Compressed air leaks drain industrial facilities of significant energy costs year after year – and most go completely undetected. A single 3mm aperture in a compressed air line at 7 bar pressure can waste over $1,200 annually. Multiply that across the dozens or hundreds of connection points in a typical industrial facility and the scale of undetected waste becomes significant.
Ultrasonic leak detection fills critical diagnostic gaps that vibration analysis and thermography leave open. Vibration monitoring is highly effective at identifying rotating equipment faults. But it cannot detect compressed air leaks, steam trap failures, electrical partial discharge, or valve leakage – failure modes that silently consume energy and create reliability risks across facilities of every type.
This guide explains how ultrasonic testing works, where it fits within a modern condition monitoring program, and how to structure a sustainable testing program that delivers measurable energy and reliability improvements.
How Ultrasonic Testing Works
Ultrasonic testing detects high-frequency sounds produced by turbulent gas flow, friction, and electrical discharge. These sounds occur in the 20-100 kHz frequency range – well beyond the upper limit of human hearing, which stops at approximately 20 kHz.
Specialised instruments convert these ultrasonic signals into audible sounds that technicians hear through headphones. Visual displays show signal intensity in decibels, allowing technicians to quantify the severity of a detected condition and compare readings over time to track changes.
The four primary targets for ultrasonic acoustic emission testing in industrial facilities are:
Gas and air leaks – Turbulent flow through any aperture or loose fitting generates a characteristic broadband ultrasonic signal. The intensity of this signal correlates with leak size and system pressure.
Steam trap failures – A healthy steam trap discharges intermittently as condensate accumulates and releases. A failed-open trap passes steam continuously, generating constant high-intensity ultrasonic noise. A failed-closed trap produces no signal.
Electrical partial discharge – Corona discharge, tracking across insulation surfaces, and arcing between conductors all emit characteristic ultrasonic signatures. These electrical faults can develop long before thermal signatures become detectable.
Mechanical friction – Bearing lubrication failure and early-stage mechanical contact produce friction-based ultrasound. This is often the earliest detectable indicator of bearing deterioration, predating vibration signatures in many low-speed applications.
The directional sensitivity of ultrasonic instruments allows technicians to pinpoint fault locations accurately even in environments with significant background noise. Sound at lower frequencies from motors, fans, and process equipment does not interfere with the ultrasonic detection band.
Why Vibration Analysis Alone Leaves Gaps
Vibration monitoring is the cornerstone of most rotating equipment reliability programs. It is highly sensitive to bearing defects, misalignment, imbalance, and gear tooth wear. But it has fundamental limitations that ultrasonic acoustic emission testing addresses.
Compressed air leaks produce no vibration signature. A 10mm leak in a compressed air distribution header is completely invisible to vibration monitoring, regardless of how comprehensive the vibration program is.
Steam trap failures do not generate vibration that monitoring can detect. A failed-open steam trap wasting thousands of dollars annually in steam costs will not appear in any vibration route data.
Electrical partial discharge and corona – which can develop in motor windings, switchgear, and cable terminations months before catastrophic failure – produce no mechanical vibration. They are invisible to accelerometers.
For low-speed equipment operating below 100 RPM, vibration energy is often too low to generate detectable defect frequencies in bearing vibration spectra. Ultrasonic contact testing picks up the friction-based acoustic emissions from developing bearing problems that vibration analysis cannot see.
A facility with excellent vibration monitoring coverage but no ultrasonic testing may be unaware that 25% of its compressed air production is escaping through undetected leaks, that 20% of its steam traps have failed, and that two motor windings are showing early signs of partial discharge.
Compressed Air Leak Detection and Quantification
Compressed air is one of the most expensive utilities in industrial facilities. Generation costs typically range from $0.025 to $0.40 per cubic metre, depending on electricity costs and compressor efficiency. System leakage rates of 20-40% are common in facilities without active ultrasonic leak detection programs.
The ultrasonic leak detection process requires no system shutdown or pressure reduction. Technicians scan compressed air distribution systems, pneumatic equipment, valve bodies, and connection points with handheld instruments while the system operates at normal pressure.
The directional microphone of the ultrasonic instrument allows leak localisation from three to five metres away in typical industrial noise environments. As the technician approaches a detected leak source, the signal intensity increases, allowing the exact leak location to be identified and marked for repair.
Leak quantification converts the decibel reading from the instrument into a financial impact estimate:
- The decibel reading correlates to approximate leak orifice size
- Orifice size combined with system pressure calculates volumetric flow loss
- Flow loss converted to compressor load gives energy consumption from that leak
- Energy cost calculation yields annual financial impact
Modern ultrasonic instruments include built-in quantification software that performs these calculations automatically from the measured decibel value and user-entered system pressure and energy cost data.
A comprehensive survey of a medium-sized industrial facility typically identifies 20-50 significant leaks. Repairing them immediately after detection can reduce compressed air consumption by 15-35%. For many facilities, the energy savings from a single leak survey pay for the instrument within months.
Steam Trap Testing During Normal Operation
Steam traps are critical components in steam distribution systems. Their function is to discharge condensate while retaining steam. When they fail, the consequences are either direct energy waste (failed open, passing steam) or process efficiency loss and water hammer risk (failed closed, not discharging condensate).
Traditional steam trap testing methods often require partial or full system shutdown, or rely on temperature measurements that miss intermittent failures. Ultrasonic testing identifies steam trap condition during normal system operation without any interruption.
The testing process takes approximately 30-60 seconds per trap. The technician applies the ultrasonic contact probe to the trap body and listens for the characteristic discharge pattern.
A functioning trap produces an intermittent signal – short bursts of high-intensity ultrasound as condensate batches discharge, separated by quiet periods. A failed-open trap produces continuous high-intensity ultrasound from steam flowing through the trap body. A failed-closed trap is completely silent.
The financial impact of failed steam traps is substantial. A single 12mm trap failing open on a 7 bar steam system can waste $8,000-$12,000 annually in steam production costs. Facilities with large steam trap populations – often hundreds of traps in petrochemical and food processing plants – typically find failure rates of 15-25% without active testing programs.
Integrating steam trap testing into quarterly or semi-annual inspection programs prevents this ongoing waste and identifies traps requiring replacement before they cause process quality problems or water hammer events.
Electrical System Inspection
Electrical equipment failures cause unplanned downtime, safety incidents, and fire risk. Partial discharge, tracking, and corona develop gradually before catastrophic insulation failure. Ultrasonic testing detects these conditions early – often before thermographic surveys identify any temperature anomaly.
Partial discharge is the term for localised electrical discharge that does not completely bridge the insulation gap. Several forms exist:
Corona discharge occurs when localised electric field strength ionises surrounding air. It is most common around sharp conductors and cable terminations at elevated voltage levels.
Tracking is surface discharge – current flowing across contaminated or deteriorated insulation surfaces. It produces characteristic crackling ultrasonic sounds and, over time, creates carbonised conductive paths that lead to flashover.
Arcing is intermittent discharge across an air gap or contaminated surface. The impulsive nature of arcing produces a distinctive irregular ultrasonic signature.
Loose electrical connections create micro-arcing at contact surfaces under load. This produces ultrasonic noise even when the connection appears visually intact.
Electrical ultrasonic testing is performed with panels closed and equipment fully energised. The technician scans switchgear, motor control centre panels, transformers, and cable terminations from the exterior. This approach eliminates the arc flash exposure risk associated with opening energised panels for visual inspection.
Problems identified ultrasonically are documented and investigated during planned maintenance windows when the equipment can be safely de-energised. The advance warning provided by ultrasonic detection typically allows months of lead time before insulation failure would occur.
Bearing Condition Assessment at Low Speed
Vibration analysis is highly effective for bearing condition assessment on equipment running above 100-200 RPM. Below these speeds, the energy content of bearing defect frequencies is often too low to generate detectable signatures in vibration spectra, and background noise can mask early-stage defects.
Ultrasonic contact probe testing addresses this limitation directly. The probe contacts the bearing housing and picks up the high-frequency friction-based acoustic emissions from bearing contact surfaces. This signal is present even at very low shaft speeds where vibration analysis is ineffective.
Paper mill rolls, kiln drives, large slow-speed gearboxes, and marine propulsion shafting are applications where ultrasonic bearing condition assessment provides information that vibration monitoring cannot.
The test procedure involves applying the contact probe to the bearing housing and recording the ultrasonic signal level in decibels. Increases above the established baseline indicate increasing friction – consistent with bearing surface deterioration, lubrication breakdown, or contamination. Trending these readings over time provides progressive warning before failure.
Aquip recommends combining ultrasonic bearing assessment with vibration analysis for critical low-speed assets to ensure comprehensive fault detection across the full speed range.
Integrating Ultrasonic Testing into Existing Programs
Effective integration starts with identifying which assets and systems in the facility will benefit most from ultrasonic testing. Not every asset requires this technique – the priority applications are those where specific fault types that ultrasonic detects are likely or where other monitoring methods are inadequate.
Priority applications for ultrasonic testing include:
- Compressed air distribution systems and pneumatic equipment
- Steam systems with significant trap populations
- Medium and high-voltage electrical equipment (switchgear, transformers, motor control centres)
- Hydraulic systems with potential internal leakage
- Process valves where seat leakage affects product quality or safety compliance
- Slow-speed rotating equipment where vibration analysis is insufficiently sensitive
Route-based inspection integrates naturally with existing condition monitoring routes. Compressed air and steam surveys can be combined with or run separately from vibration routes, depending on inspection frequency and geographic layout.
Data management should capture ultrasonic findings alongside vibration data, thermographic images, and oil analysis results in a centralised database. Cross-referencing findings from different monitoring technologies improves diagnostic confidence and reveals interactions between fault types. Condition monitoring services provide integrated analysis support that draws on all available monitoring data to generate comprehensive equipment health assessments.
Selecting Ultrasonic Equipment for Industrial Use
Instrument selection should match primary application requirements, environmental conditions, and integration needs.
Entry-level instruments suited to compressed air and steam trap surveys are available from $2,000-$3,000. Advanced systems with data logging, spectrum display, multi-frequency filtering, and condition trend analysis capabilities range from $8,000-$15,000.
Key specifications to evaluate:
- Frequency range – 20-100 kHz for comprehensive industrial coverage
- Detection sensitivity – ability to detect small leaks from a working distance of 3-5 metres
- Contact probe accessory – essential for bearing and mechanical diagnostics
- Data logging – required for trend tracking and program documentation
- Environmental protection – IP54 minimum; IP65 preferred for harsh environments
- Display quality – readable in direct sunlight for outdoor applications
Instruments with adjustable frequency focus and sensitivity allow better discrimination between target signals and background noise in complex acoustic environments. Multiple narrow frequency bands can isolate specific fault signatures from general industrial noise.
Aquip supplies ultrasonic testing equipment with the environmental specifications and measurement capabilities suited to Australian industrial conditions, from standard manufacturing environments to demanding offshore and mining applications.
Building Routes and Inspection Schedules
A sustainable program requires defined routes, documented procedures, clear recording standards, and corrective action workflows that connect findings to repairs.
Compressed air surveys are typically conducted quarterly to bi-annually, depending on system age and repair quality. A newly repaired system surveyed six months after repair will identify re-occurring leaks at repaired points and new leaks at other locations.
Steam trap testing is appropriate on a quarterly basis for systems with high failure rates, semi-annually for well-maintained systems. Trap condition varies seasonally as thermal demand changes.
Electrical inspections integrate naturally into annual or semi-annual shutdown maintenance programs. Testing before and after major maintenance provides evidence of the intervention’s effectiveness.
Documentation standards should require minimum data capture: asset identification, measurement point location, decibel reading, fault description, severity assessment, repair recommendation, and follow-up verification after repairs.
Corrective action workflows must connect findings to work order generation. Detected leaks and faults that do not generate repair work orders waste inspection effort and undermine the program’s credibility with maintenance management.
Technical training courses covering ultrasonic testing technique, instrument operation, and data interpretation build the competency teams need to run effective programs independently.
Measuring Program Return on Investment
Ultrasonic testing programs generate returns through energy conservation, failure prevention, and maintenance efficiency improvement.
Program costs include instrument purchase or hire, initial and refresher training, and ongoing inspection labour. For a medium-sized facility, annual programme operation typically costs $15,000-$30,000 including all cost components.
Quantified savings from compressed air leak repair typically range from $10,000-$50,000 annually for facilities of 100-500 personnel. Steam trap failure correction contributes $15,000-$75,000 depending on the trap population size and steam costs. Electrical failure prevention from partial discharge detection can save far more when a single prevented failure is valued.
Most facilities achieve programme payback within three to six months from compressed air savings alone. Steam trap and electrical inspection returns add to this base benefit progressively.
Energy cost increases amplify the value of ultrasonic testing programs. As electricity and gas prices rise, the financial impact of leaks and trap failures increases proportionally while programme costs remain relatively stable.
Conclusion
Ultrasonic leak detection and acoustic emission testing address critical failure modes that vibration analysis and thermography cannot detect. Compressed air leaks, steam trap failures, electrical partial discharge, and low-speed bearing deterioration all require ultrasonic methods for reliable detection.
Incorporating ultrasonic testing into an existing condition monitoring program creates comprehensive diagnostic coverage and measurable energy savings. Explore condition monitoring products for instruments suited to your facility’s monitoring requirements. Review portable vibration analysers to understand how ultrasonic capabilities complement vibration-based route monitoring.
To discuss how ultrasonic testing fits your current reliability program, speak with us and a specialist will help identify the right instruments and integration approach.