Simply defined, noise is unwanted sound. Efforts to manage noise in industrial spaces range from hearing protection for workers to blocking, breaking, absorbing, or isolating the noise at the source. Beyond managing noise in industrial processes, businesses have historically sought to reduce noise by adaptive measures such as installing absorptive panels on walls, hanging baffles, or mounting sound absorbing materials on ceilings.
More enlightened approaches to reduce noise levels include following guidelines by the National Institute for Occupational Safety and Health’s (NIOSH’s) Buy Quiet website and consulting the NIOSH purchasing roadmap to inform the purchase of low-noise equipment. Selecting equipment with lower noise levels is a highly effective solution that makes good economic sense, considering that if equipment operates more quietly, little or no future investment will be required to address sound level safety concerns. A common approach for addressing equipment noise is to build an enclosure around it, such as the industrial enclosures surrounding compressor stations, to trap sound and hinder its opportunity to emit into surrounding areas. If the enclosure does not prove effective, a next step may be adding absorption around the equipment. However, this approach can present other issues if the absorptive strategy interferes with cooling of the equipment.
While managing noise is a concern in many environments, the challenge can be more complex in industrial spaces where it is essential to both protect hearing and assure good communication. OSHA requires hearing protection be provided for employees when the noise level rises above 85 dBA for an eight-hour time weighted average. After six months, a company must initiate a hearing conservation program to monitor the hearing of employees. Reducing noise levels helps address concerns about hearing damage risk to employees and improves communication. Good communication between workers also supports safety.
A good starting place for noise reduction is to target the source. If “buying quiet” is not feasible or practical, applying principles of noise control can help reduce noise. Creating enclosures to block noise emission from machinery is an effective approach. For building fixtures, such as pipes, applying a similar design to reduce emitted sound is necessary to drive the reduction of noise level across the space. Jacketed pipe insulation is one of the essential tools for managing noise levels in an industrial space.
This treatment strategy consists of layers of absorption and blocking materials to minimize the transmission of sound from the piping to the surrounding spaces.
Assessing Treatment Performance
A best practice when it comes to installing noise control materials is to always keep in mind that the closer the noise control is to the noise source, the better it will perform. The performance of jacketed pipe insulation is evaluated by identifying how much sound energy is lost when the system is installed on a pipe. This is called “insertion loss,” and it is the difference in sound level in a laboratory test chamber with the untreated pipe and the pipe with the treatment installed. Improving insertion loss is a systemic design consideration that is integral to reducing industrial pipe noise. Taking the octave band values for the insertion loss and comparing them to the classification table provided in ISO 15665, for the diameter of pipe tested, will identify what class of pipe insulation (A, B, C, or D) to install. Pipe insulation classes range from a minimum (A) to a maximum (D) performance rating.
ISO 15665 is the industry standard for testing an insulation’s acoustic performance. However, applying this testing standard to a design can be extremely costly and the cost has limited the number of tested acoustic assemblies. These challenges inspired Owens Corning researchers to develop and test a model to help accurately estimate the performance of single and multilayered jacketed pipe insulation.
32 Tests Assess Insertion Loss Strategies
As much of the existing jacketed pipe insulation insertion loss data in the market is based on prescriptive designs identified in the ISO 15665 standard, Owens Corning conducted a range of tests, which expanded the number of designs available in the market. The testing included 32 combinations of mineral wool and cellular-pipe insulation, including loaded vinyl and jacketing in high- and low-temperature settings. Thirty-two acoustic studies performed at globally renowned research centers in Poland and the Netherlands show that a newly developed model integrating statistical and theoretical components can improve the acoustical performance of industrial pipe insulation. Such modeling can help inform acoustic solutions to reduce industrial pipe noise and inform new design strategies to improve acoustic performance. The model for predicting insertion loss findings and key insights from the research studies will be presented during the 50th International Conference and Exposition on Noise Engineering (inter.noise 2021) in August.
To appreciate the improvements in insertion loss, it is helpful to be aware of the testing standards used to evaluate the insertion loss of different diameter pipes. ASTM E1222 Laboratory Measurement of the Insertion Loss of Pipe Lagging Systems utilizes a closed-end pipe with a minimum diameter of 12 inches (305 mm) to identify the insertion loss of the pipe insulation versus frequency. ISO 15665, “Acoustic Insulation for Pipes, Valves, and Flanges” describes both testing for insertion loss using a pipe that transitions through a test chamber with no end reflections. This standard classifies the pipe insulation via a rubric and also prescribes several types of treatment for each class for three sizes of pipe diameters up to 1,000 mm (39.5 inches).
Three Research Takeaways
Takeaway 1: Models can provide fast and accurate design solutions — The testing reinforced the investment of large amount of time and resources, including cost, to develop new designs. An initial statistical model of the data afforded the opportunity to create a simple statistical model to predict performance that accounted for almost 95% of the variation between tests. Modeling is an attractive tool to inform a design strategy because so many designs can be tried at little to no cost. The combined use of a statistical and theoretical models’ prediction of insertion loss was very good. However, the statistical model applied on its own was only successful 66% of the time at predicting classes of insulation per ISO 15665. This prompted the development of a theoretical model based on the material properties used in the designs.
Takeaway 2: Utilizing a theoretical model can improve the accuracy of the prediction — Applying a theoretical model improved the predictive accuracy to describe nearly 98% of the variation between the 32 designs tested. Researchers applied well-known, widely understood theoretical techniques in an Owens Corning proprietary model for layered porous systems. The theoretical model utilizes material test data to account for the impact of the materials used in the design, providing greater accuracy. The end result is that the theoretical models focus on the properties of the materials that drive change. This also explains why the model results described almost 98% of the variation between tests. The remaining 2% is suspected to be related to the conditions surrounding testing and the limitations of testing in a laboratory. The approach got the classification per ISO 15665 correct 90% of the time.
Takeaway 3: Findings on insertion loss can improve future pipe insertion assemblies — Researchers at Owens Corning have already expanded the use of the model by validating it for the largest diameter of piping described in the ISO 15665 standard. There are very few options available for this range of diameters. In fact, an acoustics lab in the Netherlands was the only resource available to conduct tests on the large diameter pipes. The model has already provided insight into the interactions between each layer of the designs and will continue to help refine designs to optimize future performance to manage insertion loss. Expanding the number of designs available in the market offers owners, operators, and installers significantly more options for lowering the noise levels in the industrial environment.