The “cocktail party effect” is our impressive ability to focus our attention on one voice in a busy, noise-filled room. By filtering out a range of other stimuli, partygoers have no problems tuning into a single conversation and ignoring every other noise.
Vibration analysis systems are capable of the same thing. Used to detect faults in industrial parts, the systems take raw vibration data from components in a system and isolate individual frequencies to see where issues are taking place.
Each part generates its own unique frequency, which allows vibration analysis to distinguish each part across an entire vibration spectrum. With frequencies isolated for individual components comes the ability to look at the amplitude of each part’s independent vibration. This amplitude describes how strong the vibrations are.
But how does this work in practice? Something producing very low vibrations will show waves of very low amplitude. From here, you can detect whether or not the part is operating well. A healthy bearing, for example, should show little signs of vibration.
Piping systems are another application of vibration analysis, particularly for resonance prevention. Piping systems are often subject to vibration due to forces generated by compressors, pumps and engines, which cause the deck beams to vibrate.
To tackle this problem, it is important to understand the difference between two types of frequencies. First, there’s forced frequency, induced by internal pipe flow behavior such as pulsation, two phase or turbulence. This flow-induced vibration has the potential to cause damage to the piping systems.
Second, there is natural frequency. This describes the frequency at which a system tends to oscillate in the absence of any driving or damping force. Damping techniques such as the use of damping greases are used to dissipate energy in the system and reduce vibration.
One of the most common problems caused by forced vibration and natural frequency in a piping system is resonance. Resonance occurs when the vibration forcing frequency is at, or very close to, an acoustical or mechanical natural frequency of the system. Since most structures and piping systems have very little damping, the vibration amplitude becomes very high if resonance occurs.
This resonance will usually be at the lowest frequency of all individual frequencies in the system, causing adverse vibration that is detrimental to assets. This vibration can result in equipment damage, fatigue failure on process piping, and fatigue in small branch connections, including relief lines, instrumentation ports, nozzles, drains and valves.
Eliminating or isolating vibration sources is the obvious solution. However, rendering a plant piping system to a zero vibration level is not cost-effective as the fluid flow would have to be incredibly slow. Therefore, most process plant piping systems vibrate to some extent, although staying within acceptable vibration limits. In these scenarios, vibration analysis sensors are used to determine if a vibration is one to be concerned about, or whether it can be left alone.
Advanced vibration analysis sensors and software can also be used to assess piping system configuration and inform design improvements. From the results of vibration analysis, it may be deemed necessary to provide additional pipe support to prevent resonance between piping mechanical natural frequencies and the flow induced forced frequencies.
These new technologies are allowing managers to take a proactive approach to maintaining parts and systems in a plant.
By isolating frequencies — much like the cocktail party effect — plant managers are gaining valuable insight that informs maintenance decisions and piping configuration improvements.