Leaks can appear almost anywhere in a plant—systems under pressure and systems operating in a vacuum fall under this category. Internal leaks can happen through steam traps and valves, whereas external leaks might happen in the condenser and heat exchanger tubes or in the atmosphere.

These frequently minute breaches are a sign of more serious operational problems, such as reductions in efficiency, safety concerns, and complete system shutdowns. And this is where ultrasonic leak detection comes in to aid with predictive maintenance operations.

How leaks occur

A substance is said to leak when it moves from one medium to another. In a pressure or vacuum leak, the fluid (liquid or gas) travels from the high-pressure side to the low-pressure side through the leak orifice. It creates a turbulent flow when it approaches the low-pressure area. The disturbances in the air molecules result in white noise, a combination of high- and low-frequency sounds.

The majority of plant settings typically have surrounding sounds that obscure this noise. Moreover, the audible component is a broader waveform. Consequently, it can appear omnidirectional, making it challenging to locate and identify the source of the leak.

Leaks in pressured systems, like compressed air or gas systems, produce sounds at frequencies higher than those audible to the human ear. Thankfully, ultrasonic air leak detection equipment can find and locate leaks even in loud plant environments. It utilizes cutting-edge sound emission technology to identify high-frequency vibrations in the medium or air at the leak’s source.

What determines whether a leak is detectable?

Leak detection with ultrasonic equipment is possible due to a number of triggers.

Turbulence

There are two forms of viscous flow: Laminar and turbulent flow. Laminar flow is described as “fluid flow in which the fluid follows regular or smooth paths.” Every location in the fluid experiences constant pressure, velocity, and other flow characteristics. On the other hand, turbulent flow is a fluid flow that exhibits erratically changing magnitude and direction at a particular point.

The majority of leak scenarios result in a turbulent flow. Therefore, ultrasound will identify turbulent flow rather than laminar flow, which is observed, for example, in air conditioning diffusers. However, in order to detect a leak, it is important to consider other factors to ascertain whether there is sufficient turbulence to generate “detectable” ultrasound.

Fluid viscosity

A fluid’s resistance to flow, or viscosity, is a measurement of the internal friction inside the fluid. For instance, water has a larger flow resistance than steam when comparing their viscosities. The fluid’s viscosity, the pressure differential driving the flow, and the leak path’s length and cross-section all affect flow through leak sites.

For example, air will leak through a leak site considerably more than a fluid like water or oil, even at the same pressure. It’s crucial to comprehend this in case you encounter a leak where the fluid has a high viscosity but insufficient pressure to cause a turbulent leak. For instance, converting a liquid into a gas will help locate an underground water leak much more easily.

Distance from the leak

The distance from the leak is another aspect that affects how easily it can be detected. The ultrasound signal’s intensity diminishes as one gets farther away from the ultrasound source. The relative power of a sound signal at a specific moment is referred to as its intensity.

Shape of the orifice

It’s crucial to keep in mind that a smooth aperture will not generate as much turbulence as a jagged orifice, regardless of the orifice size. The “reed effect” describes how an opening with numerous edges can alter fluid flow and increase turbulence. A “pinhole” leak will create more turbulence than a narrow “slit” opening, such as a thread route leak.

Pressure differential

The majority of leak tests have a serious problem with pressure differential. A pressure differential is produced when a leak’s pressure is altered, and the flow varies proportionately to the square of the absolute pressure difference. It’s crucial to take into account the viscous flow of the pressure differential acting over the leak when conducting airborne ultrasonic leak inspection.

Finding the source of the leak

Ultrasound is shortwave; thus, its amplitude decreases exponentially as the sound moves away from the source. In this case, the detection distance starts to matter. Finding a leak will be challenging if an inspector is unable to get close enough to identify it. Therefore, accessibility of the leak is crucial.

The closer an inspector can get to the leak, as long as it’s safe, the more likely it is that they will find and assess it. If there is a leak hidden behind multiple buildings, it will likely reflect off of them. The leak’s ultrasound is then sent in several directions, bouncing off of various objects and leaving the inspector perplexed as to where the leak is coming from. Ultrasound waves may occasionally strike materials that absorb sound waves.

The likelihood of the leak weakening and attenuating increases with the distance it must travel. As an inspector, you should approach the source of the leak, take out anything that is obstructing the flow, and utilize tools to help you reach it, including flexible probes, a parabolic microphone, or a contact probe for structure-borne noises that come from enclosed cabinets.

Make sure you follow all safety precautions in case of a leak in a restricted place. Any error might be lethal in these extremely dangerous situations.

Locating the leak

It might be necessary to use specialized modules, including flexible probes for scanning in difficult-to-reach areas, a close-focus module for close-up scanning, or a parabolic microphone for long-distance scanning. To find a leak sound, move the probe in all directions while starting at maximum sensitivity.

Track the source of the loudest sound. You may find it harder to determine the leak’s direction as the leak sounds louder as you walk. As you approach the region, lower the sensitivity and listen for the strongest leak signal. Investigate every possible leaky place nearby.

Anytime it’s hard to tell which way the leak sound is coming from, turn the sensitivity up for too-low sound or down for too-high sound. You have located the leak if the leak sound continues or gets louder; if it gets quieter, keep searching.

Conclusion

When utilized appropriately, ultrasonic devices can be quite effective in finding leaks and can make a significant contribution to energy-saving initiatives.