ArtMetal

I don't know about carrying your scrap on a subway... or what shapes your tinking of, but those steel welding tanks when out of ate need to be discarded and they do it by cutting them open. Same with oxygen tanks from a dive shop and many others. Thing being they have a fabulous ring as gongs go. It is legally something they have to do, and then discard as junk. Check out the junk yards or even the welding suppliers for locations. Cutting them open is another specific test and they could also blow up if done wrong so if not sure, don't chance that part but I have cut open about 18 so far safely by uncapping and filling with water while it is being cut.