There are several different piping standards
in use around the world. This can be a
source of potential confusion. Generally, the
most widely used standard is IPS schedule
pipe size (“iron pipe size”) or NPS (“nominal
pipe size”). This categorizes pipe by sched-
ule number or “weight.” Most metal pipes of
other materials, including stainless steel and
aluminum, follow the pipe-size standard, but
there are important exceptions, particularly
for plastic pipe. Note that tubing,as opposed
topipe,follows completely different size
standards.
In the United States, there are eleven
schedules ranging from the thinnest wall at 5
through 10, 20, 30, 40, 60, 80, 100, 120, and
140, to schedule 160—the thickest wall. For
nominal size piping 6 inches (150 mm) and
smaller, schedule 40 (also called “standard
weight” in most sizes) is the normal, standard
pipe, and—veryroughly—the dimension or
size number of 40-weight pipe approximates
the inside diameter. American National Stan-
dards Institute (ANSI) pipe standards specify,
say, S.40, for steel pipe (as opposed to iron
pipe) and 40S for stainless—the S.before the
schedule number indicating “steel,” and the
Safter the number indicating “stainless
steel.” For the size of pipe used in fuel sys-
tems, the dimensions of 40 and 80 pipe are
the same for these materials.
Traditional names for U.S. NPS pipe-wall
thickness or weight are Standard (Std.),
Extra Strong (XS), and Double Extra Strong
(XXS). Std. and schedule 40 are the same in
sizes up through 10 inches. In sizes above
10 inches, Std. has a constant wall of^3 / 8 inch,
and XS has a constant wall thickness of(^1) /
2 inch. XXS has no corresponding schedule
number, but in sizes through 6 inches, XXS
has a wall thickness twice that of XS.
Regardless of the schedule or weight, all
pipes of a specified nominal diameter have
the same outside diameter whatever the
wall thickness. The outside diameter (OD) is
larger than the nominal pipe size, as the
nominal or schedule diameter roughly
relates to the bore, or inside diameter (ID).
As the schedule number increases, the OD
remains the same and the wall thickness
increases, so the ID, or bore, is smaller. For
example:
International Pipe
Standards and Pipe-Size
Tables—Pipe-to-Hose
Connections
APPENDIX B