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Temperature limits for MIL-DTL-5541 chemical conversion coatings

March 19, 2010

Q. My company uses plate and fin aluminum air to air heat exchangers. The units are constructed from 5052 series aluminum and can see continuous inlet air temperatures of 400 °F and intermittent exposure to 500 °F jet engine bleed air.

MIL-DTL-5541 [affil. link or DLA](MIL-C-5541) makes a general statement that corrosion resistance is reduced at temperatures above 140 °F. Since the coating is inorganic, is it not capable of exceeding the operating temperature of the aluminum construction material?

Steve Rigney
OEM - Seminole, Oklahoma

March 19, 2010

A. Hi, Steve. The coating is inorganic but is is not metallic; it is a gel.

If you are referring to Mil-DTL-5541 only for convenience, not as something you have an obligation to comply with, I think the temperature resistance of the chem film is actually a bit higher than 140 °F after it has had 24 hours to cure. But if this jet engine is in a flying machine, although you'll need more guidance than I'm qualified to give you, 400 - 500 °F sounds out of the question..


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

June 25, 2010

Q. Is there any information out there, as to what the Max temp rating of MIL-DTL-5541 is? We are looking to use it in an application where it is exposed one time to 600 °F for 30 minutes, but after that it will never exceed 125 °F.

David Bellig
- New Ulm, Minnesota, USA

A. Hi David. MIL-DTL-5541 [affil. link or DLA] itself says the limit is 60 °C / 140 °F. Exposure to 600 °F even momentarily sounds like a non-starter :-(

Luck & Regards,

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

Ed. note: There is a much longer, broader discussion of the temperature limit for MIL-DTL-5541 coatings as thread 34822.

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