What happens if you plug a 50 Amp RV into 22V welder plug

Since most welder receptacles don't have a neutral, there is no safe way to connect to them even if you wire an adapter. The ground & neutral should be separate wires; combining them will create shock hazards both in the RV & from the ground wiring between the RV & the source.

Trying to use the RV without a neutral will result in unusual voltages on the two legs - depending on the loads on each leg you could end up with a couple of volts on one & almost 240V on the other.

Attempting to use the ground as a neutral will put the neutral voltage on all the bonded metal between the RV & the source - not only a shock hazard for you in the RV, but also for those that touch plumbing, heating ducts, etc. In other words, unless it is a 4 pole connector wired with separate neutral & ground connections, don't use it.

A dryer is only 30A, but a range would be 50A. If I remember, a house range does not require a separate ground so it is only a 3 prong, but a mobile home range does require a separate ground and I believe it uses the same receptacle as the RV pedestal.

I'm probably not saying this right, but the receptacle has two 50A 110VAC circuits - it's the welder that combines them to make it 220VAC. There should be no impact to the RV, as it will just use both legs as 110VAC.

Be sure you have a VOM at your side before plugging in.

What is 50a service? 2007
RV electric 50a website
RV 50a wiring diagrams

If the outlet is a NEMA 14-50 you are good to go. Otherwise the plug will not fit.

Probably nothing. Most welder plugs don't have a Neutral, so none of the 120 stuff would work, but you SHOULDN'T let the smoke out.

Not a problem. 220 volts is 220 volts. I have a adapter just for that, we use it when we go to my sister's house.