About Coatings and Cathodic Protection: Electrochemical Features of Coatings Used on Pipelines

By Isabel C.P. Margarit, Oscar R. Mattos, José Roberto R.M. Ferreira, Joaquim P. Quintela

The behavior of a coal tar, a polyethylene, and a fusion bonded epoxy was evaluated. Coated samples with and without intentional failures exposing the metallic substrate were submitted to different levels of cathodic polarization. The process of delamination was monitored with current and impedance measurements. The delamination was quantified by a standard method.

No quantitative relationship between the delaminated areas and electrochemical parameters could be found; the reasons are discussed in terms of the properties of the coatings. It was shown that the higher the dielectric strength of coatings, the more critical the role of pores and mechanical damage in determining cathodic protection effectiveness.