Audit Example - Static
If it is not practical to dynamically monitor a tool on an ongoing basis a "static" audit can be
implemented. As previously discussed static auditing can be done after a fastener has been
installed. Static audits are performed downstream from the installation process. Usually
checks are made on a variety of fasteners as part of an inspection route by QA personnel.
Using the same fastening example discussed in the dynamic example, the data collector would
be set up to interface to a hand held torque wrench instead of an in-line transducer. The
significant difference in the gage setup is the use of the "Breakaway" algorithm instead of
"Peak". The wrench is then used to apply torque (usually clockwise) to the fastener. The
operator applies a steadily increasing amount of force until fastener movement is felt, pressure
is then released. The data collector then stores the torque value at which breakaway occurred.
The theory behind static auditing is:
If 90 Nm of torque was initially applied to reach a specific tightness (or tension), re-applying
90+ Nm of torque will overcome the residual friction and cause the fastener to move. In other
words, the audit will find the fastener breaking away at 90 Nm.
The reality of static auditing is:
To cause a previously tightened fastener to move, the residual friction must be overcome.
Since static friction is usually greater than dynamic friction, the breakaway point is usually
greater than the installation torque. This fasteners breakaway point could be in the 90's or in
the 100+ Nm range.
Alternatively if a gasket was part of the assembly, gasket compression could relieve tension
through time. This would yield a breakaway value less than 90 Nm due to lessened friction.
Over 200 factors have been identified which can affect the breakaway point in either direction.
See page 6-30 in the Fifth Edition DataMyte handbook for more information on this subject.
Prior to creating a static audit setup, acceptable high and low audit limits should be established
since they will probably differ from the specification (installation) limits.
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