Plant Construction Series


Iron and Pipe Sizes
Initially established for wrought-iron pipe with wall thicknesses designated by the term ‘Standard
(Weight)’, ‘extra strong’, and ‘double extra strong’. Before the schedule
number scheme for steel pipe was first published by the American Standards
Association in 1935, the iron pipe size were modified for steel pipe by
slightly decreasing the wall thicknesses (leaving the outside diameter
constant) so that the weight per foot (lb/ft) equaled the iron pipe weights.

Wrought-Iron pipe (not longer made) has been completely
supplanted by steel pipe, but schedule numbers, intended to supplant iron pipe designations
did not. Users continued to specify pipe in iron size terms, and as the mills
responded, these terms are included in ANSI standard B36.10M for steel pipe. Schedule
numbers were introduce to establish pipe wall thicknesses by formula, but as
wall thicknesses in common use continued to depart from those proposed by the scheme,
schedule numbers now identify wall thicknesses of pipe in the different nominal
sizes as ANSI B36.10M states “as a convenient designation system for use in

Stainless-Steel Sizes

American National Standard B38.19 established a range of
thin-walled sizes for stainless-steel pipe, identified by schedules 5S and 10S.

Next time

Materials for Pipe

Atilio Zelaya

Total Cad Systems Inc.

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