Technical FAQ

AET is a passive inspection method. Sensors mounted on the outside of an asset listen for stress waves released by active processes in the material, such as crack growth or corrosion-related activity, while the asset is under suitable operating or test conditions. By comparing the arrival times of a signal at several sensors, the source can be located. ^[1][2]

AET is best at finding damage that is active during the test. It is less effective for flaws that are present but dormant, because they may release little or no emission under the applied conditions. AET does not measure wall thickness or crack depth; sizing requires 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 showing activity, so that follow-up inspection can be targeted. ISO 24367 states that the method is not intended to be used on its own, and indicated areas should be examined with complementary NDT methods. 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.

Not usually for floor corrosion testing of single-wall, flat-bottom tanks: this can generally be done with the stored product in place, with the tank filled to a minimum level. ^[4][5][6] Leak testing of double-bottom tanks through the interstitial space is different and requires the tank to be emptied. Some situations may still require draining or internal access.

The tank is not opened or cleaned. A quiet test window gives the clearest data, but it does not always mean stopping all activity. Where operating noise follows a regular, repeatable pattern — for example from pumps, mixers or nearby machinery — our AE personnel can identify it from its signal characteristics and filter it out, so that signals associated with corrosion or crack activity can still be distinguished. ^[1] Which activities must pause, such as filling, draining or mixing, is agreed for each tank during inspection planning. Irregular noise, such as heavy rain, is difficult to filter; acquisition is paused until it stops and then resumed. ^[6]

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 shows where acoustic activity is located, and 3D laser scanning records the external geometry of the tank, including deformation and bulging within the survey scope. The two data sets can be viewed together on a 3D model. A deformation map shows departure from a reference shape; it is not a wall-thickness map.

There are two main approaches. In controlled-pressure testing, pressure is raised in planned stages with holding periods while emissions are recorded; ISO 24367 covers AE testing of metallic pressure equipment, both new and in service. In in-service monitoring, emissions are recorded during normal operation; ASTM E1139 is a standard practice for continuous AE monitoring of metal pressure boundaries. ^[2][3]

In-service monitoring is carried out during normal operation. Controlled-pressure testing needs a planned pressure sequence agreed with your operations team. Neither approach requires internal entry into the vessel.

Not necessarily. Controlled-pressure AET can be carried out within the vessel's operating pressure range, or combined with a hydrostatic or pneumatic pressure test where one is required. 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 test. If the vessel is later operated above the maximum pressure recorded during the test, reassessment may be needed. 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.

AE can detect signals from leaks under suitable pressure conditions, but leak detection is a separate application from damage assessment, and ISO 24367 excludes leak detection from its scope. Ask our AE personnel whether a leak-detection approach suits your system. ^[2][6]

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 crack activity at accessible stationary components, such as flanges, by recording across start-up, stable operation and shutdown. Machine noise is characterised and filtered during set-up. Suitability is confirmed for each machine — please contact our AE personnel.

AE can be used to assess corrosion and crack activity in hull and internal structures, with findings checked by visual inspection and thickness measurement. The results provide technical input to the owner's evaluation of serviceability; they do not certify seaworthiness.

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

Located AE sources, activity trends, correlation with pressure or operating data where recorded, a classification of each source (Class A–D) and recommended follow-up. Where 3D scanning is part of the scope, sources are also shown on the 3D model of the asset. Indications show where follow-up is needed; they are not confirmed defects.

Class A is a non-significant source, B a weak active source, C an active source and D a very active source. Class C and D sources are prioritised for follow-up with other NDT methods. Classification criteria are set in the agreed inspection procedure.

Not necessarily. It means no significant active sources were detected under the test conditions. 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]

Testing is carried out by Wavewurk's in-house Acoustic Emission Level I and Level II personnel, with collaborating Level III specialists in an advisory role. ISO 9712 is the international standard for qualification and certification of NDT personnel; qualification records for the personnel assigned to your project can be provided on request. ^[8]