Galvanic corrosion behavior of X80 pipeline steel welded joint in three representative soil environments

To investigate the galvanic corrosion behavior of X80 pipeline steel welded joints in three representative soil environments—acidic, near-neutral, and alkaline—the weight loss method, electrochemical testing, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were employed to systematically analyze the corrosion rate, corrosion morphology, characteristics of corrosion products, and galvanic corrosion effects. Results show that corrosion sensitivity varies significantly among different regions of the welded joint across three representative soil environments, with the corrosion rate following the order: WM > HAZ > BM, indicating that the WM is consistently the weakest region. The composition of corrosion products differs depending on the environment: Fe 3 O 4 /FeOOH predominates in acidic solution, whereas FeCO 3 /FeOOH is present in both near-neutral and alkaline solutions. In the alkaline environment, the formation of a unique CaCO 3 -rich deposit, combined with lower FeOOH content, synergistically enhances the protective performance of the film, resulting in the lowest corrosion rate. Further analysis reveals a non-monotonic relationship between the thickness of the corrosion product layer and the corrosion rate. The thickness variation is primarily governed by the chemical stability of the products in the specific medium, rather than being determined solely by the corrosion rate. Galvanic corrosion tests demonstrate that the coupling between anodic and cathodic regions significantly accelerates WM corrosion ( γ > 1), with the most pronounced effects observed in near-neutral solutions with elevated Cl − concentrations. Additionally, localization index ( LI ) values range from 0.1 to 1 across all tested environments, indicating the galvanic coupling between WM and BM exhibits a pronounced tendency to initiate localized corrosion.