Nipple removal

Drive antique, old, huge, tapered punch, (yeh, I have a couple) into pipe to hold it round, then use pipe wrench/ vise grips etc.

I have an old punch so large, back when I had the much hated "Skud Missile" (poorly guided, low flying missile), AKA 78 Ford LTDII, I ran the punch into the filler neck and instantly converted it to use leaded fuel!!!