On Saudi projects, equipment to American and European standards meets in the same line: a pump with a PN16 flange and a valve with a Class 125 flange, or the other way round. The two flanges may look alike, but the bolt circle and number of holes differ in most sizes. This guide compares the dimensions size by size from MECH product tables, and explains what to do when they do not match.
Key points
- ASME Class 125 and Class 150 flanges share the same drilling in the common sizes.
- EN PN16 flanges do not match the American bolt circle in any size from 2 to 12 inch in the table below.
- From 8″ the number of holes also differs (8 versus 12).
- Specify the flange pattern when ordering; do not assume “same size” means “same holes”.
What makes two flanges compatible?
Three dimensions: the bolt circle diameter (PCD), the number of holes, and the hole diameter. If any of them differ, the bolts will not fit. Flange outside diameter and thickness do not prevent assembly, but they affect load and sealing.
Comparison table, 2 to 12 inch
| Size | Nominal diameter | Class 125 circle | Class 125 holes | PN16 circle | PN16 holes |
|---|---|---|---|---|---|
| 2″ | DN50 | 120.7 | 4 × 19.1 | 125 | 4 × 19 |
| 2-1/2″ | DN65 | 139.7 | 4 × 19.1 | 145 | 4 × 19 |
| 3″ | DN80 | 152.4 | 4 × 19.1 | 160 | 8 × 19 |
| 4″ | DN100 | 190.5 | 8 × 19.1 | 180 | 8 × 19 |
| 5″ | DN125 | 215.9 | 8 × 22.2 | 210 | 8 × 19 |
| 6″ | DN150 | 241.3 | 8 × 22.2 | 240 | 8 × 23 |
| 8″ | DN200 | 298.5 | 8 × 22.2 | 295 | 12 × 23 |
| 10″ | DN250 | 362.0 | 12 × 25.4 | 355 | 12 × 28 |
| 12″ | DN300 | 431.8 | 12 × 25.4 | 410 | 12 × 28 |
Source: the dimension tables on the XZ41X gate valve page (ASME B16.1 CL125 flange) and the SK720X pressure reducing valve page (EN 1092-2 flange).
The closest sizes, still not a match
Warning
At 6″ the bolt circle differs by only 1.3 mm (241.3 versus 240) with the same number of holes, which tempts fitters to enlarge the holes. That is an unapproved modification that weakens the joint and voids the product’s approval. Do not assemble without a solution approved by the designer.
What to do when they do not match
- Order the valve or fitting with the required flange pattern from the start. Many MECH models are available in more than one pattern, per their tables.
- Use an approved transition piece (a flange of one pattern on each side), designed and approved by the designer.
- In grooved systems, use a grooved flange in the required pattern to connect the equipment to the line.
- State the flange pattern in the material schedule and the compliance table of the submittal.
Frequently asked questions
Are Class 125 and Class 150 compatible?
In bolt circle and number of holes, yes, in the common sizes. The difference is the flange face (flat or raised) and thickness; when bolting cast iron to a raised-face flange, allow for this in the gasket.
Are PN10 and PN16 the same?
In small sizes usually yes; they differ in some larger sizes, such as DN200, in the number of holes. Check the standard’s table.
How do I identify the flange pattern of existing equipment?
Measure the bolt circle from the centre of one hole to the centre of the opposite hole, count the holes, and compare with the table.
References
- ASME B16.1 — Gray Iron Pipe Flanges and Flanged Fittings.
- ASME B16.5 — Pipe Flanges and Flanged Fittings.
- EN 1092-2 — Circular flanges for pipes, valves, fittings and accessories, PN designated — Cast iron flanges.
Dimensions are from MECH product tables for illustration; the reference for design is the standard and the table of the model chosen.
Part of a complete guide
This article is part of Approving Fire Protection Materials in Saudi Arabia: From the Consultant to Civil Defense.
NWC approved
