FEATURE BOILERS, PUMPS & VALVES Reducing waste, improving reliability

For plants using steam or compressed air in their processes, the energy waste due to leaks can be significant. Oliver Pogmore, of AVT Reliability, explains how ultrasonic detection techniques can help to reduce this waste and improve reliability


ost manufacturers use compressed air or steam in their processes,

from air cylinders for automation to clean-in-place procedures. Leakages are common and can be

caused by a range of problems typical to any plant, such as pipework corrosion or vibration. But the 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. Because these leaks are generally

small in nature, they can be difficult to detect and easy to overlook. But over the course of a year they can cost companies 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.

COMPRESSED AIR LEAKS In a typical plant that has not been well maintained, the air leak rate may equate to between 20 and 30 per cent of total compressed air production capacity - a cost which can accrue significantly over time. As an 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 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 or 50 leaks? Air leaks also cause a drop in system

pressure, which can make air tools function less efficiently, adversely affecting production. Leaks shorten the life of almost all system equipment,

creating additional maintenance requirements and more frequent unscheduled downtime.

STEAM LEAKS Steam leaks, if ignored, 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 25,000kg 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. Again, that’s for just one leak source. Detecting leaks by normal visual or

audible methods can be ineffective, especially when they 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. 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. Ultrasound roots out bad actors. The

high frequency ultrasonic components of leakage sounds are extremely short wave, and therefore tend to be fairly directional and localised, so it is easy to separate them from plant noise and detect their precise location. Subtle changes in mechanical equipment can be detected early and pre-emptive action taken at the first sign of a leak, keeping energy loss to a minimum. 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. Ultrasound can be used as a

‘stand-alone’ inspection method and as an effective screening tool for bearings monitoring and other applications. Perhaps the simplest analogy for the

financial advantages it 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.

AVT Reliability 10 SPRING 2019 | ENERGY MANAGEMENT 

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