Hydraulic Bolt Tensioning Function
Hydraulic Bolt Tensioning Function
High pressure flanges, large diameter flanges and flanges on hazardous services are often made up using Hydraulic Bolt Tensioners. The Bolt Tensioners operate by hydraulically “stretching” the studbolt to a pre-defined limit after which the operator is then able to hand-tighten the nuts. The hydraulic load is then released and the studbolt remains tensioned. The advantage of tensioning (stretching) against torquing is that the process is not dependent on the type of lubrication used and eliminates the effect of friction under the nut and between threads. Accurate bolt tensions are therefore obtained.
To pull down the flange evenly, several bolts can be tensioned at the same time. All the studbolts will eventually be tensioned after successive “passes” of the bolt tensioning eqiupment.
Note that the use of the bolt tensioning equipment usually requires the studbolts to protrude past the nut by an additional bolt diameter . Obstructions such as pipe supports and instrument tappings may prevent the bolt tensioning equipment from being fitted over the studbolt. In such cases, hydraulic torque wrenches will then be used to tension the bolts.
Hydraulic Bolt Tensioning is a specialised activity. Only trained personnel carry out the bolt tensioning using equipment in good order .
Reference : BP Amoco Piping Joints Handbook (Document No. D/UTG/054/00)
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