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Category: Plant Basics
Question: What is the definition of the schedule number when referring to piping and fittings?
Keywords: v1i11,schedule,number,piping,definition,calculation,allowable,stress
Answer: The American National Standards Institute established the schedule number system for pipes and fittings according to the following formula:Schedule Number = (1000)(P/S)whereP = internal working pressure in psigS = allowable stress of piping material at operating conditions in psiAltogether, there are eleven different schedule numbers:5,10,20,30,40,60,80,100,120,140,and 160In practice, Schedule 40 (and sometime 80) are by far the most common schedule numbers used. The schedule number determines the wall thickness of the piping. As an example, consider a piece of ordinary steel pipe to be used at a working pressure of 350 psig. At the design conditions of the service, the allowable stress is 10,000 psi:Schedule Number = (1000)(350/10000) = 35 (so schedule 40 is used)This would be the correct schedule for welded joints and steel fittings, but not for threaded connections (engraving the threads weakens the pipe and threaded connections have to be examined on a separate basis).
Links: Standard Pipe Properties