Attributes such as outside diameter, wall thickness, and inside diameter all need to be understood when working with metal pipes. However, many times pipe is not designated directly by those dimensions. Instead, pipe is often referred to by its nominal pipe size and its schedule number. Since references to pipe schedules are common in the industry, it is vital to have some level of comprehension of how the pipe scheduling system works and also to understand the differences between Schedule 40 and Schedule 80; two of the most common types of pipe schedules.

What Does Nominal Pipe Size Mean?

Nominal pipe size is an approximate measurement of the outside diameter of a pipe. It is not an exact measurement, but a reference number that can be used to determine the exact dimensions of the outside diameter of a pipe. For instance, a nominal pipe size of 3 references a pipe with an actual outside diameter of 3.500 inches.

What is Pipe Schedule?

A pipe schedule indicates what the inside diameter and wall thickness is for a nominal pipe size. Without knowing the nominal pipe size, a schedule number does not mean much, other than the fact that higher schedule numbers will have thicker pipe walls if the nominal pipe size is held constant. However, when nominal pipe size and the schedule number are known, then the exact wall thickness, inside diameter, and outside diameter dimensions of a pipe can be determined. The best way to find these dimensions is to use a Pipe Schedule Chart for nominal pipe size and schedule number.

What is the difference between Schedule 40 vs Schedule 80?

The major difference between schedule 40 and schedule 80 pipe is the wall thickness, inside diameter, and their weight. Schedule 80 will have a greater wall thickness, a smaller inside diameter and a higher weight than Schedule 40 pipe at a given nominal pipe size. Of course, all of these numbers will vary based on the nominal pipe size. There are also many other pipe schedule numbers as well. For these reasons, it is important to also reference a pipe schedule table to ensure that the proper pipe size is being selected.

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