Bolt and Stud Fastener Tensioner Application and Review
Bolt Tensioners are used to apply and maintain a desired tension on a fastener, stud, or bolt prior to and during the application of the final securing torque applied by a nut or other torque retainer. Bolt tensioners are available for all standard imperial and metric threads, as well as, custom threads. A typical bolt tensioner design incorporates a load cell or tension reading device, and applicable hydraulics, or mechanical tension application mechanism.
Bolts and studs used in critical applications, which require careful pretension or known torque / tension are normally installed by use of a bolt tensioner. Fasteners which must withstand extreme cyclic, or thermal induced loads which must be accounted for during torque are a classic example. If you have a design application using a ASTM A490 bolt, which will be loaded to approximately 110,000 lbs or approximately 85% of yield. To prevent over or under tension due to inaccurate applied torque, one might designate a pre-tension requirement on the assembly drawing for the bolt or stud. The pretension specification will normally have a high and low tension limit, and clearly indicate the requirement for a bolt tensioner.
By using a bolt tensioner in critical applications, the engineer or designer can have more confidence that the bolted joint or installation will function as designed during anticipated extreme loading conditions.