Class 2500 Threaded Flange Dimensions
ASME B16.5 dimensions and bolting for the Class 2500 threaded flange, NPS 1/2 through NPS 2 1/2, with what the class is rated for and where this flange type is used in it.
- Standard
- ASME B16.5
- Flange type
- Threaded Flange
- Pressure class
- Class 2500
- Size range
- NPS 1/2 – NPS 2 1/2
- Raised face height
- 0.25 in (6.3 mm)
- Rating at 100 °F (A105)
- 6170 psig (425.4 bar)
Where a Class 2500 threaded flange is used
Class 2500 is the heaviest class in ASME B16.5. It is used where pressure leaves no alternative, and at this class many designs avoid flanged joints altogether in favour of welded ones.
A threaded flange at this class is a specialised item for small sizes, since a pipe thread is a poor seal against high pressure and is weakened by cycling. Most specifications restrict it to places where welding is not possible.
The number 2500 is a designation and not a pressure. A Class 2500 flange in A105 carbon steel is rated 6170 psig (425.4 bar) at 100 °F, 5280 psig at 400 °F, 4730 psig at 600 °F and 3430 psig at 800 °F. In Type 304 stainless, Group 2.1, it starts at 6000 psig and still holds 3380 psig at 800 °F, so the material and the metal temperature have to be fixed before the class can be.
Dimensions in every size
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Size | Flange OD | Thickness | Bolt circle | Bolts | Bolt dia. | Raised face OD |
|---|---|---|---|---|---|---|
| NPS 1/2 | 5.25133.35 mm | 1.1930.23 mm | 3.5088.90 mm | 4 | 3/4 in | 1.3835.05 mm |
| NPS 3/4 | 5.50139.70 mm | 1.2531.75 mm | 3.7595.25 mm | 4 | 3/4 in | 1.6942.93 mm |
| NPS 1 | 6.25158.75 mm | 1.3835.05 mm | 4.25107.95 mm | 4 | 7/8 in | 2.0050.80 mm |
| NPS 1 1/4 | 7.25184.15 mm | 1.5038.10 mm | 5.12130.05 mm | 4 | 1 in | 2.5063.50 mm |
| NPS 1 1/2 | 8.00203.20 mm | 1.7544.45 mm | 5.75146.05 mm | 4 | 1 1/8 in | 2.8873.15 mm |
| NPS 2 | 9.25234.95 mm | 2.0050.80 mm | 6.75171.45 mm | 8 | 1 in | 3.6291.95 mm |
| NPS 2 1/2 | 10.50266.70 mm | 2.2557.15 mm | 7.75196.85 mm | 8 | 1 1/8 in | 4.12104.65 mm |
Flange thickness excludes the raised face. Bolt diameter is nominal; stud bolts are normally ASTM A193 B7 with A194 2H nuts.
Across the 7 sizes published in Class 2500, the flange grows from 5.25 in (133.3 mm) across and 1.19 in (30.2 mm) thick at NPS 1/2 to 10.50 in (266.7 mm) across and 2.25 in (57.1 mm) thick at NPS 2 1/2. The bolt count goes 4 from NPS 1/2 and 8 from NPS 2, always in multiples of four so that the holes can straddle the centrelines. The largest bolt in the class is 1 1/8 in, first needed at NPS 1 1/2.
ASME B16.5 publishes the threaded flange in Class 2500 up to NPS 2 1/2 only. The Class 2500 table runs on to NPS 12 for other flange types, but there is no threaded flange in those sizes, so they are not listed here.
Not fully confirmed. The NPS 2 1/2 limit for threaded flanges in Class 2500 rests on two secondary sources and has not been confirmed against the standard.
ASME B16.5 publishes Class 2500 flanges in NPS 1/2 through NPS 12 only. Above NPS 12 there is no Class 2500 flange in the standard.
Bolt holes, spacing and torque
Bolt holes in ASME B16.5 flanges are drilled 1/8 in larger than the nominal bolt and are set to straddle the vertical and horizontal centrelines, never to sit on them. Spacing is the distance between neighbouring holes measured round the bolt circle, which shows how much room there is for a wrench or a tensioner. The torque column is a starting figure for a lubricated stud, not a joint-specific value.
| Size | Bolting | Bolt hole dia. | Hole spacing | Torque for 50 ksi bolt stress |
|---|---|---|---|---|
| NPS 1/2 | 4 × 3/4 in | 0.87522.22 mm | 2.7569.82 mm | 167 lb-ft |
| NPS 3/4 | 4 × 3/4 in | 0.87522.22 mm | 2.9574.81 mm | 167 lb-ft |
| NPS 1 | 4 × 7/8 in | 1.00025.40 mm | 3.3484.78 mm | 269 lb-ft |
| NPS 1 1/4 | 4 × 1 in | 1.12528.57 mm | 4.02102.14 mm | 404 lb-ft |
| NPS 1 1/2 | 4 × 1 1/8 in | 1.25031.75 mm | 4.52114.71 mm | 593 lb-ft |
| NPS 2 | 8 × 1 in | 1.12528.57 mm | 2.6567.33 mm | 404 lb-ft |
| NPS 2 1/2 | 8 × 1 1/8 in | 1.25031.75 mm | 3.0477.30 mm | 593 lb-ft |
Torque is T = K·F·d with nut factor K = 0.16 and a bolt stress of 50,000 psi on the tensile stress area. The bolt torque guide gives the method and other nut factors.
Guides and comparisons for this page
Common questions
How many bolts does a Class 2500 threaded flange use?
NPS 1/2 takes 4 × 3/4 in; NPS 3/4 takes 4 × 3/4 in; NPS 1 takes 4 × 7/8 in; NPS 1 1/4 takes 4 × 1 in; NPS 1 1/2 takes 4 × 1 1/8 in. Bolt count rises with size — see the table above for the full range.
What pressure is a Class 2500 flange rated for?
Class is a designation, not a pressure. A Class 2500 flange in A105 carbon steel is rated 6170 psig (425.4 bar) at 100 °F, and that rating falls as metal temperature rises. In stainless the same class starts lower at ambient but holds up far better in the heat — see the P-T rating tables.
Will a Class 2500 flange bolt to a Class 150 flange?
No. Bolt circle diameter, bolt count and bolt size all change with class, so flanges of different classes in the same NPS will not mate. The only exceptions inside B16.5 are the deliberate ones the standard calls out, such as Class 400 sharing Class 600 dimensions in NPS 1/2 through 3 1/2.