How it works


AcousticEye’s breakthrough, non-invasive solution for today’s hard-to-inspect tubes up to 4” inner diameter enables ultra-fast, accurate inspection of boilers, Fin Fans and other heat exchangers, regardless of tube shape or material.

Featuring Acoustic Pulse Reflectometry (APR) technology, Dolphin G3™ is an advanced, yet easy-to-use tool that overcomes the limitations of many conventional inspection techniques.

Providing reliable inspection of even the most challenging tube sizes and configurations, the Dolphin G3 increases inspection cycle efficiency and operational cost savings.

APR in the Dolphin G3

In this technique, an audio frequency acoustic pulse is created at the inlet of the tube. This pulse propagates in the air inside the tube, as opposed to guided wave techniques which propagate the wave in the tube wall itself. As the pulse travels up the tube, reflections are created each time it encounters any type of anomaly or discontinuity. Such discontinuities include various forms of wall loss, partial or full blockages, bulges, and through holes. Importantly, each type of discontinuity creates a different type of reflection or signature. These reflected waves propagate back to the inlet where they are picked up by a microphone, digitized and recorded. They can then be analyzed offline and interpreted, both by pattern recognition software and by a qualified individual. 

The main advantages of the APR technology in the Dolphin G3 are:

  1. Very fast inspection time – on the order of 9 seconds per tube, regardless of length, up to 20 meters (65ft)

  2. Insensitivity to tube material – since the pulse propagates in the air inside the tube, the tube wall can be ferromagnetic, non-ferromagnetic, plastic, graphite, etc., with no consequence on measurement accuracy

  3. Noninvasive – only the pulse propagates within the tube, not a physical probe, thus there is no wear and tear on the probe, nor danger of getting probes stuck.

  4. Can propagate through bends – the acoustic pulse is guided by the tube walls, whether the tube is bent, spiraled, coiled, etc., enabling the inspection U-tubes and spiral cross-section tubes

  5. High sensitivity to through holes - APR is extremely sensitive to through holes, which present a "short circuit" to the atmosphere. Holes as small as 3mm in diameter can be detected in bigger inner diameter tubes. Holes present a qualitatively different signature than pits, eliminating any confusion between wall loss and holes.

  6. Detection of bulges and blockages – APR can detect tube bulges easily, which are difficult to detect with other technologies. It can also detect and quantify blockages, whether from foreign objects or dents in the tubes. Most other technologies are severely limited by blockages, which preclude probe insertion.

  7. Computer aided analysis – using appropriately designed software, the analysis can be performed automatically, enabling the technician to rapidly focus on flagged indications instead of visually scanning all the measurements.


Acoustic Pulse Reflectometry (APR) is based on measurements of one dimensional acoustic waves propagating in tubes. Schematically, in the Dolphin G3, such a system looks like this:

Figure 1 – schematic layout of the Dolphin G3 system

In a practical implementation, the hand-held Dolphin G3 probe containing the hardware above looks more like this:

Figure 2 – A practical Dolphin G3 probe

Any change in the cross-sectional area of the inspected tube creates a reflection. Such reflections propagate back to the microphone placed in the probe where they recorded and can later be analyzed.


Sample signals shown in the Acoustic Eye software

APR is capable to detect holes, blockages and ID wall loss. Hereby some sample signatures taken from Dolphin G3 measurements:

Hole signature

Tube wall degradation

Partial blockage