ANSI Buttweld Fittings – Dimensional Tolerances

Cross-sectional tolerances for all buttwelding fittings (ASME/ANSI B16.9 and B16.28)

Nominal Pipe Size (NPS) All Fittings
OD at Bevel ID at Bevel ± Wall thickness
in mm in mm
½ to 2½ +0.06, -0.03 +1.6, -0.8 0.03 0.8 Not less than 87.5% of nominal wall thickness
3 to 3½ ±0.6 ±1.6 0.06 1.6
4 ±0.6 ±1.6 0.06 1.6
5 to 6 +0.09, -0.06 +2.4, -1.6 0.06 1.6
8 +0.09, -0.06 +2.4, -1.6 0.06 1.6
10 +0.16, -0.12 +4.0, -3.2 0.12 3.2
12 to 18 +0.16, -0.12 +4.0, -3.2 0.12 3.2
20 to 24 +0.25, -0.19 +6.4, -4.8 0.19 4.8
26 to 30 +0.25, -0.19 +6.4, -4.8 0.19 4.8
32 to 48 +0.25, -0.19 +6.4, -4.8 0.19 4.8

Tolerances for Specific Fittings

Dimensional tolerances for elbows and returns (ASME/ANSI B16.9 & B16.28)

Nominal Pipe Size (NPS) 90° & 45° Long Radius Elbows 90° Short Radius Elbows
and Tees		 180° Returns
Centre-to-End Dimension ±
A, B		 Centre-to-Centre Dimension ±
B (=2 x A)		 Back-to-Face Dimension ±
C
in mm in mm in mm
½ to 2½ 0.06 2 0.25 6 0.25 6
3 to 3½ 0.06 2 0.25 6 0.25 6
4 0.06 2 0.25 6 0.25 6
5 to 6 0.06 2 0.25 6 0.25 6
8 0.06 2 0.25 6 0.25 6
10 0.09 2 0.38 10 0.25 6
12 to 18 0.09 2 0.38 10 0.25 6
20 to 24 0.09 2 0.38 10 0.25 6
26 to 30 0.12 3 – – – –
32 to 48 0.19 5 – – – –

Dimensional tolerances for reducers, caps and stub ends (ASME/ANSI B16.9)

Nominal Pipe Size (NPS) Reducers & Lap Joint
Stub Ends		 Caps Lap Joint Stub Ends
Overall Length ±
A		 Overall Length ±
A		 OD of Lap
B		 Fillet Radius of Lap
B
in mm in mm in mm in mm
½ to 2½ 0.06 2 0.12 3 +0 +0, -1 +0 +0, -1
3 to 3½ 0.06 2 0.12 3 +0, -0.03 +0, -1 +0, -0.03 +0, -1
4 0.06 2 0.12 3 +0, -0.03 +0, -1 +0, -0.06 +0, -2
5 to 6 0.06 2 0.25 6 +0, -0.03 +0, -1 +0, -0.06 +0, -2
8 0.06 2 0.25 6 +0, -0.03 +0, -1 +0, -0.06 +0, -2
10 0.09 2 0.25 6 +0, -0.06 +0, -2 +0, -0.06 +0, -2
12 to 18 0.09 2 0.25 6 +0, -0.06 +0, -2 +0, -0.06 +0, -2
20 to 24 0.09 2 0.25 6 +0, -0.06 +0, -2 +0, -0.06 +0, -2
26 to 30 0.19 5 0.38 10 – – – –
32 to 48 0.19 5 0.38 10 – – – –

Alignment Tolerances

Alignment tolerances are concerned with the way that the ends of a fitting are cut. Exaggerated distortions are shown for clarity in the diagram below.

Alignment Tolerances (ASME/ANSI B16.9)

Nominal Pipe Size (NPS) Off Plane Tolerances, ±
A		 Off Angle Tolerances, ±
B		 Alignment of Ends, ±
C
in mm in mm in mm
½ to 4 0.06 2 0.03 1 0.03 1
5 to 8 0.12 4 0.06 2 0.03 1
10 to 12 0.19 5 0.09 2 0.06 2
14 to 16 0.25 6 0.09 3 0.06 2
18 to 24 0.38 10 0.12 4 0.06 2
26 to 30 0.38 10 0.19 5 – –
32 to 42 0.50 13 0.19 5 – –
44 to 48 0.75 19 0.19 5 – –

Dimensional Tolerances for reducers, caps and stub ends (ASME/ANSI B16.9)

Dimensions and Tolerances MSS SP-43

MSS SP-43 only covers buttweld fittings made for use with Schedule 5S and 10S pipe as defined in ANSI/ASME B36.19M (plus short pattern stub ends suitable for use with Schedule 40S pipe). The dimensions and tolerances defined in MSS SP-43 are substantially the same as those in ASME/ANSI specifications (½ to 24 in).

  • MSS SP-43 tolerances (including alignment tolerance) are the same as for ASME/ANSI B16.9 and B16.28 except with regard to the outside diameter at the bevel:
  • Tolerance of OD at Bevel =

± 0.03 in for NPS ½ to 4

+0.06, -0.03 in for NPS 5 to 8

+0.09, -0.03 in for NPS 10 to 18

+0.12, to -0.03 in for NPS 20 to 24