The conversion of quantities between systems of units involves a determination of the number of significant digits to be retained. All conversions depend upon the intended precision of the original quantity and are rounded to the appropriate accuracy.

Pipe sizes together with applicable wall thicknesses are not shown with metric equivalents. The SI (metric) values where included with the customary U.S. values in this Standard are the rounded equivalents of the U.S. values and are for reference only.

Metric units were derived utilizing the following conversion factor:

Conversion Factor
inches to millimetre 25.4
1.Scope 2.Linear Tolerances 3.Angularity and
Rotation Tolerance
4.Closer Tolerances
1.1 This standard covers
general pipe shop fabricating tolerances for
prefabricated piping assemblies.
2.1 The tolerances on linear
dimensions (intermediate or overall) apply
to the face to face, face to end, and end to
end measurements of fabricated straight pipe
and headers; center to end or center to face
of nozzles or other attachments; or center
to face of bends; as illustrated on Fig.1.
These tolerances are not accumulative.
3.1 Angularity tolerance
across the face of flanges, weld end
preparation and on rotation of flanges are
as stated on Fig.1.
4.1 When closer tolerances
than those given in paragraphs 2.2,2.3 and
2.4 are absolutely necessary, they shall be
subject to agreement between the Purchaser
and Fabricator.
2.2 Linear tolerances on “A”
are ± 1/8″ (3.0mm) for sizes 10″ and under,
± 3/16″ (5.0mm) for sizes 12″ through 24″
and ±1/4″ (6.0mm) for sizes over 24″ through
2.3 Linear tolerance on “A”
for sizes over 36″ are subject to tolerances
of ± 1/4″ (6.0mm), increasing by ± 1/16″
(2.0mm) for each 12″ in diameter over 36″.
2.4 Due to the cumulative
effects of tolerances on fittings or
flanges, when joined without intervening
pipe segments, deviations in excess of those
specified in paragraph 2.2 and 2.3 may