Pipe Schedule is the term used to describe the thickness of a pipe. The outside diameter of a pipe is the same for all schedules in a particular nominal pipe diameter. Standard standard pipe schedules or pipes sizes as given by ANSI / ASME B36.10M and API 5L. There are eleven schedule numbers commonly used: 5, 10, 20, 30, 40, 60, 80, 100, 120, 140, & 160.
standard weight pipe wall thicknesses are the same. Schedules 5, 60, 100, 120, & 140 are rarely used. This should be considered when piping is specified for a particular project.The most popular schedule, by far, is 40. For pipe 8-inches and under, Schedule 40 and
The schedule number is defined as the approximate value of the expression:
Schedule number = (1,000)(P/S)
P = the internal working pressure, psig
For example, the schedule number of ordinary steel pipe having an allowable stress of 10,000 psi for use at a working pressure of 350 psig would be:
Schedule number = (1,000)(350/10,000) = 35 (approx. 40)
Note that the pipe is not always the "weakest link" in a piping system but this should be examined each and every time pipe is sized.
Method for Determing Schedule
Measure the inside diameter and divide it by the wall thickness. (inches) R = ID/Thickness
- API Standards
- API Spec 5L - Specification for Line Pipe
- ASME Standards
- ASME B36.10M - Welded and Seamless Wrought Steel Pipe