30 Days of Piping Engineering – Day 4: Understanding Pipe Sizes and Schedules
Welcome to Day 4 of our 30 Days of Piping Engineering series on our App! So far, we’ve covered the basics of piping engineering, its key components, and common materials. Today, we’re diving into the world of pipe sizes and schedules—essential concepts for designing and selecting the right pipes for any system.
What Are Pipe Sizes and Schedules?
Pipes come in a variety of sizes and thicknesses to handle different pressures, flows, and applications. Here’s a breakdown of the key terms:
- Nominal Pipe Size (NPS): This is a standard way to describe the diameter of a pipe. For example, an NPS 2 pipe has a nominal diameter of 2 inches. However, the actual outside diameter (OD) might differ slightly depending on the pipe’s schedule. For NPS 14 and above, the NPS matches the OD, but for smaller sizes, the OD is larger than the NPS (e.g., an NPS 2 pipe has an OD of 2.375 inches).
- Outside Diameter (OD): The actual outer diameter of the pipe, which remains constant for a given NPS regardless of the wall thickness.
- Pipe Schedule: This refers to the wall thickness of the pipe, which affects its strength and pressure rating. Common schedules include 10, 40, 80, and 160, with higher numbers indicating thicker walls. For example, a Schedule 40 pipe has a thinner wall than a Schedule 80 pipe of the same NPS, making the latter better for higher-pressure applications.
- Inside Diameter (ID): The internal diameter of the pipe, which decreases as the schedule (wall thickness) increases. The ID determines the flow capacity of the pipe.
Understanding these terms helps engineers select pipes that can handle the required flow rates and pressures without failing. For instance, a high-pressure steam system might use an NPS 6 Schedule 80 pipe, while a low-pressure water system might use an NPS 6 Schedule 40 pipe.
Real-World Example
In a natural gas pipeline, engineers might choose an NPS 12 Schedule 40 pipe to transport gas over long distances. The larger diameter ensures sufficient flow, while the Schedule 40 thickness provides enough strength to handle the gas pressure safely.
Did you know ?
The term "schedule" for pipe thickness originated in the early 20th century when pipes were classified based on their pressure ratings? The term comes from the idea of a "schedule" of standard thicknesses, which was formalized by the American Standards Association (now ANSI) in the 1930s to streamline pipe manufacturing and design!
Your Day 4 Takeaway
Pipe sizes and schedules are the foundation of piping design—choosing the right combination ensures your system is safe and efficient.
Tomorrow, we’ll explore piping codes and standards.
See you then!