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Answer: Rusting on steel can be tested in the laboratory using a salt spray test (ASTM B117). This accelerated test is used to determine corrosion limits (rusting) of a particular substrate (steel) using a specific pretreatment and coating. Normally, the test product is scribed (scratched to the base metal) before it is put into the salt spray test chamber. Periodically the test part is removed from the chamber and the coating adjacent to the scribe is examined for "creep" (corrosion
under the coating)...
· Mild corrosion resistance 250 salt spray hours; requires good cleaning and a single powder coating.
· Good corrosion resistance = 250 to 500 salt spray hours; requires 70 mg/sq ft of iron phosphate and a single powder coating.
· Better corrosion resistance = 500 to 750 salt spray hours; requires 70 mg/sq ft of zinc phosphate and a single powder coating.
· Superior corrosion resistance = 750 to 1,000 salt spray hours; requires 70 mg/sq ft of iron or zinc phosphate and a zinc-rich powder primer or e-coat epoxy primer and a powder topcoat (two coats in total).
