Origin of the use of the word "schedule" to describe pipe thicknesses

[buisse]

Does anyone know why we say "schedule 40" or "schedule 80" to refer to pipe wall thicknesses? Why do we call it a "schedule"?
I am guessing the root of the use lies in sewers, but if anyone has a definitive answer......

 

[bmoorthy]

Schedule Number: They Indicate Approximate Values of Expression 1000 * P/S, where P is the service pressure and S is the Allowable stress, Both expressed in PSI.

Reference: Piping hand Book 6 th Edition Mohinder L. Nayyar.

I have verified and it does not answer for most of the current Shedule number, Material and Sizes. Probably when piping industry was in its nacent stage the available material then and the service pressure then would have answered the above expression!

 

[TBP]

I've got a couple of old ASHVE Guide books from the 1930's. The 1931 copy only mentions pipe wall thickness in terms of "standard" (S), extra strong (XS), and "double extra strong" (XXS). The 1935 edition covers schedule numbers for wall thickness. It says:

"While the demands for pipe for the heating and ventilating industry are reasonably well served by the "standard weight", and "extra-strong pipe", demands fro pipe for higher pressures and temperatures in industry resulted in the use of a multiplicity of wall thickness for all sizes. Even in heating installations, the erection of piping by welding was deemed to warrant the use of pipe lighter than standard weight. For these reasons, a Sectional Committee ib Standardization of Wrought Iron and Wrought Steel Pipe and Tubing functioning under the procedure of the American Standards Association was appointed to standardize the dimensions and materials of pipe.

The proposed pipe standard recommended by that sectional committee has set up several schedules of pipe including standard-weight and extra-strong thicknesses which are now included in Schedules 40 and 60 respectively. The schedules approved by the Sectional Committee are given in Tables 1 and 3 adn the corresponding weights in Tables 2 and 4."

In the notes under the tables, it goes on to say:

"Thicknesses marked with an asterisk in Sch 30 & 40 are indentical with thicknesses for standard weight pipe in former lists; those in Sch 60 & 80 are indentical with thicknesses for extra-strong pipe in former lists.

The Schedule Numbers indicate approximate values of the expression 1000 x P/S."

 

[buisse]

TBP,
Many thanks for your reply! Very definitive. Even some real old grey-beards I asked didn't know the answer to this question.

 

[reichertc]

If you have access to codes and standards, read the forward of ASME B36.10. It has a good discussion of why things are the way they are, and when it all cam into play. It's a page long so I don't want to re-type it....