Complete pipe schedule reference covering NPS ½" to 24" for carbon steel (ASME B36.10M) and stainless steel (ASME B36.19M). Includes Schedule 40, 80, 120, 160, XXH wall thicknesses and NPS-to-OD conversions. Used daily by Saudi Aramco engineers, procurement teams, and EPC piping designers.
NPS is a dimensionless reference number, not a physical measurement. NPS 4 does not mean 4-inch bore or 4-inch OD. For NPS ≤ 12, OD is larger than NPS (e.g. NPS 4 = 4.500″ OD). For NPS ≥ 14, OD equals NPS in inches (NPS 14 = 14.000″ OD). All flanges, fittings, and valves for a given NPS are designed to the same OD regardless of schedule.
Schedule number defines wall thickness. Higher schedule = thicker wall = smaller bore = higher pressure rating. The outside diameter stays constant for a given NPS — only the wall and bore change. Standard (STD) = Sch 40 for NPS ≤ 10″; Extra Heavy (XH) = Sch 80 for NPS ≤ 8″; Double Extra Heavy (XXH) has no schedule number — only a named weight designation.
DN (Diamètre Nominal) is the ISO/EN metric designation, approximately equal to NPS × 25. DN 50 = NPS 2; DN 100 = NPS 4; DN 150 = NPS 6; DN 200 = NPS 8; DN 250 = NPS 10; DN 300 = NPS 12. Saudi Aramco ASME-based projects use NPS; European and ISO-based projects use DN — always verify which system the engineering datasheet references before ordering.
ASME B36.10M governs carbon and alloy steel pipe dimensions. ASME B36.19M governs austenitic stainless steel pipe — it uses the same ODs but different schedule designations (5S, 10S, 40S, 80S with the "S" suffix). Never use B36.10M data for ordering stainless pipe wall thicknesses: the Sch 40 wall in B36.19M (40S) can differ from B36.10M for the same NPS, especially at larger sizes.
The OD is the same for carbon steel (B36.10M) and stainless steel (B36.19M) at a given NPS. Only the wall thickness and bore change with schedule.
| NPS | OD (inches) | OD (mm) | DN (approx.) | Note |
|---|---|---|---|---|
| ½" | 0.840 | 21.34 | 15 | OD ≠ NPS |
| ¾" | 1.050 | 26.67 | 20 | OD ≠ NPS |
| 1" | 1.315 | 33.40 | 25 | OD ≠ NPS |
| 1¼" | 1.660 | 42.16 | 32 | OD ≠ NPS |
| 1½" | 1.900 | 48.26 | 40 | OD ≠ NPS |
| 2" | 2.375 | 60.33 | 50 | OD ≠ NPS |
| 2½" | 2.875 | 73.03 | 65 | OD ≠ NPS |
| 3" | 3.500 | 88.90 | 80 | OD ≠ NPS |
| 4" | 4.500 | 114.30 | 100 | OD ≠ NPS |
| 6" | 6.625 | 168.28 | 150 | OD ≠ NPS |
| 8" | 8.625 | 219.08 | 200 | OD ≠ NPS |
| 10" | 10.750 | 273.05 | 250 | OD ≠ NPS |
| 12" | 12.750 | 323.85 | 300 | OD ≠ NPS |
| 14" | 14.000 | 355.60 | 350 | OD = NPS in inches from here |
| 16" | 16.000 | 406.40 | 400 | OD = NPS in inches |
| 18" | 18.000 | 457.20 | 450 | OD = NPS in inches |
| 20" | 20.000 | 508.00 | 500 | OD = NPS in inches |
| 24" | 24.000 | 609.60 | 600 | OD = NPS in inches |
Wall thickness in millimetres. Highlighted columns (Sch 40 / Sch 80) are the most commonly specified in Saudi Aramco process piping. STD = Standard weight; XH = Extra Heavy; XXH = Double Extra Heavy.
| NPS | OD (mm) | Sch 10 | Sch 40 (STD) | Sch 80 (XH) | Sch 120 | Sch 160 | XXH |
|---|---|---|---|---|---|---|---|
| ½" | 21.34 | — | 2.77 | 3.73 | — | 4.78 | 7.47 |
| ¾" | 26.67 | — | 2.87 | 3.91 | — | 5.56 | 7.82 |
| 1" | 33.40 | 2.77 | 3.38 | 4.55 | — | 6.35 | 9.09 |
| 1¼" | 42.16 | 2.77 | 3.56 | 4.85 | — | 6.35 | 9.70 |
| 1½" | 48.26 | 2.77 | 3.68 | 5.08 | — | 7.14 | 10.16 |
| 2" | 60.33 | 2.77 | 3.91 | 5.54 | — | 8.74 | 11.07 |
| 2½" | 73.03 | 3.05 | 5.16 | 7.01 | — | 9.53 | 14.02 |
| 3" | 88.90 | 3.05 | 5.49 | 7.62 | — | 11.13 | 15.24 |
| 4" | 114.30 | 3.05 | 6.02 | 8.56 | — | 13.49 | 17.12 |
| 6" | 168.28 | 2.77 | 7.11 | 10.97 | 14.27 | 18.26 | 21.95 |
| 8" | 219.08 | 2.77 | 8.18 | 12.70 | 18.26 | 23.01 | 22.23 |
| 10" | 273.05 | 3.40 | 9.27 | 15.09 | 21.44 | 28.58 | 25.40 |
| 12" | 323.85 | 3.96 | 10.31 | 17.48 | 25.40 | 33.32 | 25.40 |
| NPS ≥14" — OD = NPS | OD (mm) | Sch 10 | Sch 20 | STD | Sch 40 | XH | Sch 80 | Sch 120 | Sch 160 |
|---|---|---|---|---|---|---|---|---|---|
| 14" | 355.60 | 6.35 | 7.92 | 9.53 | 9.53 | 12.70 | 15.88 | 23.83 | 31.75 |
| 16" | 406.40 | 6.35 | 7.92 | 9.53 | 9.53 | 12.70 | 16.66 | 26.19 | 36.53 |
| 18" | 457.20 | 6.35 | 7.92 | 9.53 | 11.13 | 14.27 | 19.05 | 29.36 | 39.67 |
| 20" | 508.00 | 6.35 | 9.53 | 9.53 | 12.70 | 15.09 | 20.62 | 32.54 | 44.45 |
| 24" | 609.60 | 6.35 | 9.53 | 9.53 | 14.27 | 17.48 | 24.61 | 38.89 | 52.37 |
Source: ASME B36.10M. Wall thickness tolerance: −12.5% per ASTM A106, API 5L, and ASTM A53. For NPS ≥14, STD and Sch 40 diverge at NPS 18+ — always confirm with the engineering datasheet. Consult ASME B36.10M for the complete table including intermediate schedules.
Applies to ASTM A312 austenitic stainless steel pipe (TP304, TP304L, TP316, TP316L). Note the 'S' suffix schedules — do not substitute B36.10M (carbon steel) values for B36.19M (stainless) specifications without engineering review.
| NPS | OD (mm) | Sch 5S | Sch 10S | Sch 40S | Sch 80S |
|---|---|---|---|---|---|
| ½" | 21.34 | 1.65 | 2.11 | 2.77 | 3.73 |
| ¾" | 26.67 | 1.65 | 2.11 | 2.87 | 3.91 |
| 1" | 33.40 | 1.65 | 2.77 | 3.38 | 4.55 |
| 1½" | 48.26 | 1.65 | 2.77 | 3.68 | 5.08 |
| 2" | 60.33 | 1.65 | 2.77 | 3.91 | 5.54 |
| 3" | 88.90 | 1.65 | 3.05 | 5.49 | 7.62 |
| 4" | 114.30 | 1.65 | 3.05 | 6.02 | 8.56 |
| 6" | 168.28 | 2.11 | 3.40 | 7.11 | 10.97 |
| 8" | 219.08 | 2.77 | 3.76 | 8.18 | 12.70 |
| 10" | 273.05 | 3.40 | 4.19 | 9.27 | 12.70 |
| 12" | 323.85 | 3.96 | 4.57 | 9.52 | 12.70 |
Source: ASME B36.19M. Applies to ASTM A312 seamless (SMLS) and welded stainless steel pipe. Wall tolerance: −12.5% per ASTM A312. Sch 80S is maximum wall available under B36.19M — for heavier walls on SS pipe, engineering must specify B36.10M equivalent schedules explicitly.
Pipe schedule on Aramco projects is defined in the Piping Material Class Document (PMCD) for each service. The following general patterns apply across most Aramco PMCDs — always verify against the project-specific PMCD before ordering:
| Service / Material | Typical Schedule | Common Specification | Notes |
|---|---|---|---|
| Utility / low-pressure CS | Sch 40 (STD) | ASTM A106 Gr. B | Most common for instrument air, water, low-P utility |
| Process piping CS — ASME Class 600+ | Sch 80 (XH) | ASTM A106 Gr. B | Higher-pressure classes, thermal cycling services |
| Sour service CS pipe | PMCD-specified (often Sch 40 or 80) | API 5L PSL2 HIC-tested | SAES-L-133 governs; schedule set by pressure-temperature rating |
| High-pressure / erosive CS | Sch 160 or XXH | ASTM A106 Gr. B | Injection lines, high-velocity process streams |
| Stainless steel — utility / instrument | Sch 10S | ASTM A312 TP316L | Instrument tubing, clean utility, low-pressure SS systems |
| Stainless steel — process piping | Sch 40S | ASTM A312 TP316L SMLS | Standard for SS process piping; NACE MR0175 for sour service |
| Pipeline — gas / crude transmission | Wall by design (MOP / hoop stress) | API 5L PSL2 | Pipeline wall set by ASME B31.4/B31.8 design; no schedule designation |
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