What Is Pipe Diameters？
We all know that pipe dimensions are composed of the pipe’s outer diameter, inner diameter, and wall thickness. But do you know what pipe diameter means? While the first thing you think of when you think of pipe diameter is the outer diameter of the pipe, it often refers to the nominal diameter, a point that can be confusing.
Why Is Pipe Diameter So Important?
Pipe diameter is the nominal diameter of a pipe, often referred to as NPS. This is a standardized size identifier, representing a size code rather than the actual physical size. However, thanks to the pipe diameter, pipe fittings from different manufacturers can be matched. NPS is used to determine the size when ordering, avoiding ordering errors caused by differences in communication and understanding.
Pipe Diameter Development History
The IPS system was used in the 19th century. With the development of industry, the American Society of Pipe Sizing (ASA) introduced the NPS system in 1927. This separated the dimensions from the actual physical dimensions and published a standard system for pipe wall thickness (Schedule). Subsequently, Europe invented the DN system, which, along with the NPS, has become the global standard for pipe sizes today.
Why are Pipe Diameters and OD Easily Confused?
Now that we know that pipe diameters and OD are easily confused, do you know which part of the pipe is the pipe diameter and which part is the OD?
NPS1⁄8 to 12
At this stage of the pipeline, NPS is close to OD. As shown in the figure below
NPS 14 And Above
In this size pipe, NPS is the actual OD
Pipe Diameter Chart
NPS: Nominal Pipe Size , based on the metric system, approximates the inside diameter in inches. It applies to North America and some Commonwealth countries.
DN: Diameter Nominal , based on the imperial system, is merely a designation in millimeters. It applies to Europe, China, and countries that adhere to ISO standards.
How to Choose the Pipe Diameter Correctly
1. First, determine the fluid’s properties (density, viscosity, corrosiveness, state, etc.) and calculate the required flow rate, as this directly affects the inner diameter. Determine the flow rate: approximately 10-30 m/s for gases/steam, 0.5-2 m/s for slurries/solid-laden fluids, and 1-3 m/s for liquids such as water and oil.
2.Use the following formula to roughly calculate the inner diameter of the pipe
d: Pipe inner diameter (mm)
Q: Flow rate (L/min)
v: Flow velocity (m/s)
3.After calculating the minimum inner diameter, determine the wall thickness of the pipe you need. If you calculate the minimum inner diameter to be 15mm and you want a pipe with a wall thickness of SCH40, you can consult the table above and use OD minus SCH40 wall thickness to get the inner diameter. Find the NPS that matches your calculated inner diameter. Note that the inner diameter value of OD minus wall thickness must be larger than the calculated inner diameter because we calculated the minimum inner diameter. You can then determine that the pipe diameter you need is NPS 1/2.
If you are not sure about the pipe size you need, you can click below to contact a PANDAPIPE expert. PANDAPIPE is a pipe company that integrates production and application, and is a company you can trust.
