NPS 18 Class 300 Weld Neck Flange
ASME B16.5 dimensions for one size and class: 28.00 in (711.2 mm) outside diameter, 2.38 in (60.5 mm) thick, on a 24.75 in (628.6 mm) bolt circle with 24 × 1 1/4 in bolts.
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Dimension | NPS 18 Class 300 |
|---|---|
| Flange outside diameter | 28.00711.20 mm |
| Flange thickness (min) | 2.3860.45 mm |
| Bolt circle diameter | 24.75628.65 mm |
| Number of bolts | 24 |
| Bolt diameter (nominal) | 1 1/4 in |
| Bolt hole diameter | 1.37534.92 mm |
| Bolt hole spacing on the circle | 3.2482.29 mm |
| Raised face outside diameter | 21.00533.40 mm |
| Raised face height | 0.061.52 mm |
| Length through hub | 6.25158.75 mm |
Thickness excludes the raised face. Bolt hole diameter and spacing are derived from the B16.5 bolt size and bolt circle.
Bore: order the flange to the schedule
A weld neck flange is bored to match the pipe it is butt-welded to, so NPS 18 Class 300 is not one part number but 13 — one for each schedule B36.10M publishes in this size. Everything in the table above is common to all of them; the bore below is not. Specifying “NPS 18 Class 300 weld neck” without the schedule is an incomplete requisition.
| Schedule | Pipe wall | Flange bore = pipe ID | Pipe weight |
|---|---|---|---|
| Sch 5 | 0.1654.19 mm | 17.670448.82 mm | 31.4346.77 kg/m |
| Sch 10 | 0.1884.78 mm | 17.624447.65 mm | 35.7653.22 kg/m |
| Sch 20 | 0.3127.92 mm | 17.376441.35 mm | 58.9487.71 kg/m |
| Sch 30 | 0.43811.13 mm | 17.124434.95 mm | 82.15122.26 kg/m |
| Sch 40 | 0.56214.27 mm | 16.876428.65 mm | 104.67155.76 kg/m |
| STD | 0.3759.52 mm | 17.250438.15 mm | 70.59105.05 kg/m |
| Sch 60 | 0.75019.05 mm | 16.500419.10 mm | 138.18205.63 kg/m |
| Sch 80 | 0.93823.83 mm | 16.124409.55 mm | 170.93254.37 kg/m |
| XS | 0.50012.70 mm | 17.000431.80 mm | 93.45139.07 kg/m |
| Sch 100 | 1.15629.36 mm | 15.688398.48 mm | 207.96309.48 kg/m |
| Sch 120 | 1.37534.92 mm | 15.250387.35 mm | 244.14363.32 kg/m |
| Sch 140 | 1.56239.67 mm | 14.876377.85 mm | 274.23408.09 kg/m |
| Sch 160 | 1.78145.24 mm | 14.438366.73 mm | 308.51459.11 kg/m |
A bore mismatch at a butt weld leaves a step in the flow path and a stress raiser at the root — the defect the weld neck exists to avoid.
Common questions
What are the bolt holes on an NPS 18 Class 300 flange?
24 holes of 1.375 in diameter on a 24.75 in bolt circle, taking 1 1/4 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 3.24 in.
What pressure is an NPS 18 Class 300 flange good for?
740 psig (51.0 bar) at 100 °F in A105 carbon steel, falling as metal temperature rises. Class 300 is a designation, not a pressure — see the P-T tables for your material and temperature.
Is a Class 300 weld neck flange interchangeable with another type?
At the bolted joint, yes: every B16.5 type in NPS 18 Class 300 shares the 28.00 in outside diameter, 24.75 in bolt circle and 24 × 1 1/4 in bolting, so any two will mate. What is not interchangeable is how they join the pipe, and therefore what service they suit.