What Do Pipe Schedules Mean?

When working with piping systems, the term “pipe schedule” often comes up, but what does it mean? What does schedule 40 mean, and how does it compare to schedule 20? What is schedule 40 pipe in the first place? These questions are important in choosing a suitable pipe for your project.

A pipe schedule refers to a standardized system that indicates the wall thickness of a pipe. This measurement affects crucial factors like the pipe’s inside diameter and its ability to handle pressure. Here, we’ll break down what pipe schedules mean and how they are determined.

What are Pipe Schedules?

The schedule number on pipe products relates to the thickness of the wall on the pipe: as the number increases, the wall thickness becomes thicker and the inner diameter (ID) becomes smaller. Also, while the schedule number can be the same for different-sized pipes, the actual wall thickness will be different. Here are a few examples:

• Pipe size 1.000” Schedule 40 – The actual wall thickness is 0.133”
• Pipe size 2.000” Schedule 40 – The actual wall thickness is 0.154”
• Pipe size 1.000” Schedule 80 – The actual wall thickness is 0.179”
• Pipe size 2.000” Schedule 80 – The actual wall thickness is 0.218”

We can see here that the schedule number increases the wall size, and the wall thickness changes based on the nominal pipe size (NPS).

There are several schedule numbers used on pipe, such as schedules 5, 5S, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD, XS and XXS. The most common ones used are schedules 40 and 80.

What does Nominal Pipe Size or NPS mean?

The NPS size represents the approximate inside diameter (not outside) of the pipe; if the schedule number on a set size is changed, it does affect the inside diameter (ID) but not the outside diameter (OD). In 1927, the American Standard Association replaced the previously used Iron Pipe Sizing (IPS) with Nominal Pipe Sizing (NPS). This North American standard is used on pipes for high or low pressures and temperatures.   Example:

All pipes are specified using the NPS and schedule numbers. It is the schedule number that determines the approximate inside diameter. A pipe schedule chart can give you more information on the specific measurements for each pipe schedule.

Schedule 20 vs. Schedule 40 vs. Schedule 80

When comparing schedule 20 vs. schedule 40 vs. schedule 80 pipes, the primary differences lie in their wall thickness, pressure capacity, weight, and applications. Schedule 20 pipes have the thinnest walls among the three, making them lightweight and suitable for low-pressure applications. This reduced wall thickness also results in a larger inside diameter than schedule 40 or schedule 80 pipes of the same nominal size, making them ideal for non-critical systems such as drainage or ventilation where strength is not a priority. Schedule 40 pipes are the most commonly used and offer a moderate wall thickness that provides durability without being overly heavy or difficult to handle. This makes them popular for medium-pressure systems like water supply lines, gas piping, and general plumbing needs.

Schedule 80 pipes feature the thickest walls, which significantly enhance their strength and pressure resistance. These pipes are specifically designed for high-stress environments such as industrial settings or chemical processing systems where safety and reliability are critical. However, the thicker walls of schedule 80 pipes also mean they are heavier and have a smaller inside diameter than schedule 40 pipes of the same size, which can make installation more labour-intensive.

In summary, schedule 20 pipes are best suited for low-pressure scenarios, schedule 40 offers a versatile solution for medium-pressure needs, and schedule 80 is reserved for demanding high-pressure systems.

Don’t have time to read the blog?

Check out the video blog below to learn about pipe schedules.