The nipple for my tub spout is galvanized, screwed into the brass fitting. Of course, it is badly corroded.

So, I'd like to replace it. There is only about 1/2" of the pipe exposed, making it near impossible to grab externally with a pipe wrench.

I've tried two types of internal pipe extractors -- an internal cam style (something like this

http://www.gunk.com/product_images/vl_1390.JPG)

and an internal fine gage screw style like this:

http://www.gunk.com/product_images/LG_1395.JPG

The cam style starts to catch, but then just eats up the inside of the pipe and slips. The screw style for 3/4 pipe just spins with barely any friction at all.

The ID of the pipe is currently 0.840 -- possibly from just years of corrosion, though probably not helped by a few unsuccessful attempts at using these internal pipe wrenches.

Does anyone have any recommendations on a better pipe extractor that can handle this larger ID, corroded pipe?

I've seen a "walton" online that seems to have a better looking taper, maybe will give a better chance of catching:

http://www.waltontools.com/products/reps.htm

Or, I've seen a longer, coarser screw style:

http://www.plumbersurplus.com/images/prod/5/D.O.-Smith-36508-rw-59839-17108.jpg

But, I can't really tell if the taper goes to large enough ID.

And then a 3 jaw internal pipe wrench:

http://www.plumbingsupply.com/images/internal-nipple-wrench.jpg

Looks like you screw it in, so it acts by wedge rather than cam... so might act more evenly? Also, it specifically mentions iron pipe, which I think has slightly larger ID than copper?

Any recommendations from someone who's had to do this? What's the best extractor, or best way to get this thing out without opening up the wall?

Other thoughts I had: using some sort of thin sheet metal to act as a shim to help the cam style pipe wrench to grip.

Also I was thinking maybe I could use an internal pipe cutter to cut the pipe at or near the threads, at which point maybe it will be easier to remove with a chisel.

Or, hacksawing a groove across exposed pipe then use a screwdriver.

I'd like to avoid breaking through the tiled wall -- the thing is built like a tank, with ~3/4" thick mortar/metal lath bed.