1. Correct installation direction is essential.
The flange face (toothed or smooth) must face inwards towards the connected parts to ensure anti-loosening and pressure distribution.
The threaded end should face outwards for easy tightening with a wrench or socket wrench.
If the flange face faces outwards, the anti-loosening teeth will not engage, reducing the contact area and making loosening or crushing more likely.
2. Tighten in a diagonal sequence.
For multi-bolt flange connections, tighten gradually in a diagonal or star-shaped sequence to avoid unilateral force causing flange misalignment.
It is recommended to apply force in at least three stages: 50% → 80% → 100% of the design torque to prevent gasket crushing or seal failure.
3. Use appropriate tools and control torque.
In ordinary scenarios, a box wrench or socket wrench can be used for manual tightening.
For high-temperature, high-pressure, flammable, explosive, or critical equipment, a torque wrench should be used. Apply the pre-tightening force strictly according to the design value, and record the data for future reference.
4. Check Bolt Exposed Length
After tightening, at least two complete threads should protrude from the nut to ensure full engagement and avoid the risk of stripping.
5. Ensure Sealing and Leak Prevention
In piping or pressure systems, flange connections require the use of gaskets. During installation, ensure the gasket is centered and not squeezed or misaligned.
After installation, leaks can be checked using a pressure test followed by a soapy water test.
6. Special Scenario Handling
Double flange nut top-down installation (e.g., high-pressure pipelines): The flange faces of both nuts should face the central connected component, clamping the sealing gasket to achieve bidirectional sealing and anti-loosening.
Embedded installation: The flange face should be completely embedded in the material, ensuring a flush surface to prevent exposed corrosion or loosening.
7. Lubrication and Cleaning
Clean the threads and flange surfaces before installation to remove oil, rust, burrs, and other impurities.
Apply a uniform lubricant to the threaded, nut bearing surfaces, and washer contact surfaces to reduce the coefficient of friction and improve tightening accuracy.
