Tolerances for ASME B16.9 Pipe Fittings

This article introduces both dimension and angularity tolerances for butt welding pipe fittings made in accordance with ASME B16.9. These fittings include elbows, tees, crosses, reducers, caps, 180° returns, and lap joint stub ends. Click the links in Table M to view the drawing and basic dimensions of various pipe fittings.

ASME B16.9 Butt Welding Fittings
Elbow L/R	Reducing Elbow	Return L/R
Elbow S/R	Return S/R	3D Elbow
Tee & Cross	Reducing Tee	Reducing Cross
Stub End	Cap	Reducer
End Bevel	Tolerance	Wall Thickness

*Table M: drawing and dimensions of ASME B16.9 fittings.

 Tolerances for O.D. & I.D.

NPS	O.D. (mm) [inch]	I.D. mm [inch]
1/2~2-1/2	(+1.6, -0.8) +0.06, -0.03	(+0.8, -0.8) [+0.03, -0.03]
3~3-1/2	(+1.6, -1.6) [+0.06, -0.06]	(+1.6, -1.6) [+0.06, -0.06]
4	(+1.6, -1.6) [+0.06, -0.06]	(+1.6, -1.6) [+0.06, -0.06]
5~8	(+2.4, -1.6) [+0.09, -0.06]	(+1.6, -1.6) [+0.06, -0.06]
10~18	(+4.0, -3.2) [+0.16, -0.12]	(+3.2, -3.2) [+0.12, -0.12]
20~24	(+6.4, -4.8) [+0.25, -0.19]	(+4.8, -4.8) [+0.19, -0.19]
26~30	(+6.4, -4.8) [+0.25, -0.19]	(+4.8, -4.8) [+0.19, -0.19]
32~48	(+6.4, -4.8) [+0.25, -0.19]	(+4.8, -4.8) [+0.19, -0.19]

*Dimensional tolerances for outside diameter at bevel, D, mm [inch] and inside diameter at end, mm [inch], applicable to all ASME B16.9 pipe fittings.

Tolerances for Center-to-End Dimensions

NPS	CtE1 inch [mm]	CtE2 inch [mm]
1/2~2-1/2	±0.06 [±2]	±0.09 [±3]
3~3-1/2	±0.06 [±2]	±0.09 [±3]
4	±0.06 [±2]	±0.09 [±3]
5~8	±0.06 [±2]	±0.09 [±3]
10~18	±0.09 [±2]	±0.12 [±3]
20~24	±0.09 [±2]	±0.12 [±3]
26~30	±0.12 [±3]	±0.25 [±6]
32~48	±0.19 [±5]	±0.38 [±6]

*CtE₁: dimensional tolerances for center-to-end dimensions A, B of 90°, 45° long and short radius elbows, and C, M of tees and crosses. *CtE₂: dimensional tolerances for center-to-end dimensions A, B of 3D radius 90° & 45° elbows.

Tolerances for Overall Length

NPS	OVL1 inch [mm]	OVL2 inch [mm]
1/2~2-1/2	±0.06 [±2]	±0.12 [±3]
3~3-1/2	±0.06 [±2]	±0.12 [±3]
4	±0.06 [±2]	±0.12 [±3]
5~8	±0.06 [±2]	±0.25 [±6]
10~18	±0.09 [±2]	±0.25 [±6]
20~24	±0.09 [±2]	±0.25 [±6]
26~30	±0.19 [±5]	±0.38 [±10]
32~48	±0.19 [±5]	±0.38 [±10]

*OVL₁: dimensional tolerances for overall length of reducers, H and lap joint stub ends, F. *OVL₂: dimensional tolerances for overall length of caps, E.

Tolerances for 180° Returns

NPS	CtC inch [mm]	BtF inch [mm]	Aln inch [mm]
1/2~2-1/2	±0.25 [±6]	±0.25 [±6]	±0.03 [±1]
3~3-1/2	±0.25 [±6]	±0.25 [±6]	±0.03 [±1]
4	±0.25 [±6]	±0.25 [±6]	±0.03 [±1]
5~8	±0.25 [±6]	±0.25 [±6]	±0.03 [±1]
10~18	±0.38 [±10]	±0.25 [±6]	±0.06 [±2]
20~24	±0.38 [±10]	±0.25 [±6]	±0.06 [±2]

*CtC, BtF, Aln: tolerances for center-to-center dimension (O), back-to-face dimension (K), alignment of ends (U) for 180° returns.

Angularity Tolerances

NPS	Q inch [mm]	P inch [mm]
1/2~4	±0.03 [±1]	±0.06 [±2]
5~8	±0.06 [±2]	±0.12 [±4]
10~12	±0.09 [±3]	±0.19 [±5]
14~16	±0.09 [±3]	±0.25 [±6]
18~24	±0.12 [±4]	±0.38 [±10]
26~30	±0.19 [±5]	±0.38 [±10]
32~42	±0.19 [±5]	±0.50 [±13]
44~48	±0.19 [±5]	±0.75 [±19]

*Q: angularity tolerances for off angle, Q; *P: angularity tolerances for off plane, P.

Tolerances for Lap Joint Stub Ends

NPS	G inch [mm]	R	LT
1/2~2-1/2	+0, -0.03 [+0, -1]	+0, -0.03 [+0, -1]	+0.06, -0 [+1.6, -0]
3~3-1/2	+0, -0.03 [+0, -1]	+0, -0.03 [+0, -1]	+0.06, -0 [+1.6, -0]
4	+0, -0.03 [+0, -1]	+0, -0.06 [+0, -2]	+0.06, -0 [+1.6, -0]
5~8	+0, -0.03 [+0, -1]	+0, -0.06 [+0, -2]	+0.06, -0 [+1.6, -0]
10~18	+0, -0.06 [+0, -2]	+0, -0.06 [+0, -2]	+0.12, -0 [+3.2, -0]
20~24	+0, -0.06 [+0, -2]	+0, -0.06 [+0, -2]	+0.12, -0 [+3.2, -0]

*G: tolerances for outside diameter of lap; *R: tolerances for fillet radius of lap; *L_T: tolerances for lap thickness.

Besides, a minimum wall thickness of 87.5% applies unless the purchaser specifies a different wall thickness tolerance.