated marine environment solution with coexisting chloride ions (Cl−) and sulfide ions (S2−). Microstructural observation, chemical component analysis, electrochemical measurements, scanning kelvin probe (SKP) and the finite element method (FEM) were adopted to probe the corrosion failure mechanism. The results showed that the welded joints at base metal (BM), heat affected zone (HAZ) and weld zone (WZ) exhibit various microstructures and reveal pitting and intergranular corrosion, moreover, the WZ appears inter-dendrite corrosion. WZ exhibits a higher corrosion sensitivity with the highest corrosion current density of about 1.23 × 10−5 A·cm−2. The defects in passive film and the thickness and density of corrosion product film differ for the three zones resulting in the protective effect of WZ being the poorest. BM with the thickest and densest corrosion product film effectively prevents the infiltration of corrosive ions (HS−, Cl−), meanwhile, the lowest defect concentration of the passive film of BM further protects the substrate. The transition of WZ in the WZ-HAZ galvanic couple from cathode to anode aggravates the corrosion of WZ.