“Schedule 40” means the American National Standards Institute (ANSI) designation schedule number 40 for pipes and fittings computed according to the following formula: Schedule Number = (1000)(P/S) where P = internal working pressure in psig; S = allowable stress of piping material at operating conditions in psi.

Source. #7306, eff 6-13-00; ss by #9177, eff 6-13-08); renumbered by #12075 (formerly We 101.33)