ASME B16.5 covers flanges from NPS 1/2 to NPS 24 in pressure classes 150 to 2500. The class sets the flange thickness, the bolt circle and the bolting; two flanges of the same nominal size but different class do not bolt together. The table below gives the Class 150 dimensions in millimetres, followed by the class and facing rules that decide the rest.
ASME B16.5 Class 150 — flange dimensions (NPS 1/2–12)
| NPS | DN | Flange OD (mm) | Min. thickness (mm) | Bolt circle / PCD (mm) | Bolts | Bolt size | Hole dia (mm) | Raised face dia (mm) |
|---|---|---|---|---|---|---|---|---|
| 1/2 | 15 | 88.9 | 11.2 | 60.5 | 4 | M14 | 15.9 | 34.9 |
| 3/4 | 20 | 98.6 | 12.7 | 69.9 | 4 | M14 | 15.9 | 42.9 |
| 1 | 25 | 108.0 | 14.3 | 79.4 | 4 | M14 | 15.9 | 50.8 |
| 1-1/4 | 32 | 117.5 | 15.9 | 88.9 | 4 | M14 | 15.9 | 63.5 |
| 1-1/2 | 40 | 127.0 | 17.5 | 98.6 | 4 | M14 | 15.9 | 73.0 |
| 2 | 50 | 152.4 | 19.1 | 120.7 | 4 | M16 | 19.1 | 92.1 |
| 2-1/2 | 65 | 177.8 | 22.4 | 139.7 | 4 | M16 | 19.1 | 104.8 |
| 3 | 80 | 190.5 | 23.9 | 152.4 | 4 | M16 | 19.1 | 127.0 |
| 3-1/2 | 90 | 215.9 | 23.9 | 177.8 | 8 | M16 | 19.1 | 139.7 |
| 4 | 100 | 228.6 | 23.9 | 190.5 | 8 | M16 | 19.1 | 157.2 |
| 5 | 125 | 254.0 | 23.9 | 215.9 | 8 | M20 | 22.2 | 185.7 |
| 6 | 150 | 279.4 | 25.4 | 241.3 | 8 | M20 | 22.2 | 215.9 |
| 8 | 200 | 342.9 | 28.4 | 298.5 | 8 | M20 | 22.2 | 269.9 |
| 10 | 250 | 406.4 | 30.2 | 362.0 | 12 | M24 | 25.4 | 323.9 |
| 12 | 300 | 482.6 | 31.8 | 431.8 | 12 | M24 | 25.4 | 381.0 |
Thickness includes the 1.6 mm raised face. Dimensions are common to weld neck, slip-on, blind, socket weld, threaded and lap joint flanges at the same size and class; the bore, hub, socket and thread detail changes with the type. Data to ASME B16.5 — confirm against the project specification before fabrication.
What the class changes
| Class | Typical service | Size range covered here |
|---|---|---|
| 150 | Utility, water, low pressure process | NPS 1/2–24 |
| 300 | General process, moderate pressure | NPS 1/2–24 |
| 600 | Higher pressure and temperature | NPS 1/2–24 |
| 900 / 1500 / 2500 | High pressure, severe service | NPS 1/2–24 (size limits apply at the top classes) |
A Class 300 flange of a given size is larger and heavier than a Class 150 one, and the two will not mate. The class is a design rating, not a pressure in psi: the allowable pressure is read from the B16.5 pressure–temperature table for the material group, so the same Class 150 flange does not carry the same allowance in carbon steel as in stainless.
Facing: what has to match
| Facing | Gasket | Where it is used |
|---|---|---|
| Raised face (RF) | Sheet or spiral wound | The default for most process and utility lines |
| Flat face (FF) | Full-face gasket | Mating to cast iron or bronze equipment, where a raised face would crack the casting |
| Ring joint (RTJ) | Metal ring | High pressure and high temperature service |
The facing has to match the gasket and the flange it bolts to. Name all three on the enquiry: size, class and facing.
What to state on a B16.5 enquiry
Nominal size, pressure class, facing, flange type and material — and for a weld neck, the pipe schedule, because the bore is machined to the wall. Quantity and destination port follow.
Send the size, class, facing and destination port and we will confirm availability and price within one business day. Request a quotation · WhatsApp
Related pages
Flange types and ordering: pipe flanges. Large diameter above NPS 24: ASME B16.47 dimensions. Material grades: ASTM A105 and ASTM A182 F316.
Mejor Steel is the export agent for the mills that make your material: one contract, one delivery date, and the mill named on the quotation. How we supply
We reply within one business day, Monday to Friday 09:00-18:00 CST. Or write to info@mejorsteel.com / WhatsApp.