Class 150 and PN16 flanges look almost identical on the shelf. In most sizes they don't bolt together, and finding out on site costs days.
Two different families of standard
- Class 150 comes from ASME B16.5, an inch-based American standard. Sizes are in NPS (inches) and bolts are inch-sized.
- PN16 comes from EN 1092-1 (which replaced BS 4504), a metric European standard. Sizes are in DN (millimetres) and bolts are metric.
Size by size: where they differ
| Size | Class 150 OD / bolt circle / holes | PN16 OD / bolt circle / holes |
|---|---|---|
| ½" / DN15 | 90 / 60.3 mm / 4 | 95 / 65 mm / 4 |
| 1" / DN25 | 110 / 79.4 mm / 4 | 115 / 85 mm / 4 |
| 2" / DN50 | 150 / 120.7 mm / 4 | 165 / 125 mm / 4 |
| 3" / DN80 | 190 / 152.4 mm / 4 | 200 / 160 mm / 8 |
| 4" / DN100 | 230 / 190.5 mm / 8 | 220 / 180 mm / 8 |
| 6" / DN150 | 280 / 241.3 mm / 8 | 285 / 240 mm / 8 |
Figures from ASME B16.5 and EN 1092-1 as given in our flange dimension tables. Always confirm against your own copy of the standard for critical work.
Look at the 6-inch row. The bolt circles differ by only 1.3 mm, close enough that a fitter may force the bolts in. That puts the bolts and gasket under side load and is a common cause of leaking joints.
Pressure ratings are not the same either
PN16 means a nominal 16 bar. Class 150 is not a single pressure: its rating depends on the material and the temperature. For common carbon and stainless grades it is around 19 bar at ambient temperature, falling as the temperature rises. Both standards publish pressure-temperature tables, and those are what you design to.
How to tell them apart
- Read the marking. Look for "150", "#150" or "CL150" versus "PN16", and the standard, for example "B16.5" or "BS4504 / EN1092".
- Count the bolt holes and measure the bolt circle against the table.
- Check the bolt-hole diameter. Inch and metric holes differ.
Before you order
Confirm the standard of the mating flange, valve or equipment, not just the size. A pump or valve imported from Europe will usually be PN-rated, and one from the US or built to an American spec will usually be Class-rated.
What we stock
ENLIN stainless flanges to ANSI B16.5 Class 150 and to BS 4504 / EN 1092 PN16 (PN16 in F304L).