Plant Construction Series


Diameters & Wall Thicknesses of pipe

The size of all pipe is identified by the nominal pipe size, abbreviated ‘NPS’, which is seldom equal to the true bore (Internal diameter) of the pipe-the difference in some instances is large. NPS 14 and larger pipe has outside diameter equal to the nominal pipe size.

Pipe in the various sizes is made in several wall thicknesses for each size; which have benn established by three different sources:

(1) The American National Standard Institute, thru ‘schedule numbers’

(2) The American Society of Mechanical Engineers and the American Society for Testing and Materials, thru the designation ‘STD’ (standard), ‘XS’ (extra-strong), and ‘XXS’ (double-extra-strong), drawn from dimension established by manufacturer.

(3) The American Petroleum Institute, through its standard 5L, for ‘Line pipe’. Dimensions in the standard have no references for individual sizes and wall thicknesses.

‘Manufacturers weight’ were intended, as long ago as late 1930’s to be superseded by the schedule numbers. However, demand for these wall thicknesses has caused their manufacturers to continue. Certain fittings are available only in manufacturers weights. Pipe dimensions from the second and third source are incorporated in American National Standard B36.10M.

Next time: Iron Pipe Sizes, and Stainless Steel Sizes


Total Cad Systems Inc.


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