Cleaning SS kegs (not beer) of unknown use

[Ritter]

I have two 15 gal SS chemical kegs and a closed top SS 55gal drum that were surplus from a defense contractor. They look and smell clean. No indication of previous contents.

The question. Is there an accepted cleaning procedure for SS to make it food safe? My guess is no, but there are a lot of smart people here that will know better.

Thanks,
Ritter