That is just an industrial/laboratory version of the "Corny" kegs we are all familar with. The place I used to work at had cylinders just like that in their lab that were used for deionized water.
Unfortunately, the one in the picture appears to only have NPT bungs in the top which will not work for kegging. I doubt that it's coated, but it does appear to have a good passivated finish on the outside like it should, but the lid is strangley large. Besides, if you don't know what was in it, it's not safe to use for food-grade storage.