Corrosion coupons often are used to assess the effectiveness of the cathodic protection level on buried pipelines. The information gathered from the coupons usually includes the protection level, such as the instant-off potential, and the corrosion rate at the protection level, from which the present and local protection status of the pipeline is inferred. When set out in groups along a pipeline, extracted periodically, and analyzed using statistical and analytical methods, these corrosion coupons can yield additional information, including estimates of the deepest pit expected on the pipeline, the time for a pit to penetrate the pipe wall for the protection level, and the change in the minimum cathodic protection requirements with time for various allowable maximum pitting rates. The limitations of these estimates are discussed also.
Keywords: soil, corrosion coupon, cathodic protection, pitting rate, extreme-value statistics