Ultrasound Analysis

What Is Ultrasound Analysis?

Ultrasound analysis is a condition monitoring technique that translates high-frequency acoustic signals into data that maintenance teams can use to assess equipment health. The sound waves it captures are produced by turbulence, friction, and electrical discharge; all of these are present when machinery is operating outside normal parameters.

Unlike methods that require equipment to be taken offline, ultrasound inspection works on running assets. Technicians can scan bearings, valves, electrical panels, steam systems, and compressed air lines during normal production, making it one of the most practical tools in a predictive maintenance program.

The technique sits within the broader family of non-destructive testing methods, meaning it gathers diagnostic data without altering the asset in any way.

How Ultrasound Analysis Works

All friction, turbulence, and electrical discharge generate broadband sound energy. Some of that energy falls in the ultrasonic range, above 20 kHz, which human ears cannot detect. An ultrasonic detector captures this energy and converts it into an audible signal and a numerical reading that the technician can evaluate.

The process follows three steps:

1. Detection. The inspector holds a directional probe near the asset. The detector heterodynes the ultrasonic signal down to an audible frequency so the technician can hear characteristic patterns: a regular ticking for a failing bearing, a hiss for a compressed air leak, a crackling sound for electrical arcing.
2. Measurement. The instrument records a decibel (dB) value representing the intensity of the signal. This number is compared against a baseline established during a healthy inspection or against manufacturer alarm thresholds.
3. Trending. Readings taken at regular intervals are plotted over time. A rising dB trend in a bearing, for example, indicates increasing friction and signals that a lubrication action or replacement is due before catastrophic failure occurs.

Two modes of detection cover different fault types:

• Airborne ultrasound captures sound propagating through air. It is used for leak detection and electrical inspection.
• Structure-borne ultrasound uses a contact probe placed directly on the asset surface. It is the primary method for bearing and mechanical inspection.

Key Applications

Ultrasound Analysis and Bearing Lubrication

One of the most widely adopted uses of ultrasound analysis is lubrication management. Over-lubrication and under-lubrication are both common causes of premature bearing failure, yet both are difficult to detect without an objective measurement.

With an ultrasonic detector, technicians establish a baseline dB reading for each bearing. As the bearing dries out, friction increases and the dB level rises. Grease is added in small increments while monitoring the dB reading in real time. When the reading returns to baseline, lubrication stops. This method prevents both under-greasing and the damage caused by over-packing, which can collapse bearing seals.

The same dB trending approach catches early fatigue damage. A bearing that begins to show a rising trend several weeks before audible noise or vibration analysis flags an anomaly gives the maintenance team a longer planning window for a scheduled replacement.

Ultrasound Analysis for Leak Detection

Compressed air leaks are a significant source of energy waste in industrial facilities. Studies consistently find that poorly maintained compressed air systems lose 20 to 30 percent of generated capacity through leaks, yet most leaks are inaudible on a noisy plant floor.

Ultrasonic detectors find leaks by picking up the high-frequency turbulence produced as pressurized air escapes through an orifice. The directional probe allows inspectors to scan entire pipe runs and pinpoint the exact location of each leak. Results are logged with GPS coordinates or equipment tag numbers and fed into a repair work order queue.

The same approach applies to vacuum systems, refrigerant lines, hydraulic systems, and any pressurized gas application. This makes leak detection one of the fastest-payback uses of ultrasound technology.

Electrical Ultrasound Inspection

Electrical discharge faults produce acoustic energy in the ultrasonic range. Arcing, corona discharge, and tracking each have distinct sonic signatures that an experienced inspector can identify and differentiate using a heterodyne detector.

Electrical inspection with ultrasound is performed on energized equipment. Inspectors scan switchgear cabinets, transformers, bus bars, and insulators from a safe distance using a parabolic focusing attachment. Because the inspection does not require de-energizing the equipment, it eliminates the production loss associated with traditional electrical shutdown inspections.

Findings are typically combined with infrared thermography data to build a complete picture of electrical system health as part of a broader asset condition monitoring program.

Ultrasound Analysis vs. Related Techniques

Condition monitoring programs that combine ultrasound, vibration, and thermography achieve broader fault coverage than any single technique alone.

Integrating Ultrasound Analysis into a Predictive Maintenance Program

Ultrasound analysis delivers the most value when it is embedded in a structured inspection route rather than used reactively. A well-designed program includes the following elements:

• Asset register and baseline readings. Every monitored asset has a documented baseline dB reading taken when the equipment is known to be healthy. This baseline is the reference point for all future trend comparisons.
• Defined inspection routes. Inspection points are organized into logical routes that a technician can complete efficiently. Routes are standardized so that readings are always taken from the same position, with the same probe angle and sensitivity settings.
• Alarm thresholds. Action thresholds are set at a fixed dB increase above baseline (commonly 8 dB for early alert and 16 dB for urgent action for bearings). Thresholds trigger work order creation in the CMMS when exceeded.
• Data storage and trending. All readings are stored with time stamps. Trending software displays the dB history for each asset so that rate-of-change analysis can estimate remaining useful life.
• Technician training. Reliable results depend on consistent technique. Technicians must be trained in probe placement, sensitivity adjustment, and the sound signatures associated with specific fault types.

Platforms that combine ultrasonic sensing with continuous online monitoring can automate data collection for critical assets, removing the dependency on periodic manual rounds and providing real-time alerts when alarm thresholds are crossed.

Common Failure Modes Detected by Ultrasound Analysis

Ultrasound analysis is particularly effective at identifying failure modes that develop gradually and produce characteristic acoustic signatures before other symptoms appear. Common examples include:

• Bearing lubrication deficiency: Rising dB readings as protective oil film breaks down, often detectable weeks before vibration signatures appear.
• Early-stage bearing fatigue: Irregular, impulsive ticking sounds produced by surface spalling on inner or outer races.
• Compressed air system leaks: A continuous hiss localized to a specific fitting, joint, or valve body.
• Failed steam traps: A continuous flow sound indicates a failed-open trap blowing live steam; silence indicates a failed-closed (blocked) trap.
• Electrical corona discharge: A crackling or buzzing sound emanating from high-voltage insulators or cable terminations.
• Internal valve leakage: Turbulent flow sound detected through a contact probe on a valve body that is confirmed to be in the closed position.

Frequently Asked Questions

The Bottom Line

Ultrasound analysis gives maintenance teams a fast, non-invasive method for detecting bearing wear, compressed air leaks, electrical discharge, and steam system failures on live equipment. Its ability to surface faults weeks before they escalate makes it a high-value tool for any reliability program aiming to reduce unplanned downtime.

Combining ultrasound with continuous sensor monitoring extends coverage to critical assets around the clock, providing the early warning lead time that scheduled inspection routes alone cannot achieve.