Schedule 20 (Sch 20) is a pipe wall thickness designation used with nominal pipe size (NPS). It does not mean that the pipe wall is 20 mm thick. The actual wall thickness depends on the NPS size and applicable dimensional standard.
What Is Schedule 20 Pipe?
The Schedule number identifies a standardized wall thickness for a specific nominal pipe size. Therefore, a Schedule 20 pipe must always be specified together with its NPS, such as NPS 6 Sch 20 or NPS 8 Sch 20.
For the same NPS, a higher Schedule generally corresponds to a thicker pipe wall. However, Schedule numbers are not direct wall thickness measurements and should not be treated as simple multiples of thickness.
Schedule 20 ≠ 20 mm wall thickness
The actual wall thickness must be obtained from the applicable dimensional standard for the selected pipe size and material system.
Is Schedule 20 the Same for Every Pipe Size?
No. The actual wall thickness of Schedule 20 varies with NPS. Schedule 20 is not a single wall thickness applicable to all pipe sizes.
It is important to note that Schedule 20 is not available for every NPS size. The applicable Schedule 20 wall thickness depends on the nominal pipe size and the relevant dimensional standard.
Schedule 20 Pipe Dimensions
The dimensions of Schedule 20 pipe are determined by the combination of Nominal Pipe Size (NPS) and the applicable dimensional standard. Schedule 20 does not represent a fixed wall thickness; the outside diameter (OD) follows the NPS system, while the wall thickness varies according to the specified pipe size.
For carbon steel and other wrought steel pipe, dimensions should be checked against ASME B36.10M. Stainless steel pipe dimensions should be verified separately under ASME B36.19M, rather than combining the two dimensional systems.
Schedule 20 Pipe Size Chart
| NPS | DN | Outside Diameter | Schedule | Wall Thickness |
| 2″ | DN 50 | 60.3 mm | Sch 20 | 2.77 mm |
| 2½” | DN 65 | 73.0 mm | Sch 20 | 3.05 mm |
| 3″ | DN 80 | 88.9 mm | Sch 20 | 3.05 mm |
| 4″ | DN 100 | 114.3 mm | Sch 20 | 3.05 mm |
| 6″ | DN 150 | 168.3 mm | Sch 20 | 3.40 mm |
| 8″ | DN 200 | 219.1 mm | Sch 20 | 3.76 mm |
| 10″ | DN 250 | 273.1 mm | Sch 20 | 4.19 mm |
| 12″ | DN 300 | 323.9 mm | Sch 20 | 4.57 mm |
Important: The availability and exact dimensions of Schedule 20 should be verified against the applicable edition of the dimensional standard and the specified material system. Schedule 20 should not be assumed to apply to every NPS size.
For project procurement, the pipe should therefore be specified using NPS, Schedule, material grade, and applicable standard rather than Schedule 20 alone.
Schedule 20 Wall Thickness
The wall thickness of Schedule 20 pipe is determined by the pipe’s Nominal Pipe Size (NPS) and the applicable dimensional standard. Schedule 20 is a standardized designation rather than a direct measurement of wall thickness.
How Is Schedule 20 Wall Thickness Determined?
For a given pipe size, the NPS and Schedule designation together determine the standardized wall thickness listed in the applicable pipe dimension standard.
The wall thickness may also affect the pipe’s inside diameter, weight, flow area, and pressure design, so the Schedule should be selected based on the complete piping requirements rather than the Schedule number alone.
Why Does Wall Thickness Vary by NPS?
Wall thickness varies by NPS because the Schedule system assigns standardized dimensions to different nominal pipe sizes.
As pipe diameter increases, the corresponding standardized wall thickness for a given Schedule can also change. This allows pipe dimensions to remain consistent within the NPS and Schedule system while accommodating different pipe diameters.
Therefore, Schedule 20 should always be specified together with the NPS, for example:
- NPS 4 Sch 20
- NPS 6 Sch 20
- NPS 8 Sch 20
- NPS 12 Sch 20
The exact wall thickness should then be verified from the applicable dimensional standard
Schedule 20 Pipe Standards
The applicable standard for Schedule 20 pipe dimensions depends on the pipe material and the dimensional system specified for the project.
For wrought steel pipe, ASME B36.10M is the primary dimensional standard. Stainless steel pipe is covered separately by ASME B36.19M, which uses the “S” suffix for its schedule designations.
ASME B36.10M Schedule 20
ASME B36.10M covers the standardization of dimensions for welded and seamless wrought steel pipe used for high- or low-temperature and pressure service.
ASME B36.19M and Stainless Steel Pipe
Stainless steel pipe dimensions should be checked against ASME B36.19M rather than automatically applying the B36.10M table.
ASME B36.19M specifically covers welded and seamless wrought stainless steel pipe, and its schedule numbers use an “S” suffix to distinguish them from those in B36.10M.
- 5S
- 10S
- 40S
- 80S
In short:
Carbon/alloy steel pipe → check ASME B36.10M
Stainless steel pipe → check ASME B36.19M and its S-schedules
Do not mix B36.10M and B36.19M dimension tables when preparing a Schedule pipe size chart.
Schedule 20 vs Schedule 40
Schedule 20 and Schedule 40 differ mainly in wall thickness. For the same NPS, the outside diameter generally remains the same, while the wall thickness and resulting inside diameter and pipe weight change.
For example, the dimensional difference can be illustrated using a specific NPS:
| NPS | OD | Schedule 20 | Schedule 40 |
| 8″ | 219.1 mm | 3.76 mm | 8.18 mm |
This means that for NPS 8, both Schedule 20 and Schedule 40 have the same nominal outside diameter of 219.1 mm, but Schedule 40 has a substantially thicker wall.
The thicker wall results in:
- Smaller inside diameter
- Higher pipe weight
- Greater wall thickness for pressure and mechanical resistance
However, this does not mean Schedule 40 automatically has a specific pressure rating. Allowable pressure must be determined based on the material grade, design temperature, wall thickness, corrosion allowance, and applicable piping code.
FAQ
What is Schedule 20 pipe?
Schedule 20 pipe is a pipe with a standardized wall thickness designation used with a specific Nominal Pipe Size (NPS). The actual wall thickness varies according to the NPS and applicable dimensional standard.
Can Schedule 20 pipe be used for pressure applications?
Yes, where the selected pipe meets the project’s engineering requirements. Pressure suitability depends on material grade, wall thickness, design temperature, corrosion allowance, and applicable piping code, rather than the Schedule number alone.
Where is Schedule 20 pipe used?
Schedule 20 pipe may be used in water systems, utility piping, HVAC systems, and certain industrial or mechanical applications where its wall thickness meets the project’s requirements.
