Bring a section of the pipe down to the local stocking plasma machine supply house (welding supply) and ask for a demo. "IF" the pipe has water in it duplicate these conditions in the test...:thumbsup: My experience w/ plasma company claims of thickness a particular machine will cut is that they base their claims from
PERFECT CONDITIONS. Type of metal being cut, angle of cut and the operator body posistion in relation to the world, debris within and on top of the pipe like water, rusty caked buildup & GALVANIZATION, ambient temperature and I am sure other issues I can't dream up will effect how a plasma torch performs. Probably altitude and barametric pressure will factor in as well. Be SURE to take into consideration as to weather or not your in a space whereas the air quality will be compromised whilst doing the plasma dance. If your in a no ventilation area skip to plan B.
Plan B
Or build what I suggest and you would be done by now for 1/8 the co$t. Those costs being your compressor and the plasma machine and the routine maintenance on the forever clogging plasma tip, goggles on, goggles off, (what a pain and if you wear glasses? Oui Vie!) Of course the need for enough amps to run a compressor AND the plasma machine and the extra effort to drag all that equipment around etc. How long is the plasma cord from box to tip?
Grab some 14" blades for steel, a couple of bushings from 1" arbor down to whatever size grinder you buy ( GO BIG ) and make a guard. (cut the center guts out of the existing guard and fab up anew as I did ) You will use that tool for the rest of your life and wonder how the helm you ever did "it", w/o it.
BELIEVE IT. (Stihl may have the correct size arbor hole in steel, american made will probably be 1" arbor)
PS, If you go plasma,
GO BIG, or stay home. There definately great handy machines to have in the shop if this job justifies all the above plus. I mad eteh BradOMatic5000 AFTER I bought a plasma machine.