ANSI B36.19 Nickel Alloy Pipe Dimensions and Permissible Variations: The Full Schedule Table

Ordering nickel alloy pipe by nominal size and schedule is not enough to
make the purchase order complete. A schedule name fixes the
nominal wall thickness, but what arrives at site is a pipe with a
measured outside diameter and a measured wall, and the standard that governs
each grade defines how far those measurements may depart from nominal. Get
that wrong and the difference shows up as a fit-up problem at the flange
face, a weld that will not fill, or a certification query at the client’s
inspection hold point.

This guide gives the numbers themselves: the complete ANSI B36.19 schedule
table for nickel alloy pipe from NPS 1/8 to NPS 30, and the permissible
variation tables that turn nominal dimensions into enforceable tolerances.
Every figure here is reproduced from ASME Section II and can be checked
against the specification.

Which specification supplies the dimensions

ANSI B36.19 is the dimensional standard for stainless and nickel-alloy
pipe. It is reprinted in three places in ASME Section II, and the reprints
agree on every value:

• ASME SB-829 Table 1 — the general requirements
  specification for nickel and nickel-alloy seamless pipe and tube.
  SB-444 (Inconel 625), SB-407 (Incoloy 800), SB-622 (Hastelloy C-276),
  SB-165 (Monel 400), SB-163 (tube) and SB-167 all route their general
  requirements through SB-829, so its Table 1 governs the dimensions of
  seamless nickel-alloy pipe.
• ASME SB-775 Table 1 — the same reprint for
  nickel and nickel-alloy welded pipe.
• ASME SA-790 Appendix Table X1.1 — the
  dimensions of welded and seamless stainless steel pipe, including the
  duplex and super duplex grades. SA-312 carries its own equivalent table
  for austenitic stainless pipe.

One detail worth knowing: the SA-790 appendix table marks more cells with
footnote B than the SB-829 and SB-775 reprints do. The dimension values are
identical; only the annotation differs.

The complete ANSI B36.19 schedule table

Nominal outside diameter and nominal wall thickness for Schedules 5S,
10S, 40S and 80S, from NPS 1/8 to NPS 30. ASME states that the decimal
thicknesses listed for the respective pipe sizes represent their
nominal or average wall dimensions, which is why a schedule
thickness is a target and not a guarantee.

Note A — Schedules 5S and 10S wall thicknesses do
not permit threading in accordance with ANSI B1.20.1. If you need a
threaded end, 5S and 10S are not available to you; specify 40S or 80S and
have the ends threaded to the applicable thread standard.
Note B — These do not conform to ANSI B36.10. The
wall thicknesses marked B are the ones where the ANSI B36.19 schedule
departs from the carbon-steel B36.10 schedule, which matters if a line
mixes carbon and nickel-alloy spools and someone has assumed the schedules
match.

Permissible variations: seamless cold-worked pipe and tube

This is ASME SB-829 Table 2, and it is the table that should be attached
to a purchase order. It gives the permitted outside diameter variation and
the permitted wall thickness variation, separately for wall specified as a
minimum and wall specified as nominal.

The distinction between minimum wall and nominal wall is the part buyers
most often miss. Wall ordered to a minimum thickness may vary
plus or minus around that minimum, so the delivered wall is never thinner
than the figure you specified. Wall ordered to a nominal thickness
may come in thicker, with the plus allowance stated in the table, and is
never thinner. That is why an order written as “schedule 40”
and an order written as “0.109 in. nominal wall” do not
produce identical pipe even though they start from the same table row.

Note A — The permissible variations in this table
apply to individual measurements, including out-of-roundness (ovality),
except for the following: for pipe and tube having a nominal wall thickness
of 3 % or less of the nominal outside diameter, the mean outside diameter
shall conform to the permissible variations of this table and individual
measurements (including ovality) shall conform to the plus and minus values
of the table, with the values increased by 0.5 % of the nominal outside
diameter. For pipe and tube over 4-1/2 in. (114 mm) in outside diameter
with a nominal wall thickness greater than 3 % of the nominal outside
diameter, the mean outside diameter shall conform to the permissible
variations of this table and individual measurements shall not exceed twice
the permissible variations of the table.
Note B — The permissible variations in this table
apply to individual measurements including eccentricity.

Permissible variations: welded pipe

Welded nickel-alloy pipe is not held to the seamless table. ASME SB-775
Table 2 governs it, and the difference is structural: the permissible
variation in outside diameter for welded pipe applies only to material as
finished at the mill, before swaging, expanding, bending, polishing or
other fabricating operations. A welded pipe that is subsequently
manipulated moves outside the mill tolerance, and the client has to decide
whether that is acceptable for the service.

Note A — These permissible variations in outside
diameter apply only to material as finished at the mill before subsequent
swaging, expanding, bending, polishing, or other fabricating
operations.
Note B — Ovality is the difference between the
maximum and the minimum outside diameter measured at any one cross section.
There is no additional tolerance for ovality on material having a nominal
wall thickness for more than 3 % of the outside diameter.

Where the tolerance comes from for each grade

The dimensional table is common, but the tolerance table is set by the
product specification for the grade, and they are not always the same
reference:

Putting the numbers on the order

A purchase order for nickel alloy pipe that will survive inspection
carries six things: the alloy and its UNS number, the product specification
(SB-444, SB-407, SA-790 and so on), the NPS, the schedule or the nominal
wall, the dimensional tolerance reference, and the certification requirement.
Two of those are routinely left off and then argued about at goods-in.

1. State the tolerance reference explicitly. “To
   ASME SB-829 Table 2” or “to SB-407 Table 3” is a
   complete, checkable requirement. Leaving it blank means the acceptance
   criterion is whatever the mill believes it is.
2. Say whether the wall is nominal or minimum. The two
   carry different tolerances and different delivered results, as set out
   above.
3. Name the product form. Seamless and welded pipe of the
   same alloy and size are held to different tolerance tables.
4. Confirm the threaded-end question early. Schedules 5S
   and 10S cannot be threaded to ANSI B1.20.1.
5. Ask for the certification that matches the job. EN
   10204 3.1 is the working default for most projects; 3.2 when a notified
   body is specified, and the inspection release becomes a delivery
   condition.

Common questions

Does the schedule number set the delivered wall thickness?

No. A schedule sets the nominal or average wall. The delivered wall
sits inside the permissible variation for that schedule and that size, and
the permitted band is set by the grade’s product specification.

Can I order a wall thickness outside the standard schedule?

Yes, and the ordering information in the relevant specification supports
it: pipe may be ordered by nominal or minimum wall thickness as well as by
schedule. Outside a standard schedule the order should state the nominal
wall and the tolerance to be applied, and the mill confirms what its
process can hold.

Why does ANSI B36.19 not match ANSI B36.10?

B36.10 is the carbon and alloy steel pipe standard and B36.19 covers
stainless and nickel-alloy pipe. They share the NPS system but not every
wall thickness, and the table marks with footnote B the entries where they
diverge. On a line that mixes materials, that footnote is worth reading
before the pipe is ordered.

Are the tolerances different for cold-worked and hot-finished pipe?

Yes. SB-829 carries separate permissible variation tables for seamless
cold-worked pipe and tube, for hot-finished tube, and for seamless
hot-worked pipe, because the forming route changes what the mill can
hold. The product specification for the grade says which one applies.

Does a certificate confirm the dimensions?

It confirms what was ordered and what was produced, including the
measured dimensions. Ask for the certificate to show the actual outside
diameter and wall thickness against the nominal, and for the applicable
permissible variation to be stated on it.

Our nickel alloy seamless pipe
range is supplied by grade and UNS designation with full material
certification, and the
complete pipe and tube catalogue
covers the austenitic, duplex and nickel alloy families. Send us the NPS,
schedule, alloy and service condition and we will confirm manufacturability,
the governing tolerance table and the certification that will be issued
against the order. Request a quotation through
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