Seeing air system leaks with sonic imagers

• By Javier Irazola
• July 30, 2020
• Automation Basics

Summary

By Javier Irazola

An estimated 30 percent of compressed air is lost to unrepaired leaks. That means a loss in air pressure, which can lead to reduced productivity from underperforming pneumatic tools, faulty air handling units, and other industrial equipment. Neglected leaks can, over time, lead to unplanned downtime. To repair compressed air system leaks, you need to detect the leaks, prioritize the leaks based on their ability to impact production, and quantify the costs of each leak to determine savings.

Sonic imaging technology combines acoustics and imaging to create a visual representation of the sound of air leaking, so leaks can be easily found and quickly fixed.

Detecting the leaks

Part of the reason air leaks are a big issue is because they are hard to find. Air leaks can occur anywhere within a compressed air, gas, or vacuum system, including in couplings, hoses, fittings, pipe joints, quick disconnects, condensate traps, and valves. Even when found and fixed, new leaks keep popping up—a fact of life due to the wear and tear on equipment over time.

Because it can be so difficult to find air leaks, most facilities just accept them as a cost of doing business. And while it may not be possible to eliminate all leaks, it is possible to substantially reduce their number.

That is where a sonic industrial imager provides its greatest value, and where the future of leak detection is headed. Traditional leak detection methods still work, but they come with challenges and deficiencies. None of these methods is foolproof, and most require downtime, which means lost time and money.

• Sound: Hissing indicates a sizeable leak, since a decibel level of greater than 60 is audible without equipment. Because most plants are noisy and often require worker ear protection, listening for leaks must occur during downtime—between shifts, on weekends, or during scheduled maintenance.
• Sound and soap: Technicians spray soapy water on areas of audible leaks, and where bubbles appear is the leak spot. The method is protracted, far from precise, and requires cleanup, since soapy water overspray creates a slipping hazard.
• Ultrasonic acoustic detection: During downtime, technicians wearing earphones scan potential leak spots with a parabolic dish or cone-shaped accessory. When a leak-indicating noise is detected, the technician switches to a wand-shaped device that must be held a couple of inches from the leak to pinpoint the exact location.
• Using outside experts: Engineers or other experts are engaged, usually once a year to save money and disruption. They use one or all of the traditional techniques, and in-house technicians handle repairs and checks.

Today, a leak detection technology called sonic imaging has radically altered the leak detection process. Technicians can now see their leaks. This technology, introduced in 2019, is in a handheld sonic industrial imager that uses an array of tiny supersensitive microphones to detect sounds both in the human hearing range and in the ultrasonic range. The output is a visual representation of sound. Most users can get up to speed with the easy point-and-shoot imager in about 10 minutes, regardless of how little experience they have with leak detection.

Users simply scan the area of interest, and the imager applies proprietary algorithms to the identified sounds. The result is an instant, visual map of the leak. The map is layered over a visible light image of the area, so users can quickly pinpoint the location of the leak and tag it or repair it on the spot. After repairing the leak, the technician can use the sonic imager to instantly verify the repair. Scans can be saved as images or video to be a reference for future discussions with colleagues or supervisors.

The sonic imager can visually scan large areas from more than 10 m (33 ft) in heavy noise conditions and detect leaks from up to 100 m in low-noise conditions. This allows technicians to work very quickly and from a safe distance while equipment is running. It also makes it easier to find leaks in hard-to-reach areas, like behind equipment or in overhead pipes, and to distinguish between multiple leaks in the same area. The captured images eliminate the need to climb a ladder to tag the leak, because the location of the leak is clearly identified on the image.

Prioritizing the leaks

Depending on the size of your compressed air system, you could have anywhere from tens to thousands of leaks at any given time. Just like with other assets, leaks should be prioritized for fixes based on their ability to affect the bottom line.

A criticality analysis would likely classify your compressed air system as a “star athlete.” This means that the compressed air system directly determines the company’s ability to win, and by how much. Beyond simple uptime and downtime, there is a direct relationship between each percentage of incremental performance and the incremental revenue of the company. This is where maintenance must be at its peak.

To prioritize leaks, then, you need to know how big they are. How much air is leaking depends on the size of the hole the air is coming from, as well as a few other factors, such as compressor pressure and backpressure.

Sonic industrial imagers come with LeakQ technology that allows the user to estimate the size of detected leaks. Although there is no mathematical way to obtain a flow rate out of its sound signature, the LeakQ flow estimator might provide the best guidance. The way LeakQ estimates is mostly empirical, based on average sound generated by average leaks. Many leak types were measured at different flow rates and at different pressures, then a regression model was created to estimate the flow rate out of a decibel measurement.

In LeakQ mode, you position the leak within the circle on the screen. You will see the distance you are from the leak and the severity scale of the leak. It is very easy and straightforward. In this mode, you can also add notes, tags, and more for sharing with others. With this information in hand, you are now able to prioritize which leaks should be fixed first.

Quantifying the costs of the leaks

For production companies that start using the sonic imager, early results validate energy savings. One plant saw a near 26 percent recovery in compressed air capacity and close to $49,000 in annual electrical energy savings—based on their total installed capacity of air compressors equaling 330 horsepower. Before using the sonic imager to inspect for air leaks, the plant ran four compressors close to full capacity. After a one-day inspection, the technicians found and repaired more than 130 leaks. Now the facility can handle most of its compressed air needs with just three compressors.

How do you identify the cost savings? You can develop a detailed report to estimate your total cost savings, should you repair identified leaks. To create such a report, you simply upload the LeakQ images from the sonic industrial imager into the reporting tool and add some information about your system, such as:

• gas type
• pressure in pounds per square inch (psi)
• cost of gas per standard cubic feet (SCF)
• cost of electricity per kWh
• ratio of power to flow rate in kW per 100 cubic feet per minute (CFM)
• operating hours per year.

With this information, you can generate a report that will include detailed information about the leak costs as a whole and individual leak costs.

Why is this information important? One reason is that it provides a solid return on investment argument for the purchase and use of the sonic industrial imager. Another is that it can be used to show successful efforts made toward meeting plant efficiency and cost-savings goals.

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