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?

My experience is that it varies. But I have had suppliers who insisted on a vacuum purge (and associated cost) when presented with any completely depressurized bottle. The last time I built a bottle from scratch (medical D plus aviation CGA540 valve), I purged it myself using my vacuum bagging pump, put about 100 PSI of O2 in it from the welding rig, and then took it to the refill place and got it filled, no problem.

--Bob K.