Nominal Pipe Size (NPS)
NPS is a North American set of standard sizes for pipes used for high or low pressures and temperatures.
The Confusion
For pipes smaller than NPS 12, the NPS number is neither the inner nor the outer diameter. It's a "nominal" name.
- NPS 1 pipe has an outer diameter (OD) of 1.315 inches.
- NPS 2 pipe has an OD of 2.375 inches.
Schedule (SCH)
The "Schedule" (like Sch 40 or Sch 80) refers to the wall thickness. As the schedule increases, the wall gets thicker and the inner diameter (ID) gets smaller, while the OD stays the same.
Key Takeaways
- OD is constant for a given NPS
- ID varies based on Schedule
- Copper tubing uses a different system than steel pipe