I deal with sch80 and 40 on a regular basis. As a general rule 80 can handle 2500 to 3000 psi, and 40 1500psi max. I have been on jobs that were needing to handle 20,000 psi. Needless to say, I do not take any of these jobs lightly. Code all the way, period. I do not know the code for xx wall stuff, but i always make good penetration with 5p+, a super hot, hot pass, a filler and stringer passes with low hydrogen.