ASME B16.5 Flange Toleranices

1.General

For the purpose of determining conformance with this Standard,the conventionfor fixing significantdigitswhere limits, maximum or minimum values, are specified shall be rounded as defined in ASTM Practice E29. This requires that an observed or calculated value shall be rounded to thenearest unitinthe last right-handdigitusedfor expressing the limit. The listing of decimal tolerances does not imply a particular method of measurement.

2.Center-to-Contact Surfaces and Center-to-End

Tolerances Required tolerances for various flanges and flanged fitting elements are as follows:

(a) Center-to-Contact Surfaces Other Than Ring Joint Size

Tolerance, mm (in.)

NPS ≤ 10 ±1.0 (±0.04)

NPS ≥ 12 ±1.5 (±0.06)

(b) Center-to-End (Ring Joint) Size

Tolerance, mm (in.)

NPS ≤ 10 ±1.0 (±0.04)

NPS ≥ 12 ±1.5 (±0.06)

Tolerance, mm (in.)

NPS ≤ 10 ±2.0 (±0.08)

NPS ≥ 12 ±3.0 (±0.12)

(d) End-to-End (Ring Joint) Size

Tolerance, mm (in.)

NPS ≤ 10 ±2.0 (±0.08)

NPS ≥ 12 ±3.0 (±0.12)

3.Facings

Tolerances that apply to both flange and flanged fitting facings are as follows:

(a) Inside and outside diameter of large and small tongue and groove and female, ±0.5 mm (±0.02 in.).

(b) Outside diameter, 1.5 mm (0.06 in.) raised face, ±1.0 mm (±0.04 in.).

(d) Ring joint groove tolerances are shown in Table 5 (Table 5C).

Tolerances that apply to flanges are as follows:

(e) Perpendicularity of the face with the bore.

Size Tolerance, deg

NPS ≤ 5 1

NPS ≥ 6 0.5

4.Flange Thickness

Required tolerances for flange thickness are as follows:

Size Tolerance, mm (in.)

NPS ≤ 18 +3.0, −0.0 (+0.12, −0.00)

NPS ≥ 20 +5.0, −0.0 (+0.20, −0.00)

The plus tolerance is applicable to bolting bearing surfaces whether as-forged, as-cast, spot-faced, or back-faced (see para. 6.6).

5.Welding End Flange Ends and Hubs

5.1 Outside Diameter.

Required tolerances for the nominal outside diameter dimension A of Figures 7 and 8 of welding ends of welding neck flanges are as follows:

Size Tolerance, mm (in.)

NPS ≤ 5 +2.0, −1.0 (+0.08, −0.04)

NPS ≥ 6 +4.0, −1.0 (+0.16, −0.04)

5.2 Inside Diameter.

Required tolerances for the nominal inside diameter of welding ends of welding neck flanges and smaller bore of socket welding flanges (dimension B in the referenced figures) are as follows:

(a) For Figures 4, 7, and 8, the tolerances are

Size Tolerance, mm (in.)

NPS ≤ 10 ±1.0 (±0.04)

12 ≤ NPS ≤ 18 ±1.5 (±0.06)

NPS ≥ 20 +3.0, −1.5 (+0.12, −0.06)

(b) For Figure 9, the tolerances are

Size Tolerance, mm (in.)

NPS ≤ 10 +0.0, −1.0 (+0.0, −0.04)

NPS ≥ 12 +0.0, −1.5 (+0.0, −0.06)

5.3 Backing Ring Contact Surface.

Required tolerances for the bore of the backing ring contact surface of welding neck flanges, dimension C of Figures 9 and 10 are as follows:

Size Tolerance, mm (in.)

2 ≤ NPS ≤ 24 +0.25, −0.0 (+0.01, −0.0)

5.4 Hub Thickness.

Despite the tolerances specified for dimensions A and B, the thickness of the hub at the welding end shall not be less than 871 ∕2% of the nominal thickness of the pipe, having an under-tolerance of 12.5% for the pipe wall thickness to which the flange is to be attached or the minimum wall thickness as specified by the purchaser.

6.Length Through Hub on Welding Neck Flanges

The required tolerances for the length through hubs on welding neck flanges are as follows:

Size Tolerance, mm (in.)

NPS ≤ 4 ±1.5 (±0.06)

5 ≤ NPS ≤10 +1.5, −3.0 (+0.06, −0.12)

NPS ≥ 12 +3.0, −5.0 (+0.12, −0.20)

7.Flange Bore Diameter

7.1 Lapped and Slip-On Flange Bores.

The required tolerances for lapped and slip-on flange bore diameters are as follows:

Size Tolerance, mm (in.)

NPS ≤ 10 +1.0, −0.0 (+0.04, −0.0)

NPS ≥ 12 +1.5, −0.0 (+0.06, −0.0)

7.2 Counterbores, Threaded Flanges.

The required tolerances for threaded flange counterbores are as follows:

Size Tolerance, mm (in.)

NPS ≤ 10 +1.0, −0.0 (+0.04, −0.0)

NPS ≥ 12 +1.5, −0.0 (+0.06, −0.0)

7.3 Counterbores, Socket Welding Flanges.

The required tolerance for socket end counterbores is as follows:

Size Tolerance, mm (in.)

1 ∕ 2 ≤ NPS ≤3 ±0.25 (±0.010)

8.Drilling and Facing

8.1 Bolt Circle Diameter.

The required tolerance for all bolt circle diameters is as follows: ±1.5 mm (±0.06 in.)

8.2 Bolt Hole to Bolt Hole.

The required tolerance for the center-to-center of adjacent bolt holes is as follows: ±0.8 mm (±0.03 in.)

8.2 Bolt Circle Concentricity.

The required tolerances for concentricity between the flange bolt circle diameter and machine facing diameters are as follows:

Size Tolerance, mm (in.)

NPS ≤ 21 ∕ 2 0.8 (0.03)

NPS ≥ 3 1.5 (0.06)