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Wall thickness for carbon steel pipe by schedule and nominal pipe size (NPS). Pipe Schedules and Wall Thickness Chart Outside diameter (OD) is fixed per NPS - increasing the schedule increases wall thickness, which reduces the inside diameter. Values follow ASME B36.10M for carbon and alloy steel pipe. Stainless steel pipe dimensions (ASME B36.19M) are similar for the same schedule designation.
| NPS (in) |
OD (mm) |
SCH 10 (mm) |
SCH 40 / STD (mm) |
SCH 80 / XS (mm) |
SCH 160 (mm) |
XXS (mm) |
| 1/2 |
21.3 |
2.11 |
2.77 |
3.73 |
4.78 |
7.47 |
| 3/4 |
26.7 |
2.11 |
2.87 |
3.91 |
5.56 |
7.82 |
| 1 |
33.4 |
2.77 |
3.38 |
4.55 |
6.35 |
9.09 |
| 1-1/4 |
42.2 |
2.77 |
3.56 |
4.85 |
6.35 |
9.70 |
| 1-1/2 |
48.3 |
2.77 |
3.68 |
5.08 |
7.14 |
10.15 |
| 2 |
60.3 |
2.77 |
3.91 |
5.54 |
8.74 |
11.07 |
| 2-1/2 |
73.0 |
3.05 |
5.16 |
7.01 |
9.53 |
14.02 |
| 3 |
88.9 |
3.05 |
5.49 |
7.62 |
11.13 |
15.24 |
| 4 |
114.3 |
3.05 |
6.02 |
8.56 |
13.49 |
17.12 |
| 5 |
141.3 |
3.40 |
6.55 |
9.52 |
15.88 |
19.05 |
| 6 |
168.3 |
3.40 |
7.11 |
10.97 |
18.26 |
21.95 |
| 8 |
219.1 |
3.76 |
8.18 |
12.70 |
20.62 |
23.01 |
| 10 |
273.0 |
4.19 |
9.27 |
15.09 |
25.40 |
28.58 |
| 12 |
323.8 |
4.57 |
9.53 |
17.48 |
28.58 |
33.32 |
| 14 |
355.6 |
6.35 |
11.13 |
19.05 |
31.75 |
35.71 |
| 16 |
406.4 |
6.35 |
12.70 |
21.44 |
36.53 |
40.49 |
| 18 |
457.2 |
6.35 |
14.27 |
23.83 |
39.67 |
45.24 |
| 20 |
508.0 |
6.35 |
15.09 |
26.19 |
44.45 |
50.01 |
| 24 |
610.0 |
6.35 |
17.48 |
30.96 |
52.37 |
59.54 |
How pipe schedules work
Pipe NPS (nominal pipe size) is a dimensional system that originally referred to the inside diameter of thin-wall steel pipe, but now refers to neither ID nor OD directly - it's just a label. OD is fixed per NPS; schedule controls wall thickness.
Common schedules: SCH 10 is thin-wall for low-pressure applications or stainless tube. SCH 40 is the default for most industrial carbon steel pipework and is also called STD (standard weight). SCH 80 (XS, extra strong) doubles the wall thickness roughly at sizes up to 10 inch. SCH 160 and XXS (double extra strong) are used for high-pressure or wear-critical lines.
To calculate the maximum allowable working pressure, use the Barlow formula: P = (2 x S x t) / D, where S is the allowable stress (e.g. 138 MPa for A106 Gr B at ambient), t is wall thickness, and D is outside diameter. Apply the appropriate design code factor (typically 0.72 for ASME B31.3 chemical plant, lower for severe cyclic service).
Related standards
- ASME B36.10M - Welded and smooth wrought steel pipe
- ASME B36.19M - Stainless steel pipe
- ASME B31.3 - Process piping design code
- BS 1387 - Specification for screwed and socketed steel tubes and tubulars (withdrawn, replaced by BS EN 10255)
- BS EN 10255 - Non-alloy steel tubes suitable for welding and threading
- API 5L - Specification for line pipe
Pipe tools
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Frequently Asked Questions
What does Schedule 40 pipe mean?
Schedule 40 (SCH 40) is the standard wall thickness pipe for most industrial carbon steel applications. It's sometimes called STD (standard weight). For example, 2 inch NPS SCH 40 has a 60.3 mm OD and 3.91 mm wall thickness. Thicker walls (SCH 80, 160, XXS) suit higher pressures or wear service.
What is the difference between SCH 40 and SCH 80?
SCH 80 has a thicker wall than SCH 40 for the same outside diameter, reducing the internal bore and increasing pressure capacity. For a 2 inch NPS pipe: SCH 40 is 3.91 mm wall; SCH 80 is 5.54 mm. SCH 80 is sometimes called XS (extra strong). Choose SCH 80 where pressure, abrasion, or corrosion margins need extra wall thickness.
What is the OD of 2 inch NPS pipe?
2 inch NPS pipe has a fixed outside diameter of 60.3 mm (2.375 inches) regardless of schedule. Wall thickness varies with schedule: SCH 10 is 2.77 mm, SCH 40 is 3.91 mm, SCH 80 is 5.54 mm, SCH 160 is 8.74 mm, XXS is 11.07 mm.
What does the Pipe Schedules and Wall Thickness Chart specify?
The Pipe Schedules and Wall Thickness Chart specifies wall thicknesses for carbon steel pipes based on nominal pipe size (NPS) and schedule, adhering to ASME B36.10M standards.
How do different schedules affect a pipe's dimensions in the chart?
Different schedules increase the wall thickness of a pipe while keeping the outside diameter constant, as defined by NPS; for example, Schedule 40 has a thicker wall than Schedule 10 for the same NPS size.
What materials are covered under ASME B36.10M and B36.19M in this chart?
The Pipe Schedules and Wall Thickness Chart covers carbon steel pipes according to ASME B36.10M, with similar dimensions applying to stainless steel pipes as per ASME B36.19M.
How should engineers select the appropriate schedule from the chart for their project needs?
Engineers should choose a pipe schedule based on pressure requirements and expected operating conditions; higher schedules offer thicker walls and greater pressure tolerance but are heavier and more expensive.
Are there UK suppliers listed in this chart, or does it provide details relevant to finding them?
The Pipe Schedules and Wall Thickness Chart itself doesn't list specific UK suppliers but provides the necessary dimensions engineers need to consult with local steel pipe suppliers that conform to ASME standards.
What are the cost implications of choosing higher schedule pipes according to this chart?
Higher schedule pipes have thicker walls, making them more expensive due to increased material usage; for example, Schedule 160 pipes cost significantly more than Schedule 40 but offer greater strength and durability.
How does wall thickness variation impact the inside diameter as shown in the Pipe Schedules and Wall Thickness Chart?
As the schedule increases, wall thickness also increases, which reduces the inside diameter of the pipe; for instance, a 1-inch NPS pipe with Schedule 40 has an inside diameter that's smaller than one with Schedule 10.