Technical FAQ

AET is a passive inspection method. AE sensors attached at selected accessible locations on a structure record transient elastic waves generated by acoustically active processes during suitable operating or test conditions. These processes include crack growth and corrosion-related activity; friction, leaks and process noise can also produce signals, so recorded acoustic activity is evaluated rather than taken at face value. Where a signal reaches several sensors, the arrival times and the wave velocity in the material can be used to estimate its source location; not every recorded signal can be located. ^[1][2]

AET responds to processes that are acoustically active under the examination conditions, such as growing cracks or active corrosion. Flaws that are present but dormant may release little or no emission and can go undetected. An AE indication does not by itself establish the damage mechanism, flaw size or remaining wall thickness, and a stronger signal does not necessarily mean more severe damage; sizing and thickness measurement require methods such as ultrasonic testing. Results also depend on loading, background noise, sensor layout and interpretation by qualified personnel. ^[1]

No. AET is used to screen an asset and locate areas of recorded acoustic activity, so that follow-up inspection with complementary NDT can be targeted where it is most needed. For metallic pressure equipment, ISO 24367 states that the method is not intended to be used on its own, and other NDT methods may be used to verify and supplement the results; other applications follow their own standards and procedures. Decisions on internal inspection rest with the asset owner and, where applicable, the regulating authority. ^[1][2]

Sensors need good acoustic coupling to the metal surface. Whether a coating can stay in place depends on its type and thickness, and this is checked during sensor installation and verification. Insulated or clad assets normally need local access points for the sensors. These details are confirmed during the preliminary assessment — please ask our AE personnel about your asset.

For suitable liquid-filled flat-bottom tanks, AE assessment of floor-corrosion activity may be performed with the product remaining in place, subject to the required liquid level, sensor arrangement and examination conditions. Leak-location testing in double-bottom tanks is a different application and may require emptying the tank and obtaining internal sensor access. For the vacuum-interspace method described by TÜV SÜD, sensors are installed on the upper tank bottom from inside the emptied tank. Preparation requirements depend on the selected method and are confirmed during the preliminary assessment. ^{[5][6][9][10]}

A full plant shutdown is not always necessary. For suitable tank-floor examinations, the stored product may remain in the tank, although a controlled quiet period is normally required. Filling, draining, agitators and nearby noise-producing equipment may need to pause. Background noise is assessed during the examination; filtering cannot always recover reliable AE data when interference is excessive. ^[4] Required operational restrictions are agreed during inspection planning. ^[5][6][9]

It depends on the tank size, the number of sensors, background noise and the objectives of the test. On-site data acquisition is planned around the quiet test window, and the data are then evaluated and reported. For a time estimate for your tank, please contact our AE personnel. ^[6]

Yes. AET provides estimated AE source locations, and 3D laser scanning records the external geometry of the tank within the survey scope, including deviations such as bulging from a reference shape. Change over time is established by comparison with an earlier baseline survey. The two data sets can be viewed together on a 3D model, although the precision of the survey does not make AE source locations equally precise. A geometric-deviation map is not a wall-thickness map.

There are two main approaches, each covered by its own standard. In a controlled-pressure AE examination, pressure is raised in planned stages with holding periods while emissions are recorded; ISO 24367 specifies this kind of AE testing for new and in-service metallic pressure equipment, including the classification and evaluation of results, but does not cover in-service monitoring or leak detection. In continuous monitoring, emissions are recorded during normal operation; ASTM E1139/E1139M is a standard practice for continuous AE monitoring of metal pressure boundaries. ^[2][3]

The operating requirements depend on the selected AE method. Continuous monitoring may be performed during normal operation, while controlled-pressure AE examination requires an agreed loading sequence and appropriate operational controls. External sensor installation may avoid internal entry for AE data acquisition, but other inspection activities or statutory requirements may still require additional access. ^[2][3]

Not necessarily. Depending on the approved examination arrangement, controlled-pressure AET may be carried out within the vessel's operating pressure range using the process medium, or combined with a hydrostatic or pneumatic pressure test where one is required. The test medium, loading sequence and safety controls are agreed before the examination. Whether AE testing can be used in place of a statutory pressure test is a regulatory matter — see "Regulation & qualifications".

AE results relate to the loads reached during the examination. If the vessel is later operated above the maximum pressure reached during the test, or under significantly different conditions, reassessment may be needed. AE results alone do not determine remaining life. Please discuss your operating envelope with our AE personnel when planning the test.

AE can be applied to pressurised metal piping and pipelines, typically during a controlled pressure test or as monitoring of a selected section. Signals weaken with distance along the pipe, so sensor spacing depends on pipe size, material, coating, contents and supports, and coverage is planned section by section. ^[1][6] Please discuss piping applications with our AE personnel, who will confirm whether AET suits your line.

Yes, in suitable conditions. Flow through a leak path under a pressure difference generates acoustic emission, which can be detected and, with suitable sensor spacing, located. Leak detection is a separate application from structural damage assessment: ISO 18081 sets out the general principles for leak detection by AE, while ISO 24367 excludes it from its scope. Detectability depends on the pressure difference, the fluid, the leak path and background noise. Ask our AE personnel whether a leak-detection approach suits your system. ^[2][6][10]

Sensors need access to the metal surface, so buried or insulated sections need access points, such as excavations or insulation windows. This affects feasibility and cost, and is confirmed during the preliminary assessment.

AE can be used to assess acoustic activity at accessible stationary components, such as flanges, by recording across start-up, stable operation and shutdown. Machine noise is characterised during set-up and filtered where its signal characteristics allow. Interference that cannot be reliably separated may limit the assessment. Changes in recorded activity are evaluated with the operating data and, where needed, complementary NDT before any conclusion is drawn about crack activity. Suitability is confirmed for each machine — please contact our AE personnel.

Under suitable examination conditions, AE can provide indications of corrosion- or crack-related activity in hull and internal structures. Visual inspection, thickness measurement and other NDT are used to establish corrosion, thickness loss or crack characteristics. The results provide technical input to the owner's evaluation of serviceability. AE findings do not certify seaworthiness.

Possibly. AET is used on many metallic structures, but feasibility depends on the material, loading, sensor access, wave propagation and noise. Send us details through the site assessment form and our AE personnel will advise.

An AE report typically describes the examination scope, test conditions, sensor arrangement, recorded acoustic activity, estimated source locations, applicable evaluation criteria, relevant limitations and recommended follow-up. Where the governing procedure defines source classes, these are reported with their meaning and required actions. If 3D surveying is included, suitable AE indications and survey measurements may also be presented together on an asset model.

AE sources are evaluated and classified in accordance with the procedure applicable to the asset and examination method. Classification considers the recorded acoustic response, examination conditions and relevant evaluation criteria. The resulting class and recommended follow-up are explained in the project report. Source classification alone does not determine defect size or confirm asset safety.

Not necessarily. It means no significant active sources were detected under the test conditions and within the sensor coverage. Dormant flaws may produce little emission, so AET results should be read together with the asset's inspection history and other NDT data. ^[1]

In Malaysia, periodic inspection of plant that requires a certificate of fitness is regulated by the Department of Occupational Safety and Health (DOSH/JKKP). AET results can be used by an asset owner as technical evidence within an inspection strategy or Scheme of Examination. Whether that evidence is accepted, and on what terms, is decided by DOSH/JKKP; Wavewurk does not make or guarantee regulatory decisions. For reference, the JKKP guideline on periodic inspection by advanced technology (PSTT) for pressure vessels and steam boilers, issued in 2025, names methods such as ultrasonic testing, corrosion scanning, profile radiography and thermography; it does not name AE. Please consult DOSH/JKKP and your appointed competent person before planning any change to statutory inspection arrangements. ^[7]

AE examinations are conducted by personnel qualified for their assigned duties, with appropriate supervision and technical review. Personnel qualifications and role assignments for each project are confirmed against the examination requirements. Relevant qualification records can be provided upon request. ^[8]