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What is Nominal Pipe Size (NPS)? Demystifying Nominal Pipe Size (NPS) Material in Fabrication

What is Nominal Pipe Size (NPS)? Demystifying Nominal Pipe Size (NPS) Material in Fabrication

When working with pipes in automotive and industrial fabrication, understanding pipe sizing is critical, but it's not always as straightforward as it may seem. Enter Nominal Pipe Size (NPS), a North American industry standard that uses a "nominal" number to refer to the general diameter of a pipe, rather than its precise measurements.

This sizing convention was standardized by the American Standards Association to bring consistency across industries, but it can be somewhat misleading at first glance. For example, a commonly used size for turbo manifold fabrication is 1-1/2" Schedule 10. Despite what the name suggests, neither the outside nor inside diameter of this pipe size actually measures 1.5 inches. In reality, the outside diameter is approximately 1.900 inches, and the inside diameter is around 1.682 inches. Due to the nominal sizing of pipe we never list or reference the material on our website as a decimal (e.g., 1.500") like we do with tube size material.

For reference, below is a chart of standard pipe sizes ranging from 1/8" to 4":

Pipe Size Chart | Ace Race Parts

So, why the discrepancy? The term "nominal" in NPS doesn't refer to the pipe's exact dimensions but rather to a standard designation used for identification purposes. This system arose from the historical development of pipe sizing, which aimed to standardize pipe sizes for consistency across industries, rather than basing them on exact dimensions.

Understanding the implications of this system is crucial for professionals in the fabrication field, as it affects the selection of compatible materials and components for various projects. The use of nominal sizes, rather than exact measurements, highlights the importance of referring to detailed specifications when planning and executing fabrication projects.

By grasping the nuances of the NPS system, fabricators and engineers can ensure they choose the right materials for their needs, avoiding costly mistakes and inefficiencies. It is important to note that pipe size material is only compatible with other pipe size material (elbows, tees, reducers, straights, etc) and it is not compatible with tube size material which is sized by the true outside diameter (mandrel bends, reducers, slip joints, straights).

In the world of fabrication, understanding NPS is essential for navigating the complexities of industrial materials with confidence. By demystifying this system, you can make informed decisions and execute projects with precision, ultimately contributing to the success of your fabrication endeavors.

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