Page 172 - Machinery Component Maintenance

154 Machinery Component Maintenance and Repair

Hot Bolting Procedure

The objective of hot bolting is to restore the original bolt stress which
has dropped due to yielding and/or creep of the flange joint components.
If possible, this should be done with a bolt tensioning device. Hot bolting
should start at the point of leakage and proceed in a crisscross pattern as
described previously. Seized bolts sometimes present a problem when hot
bolting. In such cases, it is necessary to use a wrench on both nuts.

Using Bolt Tensioners

There exists considerable experience with the use of various bolt ten-
sioners for hot bolting. These procedures typically involve first running a
die over the stud projections to facilitate subsequent installation of the
tensioner heads. Mechanics are instructed to leave the heads in place for
the minimum time necessary so as to prevent leakage of hydraulic fluid at
the seals. Past procedures called for immersion of heads in water be-
tween applications; however, this is no longer necessary.

Using Hammer and Wrench or Torque Wrench

If leaks occur, it may be necessary to employ a 7 lb or heavier hammer
to stop the leak. Tightening should first be done where the leakage has
originated and the crisscross pattern should be used from there. Joints
with spiral-wound gaskets can be tightened only to the limit of the steel
centering ring thickness. Further tightening is fruitless if a spiral-wound
gasket has already been tightened to this point.

If Hot Bolting Does Not Stop Leak

If leakage cannot be stopped by tightening, the line must be isolated
and the joint broken to determine the cause:

Examine flange facings for damage, distortion (warping), or foreign
matter.
Check flange alignment, cut and realign piping if necessary.
Check gasket for proper material, dimensions, and type. Use a new
gasket for reassembly of the joint.
Check gasket deformation to determine if it was centered. This is
best done by noting the position of the gasket before it is withdrawn
and examining it immediately after withdrawal.
Reassemble the joint.