Effect of Surface Finish on CO₂ Corrosion of Low-Alloy Steel in Simulated Sea Water and Well Environments

The study investigates the influence of surface finish on corrosion of a grade API L80 low-alloy steel. Samples of this steel with different surface finishes produced by rough mechanical grinding (RG sample) or by finer polishing (FP sample) have been studied after exposure to corrosive environments. It is found that the dissolution rate is one to two orders of magnitude higher for the RG sample with a rougher surface than for the FP samples with a smoother surface. Scanning electrochemical microscopy shows selective corrosion of the RG sample, while the FP sample undergoes slow uniform corrosion, followed by localized corrosion after long exposure. A detailed analysis of the corrosion process indicates that in a simulated well environment containing Fe²⁺ and Ca²⁺ ions, fast precipitation of CaCO₃ on the rougher surface initially reduces the corrosion rate. However, once a protective scale starts forming on the surface, the effect of surface finish on corrosion resistance becomes less significant. The scale morphology and phase composition vary between the samples with the different surface finishes.