“How does poor quality rinse water or pretreatment cause accelerated corrosion?”
“Rinse water quality directly affects corrosion resistance in several ways. First, polluted rinse water will not sufficiently remove the soils or active chemistry from the previous working stage. If the product isn’t full cleaned and neutralized, then the next working stage (i.e. iron phosphate, zinc phosphate, alodine, etc.) will not deposit evenly or in the correct amounts to prevent corrosion in the field.
For instance alkaline wash solutions normally precede acidic iron phosphate stages. If the rinse doesn’t remove all the soils or neutralizes the surface, the pH of the iron phosphate will be difficult to control leading to poorly formed phosphate coverage. Secondly, rinse water in the final stage must passivate the surface to provide maximum corrosion resistance. This is performed with a slightly acidulated rinse solution (sometime called a sealer rinse). Lastly, all rinse water must be free of chlorides and other contaminants (i.e. CaCo, and salts). If your city or well water isn’t up to par, then you will have contaminates (salts) under the coating that will eventually mix with moisture and lift the coating (blisters). This is the normal failure mechanism seen in corrosion failure and is the reason to buy a DI or RO water system for the final rinse.”