Field and laboratory assessment of electrochemical probes for visualizing localized corrosion under buried pipeline conditions

Corrosion probes designed based on an electrochemically integrated multi-electrode array have been evaluated in an extensive field and laboratory evaluation program in order to identify their capabilities in visualizing and probing critical forms of buried steel corrosion, in particular, corrosion under disbonded coatings (CDC) and stray current corrosion. Probes of different designs were installed in the pipeline field to simulate and measure the influence of stray currents and cathodic protection (CP) deficiency on corrosion as well as CDC. Accelerated laboratory tests were also performed, where electrochemical measurements can be taken more frequently and the corrosion condition can be more precisely controlled. Corrosion patterns and rates were calculated with a sensitivity in the order of 10 µm/year. Testing results correlated reasonably well with long-term pipeline corrosion behavior. On the other hand, single element electrical resistance probes were not able to simulate or measure CDC occurring on pipeline surfaces. These results demonstrate the capability and some unique advantages of the electrode array probes for monitoring pipeline corrosion.