Stainless Steel D.I. Rinse Tank is Rusting
Q. We have a phosphate and e-coat dip system with what we thought was stainless steel in our DI rinse stages. In the DI rinse stage, after the iron phosphate and city water rinse, the floor is rusting. We have heard there may be a coating that the Navy uses to seal the rust. The system was installed by Haden, 2 1/2 years ago, so this rust is surprising. It has already started to eat into the floor, and to spend capital is impossible. I am looking for a short term, 2 year, fix. Any ideas out there, no matter how crazy they may seem? Thanks!Rick J [last name deleted for privacy by Editor]
- Racine, Wisconsin
A. If the tank is stainless steel, it should not be corroding, i.e "rusting" in DI water unless the water is contaminated or there is a build up of deposits on the tank floor. Stainless steel is susceptible to "under deposit corrosion" which occurs if the surface is partially coated with debris, especially steel. Depending on the grade of stainless steel, a high chloride content in the water could be a problem. There is also a possibility that the corrosion is due to microbiological activity in the tank. Your fix may depend on the extent of damage. If there is no deep pitting, you may be able to clean up the surface to restore a good corrosion resistant finish.
Of course, you will have to eliminate whatever was causing the corrosion in the first place, so some analysis of the problem will be the first order of business. If the surface is pitted, you will probably have to do further restoration. That solution will depend on the configuration of the tanks and knowing more about the environment. I would not try to "seal the rust" rather than removing it from the surface prior to any coating application. Good luck!
materials testing laboratory
September 21, 2012
A. Hi, Rick. When you say "floor", I assume that you are speaking of the bottom of the tank or "floor" of the tank, not the concrete floor below the tank.
In the plating and metal finishing industry it is common to address this kind of problem either with a drop-in vinyl liner, or a sprayed coating of plastisol. It shouldn't be a big deal.
Ted Mooney, P.E.
Pine Beach, New Jersey
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