BIZOMAT MAKEOS · Fasteners
Gasketed Flange Bolt Load Check
Do these flange bolts give enough load to seat the gasket and hold the pressure, and what torque do they need?
Bolt load check for a gasketed bolted flange by the widely used ASME Section VIII Appendix 2 approach: hydrostatic end force and gasket load at operating pressure (gasket factor m), gasket seating load (seating stress y), the required bolt area at the allowable bolt stress, the area provided by the bolts, the load per bolt and the tightening torque from the nut factor.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Design pressure | MPa | Internal design pressure. |
| Diameter at gasket load reaction | mm | Gasket load reaction diameter (per the code: the gasket mean diameter or outside of the contact width less 2b). |
| Effective gasket seating width | mm | Effective gasket seating width from the code’s basic width. |
| Gasket factor m | Gasket factor m for the gasket type (from the code or gasket maker). | |
| Gasket seating stress y | MPa | Minimum design seating stress y for the gasket. |
| Number of bolts | Number of flange bolts. | |
| Bolt diameter | mm | Bolt diameter. |
| Thread pitch | mm | Thread pitch. |
| Allowable bolt stress | MPa | Allowable bolt stress (at ambient for seating; at temperature for operation). |
| Nut factor | Nut factor for the bolt condition. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Design pressure
- What it is
- Internal design pressure acting on the flanged joint.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 100 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- MPa, not bar: 1 MPa = 10 bar.
What this means: Diameter at gasket load reaction
- What it is
- Diameter at which the gasket reaction is taken, defined by the flange code from the gasket contact width.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The hydrostatic end force rises with the square of this diameter.
What this means: Effective gasket seating width
- What it is
- Effective gasket seating width, worked out by the code’s rules from the gasket’s basic seating width.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Gasket factor m
- What it is
- Gasket factor m: the ratio of gasket stress to internal pressure needed to keep the joint tight in service, from the code or gasket maker.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 20. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Gasket seating stress y
- What it is
- Minimum design seating stress for the gasket, the stress needed to seat it at bolt-up, from the code or gasket maker.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 69 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Number of bolts
- What it is
- Number of bolts or studs around the flange.
- Units and format
- Enter a plain number with no unit. The form accepts 2 to 200. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Load per bolt falls in inverse proportion; the total bolt area provided rises in proportion.
What this means: Bolt diameter
- What it is
- Nominal diameter of the flange bolts or studs.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Thread pitch
- What it is
- Pitch of the bolt thread, used with the diameter to find the tensile stress area.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Allowable bolt stress
- What it is
- Allowable stress for the bolt material from the code: the ambient value for seating and the design-temperature value for operation.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1500 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 172 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Required bolt area is inversely proportional to it.
What this means: Nut factor
- What it is
- Nut factor relating tightening torque to bolt tension for the thread condition and lubricant.
- Units and format
- Enter a plain number with no unit. The form accepts 0.05 to 0.5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Tightening torque is proportional to it.
- Get it right
- It depends strongly on lubrication; use the value for the lubricant actually applied.
Method and formulas
- End force H = π ÷ 4 × G² p; gasket load H_p = 2π b G m p; operating W_m1 = H + H_p.
- Seating W_m2 = π b G y.
- Required bolt area A_m = max(W_m1, W_m2) ÷ S_a; provided = bolts × A_t, A_t = π ÷ 4 (d − 0.9382 P)².
- Load per bolt = max(W_m1, W_m2) ÷ bolts; torque = K F d.
- Example: the flange needs 346.83 kN of bolt load, 28.903 kN and 115.61 N·m per bolt.
Limitations
- Bolt load only; flange ring stresses, rotation and leakage tightness need the full code analysis.
- Gasket factors are user inputs from the code or gasket maker.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check bolts on a pipe or vessel flange
- Set tightening torque for a gasketed joint
- Compare gaskets by the bolt load they need
Who it is for
- Mechanical engineers
- Maintenance engineers
- Pipefitting supervisors
What you get
- Operating and seating bolt loads
- Required and provided bolt area
- Load and torque per bolt
Interpreting the result
- Soft gaskets need little seating load; spiral-wound and metal gaskets need much more.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1536, 3392–3404. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Gasketed flanges: seating the gasket and holding the pressure
In Bolted Joints by the Numbers
What it covers: How the bolts of a gasketed flange are sized: the load to seat the gasket, the load to hold it tight under pressure, gasket factors, bolt area, and an old empirical rule compared.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.