Serious Education ... plus the most fun you can have in metal finishing.
Mil-13924 class 2 vs class 4February 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? ThanksBob West
QA rep - Phoenix, Arizona
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.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
February 21, 2017
Thanks 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