Finding the Source of All that Noise(1)

Processing plants today do everything they can to increase efficiency and productivity. Frequently, that involves operating at higher temperatures, pressures and flow rates, which means higher pressure differentials across critical control valves as well other conditions that generate more noise. While this noise has always been a problem, it is even more so in today’s high-throughput processing plants.

When this cacophony is generated by air and other gases flowing through valves and piping systems, it is called “aerodynamic noise.” Aerodynamic noise is not only annoying, it also presents a health threat that may be subject to a variety of regulations. Most of those regulations limit maximum allowable noise levels to less than 85 decibels (dBA).

Even beyond the health and annoyance factors, aerodynamic noise causes problems. Such noise can generate substantial shock and vibration that can damage or alter the performance of control valves and instrumentation, degrading their performance and shortening maintenance intervals. This damage starts to occur at sound pressure levels in excess of 100 dBA.

Damage from acoustic shock and vibration can be minimized through the use of robustly designed valves, piping and instrumentation. But even these robust configurations should not be subjected to noise levels predicted to exceed 110 dBA.

In short, aerodynamic noise is a significant problem on many levels that need to be addressed. This can be accomplished by limiting the factors that generate the noise (called a source treatment), dampening the noise that has already been generated or a combination of those two solutions. The most cost-effective approach is to limit the level of noise through meticulous valve sizing and piping configuration design. However, that’s not always going to happen—valves are sometimes improperly sized, and unanticipated conditions arise that can result in surprising levels of noise.

When the horse is already out of the barn and making a racket, it may be expedient to use path abatement procedures, rather than trying to redesign the system and replace most of the noise-generating components. If a great deal of noise is generated, however, the best approach might be to determine the most cost-effective combination of source abatement and path dampening. To do this requires finding a way to analyze control loops to accurately determine how much noise will be produced or abated by various source and path treatment options.

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