Cathodic Protection Shielding and Prevention of the Corrosion under Disbonded Coating in Soils

Abstract Cathodic protection shielding of pipeline coatings is largely debated among coatings specialists. Under disbonded coating with or without electrolyte renewal, the amount of current passing through is the key of the protection. In this study, the shielding character of field coatings, such as single and dual layers FBE and liquid epoxy was assessed. Different thicknesses were investigated from 350 to 1000 μm. An experimental setup was designed to assess the ability of a disbonded coating to allow the CP currents to protect the steel underneath. Conditions at low and high oxygen contents were considered. This setup aims at reproducing blistering conditions with and without renewal of confined electrolyte. For this purpose, substrate free coating samples were used (membrane type samples). Additional experiments were performed to measure the CP currents passing through similar coatings on steel substrates for 12 months. Finally, a 30 years old FBE disbonded coating, collected from the field and presenting a low shielding behavior, was similarly characterized. The obtained results allow discussing the ability of tested coating (presenting low and high shielding properties) to protect the steel under blistering conditions. Specific soils conditions in terms of resistivity and polarization curves at various moisture level were considered.