Nonmetallic coatings corrosion effects

Several corrosion inhibitors such as polyamide, polyamine, dithiocarbamate, thiophosphate ester, organic acid, sulfide, and selenide types have all been tried in methanol without significant success [3.5]. Similarly, nonmetallic coatings of metals to effectively prevent corrosion have not been developed to date. One application where coatings have proven effective is in prevention of anodic dissociation of fuel pumps immersed in methanol. Since methanol is many times more conductive than gasoline, components such as fuel pumps and electrical fuel level gauges can cause induced currents that in turn remove metal from these... 

The overall reaction takes place at a rate determined by the more difficult of these two steps. This simple concept, independent anodic and cathodic half-reactions, is the basis of the electrochemical mechanism of corrosion. The mechanism has profound effects on the corrosion protective properties of nonmetallic coatings materials. Some tests exploit the electrochemical mechanism to determine specific corrosion susceptibilities of coatings systems such as cathodic disbond-ment and pinhole detection. Coatings that are permeable to oxygen may be vulnerable to damage due to an alternative cathodic reaction... 

---