Abstract
Metallic structures such as underground oil and gas pipelines are typically protected from corrosion by a combination of barrier coatings and cathodic protection (CP) systems. Although coatings and CP systems have been proven to be effective for protecting buried steel from general forms of corrosion, unfortunately localized corrosion and coating degradation can occur under dynamically changing local environmental conditions. For instance corrosion and coating failure on buried steel pipeline frequently can occur under the dynamic effects of stray currents, anodic transients, cathodic shielding and coating disbondment. Under these dynamically changing local environmental conditions, corrosion rates and patterns change with time and thus there is a need to perform in-situ monitoring of corrosion and coating failure. This paper presents cases illustrating the capability of the multi-electrode array in detecting the initiation and propagation of localized corrosion and coating failure: (i) Monitoring localized corrosion under a simulated pipeline coating; (ii) Visualizing passivity and its breakdown, and localized corrosion of buried steel under the effect of dynamic anodic transients; and (iii) Imagining coating disbondment under overprotection.
