This paper covers a case study performed on 10-inch diameter steel pipelines in an urban environment to detect and locate coating anomalies (such as holidays and disbondment) with a novel technique and methodology. A survey tool and theoretical framework have been introduced, and the practical feasibility of wielding reflectometry of electromagnetic waves in buried steel pipelines to assess coating condition was trialed. The authors were able to model different reflectometry signatures obtained from different coating conditions. Differential Reflectometry Mapping (DRM) methods were found to be able to detect coating defects, including coating delaminations; and to accurately locate those defects at a distance of 1500 ft. This presents a clear progress for current state of the art capabilities in terms of remote coating assessment in buried pipelines while detecting disbondment conditions. DRM permits a unique improvement regarding integrity management for transmission and distribution of liquid assets.
Corrosion control of buried assets usually involves a double shield: a coating system as a physical insulation barrier, and a cathodic protection system as an additional ad hoc defense. Detection of a corrosion spot at the coating defect stage is the only way to identify the threat before significant metal loss occurs. Furthermore, detection of defects in the coatings of such assets is especially important, since large defects, if left unrepaired, will not only leave the asset locally prone to corrosion, but also drain and weaken the cathodic protection effectiveness for the entire structure. Therefore, identification and characterization of coating anomalies is critical for the integrity of buried assets.
A type of coating defect known as delamination or disbondment of the coating has received renewed interest. A coating delamination consists in an area of non-adherence between the coating and the metal, associated with a local porosity that allows the intake of water and electrolytes beneath the coating. It generates an especially dangerous risk for the pipeline asset: not only does it make the metal beneath it prone to a localized attack, but it also shields it from the cathodic protection system. This unique threat, also known as CUI (Corrosion Under Insulation), has attracted special attention due to the lack of technologies able to detect this condition.
