Measuring and understanding the critical duration and amplitude of anodic transients

Anodic transients are known to affect buried pipeline cathodic protection (CP) systems; however, their actual effects on pipeline corrosion have not been sufficiently quantified due to the lack of direct experimental evidences. In this work, a novel methodology developed based on an electrochemically integrated multi-electrode array has been used to visualise the dynamic effects of anodic transients on localised corrosion processes occurring on buried steel surfaces. It is shown that anodic transients do not necessarily cause steel corrosion, as long as their amplitude and duration are below critical values. The electrode array is able to determine these critical values accurately due to its ability to detect localised corrosion initiation, while the conventional coupon electrode is only able to estimate these values. The critical anodic transient duration has been explained as the incubation period for the breakdown of passivity formed on the steel surface exposed to CP-generated high pH conditions.