Using ultrasonic to detect leaks

Compressed air and steam are key features of manufacturing processes across the majority of industries.

They have many varied applications at different stages of production, from cooling, heating and cleaning to hydraulic lifts and tools.

When margins are tight and productivity key, it therefore makes sense to pay careful attention to the costs associated with these processes. 

Most leaks are small in nature, which makes them both difficult to detect and easy to overlook or, in some cases, simply to ignore. But the energy wasted as a result of them can be significant. When considered collectively over the course of a year they can cost tens, if not hundreds, of thousands of pounds. 

To ignore them is to ignore the potential for quick-win operational efficiencies, improved safety, extended equipment lifespan and long term cost savings.

Leaks can be caused by a range of problems typical to any plant, including pipework corrosion, vibration from unsupported pipework, or insufficiently tightened fixings. But the end result is the same. The compressor runs less efficiently, more pressure is placed on the motor running it, so more energy is needed to maintain continuous production. 

Compressed air leaks

In a typical plant that has not been well maintained, the air leak rate may equate to between 20 and 30 percent of total compressed air production capacity. The financial impact of these leaks can accrue significantly over time.

As one example, based on 100psi, at a cost of £7/million per m³ for one year (8,760 hours), a leak as small as 0.16cm can cost £846.00 annually. By doubling this to 0.32cm, the cost jumps to £2,721 annually. That’s just for one leak – imagine if a plant had ten leaks, or 50 leaks? This really is not an uncommon situation.

In addition to being a source of wasted energy, air leaks cause a drop in system pressure, which can make air tools function less efficiently, adversely affecting production. By forcing the equipment to run longer, leaks shorten the life of almost all system equipment, including the compressor package itself. Increased running time can also lead to additional maintenance requirements and more frequent unscheduled downtime. 

Steam leaks

Steam leaks are typically found at valve stems, pressure regulators, connection flanges and pipe joints. If ignored, they can contribute to a drop in system pressure, resulting in heat loss and lower operating efficiency. At a pressure of seven bar (100psi), a cavity measuring just 3mm can cause the loss of 25,000 kg of steam per annum. Multiplying this by a typical steam production cost of £5.30 per kilogram would incur a loss of £132 a year. Considering that leaks are often not limited to one point of emission gives some measure of the potential for significant annual costs across a plant. 

Leak detection using ultrasonic detection techniques

Detecting leaks by normal visual or audible methods can be ineffective, especially when the leaks are small and set in the context of a noisy plant environment. 

Ultrasound circumvents both these barriers to pinpoint emissions and prevent small leaks from turning into big financial losses.

During a leak, liquid or air moves from a high pressure to a low pressure and as it passes through the leak site, a turbulent flow is generated. This turbulence has strong ultrasonic components and typically the larger the leak, the greater the ultrasound level. 

Ultrasound is a high frequency, short wave signal and the intensity of the ultrasound produced by a leak drops off rapidly as the sound moves away from its source. The sound will therefore be loudest at the leak site. Both steam and air leaks can be located, via both the atmosphere and solid surfaces, using a simple handheld portable ultrasonic detector. This electronically translates ultrasound frequencies down into the audible range, where they are heard through headphones and observed as intensity and/or decibel (dB) levels on a display panel. 

The more advanced digital instruments contain onboard sound recording to capture sound samples for spectral analysis, providing both visual and audible reporting. They are connected to data management software, so the logged data can be downloaded to a computer for analysis. 

The benefits of ultrasound

Energy efficiency should be a key focus for any company keeping a close eye on both the bottom line and its commitment to International Standards Organisation (ISO) 50001 standard for energy management systems. Unidentified leaks can be their silent enemy, nudging up energy use imperceptibly by reducing the efficacy of equipment, while at the same time diminishing its reliability and adding to the risk of unscheduled downtime and generating avoidable maintenance costs.

Ultrasound roots these bad actors out. Because the high frequency ultrasonic components of leakage sounds are extremely short wave in nature, and a short wave signal tends to be fairly directional and localised, it is easy to separate them from background plant noises and to detect their precise location. 

This directional element also means that subtle changes in mechanical equipment can be detected early, before a machine gets to the point of failure. Pre-emptive action can be taken at the first sign of a leak, meaning energy loss is kept to a minimum and the risk of unscheduled downtime is reduced.

A comprehensive overview of operations is central to any effective condition based maintenance programme. The visual and audible reporting offered by digital ultrasound allows for enhanced diagnostics and intelligent decision-making. Users are able to review test results, compare current data with baseline data and trend changes. The reports produced can be shared widely and speedily, promoting a more cohesive approach to condition based maintenance programme.

The range of diagnostic and analytical software tools offered by digital technology can also keep users informed of the savings generated through compressed gas surveys and steam surveys, so they can evidence their savings in energy and carbon gases – a particular bonus for companies involved in carbon trading.

One US company recorded more than $56,000 savings in the course of just a few months after identifying and remedying compressed gas leaks, with the cost of those repairs amounting to little over $7,000.

Advances in ultrasound technology over the past decade mean it can be used as both a ‘stand-alone’ inspection method and as an effective CBM screening tool for bearings monitoring and other electrical and mechanical applications. What all have in common is ease of use, faster and more efficient reporting and greater insight into the condition of assets and what action is required to optimise their performance and reduce unnecessary expenditure.

Perhaps the simplest analogy for the financial advantages this presents is that of fitting loft insulation in the home. The energy efficiency benefits may not be instantly obvious - but just a few months down the line the savings are certain to be strongly in evidence.