ABSTRACT
In this chapter, degradation by corrosion is divided into three mechanisms: cathodic disbonding (CD), corrosion creep, and filiform corrosion. CD is the most important degradation mechanism for organic coatings on submerged steel, but it can also play an important role in corrosion creep. Various mechanisms for CD can be classified in three groups: (1) dissolution of the iron oxide layer on the substrate; (2) chemical degradation of the coating; and (3) interfacial failure caused by the high pH. The chapter focuses on steel since corrosion creep is the main degradation mechanism on painted steel exposed in corrosive atmospheres. The most common errors are probably too-low film thickness and various types of pores. Filiform corrosion may occur on coated aluminum, steel, and magnesium, but is mainly associated with aluminum. Filiform corrosion occurs in a humid atmosphere, typically above 75" relative humidity (RH). The role of the chlorides during filiform corrosion is to destabilize the metal oxide and acidification of the electrolyte.
