When working within the piping industry, understanding how pipe is measured is crucial for ensuring that you are selecting the right materials for your projects. This blog post will explain the fundamentals of pipe measurement, including Nominal Pipe Size (NPS), wall thickness defined by Schedule (SCH), and the weight of steel pipe. 

How is Pipe Measured?

Pipe is primarily identified by its Nominal Pipe Size (NPS), which is a dimensionless designator that indicates the size of the pipe but does not correspond to actual dimensions. This can create confusion, especially for those new to the piping industry. The outside diameter (OD) of pipes ranging from NPS 1/8 to NPS 12 is defined according to ANSI pipe sizes. For example, in standard practice, a Schedule 40 pipe dimension for sizes up to NPS 12 is roughly equal to its inside diameter (ID).

Beyond NPS 12, pipe sizes become less ambiguous. A 14 NPS pipe directly equals a 14” outer diameter. This straightforward correlation helps simplify the selection process for pipes of larger sizes.

Pipe Size Chart and Industry Standards

To delve deeper into pipe sizes, ASME B 36.10 provides comprehensive details. It’s important to note that the industry norm for pipe size can vary between different types of pipe. For instance, in the context of standard pipes, a pipe with a 4.5” OD is designated as a 4” NPS. However, for line pipes and Oil Country Tubular Goods (OCTG), it is referred to purely by its OD—as 4.5”.

Additionally, wall thickness is designated differently across various types of piping. Standard pipes utilize pipe schedule to indicate wall thickness, while line pipes generally refer to thickness in terms of actual wall dimensions. Conversely, for OCTG, wall thickness is often described in terms of weight per foot.

Calculating the Weight of Steel Pipe

The weight of pipe plays a significant role in selecting the appropriate materials for construction and transportation. The weight is measured in pounds per foot or kilograms per meter. It is essential to understand that the weight presented in the ANSI pipe size chart is considered "theoretical" and may not reflect actual weights, which can fluctuate based on pipe size tolerances.

To calculate the weight of steel pipe, you can use the following formula:

W = [{OD-WT} x WT] x 10.69

Where:

- W = Weight per linear foot

- OD = Outer Diameter

- WT = Wall Thickness

In conclusion, understanding how pipe is measured is fundamental in the piping industry. Utilizing the concepts of Nominal Pipe Size (NPS), Schedule (SCH), and the applicable weight calculations becomes essential for engineers, contractors, and industrial buyers. By familiarizing yourself with these standards and metrics, you ensure greater accuracy in material selection and project execution.