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Pipe Schedule

  • 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 pipe schedules or pipes sizes as given by ANSI / ASME B36.10M and API 5L. These schedule numbers bear a relation to the pressure rating of the piping. There are eleven Schedules ranging from the lowest at 5 through 10, 20, 30, 40, 60, 80, 100, 120, 140 to schedule No. 160.
  • Regardless of schedule number, pipes of a particular size all have the same outside diameter (not withstanding manufacturing tolerances). As the schedule number increases, the wall thickness increases, and the actual bore is reduced. For example:
  • A 100 mm Schedule 40 pipe has an outside diameter of 114.30 mm, a wall thickness of 6.02 mm, giving a bore of 102.26 mm.A 100 mm Schedule 80 pipe has an outside diameter of 114.30 mm, a wall thickness of 8.56 mm, giving a bore of 97.18 mm.
  • The schedule number is defined as the approximate value of the expression:Schedule Number = (1,000)(P/S)Where,P = the internal working pressure, psig S = the allowable stress (psi) for the material of construction at the conditions of use.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)
  • Method for Determining Schedule Measure the inside diameter and divide it by the wall thickness. (inches) R= ID/Thickness


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