Well, my pipe fitters manual isn't very helpful with Sch 40 for 36" - 60". It lists a wall thickness of 0.75" for sch 40, 36" pipe. And then it stops listing schedule numbers beside the pipe diameters and various thicknesses. I would almost assume that pipe is no longer sold as schedule 40, 80 etc once one passes 36". I know this is the case with non-metallic pipe where they sell by DR (dimensional ratio where D/r = OD/thickness).