Understanding pipe dimensions primarily involves two key measurements: the Nominal Pipe Size (NPS) and the Schedule (SCH).
Pipe dimensions work by using a standard system that designates both the approximate size and the wall thickness, which in turn determines the pipe's strength and flow capacity. The most common way pipe sizing is written is like: 1” SCH 40 x 20'.
Understanding the Key Components
Let's break down the common format and what each part signifies:
Nominal Pipe Size (NPS)
The first part of the designation, like 1” in the example, refers to the Nominal Pipe Size (NPS). This is a standard set of sizes used for pipes in high or low pressures and temperatures. It's important to note that the NPS is not the actual physical outside diameter (OD) of the pipe, especially for smaller sizes.
- As the reference states, for a 1” NPS pipe, the outside diameter is actually 1.315”.
- This standardized OD for a given NPS allows different pipe schedules (wall thicknesses) to be used interchangeably with the same fittings (like flanges or valves) based on the NPS.
Schedule (SCH)
The second part, such as SCH 40, indicates the schedule of the pipe. The schedule is a standard number that relates to the wall thickness of the pipe.
- A higher schedule number means a thicker pipe wall for a given NPS.
- Different schedules exist (e.g., SCH 10, SCH 40, SCH 80, SCH 160) to provide varying pressure ratings and structural strength.
- As the reference specifies, for a 1” pipe, SCH 40 means the wall thickness is 0.133”.
Inside Diameter (ID)
While not explicitly stated in the common format, the inside diameter (ID) is a crucial dimension, as it affects flow capacity. The ID is determined by the NPS and the Schedule:
- ID = Outside Diameter (OD) - (2 * Wall Thickness)
- Using the reference examples: For a 1” NPS SCH 40 pipe, the OD is 1.315” and the wall thickness is 0.133”.
- Therefore, the ID = 1.315” - (2 * 0.133”) = 1.315” - 0.266” = 1.049”.
Pipe Length
The final part, like x 20', simply specifies the length of the pipe section. This is the actual cut length and is straightforward.
Practical Implications
- Standardization: The NPS system allows components from different manufacturers to fit together as long as they share the same NPS and compatible schedules.
- Pressure Rating: The schedule (wall thickness) is a primary factor determining the maximum internal pressure a pipe can withstand. Higher schedules are used for higher pressure applications.
- Flow Capacity: The inside diameter (ID), which changes with schedule for a given NPS, affects the volume of fluid or gas that can flow through the pipe.
In summary, pipe dimensions work by combining a nominal size designation (NPS) with a standard for wall thickness (Schedule) to define a pipe's physical characteristics and functional properties.
