“Schedule” (SCH) is the standard way of specifying wall thickness for pipes and butt-weld fittings. The same 6-inch elbow can weigh — and cost — very differently depending on its schedule, so getting this right is essential for both budget and safety.
What Schedule Actually Means
Schedule numbers (SCH10, 20, 40, 80, 160…) index a table of wall thicknesses defined in ASME B36.10M. The higher the schedule, the thicker the wall and the higher the pressure rating. Wall thickness for the same schedule changes with pipe size:
| Nominal Size | SCH40 Wall | SCH80 Wall |
|---|---|---|
| 2” (DN50) | 3.91 mm | 5.54 mm |
| 4” (DN100) | 6.02 mm | 8.56 mm |
| 6” (DN150) | 7.11 mm | 10.97 mm |
| 8” (DN200) | 8.18 mm | 12.70 mm |
| 12” (DN300) | 10.31 mm | 17.48 mm |
SCH40 or SCH80?
- SCH40 is the workhorse for water, air, and general low-to-medium pressure service. If your system pressure is modest, SCH40 is usually sufficient and significantly cheaper.
- SCH80 is chosen for higher pressure, threaded connections (extra wall compensates for cut threads), abrasive media, or where corrosion allowance is needed.
The correct choice ultimately comes from your piping engineer’s pressure calculation — as a supplier we always manufacture to the schedule you specify, and fittings should match the schedule of the pipe they weld to.
The STD / XS Trap on Large Diameters
Many inquiries say “STD” (standard) or “XS” (extra strong) instead of a schedule number. Be careful:
- Up to 10”, STD = SCH40 exactly
- From 12” and above, STD stays at 9.53 mm (3/8”) while SCH40 keeps increasing — so 12” STD ≠ 12” SCH40
- Similarly, XS = SCH80 only up to 8”
This is one of the most common causes of wrong-thickness orders on large diameter fittings. If your list mixes STD/XS with schedule numbers on sizes above 10”, double-check what the design actually requires.
Our Advice When Ordering
- Always write the schedule (or exact wall in mm) for every size on your list
- Never assume STD/SCH40 equivalence above 10”
- Ask your supplier to confirm wall thickness in mm on the order confirmation — we do this on every specification sheet before production
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