Galvanic corrosion of X80 pipeline steel double‐sided submerged arc welded joints in simulated near‐neutral soil solution

Abstract

AbstractThe corrosion behaviors of double‐sided submerged arc welded joints in X80 pipeline steel with or without coupling were studied in simulated near‐neutral soil solution. The galvanic effect in the welded joint was evaluated by corrosion morphology, corrosion depth, and electrochemical measurements. When the weld metal (WM), heat affected zone (HAZ) and base metal (BM) samples were immersed in the solution isolated, pitting holes occurred around the martensite/austenite constituents in the weld metal and base metal samples, which was mainly due to the preferential corrosion of ferrite. However, no pitting holes occurred in the heat affected zone due to small specific surface area induced by the coarse martensite/austenite constituents. Polarization curves results showed that the corrosion current density of coupled base metal was 5 times larger than that of isolated base metal and the corrosion current density of isolated heat affected zone was three times larger than that of coupled heat affected zone after 48 h immersion. The corrosion current density of coupled heat affected zone was one order of magnitude lower than that of coupled weld metal and base metal. When the welded joint was exposed to an aggressive environment, the base metal samples were determined to be the most anodic zone while the heat affected zone was the most cathodic zone. The weld metal underwent little galvanic interaction, as its corrosion potential was close to the coupled potential. In addition, the galvanic effect among the welded joints decreased with the prolong of immersion time.