Assessment of non-uniform corrosion and film formation characteristics of pipeline weldment using a multiring electrical resistance sensor array

With the booming progress of offshore oil and gas development into the deep sea, the internal conditions of submarine pipelines are becoming more severe, and especially in CO₂ medium, the pipeline weldment is faced with severe non-uniform corrosion risks. In this paper, two welding processes of AWS E9015-G/ER80S-Ni1 and AWS E6010 are used to weld X65 pipeline steel respectively, and the heterogeneous areas are sliced and processed respectively. Furthermore, a multi-ring electrical resistance sensor array is established, which can realize the simultaneous online monitoring of the corrosion difference between heterogeneous welding areas and the corrosion difference within the circumferential homogeneous region. Through the non-uniform corrosion depth monitoring and corrosion morphology characterization, it is shown that the FeCO₃ corrosion product film can increase the potential of the film-covered area. At the same time, the microstructure with irregular size and uneven distribution will reduce the corrosion resistance of the welding area, while the uniformly distributed "pearlite/ferrite" microstructure facilitates the development of a compact and complete FeCO₃ as a corrosion product film. Furthermore, in the welding area with earlier film formation and better density, the polarity of the galvanic current could be changed.