CHROMATE CONVERSION COATING

 Q. I’m just doing a little research prior to meeting with a potential client next week. They are currently sandblasting an aluminum substrate and applying 4–6 mils of a fairly standard white powder. The end product goes on yachts, cruise ships, oil platforms and is a desalination unit. It is my intention to discuss eliminating the blasting and replacing it with chem film. The idea would be to save on powder material, as I would think 2–3 mils over chem film would be a great system. I am looking for information to support this suggestion. Any help would be greatly appreciated!

Also, I was just reading a Q&A where it states there is no reason to worry about chem film being exposed to temperatures above 180ºF. Can you touch on what happens to the chem film when the powder is cured at nearly 400ºF? D.J.

 

A. I think that your client is at risk by putting an untreated surface out to sea even with 4–6 mils of good powder. Your idea of using the chem film (chromate conversion coating) is good but I would still go for a minimum of 3 mils of powder to limit thin areas that could lead to failure. The film thickness is part of the corrosion performance.

The chromate is a hydrated gel that can survive high heat if the powder covers the treated surface. Exposed areas (not covered by powder) will dehydrate above 140º F, so areas with no powder will be vulnerable but the covered area will be fine. So your solution will work and it will save money while providing better performance.