We locked our PVC buyout in week 6 and a junior asked me what the “schedule” in 3-inch Sch 40 refers to — pressure rating, wall ratio, or an old ASA table. I’ve always treated it as a standardized series from the ASA/ASME era rather than a direct property, but I’d like the clean origin story so I can brief the crew and keep the submittal review moving.
It’s from the old ASA/ASME wall‑thickness series (B36.10/36.19), so Sch 40 names the series, not a pressure rating; PVC just inherits the OD/thickness, while psi comes from ASTM D1785 tables. Since you locked the buyout in week 6, I add a submittal note like “ASTM D1785 PVC, Sch 40 (IPS OD), pressure per mfr table at 73°F” and paste the size‑specific psi to keep review moving. For a quick origin explainer: Nominal Pipe Size - Wikipedia.
@nolan_smith56 has it, and the clean way I tell juniors is: the ‘schedule’ is just the dimensional series, not a psi stamp. On our week‑6 PVC buyouts I attach the ASTM listing and the manufacturer’s pressure/temperature chart to the submittal so it doesn’t stall — , seen that movie. Minor caveat: plastics often keep the steel OD but their wall and rating depend on their own spec, so verify the stated psi at 73°F and apply derate.