Flange Coupling Calculation.

Quick and fast way to determine the torque capacity of a flange coupling,
Calculation is based on the combination between bolt tension and the coefficient of friction between surfaces.

This calculation do not consider, in any case, that bolts could work under shear load therefore all torque must be transfer between the surfaces.
It was observed in many cases, that once any of the bolts that belong to the pattern, starts to work under shear load, the torque distribution changes within the bolt pattern. 
Bolt will start to work also under combined bending loads which at the end will lead into a premature failure.

The tightening torque is determined using an "utilization factor" of 0.8.












































                                                                Flange Coupling Calculation

Additional Information about Flange Couplings:

Lessons Learned:

• A bolt that is not properly tightened can become loose after a short period of time
• If the fasteners are loose, they are subjected to alternating forces and may fail through fatigue.
• Few bolts could work only in tension, ans some of them work also in shear. Do not overload the flange to avoid premature failures.
• If it is possible, tight always the nut and not the bolt.
• Replace locknuts after some installations. Five or six is a good number.
• Try to keep the oil or grease out of the flange contact as well as from the bolt or nut area.
• Assembly instructions:
• Tight the bolt in pairs crosswise, looking for the opposite one each time.
  During all of the following steps, keep any gap between flanges even all around the circumference, and nuts made up approximately the same amount on each end of the bolt.
  • First time around just snug the nuts with a hand wrench.
  • Second time around tighten the nuts firmly with the same wrench.
  • Third time around apply approximately 25% recommended torque.
  • Fourth time apply approximately 75% of recommended torque.
  • Fifth time around, apply 100% of recommended torque.
  • Continue tightening nuts all around until nuts do not move under 100% recommended torque.
  • If possible, re-torque after 24 hours. Most of any bolt preload loss occurs within 24