When buyers order stainless steel pipe, the NPS (nominal size) alone is not enough — the schedule (Sch) defines the wall thickness, which directly sets the pressure rating, weight and cost. This guide explains Schedule 10S, 40S and 80S, how to read a pipe size, and what to specify on your RFQ.
What is a pipe schedule?
The schedule number is a standardized wall-thickness designation published in ASME B36.19 for stainless pipe. For a fixed NPS, the outside diameter stays constant while the inside diameter shrinks as the wall gets thicker. A higher schedule number means a thicker wall, a higher pressure rating, and more weight per meter.
Common stainless schedules: 10S, 40S, 80S
- Schedule 10S: the lightest common wall. Used for low-pressure drainage, ventilation, decorative and structural tubing where corrosion resistance matters more than pressure.
- Schedule 40S: the standard-weight wall, the default for general process, water and HVAC piping. Most off-the-shelf stainless pipe is 40S.
- Schedule 80S: extra-strong wall for higher pressure, high-temperature and heavy-duty process lines; it weighs noticeably more than 40S.
The trailing “S” marks stainless dimensions under ASME B36.19; it differs slightly from carbon-steel schedule tables in some sizes, so always quote the S version for stainless.
NPS vs OD: why size alone can confuse buyers
NPS is a nominal number, not the actual outside diameter. For example, NPS 1″ does not measure exactly 1 inch outside; the true OD is fixed by the standard. When you send an RFQ, state both NPS and schedule (e.g. NPS 2″ Sch 40S) rather than a guessed diameter, so the supplier can match the correct OD and wall.
How schedule affects your purchase
- Pressure rating: thicker wall (higher Sch) supports higher working pressure at a given temperature.
- Weight and cost: 80S weighs roughly twice as much as 40S for the same NPS, so material and freight cost rise.
- Threading and welding: heavier walls thread more reliably; for welded lines, confirm the end preparation (beveled, plain or threaded) — see our guide on seamless vs welded pipe.
Buyer’s RFQ checklist
- NPS size (e.g. 1/2″, 2″, 4″) and schedule (10S / 40S / 80S).
- Grade: 304/304L or 316/316L.
- Manufacturing type: seamless or welded.
- Ends: plain, beveled, threaded or grooved.
- Length (random cut, 6 m / 20 ft, or cut-to-length).
- Material certificate EN 10204 3.1 — see our mill test certificate buyer checklist.
Send us your NPS, schedule, grade and working pressure, and we will confirm the matching wall thickness and quote.
SOROYA PTE. LTD.
Email：nancy@soroya.com.sg
WhatsApp：+65 8058 3416
