The effect of shielding is often discussed in the context of cathodic protection. In certain countries the concern with respect to shielding has led to the use of so called non-shielding coatings based on Fusion Bonded Epoxy (FBE). In contrast, the use of three layer Polyethylene (3LPE) coatings in large parts of the world has not led to relevant damages due to shielding, despite of the excellent dielectric properties and extensive disbondment. Nevertheless, there are certain instances where significant corrosion was observed due to shielding in specific cases. The evaluation of different national normative situations, the more recent investigations on shielding as well as the current understanding of the underlying processes associated with cathodic protection allow for identifying the particular conditions that are critical from an integrity point of view. These data are compared with model calculations. Based on this consideration the relevant conditions required to cause detrimental effects with disbonded coating systems are identified and discussed. Based on this consideration very specific conditions are required to cause an integrity problem with disbonded coatings. The excellent behaviour of the various coating systems that were successfully used in the past decades and the absence of damages even in the case of extensive disbonding of highly dielectric coatings are discussed based on literature data.
Effectiveness of cathodic protection under disbonded coatings: On the implications of shielding conditions on the integrity of pipelines
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