On Sunday, June 3, 2018 at 9:14:57 PM UTC-7, wrote:
So what happens if I rent a welding cylinder, weld until it's empty, remove the regulator, forget to close the valve, and just for fun it gets rained on?

Do they just refill it or dry and purge it first?

If folks who rely on that cylinder find out the back of you head might hurt :-)

I would ask your specific supplier. Many places will get more cautions with cylinders that have no pressure in them, simple purging at a minimum. if the cylinder was suspected of containing water the fill station can fully dry it and if they want wan to internally inspect it or fully test it. Remember the cylinders are fully wet internally when hydrotested... but they are dried and purged before refilling.

If you abuse a cylinder and it causes serious internal damage I hope that is found in time by the next cylinder test, in the internal or ultrasound inspection or pressure test.