Page 57 - banneredThermosealCatalog2010

Page 3 of 3 Torque to Achieve Bolt Utilization 061207
2. Multiple passes can provide the following:
a. Control the pressure on the gasket and the load of the bolt,
b. Pull the flanges up evenly,
c. Allow relaxation to take place as you tighten, and
d. Control the relaxation so that you don’t see it all at the end of the job.
3. You may have as many passes as you want, however do not use less than 3 star pattern
passes and the optional 2 chase (1 clockwise and 1 counter-clockwise).
RELAXATION:
1. Some of the joint relaxation is due to cross-talk in the bolts. Multiple passes, repetition,
friction control and good craftsmanship can compensate for this.
2. Another form of relaxation takes place after initial tightening. This is when the majority of
thread yielding and gasket creep occurs. The joint is responding to all of the forces that
have been applied. Deal with this by repeating the chase patterns before start up (Usually
within 24 hours of equipment start up).
3. The most critical form of relaxation takes place during pressurization start up and operation.
Additional loads due to temperature and media are introduced. Everything changes but we
have built in enough safety factor and control to do the job.
4. Hot torquing is generally not recommended. If hot bolting is required consult fastener,
gasket and flange vendor before applying additional loads (be prepared to discuss the
application, pressure, temperature and final torque applied to fasteners).