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In this paper, a new method has been proposed to study the localized corrosion of pipeline different areas based on the multiple ring pair electrical resistance sensor (RPERS) array. The sensor array arranged multiple sets of ring pairs along the flow direction, and each ring pair was divided into six segments along the circumference. The sensor system not only can monitor the circumferential corrosion depth of the pipe, but also can monitor the corrosion depth along the flow direction. Based on the new sensor system, the corrosion behavior of the welding structure at the pipeline elbow location was studied. The corrosion propagation of the different welding zones, i.e. base metal (BM), heat affected zone (HAZ) and weld metal (WM) at the pipeline welding area, was on-line monitored by the RPERS array. The surface characterization was conducted to observe the surface morphology and the compositions of the corrosion scales. The SEM images show that dense and protective film formed at 60℃ in the brine solution with a pH 6.6. The measurement results demonstrate that the decrease of the corrosion rates at the WMs area was nearly one day delayed than those of the BMs and the HAZs, which is related to the inhibition effect of the acicular ferrite and the widmanstatten ferrite to generate a dense FeCO3 layer.