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Mil-13924 class 2 vs class 4

February 21, 2017

Q. I have a requirement for Black Oxide per MIL-DTL-13924 [link is to free spec at Defense Logistics Agency / dla.mil] Class 2 on a 304, 316, welded assembly subjected to intermittent high heat approaching 900 deg. F. My suppliers don't do class 2 and suggest class 4. I know the EPA difference, but I cannot discern the functional difference from the spec. Can someone help? Thanks

Bob West
QA rep - Phoenix, Arizona


February 2017

A. Hi Bob. It seems from a quick read that the biggest difference is that Class 4 requires the parts to pass a 96-hour salt spray test without any supplemental treatment -- which your shops apparently aren't worried about passing.

I think you'll find paragraph 6.3.2 helpful to your understanding. Although it's problematical for anyone to interpret a spec as it pertains to your parts, when they really don't know much about your parts, Class 4 sounds quite reasonable to me for your type 304 & 316 parts. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


February 21, 2017

thumbs up signThanks Ted. I've read it several times and just couldn't grasp a functional difference. I appreciate the help!

Bob West [returning]
- Phoenix, Arizona USA

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