I should have been more clear on the discoloration...it was on the shaft/coupling bore I.D. The O.D. of the coupling body is 22.25". That would be 6.125 wall thickness -1.250 for the key on one side. The grid portion of the coupling is larger than that. Ditto on the drilled and tapped face for the puller bolts. They are even more important on the gear type couplings as you can't remove the cover and get a good O.D. for the puller jaws.
I use 2 Propylene torches for heat. They are 475,000 BTU's per torch. They have long handles so we can get back away from the heat. The end of the torch looks like the afterburner on a jet engine. Sounds like it too. The end of the torch is larger than a silver dollar, perhaps 2 1/4" in diameter.
Something I do before installing a coupling is to check the key in the broached hub to make sure it fits. I have seen more couplings stuck from too shallow keyways or keyways in hubs which aren't straight to the hub bore than from having undersized bores. Also, I use light oil (EZ-1) on the shaft rather than anti-seize. The anti-seize gets hot and it piles up on the shaft like fish scales and the coupling invariably sticks.
One of the problems I have had on removing couplings is the galling of metal while the coupling is coming off. Sometimes it will really tear the shaft. A work-around for that is to put the puller on but put just enough pressure on the jaws to keep them from coming off. Then heat the coupling as quickly as possible over the keyway. When it is smoking hot you can then apply the hyd. pressure. If there is a lot of pressure applied early and the coupling moves prematurely it really seems to tear.
I also use an inside mic. and set it to about .006" larger than the shaft diameter. I will check the bore I.D. during the heating process on both ends and the middle and at at different points like 12 o'clock, 3 o'clock, etc. Sometimes heat isn't evenly applied. A little care here can save a lot of grief.
A lot of the couplings here are shot and can't be salvaged. On those we will make an axial cut with a Metabo over the key and then pulling the coupling is a snap.
OBTW: I will cut the keyway with the big draw type key cutter we picked up used from an equipment dealer last fall. D.C. Morrison retro-fit the draw bar to take their cutters. It will use their 4-bolt cutter, and they included in the job an insert that will hold one of their 2-bolt cutters. This machine will cut a keyway up to 4.5" wide. It will do 3.5" wide with a single cutter, the 4.5" will need two passes. This 'little' one at 2.5" wide should be a snap. It also will cut up to 30" in length.
Thanks for all the ideas and I'll keep you posted on how things go...KQ