Class 400 Socket Weld Flange Dimensions
ASME B16.5 dimensions and bolting for the Class 400 socket weld 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
- Socket Weld Flange
- Pressure class
- Class 400
- Size range
- NPS 1/2 – NPS 2 1/2
- Raised face height
- 0.25 in (6.3 mm)
- Rating at 100 °F (A105)
- 985 psig (67.9 bar)
Where a Class 400 socket weld flange is used
Class 400 is published but seldom specified. Most piping specifications step from Class 300 straight to Class 600, so Class 400 flanges are rarely held in stock and usually have to be made to order.
Socket weld flanges are a small-bore item. At this class they are typically found on small high-pressure lines such as hydraulic, chemical injection and steam tracing piping.
The number 400 is a designation and not a pressure. A Class 400 flange in A105 carbon steel is rated 985 psig (67.9 bar) at 100 °F, 845 psig at 400 °F, 755 psig at 600 °F and 550 psig at 800 °F. In Type 304 stainless, Group 2.1, it starts at 960 psig and still holds 540 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 | 3.7595.25 mm | 0.5614.22 mm | 2.6266.55 mm | 4 | 1/2 in | 1.3835.05 mm |
| NPS 3/4 | 4.62117.35 mm | 0.6215.75 mm | 3.2582.55 mm | 4 | 5/8 in | 1.6942.93 mm |
| NPS 1 | 4.88123.95 mm | 0.6917.53 mm | 3.5088.90 mm | 4 | 5/8 in | 2.0050.80 mm |
| NPS 1 1/4 | 5.25133.35 mm | 0.8120.57 mm | 3.8898.55 mm | 4 | 5/8 in | 2.5063.50 mm |
| NPS 1 1/2 | 6.12155.45 mm | 0.8822.35 mm | 4.50114.30 mm | 4 | 3/4 in | 2.8873.15 mm |
| NPS 2 | 6.50165.10 mm | 1.0025.40 mm | 5.00127.00 mm | 8 | 5/8 in | 3.6291.95 mm |
| NPS 2 1/2 | 7.50190.50 mm | 1.1228.45 mm | 5.88149.35 mm | 8 | 3/4 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 400, the flange grows from 3.75 in (95.2 mm) across and 0.56 in (14.2 mm) thick at NPS 1/2 to 7.50 in (190.5 mm) across and 1.12 in (28.4 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 3/4 in, first needed at NPS 1 1/2.
ASME B16.5 publishes the socket weld flange in Class 400 up to NPS 2 1/2 only. The Class 400 table runs on to NPS 24 for other flange types, but there is no socket weld flange in those sizes, so they are not listed here.
Not fully confirmed. ASME B16.5 has no separate table for the Class 400 socket weld flange. It may be supplied in NPS 1/2 through NPS 2 1/2 using the Class 600 dimensions, which is what the table on this page shows. This rests on a single secondary source and has not been confirmed against the standard.
In NPS 1/2 through NPS 3 1/2 the Class 400 flange is dimensionally identical to the Class 600 flange; ASME B16.5 does not publish a separate Class 400 table for those sizes.
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 × 1/2 in | 0.62515.88 mm | 2.0652.27 mm | 47 lb-ft |
| NPS 3/4 | 4 × 5/8 in | 0.75019.05 mm | 2.5564.83 mm | 94 lb-ft |
| NPS 1 | 4 × 5/8 in | 0.75019.05 mm | 2.7569.82 mm | 94 lb-ft |
| NPS 1 1/4 | 4 × 5/8 in | 0.75019.05 mm | 3.0577.40 mm | 94 lb-ft |
| NPS 1 1/2 | 4 × 3/4 in | 0.87522.22 mm | 3.5389.77 mm | 167 lb-ft |
| NPS 2 | 8 × 5/8 in | 0.75019.05 mm | 1.9649.87 mm | 94 lb-ft |
| NPS 2 1/2 | 8 × 3/4 in | 0.87522.22 mm | 2.3158.65 mm | 167 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 400 socket weld flange use?
NPS 1/2 takes 4 × 1/2 in; NPS 3/4 takes 4 × 5/8 in; NPS 1 takes 4 × 5/8 in; NPS 1 1/4 takes 4 × 5/8 in; NPS 1 1/2 takes 4 × 3/4 in. Bolt count rises with size — see the table above for the full range.
What pressure is a Class 400 flange rated for?
Class is a designation, not a pressure. A Class 400 flange in A105 carbon steel is rated 985 psig (67.9 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 400 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.