Schedule 40 Seamless Pipe Dimensions, Wall Thickness and Pressure Rating

1. Schedule 40 Pipe Dimensions Chart

Schedule 40 seamless pipe is seamless steel pipe manufactured to the SCH 40 wall-thickness designation under ASME B36.10M. The actual wall thickness varies with nominal pipe size (NPS). The Schedule 40 pipe dimensions chart below lists NPS, DN, outside diameter (OD), wall thickness (WT), inside diameter (ID), and weight.

Common Schedule 40 sizes include NPS 1", 2", 3", 4", 6", 8", 10", and 12". Larger sizes are also available depending on the applicable standard and manufacturing capability.

How Schedule 40 Dimensions Are Determined

Schedule 40 wall thickness varies by Nominal Pipe Size (NPS). ASME B36.10M specifies the outside diameter (OD) and nominal wall thickness (WT) for each pipe size. The inside diameter (ID) is calculated from the OD and WT:

ID = OD − 2 × WT

Pipe weight is calculated from the finished pipe dimensions and steel density.

NPS and DN Reference

NPS (Nominal Pipe Size) is the inch-based nominal size system used for pipe dimensions, while DN (Nominal Diameter) is the metric designation. NPS and DN are nominal designations and do not represent the actual outside diameter of the pipe.

2. What Is Schedule 40 Seamless Pipe

Schedule 40 seamless pipe is a seamless steel pipe manufactured with a wall thickness designated as SCH 40 under ASME B36.10M.

"Seamless" refers to pipe produced without a longitudinal weld seam. "Schedule" indicates the pipe wall thickness series, while "SCH 40" represents one of the most commonly used standard wall thickness classifications.

SCH 40 is commonly used for water transmission, oil and gas pipelines, process piping, fire protection systems, and general industrial service.

3. Schedule 40 Pipe Wall Thickness

SCH 40 wall thickness varies by Nominal Pipe Size (NPS). For the sizes listed in the chart, wall thickness ranges from 1.73 mm at NPS 1/8 to 17.48 mm at NPS 32.**

Small sizes (NPS 1/2–1-1/2): 2.77–3.68 mm

Medium sizes (NPS 2–8): 3.91–8.18 mm

Large sizes (NPS 10–32): 9.27–17.48 mm

4. Schedule 40 Pipe Pressure Rating and Pressure Calculation

The theoretical pressure values below are calculated for ASTM A106 Grade B seamless carbon steel pipe at 100°F (38°C), using Barlow's Formula:

P = 2SEt / D

where S = 20,000 psi is the allowable stress, E = 1.0 is the joint efficiency, t is the nominal wall thickness, and D is the outside diameter.

Note: These figures are nominal theoretical values calculated from the stated assumptions and are provided for reference only. Actual allowable pressure for an installation must account for mill undertolerance, corrosion allowance, design temperature, material properties, and applicable piping code requirements, including ASME B31.3 where applicable.

5. Common Materials for SCH 40 Seamless Pipe

Material Grade	Standard	Typical Application
ASTM A106 Gr.B	ASTM A106	High-temperature service, steam and process piping
ASTM A53 Gr.B	ASTM A53	Water, gas, structural and general industrial piping
API 5L Gr.B	API 5L	Oil, gas and pipeline transportation systems

The most commonly specified grades for seamless pipe schedule 40 are ASTM A106 Gr.B, ASTM A53 Gr.B, and API 5L Gr.B. API 5L Gr.B is primarily used in oil and gas transmission projects.

6. Applications of Schedule 40 Seamless Pipe

SCH 40 seamless pipe is commonly used in applications requiring moderate pressure capacity and reliable mechanical performance.

Typical applications include:

1) Water transmission systems

2) Oil and gas pipelines

3) Steam and process piping

4) Fire protection systems

5) Compressed air systems

6) Structural applications

7) Chemical and petrochemical facilities

8) Power generation plants

7. Schedule 40 vs Schedule 80

Schedule 40 and Schedule 80 pipes have the same outside diameter for a given NPS size. The primary difference is wall thickness.

Item	SCH 40	SCH 80
Wall Thickness	Standard	Thicker
Weight	Lower	Higher
Pressure Rating	Lower	Higher
Inside Diameter	Larger	Smaller
Material Cost	Lower	Higher
Typical Applications	General industrial piping	High-pressure service

For the same NPS, SCH 40 and SCH 80 generally have the same outside diameter, while SCH 80 has a thicker wall and therefore a smaller inside diameter. SCH 40 is typically selected for general industrial service, while SCH 80 is used where higher pressure resistance is required. For a detailed comparison, see SCH 40 vs SCH 80 Pipe.  

8. Schedule 40 Seamless Pipe vs. Welded Pipe

Both seamless and welded steel pipes can be manufactured to Schedule 40 dimensions; the "Schedule" designation defines the standard wall thickness for a given Nominal Pipe Size (NPS), not the manufacturing method.

For a detailed comparison of manufacturing tolerances, pressure design, and cost, see our guide on Seamless Pipe vs. Welded Steel Pipe.

9. FAQs

Q1. What is SCH 40 pipe?

Schedule 40 (SCH 40) is a standardized pipe wall thickness designation under ASME B36.10M. The specified wall thickness varies with Nominal Pipe Size (NPS).

Q2. How thick is Schedule 40 pipe?

Wall thickness varies with pipe size. For example, NPS 1" SCH 40 has a wall thickness of 3.38 mm, while NPS 6" SCH 40 has a wall thickness of 7.11 mm.

Q3. What is the outside diameter (OD) of Schedule 40 pipe?

Outside diameter is determined by Nominal Pipe Size (NPS), not by the Schedule designation. For example, NPS 2" steel pipe has a standardized OD of 60.3 mm.

Q4. Is Schedule 40 pipe always seamless?

No. Schedule 40 specifies wall thickness, not the manufacturing process. Both seamless and welded steel pipes can be manufactured to Schedule 40 dimensions.

Q5. What is the pressure rating of Schedule 40 pipe?

Pressure capacity depends on pipe size, material grade, operating temperature, and applicable design requirements. The theoretical reference values in this article are calculated using Barlow's Formula under the assumptions stated in Section 5.

Read more: 

Seamless Steel Pipe Size Chart – OD, Wall Thickness
Schedule 80 seamless steel pipe 
SCH 40 Carbon Steel Pipe

DIN EN 10220 – Steel Pipe Dimensions