http://mysite.verizon.net/fdraw/pipe.jpg
Rusted galvanized pipe nipple is stuck in fitting in wall behind tile under bathroom sink. :(
I have tried to remove it with a large pipe wrench, but it won't turn. I looking for any suggestions to get it out without damaging threads in fitting; WD40? Heat? Cold chisel?
Any advice appreciated. Thanks.

Don't get the chisel out yet. First WD 40 but I doubt it will do much. Alternate with heat and cold. If you can safely use a prppane torch try heating the pipe and then splash a bit of cold water on it.You could improve your leverage by sliding a piece of long pipe over the handle of your wrench.

Don't get the chisel out yet. First WD 40 but I doubt it will do much. Alternate with heat and cold. If you can safely use a prppane torch try heating the pipe and then splash a bit of cold water on it.You could improve your leverage by sliding a piece of long pipe over the handle of your wrench.

Thanks for the quick response. I'm a bit concerned about using a propane torch (open flame); it's a 1 1/2" drain. Wouldn't there be a possibility that sewer gases might ignite / explode? TIA :D

Sewer gas should vent long before it reaches the point where it could flame. However, that is a slight chance so try a paint gun heater, much hotter than a hair dryer. Try the longer handle first, it may save you the trouble of heating. You can probably pull down with more force than you can push up. Try orienting your wrench to pull down.

I would try giving it a good squirt with something and then hammering good on the end of it. That flexes the threads breaking the corrosion loose. It also helps the oil wick into the joint. I prefer a silicone to WD-40.

If you use a long handle before losing it up, you risk twisting it off.