Corrosion Risk Assessment of Steel Gas Pipelines under Dynamic DC Interference according to In Situ Measurements

Direct current (DC) traction systems such as a subway can cause time-resolved stray current interference in adjacent gas pipelines, leading to serious corrosion risk. It is important to evaluate risk according to the field test. In this paper, a new approach based upon probability analysis is proposed to determine the distribution characteristics of the measured potentials over a long period to evaluate the corrosion risk of pipeline exposed to dynamic stray current interference. It was found that the measured potential within a day can be perfectly characterized by a Gaussian function. Therefore, the time-resolved potentials within a day can be replaced by two parameters to characterize the daily potential changing with time. A 2D diagram based on two characteristic parameters, together with corrosion criteria, was proposed to evaluate corrosion risk in a more visually direct way. The gradual development of pipeline risk level in the long-term corrosion process can be readily observed. The real-time measured corrosion rates of the test coupons were compared with evaluation results, and quite good agreement was found. The influence of the stray current inflow and outflow on the pipeline’s cathodic protection potential shift was also analyzed. The proposed approach can provide a reference for pipeline corrosion risk assessment where gas pipelines intersect or parallel with subways.