Overview
A flange bolt chart links a specific flange standard, nominal size, pressure class, and series to the number of bolts or studs, nominal diameter, bolt-hole diameter, and bolt-circle diameter. Some charts also estimate stud length. A chart is valid only when its standard, edition, unit system, facing, and joint arrangement match the actual connection.
There is no safe universal flange-to-flange bolt chart. ASME B16.5, ASME B16.47, EN, DIN, JIS, API, AWWA, and project-specific flanges use different dimensional systems. Changing class or series can change the pattern even at the same nominal size.
Why It Matters for Pipe Components
Incorrect bolting can prevent assembly, reduce nut engagement, damage the gasket, or create uneven gasket stress. A stud that passes through the hole is not automatically correct. Diameter, material, thread series, length, nut grade, washers, coating, and tightening procedure all matter.
Stud length depends on both connected parts, gasket thickness, nuts, washers, insulation kits, line blanks, and required thread projection. A chart for two raised-face flanges may not apply to a flange connected to a valve body or a joint containing an isolation kit.
Bolt torque is a separate engineering subject. A dimensional chart does not provide one universal installation torque. Torque or tension depends on gasket, lubricant, bolting material, target stress, flange condition, and the approved assembly procedure.
Methods, Parameters, or Process
Read or build a flange bolt chart in the following order. Do not start from bolt diameter alone.
| Chart field | What it controls | Common error |
|---|---|---|
| Standard and edition | Defines the dimensional table | Mixing ASME, EN, API, or old project data |
| NPS or DN | Selects nominal connection size | Using measured OD as the nominal size |
| Class or PN | Selects rating and drilling pattern | Treating Class 150 and PN16 as interchangeable |
| Series | Distinguishes large-diameter patterns where applicable | Omitting Series A or Series B |
| Number and hole diameter | Defines drilling and nominal bolting | Confusing hole diameter with bolt diameter |
| Bolt circle diameter | Locates holes around the flange | Using another class or series |
| Stud length | Provides assembly length for the exact stack | Ignoring gasket, washers, valve thickness, or blank |
Supplier and Inspection Checklist
- Identify standard, edition, size, class or PN, flange type, and series.
- Check both mating components, including valve bodies and equipment nozzles.
- Verify number of holes, nominal bolting diameter, hole diameter, and bolt circle.
- Confirm studs versus machine bolts, washers, insulating sleeves, and coatings.
- Specify bolting and nut materials separately from flange material.
- Calculate stud length from the complete joint stack.
- Confirm thread engagement and required projection.
- Use a controlled tightening procedure with the approved lubricant and gasket.
- Keep dimensional selection separate from torque or bolt-tension engineering.
- Mark every chart with its source, edition, units, and limitations.
Application to Pipe Fittings, Valves, and Flanges
Weld-neck, slip-on, threaded, socket-weld, lap-joint, and blind flanges in the same standard, size, and class normally share a drilling pattern, but their thicknesses and hubs differ. The actual joint stack still controls stud length.
Blind flanges, spectacle blinds, spacers, and paddle blanks can add weight or thickness and may require longer studs. Valve bodies can limit wrench access even when drilling matches the flange standard.
The installation team should confirm that nuts and tools clear the valve body, actuator, insulation, pipe supports, and nearby equipment.
FAQ
Can one Class 150 bolt chart be used for every standard?
No. Other flange systems can use different drilling and dimensions even when the service rating appears similar.
Is bolt-hole diameter the same as bolt diameter?
No. The clearance hole is larger than the nominal bolt or stud diameter.
How is stud length selected?
Add the actual thickness of connected parts, gasket or inserts, nuts, washers, and required projection, then apply the project rounding method.
Does a bolt chart give tightening torque?
Normally no. Torque depends on the complete joint design and approved assembly procedure.
Can PN16 and Class 150 flanges be bolted together?
Do not assume compatibility. Compare all dimensions, facing, ratings, materials, and obtain design approval.
Next Steps
Use the project flange standard or a licensed dimensional table. Provide the complete joint stack so the supplier can verify bolting material, diameter, quantity, and length.
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