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Foreign buildup on AL tanks

We produce a touchless carwash system. Eight months ago, we switched from a stainless steel water tank on our machine to one made of 6061-T6. Recently, some of our machines we've sold are experiencing some kind of buildup on the inside of the water tank, pieces of which are going through the system and clogging spray nozzles. What could this buildup be, and why is occurring at some sites and not others?

BRANDON ANDERSON
POWERAIN SYSTEMS INC - TOWER, MN, USA

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Sorry, aluminum is not as resistant to corrosion as stainless steel. Strong detergents, which are highly alkaline, will attack aluminum. I don't know whether it will be practical to anodize these tanks, but if you have found detergents that do not attack them, stick with them.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

Thanks for the response, but I don't believe detergents are the problem. The tank in question receives clean city water and has a cover on top to keep out any contaminants. What is particularly bothersome is that this corrosion is not consistent--it occurs horribly at some locations and hardly at all at others.

BRANDON ANDERSON
POWERAIN SYSTEMS INC - TOWER, MN, USA

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Here in Minnesota, we have water that is very high in mineral content, also if your equipment is in your area, you have high levels of clear water iron, and red iron in the water. You stated that it is city water, typically they don't remove the minerals and clear water iron. You can easily in a short period of time accumulate deposits from good ol Minnesota water, city water included. If I was going to solve this I would start by a water analysis. Deposits don't sound like a corrosion problem, however they can start corrosion problems though. One last thing, is there are good tank designs and bad tank designs, hopefully yours does not have a drainage or flow problem.

How's fishing on Vermilion this winter?

Best regards,

Bradford Maas
Frigoscandia - Northfield, Minnesota

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Do the tanks receive any corrosion-proofing (anodizing, chromate conversion coating, etc.)? Aluminum is a very active metal--is galvanic corrosion a possibility (contact with copper piping, or even iron piping)? Could the tank be isolated from the piping system with high pressure hose or dielectric unions?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey