Field Assessment of FBE-Coated Pipelines and the Implications for Stress Corrosion Cracking

Abstract

One proposed method for preventing the initiation of SCC on pipelines is through the use of high-performance coatings in conjunction with effective cathodic protection. High-performance coatings include fusion bonded epoxy (FBE), urethanes, liquid epoxies, extruded polyethylene, and multi-layer coatings. This paper reports the results of a CEPA-sponsored project to determine the long-term performance of FBE coatings on underground pipelines using in situ field measurements. The barrier properties of FBE coatings were measured after several years field service using Electrochemical Impedance Spectroscopy (EIS). Measurements were made on four FBE-coated pipelines that had been exposed for periods of between 5 and 20 years. The coatings studied included three different formulations from two different manufacturers. A variety of site, soil and CP conditions were also examined. The combination of EIS measurements and analyses of trapped water samples demonstrated that the FBE coatings continued to perform well after having been exposed for up to 20 years. Although some blistering and disbondment was observed in some cases as a result of poor application and storage procedures, in all cases the pipe surface was still protected either by the coating itself or by the joint action of the CP system and the CP-compatible FBE coating. The results of this study provide strong evidence that FBE-coated pipelines should not be susceptible to the initiation of SCC, due to (i) the barrier properties of the coating, (ii) the CP-compatible nature of the coating, and (iii) good surface preparation techniques that involve the removal of millscale and the introduction of compressive surface residual stresses.