Abstract
Cathodic protection (CP) conveys an active protection against corrosion to pipeline steel surface in case of coating defect. This work studies depolarization phenomena that occurs after CP interruption. The term “depolarization” refers to the pipes returning to its free potential value after cessation of CP. Here we present a laboratory study in soils, using metallic coupons to simulate pipeline coating defect behavior with metallic surface exposed to the electrolyte. After CP interruption the potential value of the steel coupon doesn’t return to initial value before CP (around -0.6 V/CSE) but remains higher (up to -0.2 V/CSE) for a long period of time (up to 11 days). This effect can be attributed to the formation of a passivation layer at the metallic surface due to pH increase during CP application. This passive layer confers a remanence to the protection against corrosion of the metallic surface after cessation of CP. This study focuses on understanding this depolarization behavior depending on various parameters: level of CP, time duration of uninterrupted CP, shape of the metallic coupon, composition of the soil media. The objective is to give insight to pipeline operators as to the safety of cathodic protection interruptions on the network depending on environmental conditions.
