Natural gas pipelines tend to produce loud noise as gas flows through pressure regulating valves. This is usually not a problem in isolated locations, but when neighborhoods develop or expand nearby, it becomes a pressing issue.
Our article in the January 2024 issue of Pipeline & Gas Journal, titled “New Alternatives for Noise Reduction in Gas Pipelines,” describes the difficulties of pipeline pressure reduction, and it discusses a new noise abatement solution employed successfully by a large utility company.
Pressure reduction and noise
Gas pressures typically exceed 800psi during transport, far too high for most consumer applications. To reduce pressure to an appropriate level, gas flows through one or more pressure control valves at a station near the point of use.
As natural gas passes through the restricted portion of the control valve, the pressure decreases, and gas velocity increases significantly. This turbulent flow generates noise that travels down the pipeline, radiating in all directions.
Noise levels can reach 110 dBA or more and create vibrations that induce metal fatigue, shortening valve life and posing reliability concerns. At lower levels, noise is generally not a mechanical concern, but it can still be a nuisance for residential or commercial neighbors.
Noise control techniques
Utility companies have taken several approaches to noise control, each with tradeoffs. Pipe insulation and site enclosures reduce noise in the vicinity, but they cannot prevent noise from propagating downstream or damaging equipment.
On the other hand, low-noise valve trims reduce noise within the pipe itself by managing turbulent flow, but they restrict flow capacity and are more susceptible to plugging.
Building and switching between multiple pressure runs designed for different flow conditions is effective, but it requires a high initial investment, more maintenance, and lots of space.
Introducing modal attenuators
A gas utility in the Midwest explored these approaches as they set out to address noise complaints, but after investigating, they found issues with each option. To solve this problem, Experitec, an Emerson Impact Partner, introduced the company to Emerson’s Fisher WhisperTube™ solution.
The solution is called a modal attenuator, and it is composed of a number of carefully designed resonant cavities, surrounding a straight through, full bore screen.
Each cavity creates destructive interference for a specific set of frequencies, reducing total noise by 10 to 15 dBA, without any pressure drop and with low risk of plugging. The utility company design team calculated an expected noise reduction of 12 dBA, easily meeting their requirements, and with no reduction of flow capacity.
Sound level calculations were run on the same NPS 6 control valve at the same flow conditions. The modal attenuator provided a 12 db reduction of sound, with no pressure drop.
After implementation, overall noise levels fell below 85 dBA, reducing complaints and enabling stations to significantly extend intervals between maintenance outages. Since then, the company has incorporated the WhisperTube solution into their standard pressure reduction station design.
Valve vendors can help
High noise levels can hinder gas utilities in their efforts to provide safe and reliable service, as they pose a safety risk to workers, provoke customer dissatisfaction, may incur regulatory penalties, and adversely impact mechanical integrity and reliability.
If your application is facing noise challenges, the right valve vendor can provide the expertise to find an effective solution. Among the available options, modal attenuators are finding widespread use in a broad range of applications, and especially in natural gas pressure reduction applications.
Visit the Fisher™ 6060 WhisperTube Modal Attenuator on Emerson.com to know how you can achieve system noise reduction across a wide range of conditions without impacting the flow capacity or process.
