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Why hydraulic bolt and stud tensioning

Why Hydraulic Bolt and Stud Tensioning? 

HTI’s Hydraulic Stud and Bolt Tensioning Systems are the simple and efficient answer to common stud and bolt tightening problems, and provide:

  • Accurate and Repeatable Stud Loading – Engineers design a flange or joint knowing the stud tension necessary for it to function as intended. Under–tightened, over–tightened or unevenly–tightened studs can lead to the failure of the joint. Bolt tensioning produces a known tension in the stud.

    Accurate stud tension is difficult to attain using torque, because friction has a significant effect on the torque–tension relationship. For example, the torque required to stretch a 2″–8UN stud to 35% of its yield strength varies between 1,400 ft–lbf (using a moly–based lubricant) and 8,360 ft–lbf (“dry”, with no lubricant). If the operator failed to lubricate the threads and nut surface and torqued dry, the resulting stud tension would be only 6% of yield (Tension = 17,100 lbf) instead of 35% of yield (Tension = 102,300 lbf)!

  • Fast Operation – Using Hydraulic Stud Tensioners is usually faster than using hydraulic torque wrenches. Compared to torque, using one Tensioner for every four studs on the flange, or “25% cover” will typically cut the tightening time by fifty percent (50%). With one Tensioner for every two studs, or “50% cover”, the time can be cut by an additional one–third (33%).

  • Even Flange Closure – Using multiple Hydraulic Stud Tensioners on a bolt pattern allows even flange closure and even gasket loading. No pinched gaskets or over–stressed studs, which is possible when using one torque wrench and a star torque pattern.

  • Gall–Free Operation – High levels of torque, especially in studs over 2–1/2″ diameter, can produce thread galling and nut–surface galling. In the Hydraulic Stud Tensioning process, the nut is not under load and turns freely. Galling is not a problem.

  • Conformation to the Specification and Design Intent – If there is extra thread protruding above the nut (for example, for a 2″” stud there would be about 2″ of thread) the application was intended to be tensioned. Applications with either round nuts or drilled, hexagon nuts are also designed for Hydraulic Stud Tensioning.

  • Ease of Use – HTI’s Hydraulic Stud and Bolt Tensioners have a very high power to weight ratio, which is especially important for larger stud sizes. The operator handles the Hydraulic Stud Tensioner parts (Load Cell, Puller Bar and Bridge) separately. The weight of any one part can be significantly less than the weight of the hydraulic torque wrench for the same stud size.


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