You should return that tank. Take the wrench with you and don't bring home a new tank with out being sure you can open it. 

Was this a new tank to start with?

KrisMarie,

Since there is no such thing as a "disposable" acetylene tank, I'm going to assume you have a standard cylinder of some sort, either a B, MC or the like, that uses the square shaft for the valve. If that is stripped, then it will have to be replaced. That isn't particularly expensive, but it must b e done by someone who knows how to do it correctly and has the right parts - your welding supplier, in other words.

There may be other issues with the cylinder valve besides the shaft being rounded off, too. If you couldn't open it with a regular Crescent wrench then it was probably shut off way too tight and may have a damaged seat. That would be the fault of whoever closed initially. Again, your welding supplier should be able to deal with this.

Acetylene is dangerous if not handled properly. You cannot simply open the valve in free air safely - doing so may result in spontaneous combustion or detonation. This is why I keep saying that the welding supplier should deal with this problem. Safety has to come first.

Let us know how it works out.

Rich

I like to look at the square thingie that I think you are talking about and make sure that it is square. It's too easy to get home and find that it is not square because someone has used vice grips or something simular and has rounded it off. I make a point of telling them that it is going into a home studio and not the back of someone's pickup.