BIZOMAT MAKEOS · Fasteners
Working Strength of Bolts in Packed (Gasketed) Joints
What external load can this bolt safely carry in a packed joint after allowing for the tightening load?
Empirical working strength of studs and bolts in packed or gasketed joints (where the gasket is more elastic than the bolts) by the handbook’s Cornell formula W = S_t (0.55 d² − 0.25 d), and by the alternative using the thread root area, with the bolt count for a total load.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal bolt diameter | mm | Nominal outside diameter of the bolt or stud. |
| Area at the thread root | mm² | Root (minor diameter) area of the thread, for the alternative formula. |
| Allowable working stress in tension | MPa | Allowable tensile working stress you use for the bolt material. |
| Total external load on the joint | kN | Total separating load on the joint (pressure × area), to find the bolt count. |
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: Nominal bolt diameter
- What it is
- The nominal outside diameter of the bolt or stud in the packed joint, used in the empirical working strength formula.
- 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 25.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The working strength rises a little faster than the square of the diameter.
- Get it right
- Use the nominal thread diameter; bolts under 16 mm draw a warning for tight joints.
What this means: Area at the thread root
- What it is
- The cross-sectional area at the root (minor diameter) of the thread, used only for the alternative working strength formula.
- Units and format
- Enter a number in mm²: square millimetres. The form accepts 0.000001 mm² to 100000 mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 357.8 mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The alternative working strength rises with root area.
- Get it right
- Take it from a thread table for the actual thread size and pitch, not the area of the nominal diameter.
What this means: Allowable working stress in tension
- What it is
- The allowable working stress in tension you use for the bolt material, set by your design practice, standard or code.
- 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 68.95 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Both working strengths are directly proportional to it.
- Get it right
- This is an allowable working stress, not the material’s yield or tensile strength.
What this means: Total external load on the joint
- What it is
- The total separating load on the whole joint, such as pressure times the area inside the gasket. It is divided by the working strength to find the bolt count.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The number of bolts rises in steps with the total load.
- Get it right
- This is the total load on the joint, not the load per bolt.
Method and formulas
- W = S_t (0.55 d² − 0.25 d), with W in pounds, S_t in psi and d in inches (converted here).
- Alternative: W = S_t (A − 0.25 d), with A the thread root area in square inches.
- Handbook example: a 1-in. bolt at 10,000 psi has a working strength of about 3,000 lb.
- Example: a 25.4 mm bolt at 68.95 MPa carries about 13.345 kN in a packed joint.
Limitations
- Empirical rule for hand-tightened bolts in gasketed joints; bolts under 5/8 in. (16 mm) are not recommended for tight joints.
- Pressure equipment must be designed to its code (for example ASME VIII Appendix 2).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check studs on a gasketed cover or cylinder head
- Choose the number of bolts for a flange load
- Compare a legacy design rule with a modern joint analysis
Who it is for
- Design engineers
- Maintenance engineers
- Pressure equipment technicians
What you get
- Working strength per bolt (both formulas)
- Bolts needed for the load
- Formula in the handbook units
Interpreting the result
- The 0.25 d term allows for the extra load put on by tightening; it penalises small bolts most.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1535–1536. 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.
Useful alongside · 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.
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Open the Working Strength of Bolts in Packed (Gasketed) Joints calculator