What is Nominal Pipe Size Schedule?

What is Pipe Size Schedule?
Nominal Pipe Size Schedule refers to a collection of standard pipe sizes. Among them:

NPS, DN or NB determines the outer diameter of the pipe.

SCH determines the wall thickness of the pipe.

When NPS (DN/NB) and SCH are given, you can find the corresponding outer diameter and wall thickness in the comparison table in ASME B36.10 or ASME B39.19.

If you use pipe products in your project, you will definitely come across the Nominal Pipe Size Schedule. Whether you are a pipe buyer or a pipe manufacturer, you need to use the Nominal Pipe Size Schedule to confirm the size of the pipe. However, do you clearly understand what the Nominal Pipe Size Schedule is?

This article will introduce the Nominal Pipe Size Schedule and the related ASME B36.10 / ASME B39.19 standards in detail. If you have questions in this regard, or you have just entered the pipe industry, I believe this article will help you.

Before formally introducing the Nominal Pipe Size Schedule, we must clearly understand how to express pipe size.

The cross section of the pipe is a ring. The diameter of the outside of the ring is called the outer diameter (OD). The diameter of the inside of the ring is called the inner diameter (ID). The width of the ring is called the wall thickness (THK). The outer diameter, inner diameter and wall thickness determine the cross-sectional size of the pipe.

However, among the outer diameter, inner diameter and wall thickness, only two of the data are needed to determine the size of the pipe. The other data can be calculated by the following formula:

THK = (OD - ID) ÷ 2
In addition, the length of the pipe is also an important part of the pipe size. However, the adjustment of the length can be achieved only by cutting. The specific outer diameter, inner diameter and wall thickness require complex processing to obtain.

Therefore, the Nominal Pipe Size Schedule mainly determines the outer diameter and wall thickness of the pipe. Now let's start to formally introduce the Nominal Pipe Size Schedule.

What is Nominal Pipe Size Schedule?
The Nominal Pipe Size Schedule is a comparison table. It establishes a standard for the size of pipes. The following table is the Nominal Pipe Size Schedule:

NPS, DN, NB
NPS, DN, and NB determine the outer diameter of the pipe.

NPS is the abbreviation of Nominal Pipe Size. It is expressed in inches, such as: ⅛, ¼, ⅜, …, 44, 46, 48. It should be noted that NPS is not exactly equal to the outer diameter of the pipe. For pipes above NPS14, NPS can be directly equivalent to the outer diameter. For example: NPS14 means the outer diameter is 14 inches. However, for small-sized pipes, NPS is often smaller than the actual outer diameter. For example: the actual outer diameter corresponding to NPS2 is 2.375 inches. Therefore, in most cases we still need to refer to the table to confirm the specific outer diameter.