Professional Article on Pipe Dimensions

From Foreign Trade Department, Hebei Hongcheng Pipe Industry Co., Ltd.

In global pipeline engineering, petrochemical, power, thermal, gas transmission and shipbuilding industries, accurate dimension control is the core guarantee for pipe interchangeability, installation compatibility, structural safety and service life. HC as a professional manufacturer integrating production, sales and export of alloy steel pipes, pipe fittings and prefabricated piping, strictly abides by international and domestic mainstream dimension standards to provide customers with reliable dimension solutions for seamless steel pipes, alloy pipes, high-pressure pipe fittings and factory-prefabricated piping.

Core Dimension Terminology & Definitions

OD (Outside Diameter): Actual outer diameter of the pipe, fixed value under corresponding standards, the basic dimension for connection and matching.

WT (Wall Thickness): Thickness of pipe wall, directly determining pressure bearing capacity, corrosion allowance and structural strength.

ID (Inside Diameter): Flow passage dimension, calculated by ID = OD − 2 × WT.

DN (Diamètre Nominal / Nominal Diameter): Metric nominal diameter (mm), general reference for pipeline system, not equal to actual OD or ID.

NPS (Nominal Pipe Size): Imperial nominal size (inch), widely used in American standard systems; for NPS ≤ 12, actual OD is greater than nominal value; for NPS ≥ 14, OD equals nominal size.

SCH (Schedule): Wall thickness series under ASME B36.10M / B36.19M, such as SCH 40, SCH 80, SCH 160, representing pressure grade and wall thickness.

de / dn: Nominal outer diameter for plastic pipes, commonly used in PE, PVC-U, PPR systems.

Mainstream Dimension Standards Adopted

ASME B36.10M: Welded and seamless wrought steel pipes, applicable to carbon steel and alloy steel pipes.

ASME B36.19M: Stainless steel pipes.

ASTM A335: Seamless ferritic alloy steel pipes for high-temperature service, matching our A335 P5 / P9 / P11 / P22 / P91 / P92 products.

GB/T 5310、GB3087、GB/T 9948、GB6479、GB/T 8163: Chinese seamless steel pipe standards.

ISO 161: Thermoplastic pipe nominal outer diameter and pressure series.

Dimension Matching & Conversion Principles

1、DN–NPS–OD Corresponding DN is the metric equivalent of NPS, while OD is the fixed matching dimension. For example:

NPS 2 ≈ DN 50, OD = 60.3 mm

NPS 3 ≈ DN 80, OD = 88.9 mm

=NPS 4 ≈ DN 100, OD = 114.3 mm

2、Wall Thickness & Schedule Matching Schedule number increases with wall thickness and pressure rating. Under the same OD, higher SCH means thicker WT and smaller ID.

3、Metric–Imperial Conversion 1 inch = 25.4 mm; dimension conversion must follow standard tabulated values, not simple mathematical conversion.

Dimension Expression Specifications

Steel pipe: OD × WT (e.g., 168.3 × 7.11 mm) or NPS + SCH (e.g., NPS 6 SCH 40)

Pipe fittings: Consistent with mating pipe OD + wall thickness grade (e.g., 90° Elbow 660 × 20)

Metric plastic pipe: dn × PN (nominal outer diameter × pressure rating)

HC Pipe Dimension Capability

Our dimension range covers:

Outer diameter: φ10 mm – φ1340 mm

Wall thickness: 2 mm – 260 mm Products include seamless alloy pipes, elbows, tees, reducers, caps, flanges and prefabricated piping, suitable for high-temperature, high-pressure and corrosive working conditions in power, petrochemical and other fields. All dimensions are inspected by precision measuring equipment to ensure compliance with standards and drawing requirements.

Suggestions for Dimension Selection

1、Confirm system standard: metric (DN) or imperial (NPS).

2、Determine OD and SCH/WT as core dimensions.

3、Match fitting dimensions with pipe OD.

4、Reserve corrosion allowance and construction tolerance.

5、Verify interchangeability with valves, flanges and equipment nozzles.

Hebei Hongcheng Pipe Industry Co., Ltd. relies on standardized dimension management, stable production accuracy and complete quality control, providing global customers with dimension-clear, interchangeable and reliable pipe products. We are committed to offering professional dimension consultation, customized processing and full-process technical support to ensure your project safety and efficiency.