Ultrasonic Leak Detection in Pneumatic Networks: Audit Methods and Energy Efficiency Calculation

1. Introduction

Compressed air is one of the most expensive energy carriers on an industrial site. According to European research data, up to 30% of the electrical energy consumed by compressor stations is lost due to leaks in the distribution network, valves, and actuators. For Ukrainian industrial enterprises operating under conditions of constant increase in energy carrier tariffs, minimization of these losses is a critical task for reducing product cost and increasing overall energy efficiency in accordance with the requirements of standard ISO 50001.

Traditional methods of detecting leaks, such as soap solution or acoustic listening "by ear", have low efficiency in large-scale production and do not allow for quantitative assessment of losses. Modern engineering practice relies on the use of active and passive ultrasonic testing. This method is based on the registration of high-frequency vibrations (in the range of 20–100 kHz), which are created by turbulent air flow passing through micro-defects in the walls of pipelines or seals.

2. Fundamental Principles

When a pressurized gas flows through an opening into the surrounding environment, the flow transitions from laminar to turbulent. Turbulence generates a wide spectrum of acoustic waves, including a significant component in the ultrasonic range (over 20 kHz). Unlike low-frequency sound waves (audible to humans), ultrasonic waves have two important advantages for industrial monitoring:

• Directionality: high-frequency waves propagate in a narrow beam, allowing the operator to clearly identify the source even in a noisy workshop environment.
• Згасання: фоновий шум важкого машинобудування (робота пресів, верстатів з ЧПК, транспортерів) концентрується переважно в низькочастотному діапазоні (до 10 кГц), тому ультразвукові детектори ефективно відсікають цей шум за допомогою гетеродинного перетворення частоти.

The physical model of leakage is described by Bernoulli's law and the equation of gas flow through a throttling orifice. The volumetric flow rate ($Q$) depends on the system pressure, the diameter of the defect and the flow coefficient:

Where $C_d$ — discharge coefficient (usually 0.6–0.8 for sharp edges of microcracks), $A$ — area of the defect cross-section, $\\Delta P$ — pressure drop, and $\rho$ — air density. The ultrasonic detector measures the amplitude of the signal in decibels (dB), which is proportional to the intensity of turbulence and, accordingly, the level of compressed air loss.

3. Technical Specifications and Standards

Conducting pneumatic network audits and operating measuring equipment should be governed by current international and national standards:

• ISO 50001:2018 — Energy Management Systems. Requirements and guidance for use.
• ISO 11011:2013 — Compressors and pneumatic systems. Energy audit. Defines the methodology for measurement and calculation of compressor equipment efficiency.
• ASTM E1002 — Standard Test Method for Leak Detection Using Ultrasonic Devices.
• DSTU EN 61326-1 — Electrical equipment for measurement, control and laboratory use. Requirements regarding electromagnetic compatibility (EMC).
• Technical Regulation on Measuring Instruments Subject to Legal Regulation (approved by the Decree of the Cabinet of Ministers of Ukraine No. 94).

For industrial enterprises, the cleanliness class of compressed air is determined according to the standard ISO 8573-1. The presence of leaks is often accompanied by a pressure drop, leading to delayed actuation of pneumatic cylinders and disruption of the equipment operation cycle diagrams.

4. Selection and Dimensioning of Equipment

Selection of an ultrasonic detector is based on the technical characteristics of the device and the operating conditions in the workshop. Modern devices are divided into contact types (with a probe) and non-contact types (with a parabolic reflector or acoustic chamber).

Selection criteria for the reliability engineer:

1. Availability of CE certification and compliance with UkrSEPRO standards (if required).
2. Degree of protection of the housing is at least IP54 (for heavy workshop conditions — IP65).
3. Quantitative assessment of leakage (conversion from dB to liters per minute or cubic meters per hour).

5. Best Practices for Installation and Audit

Conducting a pneumatic network audit requires a systematic approach. Incorrect methodology will lead to false results and unjustified time consumption.

• Pre-planning: divide the plant into zones (compressor station, main pipelines, workshop distribution, end users).
• Conditions of execution: perform the audit during working pressure in the system (nominal pressure is usually 6.0–8.0 bar). It is preferable to carry out the check during planned shutdowns or in non-working shifts to reduce the level of workshop noise.
• Scan Angle: position the sensor at a 45 degree angle to the pipeline surface for maximum capture of reflected waves.
• Recording of results: each detected leak must be marked with a unique tag number, photographed, and recorded in the defects log with an indication of the estimated volume of loss.

Company UNITEC-D GmbH recommends conducting a full audit of pneumatic systems no less frequently than twice a year, combining it with scheduled technical maintenance of distribution collectors and shut-off valves.

6. Typical Faults and Root Cause Analysis (RCA)

Analysis of the causes of leaks allows eliminating the problem itself, not only its consequences. Below are the main types of defects in pneumatic networks:

• Wear of quick-disconnect fittings: Occurs due to mechanical damage to the sealing rings made of butyl-nitrile rubber (NBR) or fluororubber (FKM). Visual indicators: stem play, oil or dust traces around the coupling.
• Corrosion of metal in carbon steel pipelines: Occurs due to insufficient effectiveness of air dryers (dew point higher than +3 °C). Visual indicators: presence of moisture in lower drain points, whistling sounds in weld zones.
• Leakage from threaded connections: Caused by cyclic vibrations from compressors or process equipment. Failure of sealants or Teflon tape.
• Condensate trap failure: Mechanical float valve clogging causes continuous discharge of compressed air to atmosphere together with condensate.

7. Predictive Technical Maintenance and Condition Monitoring

Integration of ultrasonic testing into the Condition Monitoring (CM) system allows transition from reactive maintenance to a Predictive Maintenance (PdM) strategy. Continuous monitoring of valve condition and pneumatic lines reduces the MTTR (Mean Time to Repair) and increases the MTBF (Mean Time Between Failures).

Recommended measures:

• Installation of stationary ultrasonic sensors on critical mainline sections for automatic notification of sudden pressure drop or appearance of new noises.
• Periodic pressure drop monitoring during night technological breaks using digital pressure sensors with data logging capability (data loggers).
• Use of thermography in combination with ultrasonic testing for checking the tightness of shut-off valves (temperature difference at the inlet and outlet of closed valve indicates leakage).

8. Comparative matrix of seal integrity testing methods

9. Conclusion

Ultrasonic leak detection of pneumatic systems is a mandatory element of modern industrial operation. Regular audits and leak elimination allow reducing the electricity consumption of compressor stations by 10–25%, ensuring a quick return on investment in measuring equipment (usually less than 6 months). For selection of certified components, valves, seals and pneumatic elements of European quality, visit our electronic catalog.

Go to the electronic catalog of UNITEC-D GmbH for selecting industrial components

10. References

1. ISO 50001:2018. Energy management systems — Requirements with guidance for use. International Organization for Standardization.
2. ISO 11011:2013. Compressed air — Energy efficiency — Assessment. International Organization for Standardization.
3. ASTM E1002-11. Standard Test Method for Leaks Using Ultrasonics. ASTM International.
4. ISO 8573-1:2010. Compressed air — Part 1: Contaminants and purity classes.
5. Technical materials and energy efficiency recommendations for pneumatic systems Festo AG & Co. KG and SMC Corporation.