NPS 3 1/2 Class 150 Blind Flange
ASME B16.5 dimensions for one size and class: 8.50 in (215.9 mm) outside diameter, 0.94 in (23.9 mm) thick, on a 7.00 in (177.8 mm) bolt circle with 8 × 5/8 in bolts.
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Dimension | NPS 3 1/2 Class 150 |
|---|---|
| Flange outside diameter | 8.50215.90 mm |
| Flange thickness (min) | 0.9423.88 mm |
| Bolt circle diameter | 7.00177.80 mm |
| Number of bolts | 8 |
| Bolt diameter (nominal) | 5/8 in |
| Bolt hole diameter | 0.75019.05 mm |
| Bolt hole spacing on the circle | 2.7569.82 mm |
| Raised face outside diameter | 5.50139.70 mm |
| Raised face height | 0.061.52 mm |
Thickness excludes the raised face. Bolt hole diameter and spacing are derived from the B16.5 bolt size and bolt circle.
Weight and end load
A blind flange has no bore, so its outside diameter and thickness are the whole of its dimensional definition — and its weight and the load it carries are the two things people actually need. Both are calculated here from the B16.5 figures above.
| Quantity | NPS 3 1/2 Class 150 |
|---|---|
| Approximate weight | 15.1 lb (6.9 kg) |
| End thrust at rated pressure | 6771 lbf (30.1 kN) |
| Load per bolt | 846 lbf |
Weight is a solid-disc estimate from the outside diameter and the minimum thickness at 0.2836 lb/in³, and ignores the raised face, so it runs slightly light against a real forging. End thrust is the rated pressure acting on the raised face area; it is not a bolt-load calculation, which must also cover gasket seating.
Common questions
What are the bolt holes on an NPS 3 1/2 Class 150 flange?
8 holes of 0.750 in diameter on a 7.00 in bolt circle, taking 5/8 in bolts. B16.5 holes are 1/8 in larger than the nominal bolt. They straddle the vertical and horizontal centrelines rather than sitting on them, so hole spacing round the circle is 2.75 in.
What pressure is an NPS 3 1/2 Class 150 flange good for?
285 psig (19.7 bar) at 100 °F in A105 carbon steel, falling as metal temperature rises. Class 150 is a designation, not a pressure — see the P-T tables for your material and temperature.
Is a Class 150 blind flange interchangeable with another type?
At the bolted joint, yes: every B16.5 type in NPS 3 1/2 Class 150 shares the 8.50 in outside diameter, 7.00 in bolt circle and 8 × 5/8 in bolting, so any two will mate. What is not interchangeable is how they join the pipe, and therefore what service they suit.