Introduction

Nominal pipe size is a standardized system used to mark the inner diameter of pipes. But it is not the only accurate pipe measurement standard. If you are new to the piping system, it is also necessary to understand the nominal pipe size. Below we will introduce the meaning of nominal pipe size, how to use it and its importance in pipes.

Now that we know that the nominal pipe size is NPS, let’s start to introduce its other meanings and functions.

What Is Nominal Pipe Size (NPS)?

NPS is a standard for the inner diameter size of pipes used in the United States. It is only a way of expression, which is used as a basis for measuring the specific size of the inner diameter of the pipe. For example: the nominal diameter of the PNS10 pipe is 10 inches, but its specific measurement may have tolerances. The specific inner diameter size within the upper and lower tolerance range is qualified.

The NPS expression is mostly used in the United States and Canada, and DN is mostly used in other regions. NPS and DN both indicate the inner diameter size of the pipe, NPS is in inches, and DN is in millimeters.

Why Use Nominal Pipe Size?

The use of nominal pipe size NPS is to standardize the production and design of pipelines. There is a clear data reference standard in the manufacturing process. In this way, during the installation process, engineers can also know the sizes of various pipes, pipe fittings and accessories more clearly, and can install them better.

Another reason is that after the unified standard, the production of various accessories is more complete. Due to different wall thicknesses, the actual inner and outer diameters may differ. But after using the NPS system specification, the steel pipes, pipe fittings, flanges and other accessories in the pipeline system are standardized. This ensures seamless installation.

The Difference Between Nominal Size and Actual Size

The nominal pipe size NPS is a standardized size representation, which may be slightly different from the actual measured size, and the size specified by NPS is allowed to have an upper and lower difference. That is, it is in compliance with the standard within the allowable range. Generally, the upper and lower differences are mostly ±2.

What Does DN Mean?

DN refers to the nominal diameter, which is measured in millimeters and also refers to the inner diameter of the pipe. It is commonly used in countries such as Europe and Asia, and is usually used together with the corresponding DIN standard to indicate the quasi-inner diameter. NPS also refers to the inner diameter of the pipe, which is mostly used in the United States and Canada.

When two different standard pipes need to be connected, the appropriate size can be found by conversion.

Nominal Pipe Size Chart

The nominal pipe size chart can help us convert between different pipe sizes. The following are several common NPS size charts:

As shown in the table, the inner diameter of the pipe will vary depending on the wall thickness and specifications. But the NPS number is always kept uniform. This is more conducive to the installation of various pipes and accessories.

How NPS Relates to Pipe Schedules

Usually NPS is used in conjunction with schedule, and the two together represent a more accurate inner and outer diameter size and wall thickness. It is its conventional standard.

Commonly used schedules are: schedule40, schedule60, schedule80, schedule160, etc.

What does the combination of the two specifically represent? The following example illustrates:

NPS 2 Schedule 40** The outer diameter of the pipe is 2.375 inches and the wall thickness is 0.154 inches.

NPS 2 Schedule 80** pipes also have an outer diameter of 2.375 inches, but a wall thickness of 0.218 inches.

Common Applications of Nominal Pipe Size

Pipes expressed in nominal diameters are widely used. Here are some common application industries:

Residential and commercial plazas

Oil and gas pipelines

Chemical and water treatment plant pipelines, etc.

Summary

In short, understanding the nominal pipe size (NPS) is very useful for you to work in the pipeline industry. Although it is mostly used in the United States, the DN standards of other countries are also introduced above, and the two can be used interchangeably. If you have any questions during use, you are welcome to consult us, and our professional engineers will provide you with professional answers.