De-Tensioning Procedure

When de-tensioning, specific tool pressures are not normally available as it is not always possible to calculate the pressure at which the flange nut will break free. As a guide, if the original flange bolt tightening pressures are available, the de-tensioning pressure is usually marginally higher than the original tensioning pressure (but not always).

The maximum pressure that can be applied has been calculated to ensure that either 95% of the bolt material yield is not exceeded, or the maximum tool pressure is not exceeded, whichever is the lower. Pump must be pre-set to achieve this.

  1. Assemble the tensioning tools to the bolts. With the reaction nut fully screwed down and seated on the piston, unscrew the reaction nut one and a half turns. This will prevent the reaction nut from becoming locked onto the piston when the bolt tension is released.

  2. Insert a tommy bar through the tensioner access window and into a hole in the flange hexagon nut. Apply hydraulic pressure to the system until the flange nut can be rotated, ensuring that the piston does not exceed maximum stroke or system pressure does not exceed maximum pressure allowed.

  3. Turn back each flange nut one full turn.

  4. De-pressurize the system and check to see that the flange nuts are still free to rotate.

  5. Remove the bolt tensioners.