Preventative maintenance through balancing vibration analysis

Turbine Technology

Preventative maintenance through balancing and vibration analysis

By Jerry Justice

October 2000

Have you ever had a dead battery in your car? Did you discover it right when you really needed to get somewhere? Do you wish you could prevent things like this from happening? The key word here is prevent.
Most of us take preventative measures in many areas of our day to day lives. We change the oil in our cars to prevent excessive engine wear and check the battery for its electrolyte level to prevent it from going dry and dying on us at inopportune times.
Structures and components on aircraft are inspected to prevent unexpected failures. An unexpected failure is bad. A catastrophic failure is...well, catastrophic.
There are limits set on how much wear, crack, leak, and a host of other common faults or malfunctions is acceptable. All these limits were established to prevent failures. We measure these inspection points with the tools we have available and base our repair, replace, or condemn decisions on the known factors, past behaviors, or experience by which those limits were set.
What if you had an automated means of detecting a failure before it happened? Would it be beneficial if you could say with reasonable accuracy that a component would probably fail within the next hundred hours of operation? Could you save money by removing and replacing a component for overhaul or exchange before it experienced a structural failure?
All these things can be accomplished. They have been routinely used with industrial machines for over 25 years! It began with vibration trending and predictive analysis. Industrial-based predictive maintenance now uses even more advanced techniques, which provide even greater odds of successful prediction and thus greater economy of operation.
In aviation today, vibration analysis and balancing have, to a great degree, been relegated to the task of reducing discomfort to passengers and crew caused by noise or to certify the engine as airworthy following overhaul or, in some cases, STC completion. While noise reduction is one great use of modern balancing and analysis tools, it falls well short of achieving the long-term benefits of vibration trend analysis and predictive based maintenance these tools are capable of. Balancing is still one of the best methods of reducing component stress and premature failure. Predictive maintenance can play an irreplaceable role in life extension and damage control. Leading edge technology available today can collect, analyze, and even predict useful component life based on various factors including vibration.

Predicting failure
The U.S. military is currently attempting to perfect prognostic hardware and software that will predict an impending failure with greater accuracy. If adequate warning is provided, logistics and planning requirements can be completed in a timely manner, thereby reducing spares inventory, preventing unexpected failures, and providing a basis for improving design and engineering techniques for components and processes. Trending may also be expanded to include oil analysis, ultrasonic, and thermographic, methods.

Trending engine performance factors
Engine performance factors may also be trended for tracking thermodynamic characteristics and other performance factors. Trending isn't a new science, but one that is just beginning to mature in the aviation arena. The following is a very basic synopsis of how a trending program works.