>>>>Torquing is more of a science than the books let on. At the Savannah River
Site
(Department of Energy) facility we have built a torque demonstration rig to
train
our mechanics in torquing piping flanges. It is equipped with strain gauges
that
read the actual torque values applied. What is really interesting is this
effect,
on reaching final torque on one bolt, it tends to release torque on the
adjacent
ones to a larger degree than you would think possible.
We train them to bring torque up in at least three stages using a staggered
pattern
dependent on the number and size of the fastener used. After reaching final
torque
we train them to do a reverse rotation at final torque in a sequential pattern
completely around the flange. This negates the effect of adjacent studs
relieving
each other to something less than the final torque value.
It was really amazing to see how the fasteners interacted with one another
especially at high torque values when using a metallic sealing gasket. Dog-gone
gaskets flowed around the joint despite the high clamping forces.
I would expect that a last pass with the torque wrench in a round robin pattern
would have the same effect on an automobile head (flange) ensuring that all
bolts
are up to final torque.
Very interesting! This is good stuff and bears repeating!
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