Compressed air is one of the most expensive and essential utilities to many industries. Often, it costs more than does many of the uses of electricity, natural gas or water in maintaining and operating a plant. Yet up to a third of that compressed air is lost annually due to leaks and inefficiencies. Ultimately, finding and fixing leaks is vital to lowering costs, operating efficiently and reduc­ing the organization’s carbon footprint while potentially improving key stakeholder and investor relations.

Preventing wasted energy

Leaks are a large source of wasted energy for compressed air systems, and according to the Office of Energy Effi­ciency & Renewable Energy, those leaks approximate 20-30% of the total air compressor output within a facility. Further, leaks contribute to system operation problems such as fluctuating system pressure, which can cause air tools or air-operated equipment to func­tion less efficiently and possibly affect production. Unknown leaks may also require excess compressor capacity, potentially requiring additional compressors that may otherwise be uneeded, resulting in higher-than-necessary costs. They can also lead to decreased service life while increasing maintenance needs due to unnecessary cycling and increased run time.

Figure illustrates how microphones impact the ability to ‘see’ problems. Courtesy: Teledyne

Alongside energy and resource preservation, costs can be lowered significantly through proactive leak detection. The Office of Energy Efficiency & Renewable Energy conducted a study at a chemical plant that undertook a leak-prevention program following a compressed air audit, proving how plant costs can be lowered significantly through remediation efforts. By remediating just the 10 largest leaks found at the plant, operators could generate 70% of the overall potential cost savings.

To improve energy standards, reduce excess waste and align with regulatory, tax and investor expectations. Many industrial organizations are also looking to align with ISO 50001 energy management standards. Like other ISO management system standards, ISO 50001 certifica­tion isn’t mandatory, but it does require organizations to develop policy for more efficient energy use. This includes fixing targets and objectives to meet the policy; using data to better understand and make decisions about energy use; measuring the results; reviewing how well the policy works and continually improving energy management. When organization leaders decide to implement these standards it empowers them to understand the organi­zation’s respective carbon footprint and show external parties and investors that the business has implemented an effective energy management system.

Find the detection method

Whether an organization plans to implement ISO 50001 or simply wants to improve plant efficiency for cost savings, identifying compressed air leaks is vital, but they can be particularly tricky to identify in a noisy manufacturing environment. Therefore, identifying the most appropriate methods or tools for the situation is crucial to a successful program.

Soap bubble test

The traditional leak detection tool is a specialty soap solution, which entails saturating a suspected leak area with an approved soap solution. Simply stated, if a leak is present the soap will begin to bubble. This method works if the leak site is known and the system is well pressurized. However, in cases where the leak site is unknown, this can be a cumbersome process where operators may need to apply the solution to the entire suspected piece of equipment in hopes of pinpointing the leak. Therefore, soap bubble tests can become time consuming and messy without necessarily providing suf­ficient data to confirm accurate leak sizes and flow rates.

Single microphone leak detection

Ultrasonic (acoustic) leak detectors offer a solution that can detect leaks using a single microphone system operating around 40 kilohertz (kHz). This method relies on “heterodyning” to enable the operator to distinguish between noise generated by the leak and background noise. Heterodyning converts high fre­quency noise to lower, audible frequencies, which the operator must be trained to recognize based on the sound characteristics. The microphone is scanned back and forth over the process piping being inspected until a suspected leak is found and measured. False alarms on non-existent leaks and missing actual leaks can be common for inexperienced inspectors. Furthermore, manually moving the microphone around equipment to locate leaks can be time consuming and may put the operator in harm’s way. In addition, this system requires significant training time to master.

High-definition acoustic imaging

High definition (HD) acoustic imaging devices that rely on a series of specialized integrated microphones can be up to 10 times faster at detecting leaks compared to tradi­tional methods, such as the soap bubble and single-micro­phone ultrasonic options. Generally, the higher number of microphones, the better the acoustic performance. The optimal choice in this case would be MEMS (microelec­tron mechanical systems) microphones, which are small, consume less power and provide better performance and stability than other systems.

HD acoustic imaging provides precise acoustic imag­es that visually display ultrasonic information, even in loud environments. Images are transposed in real time on top of a digital camera picture, which allows for pinpoint accuracy of the sound source. Depend­ing on the tool, it can be equipped with networking capabilities that automatically save images to the cloud for post-inspection review and processing. This allows for easy access to stored files and easier separation of sound sources for a deeper analysis and classification of the problem back at the office. When paired with a regular maintenance routine, acoustic imaging can help facilities save money on utility bills and delay the potentially large capital expense required to replace compressors and other related equipment.

Some handheld devices only require one hand to operate along with the ability to conduct accurate assess­ments more than 100 meters away for safe problem detection and analysis, further improving safety and convenience. Operators can conduct a quick scan of large areas from a safe distance without the need to physically touch machinery or shut down the production line.

Leaks in noisy environments

Noisy plants and manufacturing environments can make it nearly impossible to detect a leak with the human ear, so frequency range is crucial to leak detec­tion technology. The most effective frequency range for detecting compressed air leaks is between 20 and 30 kHz, as that range aids in distinguishing compressed air leaks from the background noise in a plant envi­ronment. The amplitude of machinery noise typically peaks below 10 kHz and trends down to zero at 60 kHz, and since there is a greater difference between air leak noises and background noises between 20-30 kHz compared to higher frequencies, it’s easier to detect the air leak in this range.

Air leak noise versus background noise compared to find the optimal frequency in a noisy environment. Courtesy: Teledyne

Nevertheless, background noise interference can still be an issue. In this case, devices must be able to differenti­ate sound sources that resemble a leak from other inter­fering sounds. The majority of acoustic cameras on the market require the user to manually filter out interfering noises using sliders to change the frequency range, but the ideal device can automatically detect sound patterns that resemble those of air leaks and remove interfering noises for both single and multiple sound sources using advanced on-camera, AI-based filters. In essence, these devices can recognize whether the sound resembles an air leak or background noise, without manual user interven­tion, much the same way people are able to distinguish the same note played by two different instruments.

Microphone quantity also plays a large role in leak detection – specifically with very high frequency sound sources. To accurately hear these sounds, acoustic cam­eras must have a multitude of microphones, preferably close to each other, otherwise issues of spatial alias­ing will occur, leading to erroneous results and sound sources displayed at improper locations.

An illustration of detection range loss at different frequencies. Courtesy: Teledyne

Long-term benefits

Beyond cost savings, HD acoustic imaging provides organizations with an effective tool to mitigate inef­ficiencies, reduce the overall carbon footprint of plant operations and improve the safety of personnel who operate and test air compression equipment.

Ultimately, preventative leak detection measures can play a vital and strategic role in the sustainable future of manufacturing environments. Compressed air leak repair and mitigation can be a fast way for organizations to reduce energy consumption and enjoy the requi­site cost and safety improvements. With energy being one of the largest controllable operating expenses for organizations using industrial compressed air systems – resources, time, money and key stakeholder relation­ships can all be safeguarded.

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