Use Of Backing Wrenches; Torque Wrench Selection; Tightening Bolts; Tightening A Flanged Joint - SPX TWLC Series Operating Manual

Operating Instructions continued

Use of Backing Wrenches

Backing wrenches are often used to prevent the non-tightening nut on the opposite side of the joint
assembly from turning during the torquing operation. Verify that the backing wrench is the correct
size and securely fastened in position (using straps, ropes, etc.). As the torquing operation begins, it
is normal for the backing wrench to move/rotate in conjunction with the torqued nut, until the backing
wrench contacts an adjacent reaction point. It is important that the operator stand clear of the moving
backing wrench to prevent accidental entrapment. The operator must also verify that the reaction point
is secure and sufficiently rigid to prevent damage to the structure.

Torque Wrench Selection

To choose the correct capacity Torque Wrench for the application, the estimated break-out torque
should be considered, not the tightening torque. Loosening bolts usually requires a higher torque, and if
a wrench has been selected on tightening criteria only, it will seldom perform in a break-out situation.
Break-out Considerations
Nuts / Bolts which have been correctly lubricated at the make-up / tightening stage will require
approximately 1.5 x tightening torque to loosen following a period of service, PROVIDED THEY HAVE
NOT BEEN SUBJECTED TO HEAT.
Corroded / rusted bolts, and bolts without lubrication applied at make-up, will require approximately 2 x
tightening torque to loosen. PROVIDED THEY HAVE NOT BEEN SUBJECTED TO HEAT.
Nuts / bolts subjected to heat, seawater corrosion, chemical corrosion, can require 3 to 4 x tightening
torque.
Before selecting a torque wrench for the application, ensure that the above has been considered.

Tightening Bolts

1. Apply the hydraulic torque wrench to the nut to be tightened and verify that the reaction pad is braced
firmly and squarely against the selected reaction point.
2. Start the pump and advance the hydraulic torque wrench. As the wrench strokes forward, the reaction
pad will press against the reaction point and the socket will rotate. When the hydraulic torque wrench
reaches the end of its stroke, the pump pressure will build rapidly. Fully retract the hydraulic torque
wrench (the wrench ratchet mechanism will be heard clicking as it retracts), and apply another
forward stroke.
3. Several forward strokes are made until the nut ceases to rotate during the stroke (known as stalling),
but bear in mind that nut rotation will always cease at the end of the wrench stroke and must not be
confused with the wrench stalling. When the wrench stalls, apply another forward stroke and observe
the pump pressure gauge. The pump pressure gauge should read the desired preset pressure.
4. Retract the hydraulic torque wrench, stop the pump unit, and remove the wrench from the nut.

Tightening a Flanged Joint

This procedure outlines the basic steps to torque-tighten a flanged joint with a TWLC hydraulic
torque wrench. It is important that personal protective equipment (gloves, footwear, safety helmet,
eye protection, etc.) is worn at all times by the operator and any other personnel in the work area.
The torquing procedure uses a single hydraulic torque wrench to accurately achieve a predetermined
residual bolt stress.
© SPX
13
Form No. 1000529
Rev. 1 December 6, 2011