Seamless steel pipe sizes

Seamless steel pipe sizes are mainly specified by Nominal Pipe Size (NPS) or Nominal Diameter (DN), outside diameter (OD), wall thickness (WT), and pipe Schedule (SCH). The actual dimensions depend on the applicable standard, such as ASME B36.10M for carbon and alloy steel pipe or ASME B36.19M for stainless steel pipe. For example, an NPS 2 pipe has an actual outside diameter of 60.33 mm, while its wall thickness changes according to the selected Schedule, such as SCH 40 or SCH 80.

1. Understanding the Standards: NPS vs. DN vs. Schedule
Before diving into the dimension charts, it is vital to understand how seamless steel pipe sizes are labeled under international standards like ASME B36.10M (for carbon/alloy steel) and ASME B36.19M (for stainless steel).

NPS (Nominal Pipe Size): A North American standard designation based on inches. For pipes with an NPS of 1/2 to 12 inches, the NPS is different from the actual outside diameter (OD). For NPS 14 and above, the NPS is exactly equal to the OD.

DN (Diameter Nominal): The European and international metric equivalent (mm) to NPS. For example, NPS 2 corresponds to DN 50.

Pipe Schedule (SCH): This indicates the pipe's wall thickness. Common schedules include SCH 40, SCH 80, SCH STD (Standard), and SCH XS (Extra Strong). As the schedule number increases, the wall thickness becomes thicker, enabling the pipe to withstand higher pressures.

2. Comprehensive Seamless Steel Pipe Sizes & Dimensions Chart
The following chart outlines the most frequently requested seamless steel pipe dimensions, covering outside diameter (OD), wall thickness, and theoretical weight per meter for standard industrial grades (ASTM A53, ASTM A106, API 5L, and ASTM A312).

Standard Seamless Steel Pipe Dimension  Table

3. How to Calculate Seamless Steel Pipe Theoretical Weight

When arranging shipping budgets or calculating structural loads, you can manually calculate the weight of seamless carbon steel pipes using the standard industry formula:

Weight (kg/m)= 0.0246615x(OD - WT) xWT

OD: Outside Diameter in millimeters (mm)
WT: Wall Thickness in millimeters (mm)

Example Calculation:
For a 2-inch ASTM A53 Schedule 40 seamless pipe (OD = 60.33 mm, WT =3.91 mm):

Weight =0.0246615x(60.33-3.91) x 3.91≈5.44 kg/m

Seamless Steel Pipe Size vs. Schedule

A common misconception is that a larger Schedule number means a larger pipe diameter. This is not correct.

For the same NPS, the outside diameter generally remains fixed while the wall thickness changes.

Nominal Pipe Size (NPS)	Schedule	Outside Diameter (OD)	Wall Thickness (WT)	Approx. Internal Diameter (ID)
2"	SCH 40	60.33 mm	3.91 mm	52.51 mm
2"	SCH 80	60.33 mm	5.54 mm	49.25 mm
2"	SCH 160	60.33 mm	8.74 mm	42.85 mm
4"	SCH 40	114.30 mm	6.02 mm	102.26 mm
4"	SCH 80	114.30 mm	8.56 mm	97.18 mm
6"	SCH 40	168.28 mm	7.11 mm	154.06 mm
6"	SCH 80	168.28 mm	10.97 mm	146.34 mm
8"	SCH 40	219.08 mm	8.18 mm	202.72 mm
8"	SCH 80	219.08 mm	12.70 mm	193.68 mm

Frequently Asked Questions (FAQ)

Q1: Do "SCH 40" and "STD" have the exact same wall thickness?
Yes, for seamless steel pipe sizes up to NPS 10, Schedule 40 and STD (Standard) share identical wall thicknesses. However, for NPS 12 and larger, SCH 40 and STD begin to vary. Always cross-check the dimension table for larger sizes.

Q2: What is the main size difference between seamless and welded pipes?
While both adhere to ASME B36.10 dimensional sizes, seamless pipes generally feature excellent wall thickness uniformity without a longitudinal weld line, making them ideal for high-vibration and high-pressure settings. For exceptionally large outer diameters (above 24 inches), Spiral Welded Pipes are typically utilized.

Q3: Can Central Steel customize lengths for seamless steel pipes?
Absolutely. We offer Single Random Lengths (SRL, 5-7 meters), Double Random Lengths (DRL, 10-12 meters), and customized fixed cut-to-length options to match your exact pipeline layouts and minimize on-site welding.

Read more： What is seamless steel pipe?