What Is the Nominal Pipe Size?

Nominal diameter (also known as mean outside diameter ). Refers to the standardized diameter series of containers, pipes and their accessories. The use of a nominal diameter is conducive to the standardization of parts and components, and is also convenient for design, manufacturing, repair and management, and reduces manufacturing costs. For containers, the nominal diameter is expressed by the inner diameter; for pipes, it is expressed by a size smaller than the outer diameter and larger than the inner diameter. Corresponding to a certain nominal diameter of the pipe, its outer diameter is a certain value, and its inner diameter varies with wall thickness. ^[1]

National standard

The nominal diameter is indicated by the letter "DN" followed by a number mark. As a glyph, the size is in millimeters. Nominal diameter is the nominal of pipes such as cast iron pipes, seam steel pipes, concrete pipes, etc., but this notation is not used for seamless steel pipes. For example, DN50, which is a pipe with a nominal diameter of 50mm. The relationship between inch NB (inch) and nominal diameter DN (mm) and outer diameter OD (mm) is as follows:

NB (inch) ----- DN (mm) ------ OD (mm)

1/2 -------------- 15 ---------- 21.3

3/4 -------------- 20 ---------- 26.7

1 -------------- 25 ------------ 33.4

1 1/4 ------------ 32 --------- 42.2

1 1/2 ------------ 40 ---------- 48.3

2 -------------- 50 ------------ 60.3

2 1/2 --------- 65 ------------ 73.0

3 -------------- 80 ------------ 88.9

4 ------------- 100 ------------ 114.3

5 ------------- 125 ------------ 139.8

6 ------------- 150 ------------ 168.3

8 ------------- 200 ------------- 219.1 ^[2]

1. Scope This standard specifies the definition and series of DN (nominal size). This standard applies to piping components specified in the relevant standards using the DN mark. Note: It is also possible to use other marking dimension methods different from this standard, such as threaded, press-fitted, socket welded or butt-welded pipe elements. NPS (nominal pipe size), OD (outer diameter), ID (inner diameter) or G (pipe thread size marking) and other identified pipe components. ^[2]

2. Define DN: the size identification of the combination of letters and numbers used for piping system components. It consists of the letter DN followed by a dimensionless integer number. This number is directly related to the characteristic dimensions of the hole diameter or outer diameter (in mm) of the end connection. Note 1: Unless otherwise specified in the relevant standards, the number after the letter DN does not represent the measured value and cannot be used for calculation purposes. NOTE 2 For those standards using a DN identification system, the relationship between the DN and the dimensions of the piping components should be given, such as DN / OD or DN / ID. ^[2]

3.DN series

The preferred DN values are as follows:

DN 6 DN 100 DN 700 DN 2200

DN 8 DN 125 DN 800 DN 2400

DN 10 DN 150 DN 900 DN 2600

DN 15 DN 200 DN 1000 DN 2800

DN 20 DN 250 DN 1100 DN 3000

DN 25 DN 300 DN 1200 DN 3200

DN 32 DN 350 DN 1400 DN 3400

DN 40 DN 400 DN 1500 DN 3600

DN 50 DN 450 DN 1600 DN 3800

DN 65 DN 500 DN 1800 DN 4000