Probing the nonuniform corrosion of pipeline weldments under stepwise increasing solution temperature using a coupled multielement electrical resistance sensor

A coupled multielement electrical resistance sensor (MERS) was designed to probe the nonuniform corrosion of an X65 pipeline weldment under a stepwise increasing solution temperature. In conjunction with electrochemical impedance spectroscopy (EIS) measurements, the initiation and propagation of the nonuniform corrosion on different welding areas, that is, base metal (BM), heat-affected zone (HAZ), and welding metal (WM) were well understood. The results show that the contributions of galvanic current (current flowing across the three different welding areas) and internal current (current flowing in a certain welding area) for the steel loss of BM, HAZ, and WM were significantly different under each solution temperature. The main contributor to the steel loss of HAZ gradually transformed from internal current to galvanic current with the solution temperature increasing. The WM would change from anodes to cathodes due to the preprecipitation of the FeCO₃ crystals on WM when the solution temperature increased over 40°C. The BM would transform from cathodes to anodes at 40°C and the steel loss of BM was mainly induced by the internal current in BM over the whole test duration.