Guidelines
for Preventing Torsional Vibration Problems
in Reciprocating Machinery T. Feese and C. Hill, 2002
GMC Gas Machinery Conference, Nashville, TN, October 2002.
There are numerous books and technical papers on the subject of
torsional vibration, so the phenomenon should be well understood
and easily controlled. However, numerous torsional vibration problems
continue to occur in reciprocating and rotating machinery. One reason
for this is the mating of equipment traditionally used in non-reciprocating
applications (such as variable speed motors) with reciprocating
compressors. Other reasons may include lack of monitoring engine
or compressor performance, as well as improper application and maintenance
of viscous dampers and elastomeric couplings.
The purpose
of this short course is to raise awareness of torsional vibration
problems that can occur in reciprocating equipment, and to give
guidelines based on experience with actual systems to avoid these
problems in the future. A list of recommended items that should
be considered in the initial design stage, analysis stage, and
after the system is in service is provided to help attain maximum
reliability. The need for torsional vibration measurements during
commissioning to verify acceptability of critical applications
is also discussed.
Ten different
case histories are presented where failures were linked to torsional
vibration. In general, the solutions to these problems were based
on practical considerations that could be retrofitted in the field.
Of particular interest are the failures that could not have been
predicted if only an “ideal” operating condition was
analyzed. The results of these investigations emphasize the need
for more comprehensive torsional analyses in the design stage
of critical systems. Advanced software for performing steady-state
and time-transient torsional analyses should have the following
capabilities:
•
Undamped and Damped Torsional Natural Frequencies and Mode Shapes
• Interference/Campbell Diagram
• Forced Response: Dynamic Torque, Shear Stress, Torsional
Oscillation, and Heat Dissipation
• Nonlinear Stiffness Couplings
• Viscous Dampers
• Standard Gearboxes and Epicyclic Gears
• Variable Frequency Drives
• Multiple Compressor Load Steps and Speeds
• Combined Response of Multiple Orders or Excitation Sources
• Determining and Comparing Results to Allowable Levels
• “Non-Ideal” Operating Conditions: Engine
Misfire and Compressor Valve Failures
• Transient Events: Synchronous Motor Start-up, Electrical
Fault, and Loaded Shutdown of Reciprocating Compressor
• Rainflow, Fatigue Damage, and Allowable Number of Events
|
