Acoustic emission testing (AET)

Acoustic emission testing listens for energy released by the structure; it does not send a search pulse into the weld. Sensors coupled to the surface receive transient elastic waves while a controlled mechanical or thermal stimulus changes stress in the component. The AET system then detects, locates and classifies source activity. ASTM E569/E569M scopes that workflow for stimulated structures and states that other NDT methods may be used to further evaluate the significance of reported acoustic emission sources. ISO 12716:2026 supplies the vocabulary for the method. ISO 24367:2023 scopes the technique to active sources in metallic pressure equipment and states that it is not intended as a stand-alone method for testing and evaluation.

The closest neighbouring method here is phased array ultrasonic testing. PAUT transmits controlled ultrasonic beams and interprets their reflections to image a local volume. AET instead waits for an active source to emit a stress wave during the load sequence. This lets an AET arrangement monitor a broad structure, but an emission location is not automatically a defect type or a measured flaw size. The inspection plan records AET source location separately from any follow-up local examination; personnel competence and authorization remain a separate ISO 9712 question.

Worked example: source location or flaw image?

During a controlled pressure test, an AET sensor array records repeated events that locate to one region beside a vessel seam. The correct AET result is an active source region requiring evaluation. It is not yet a statement that the seam contains a crack of a particular length or height.

The inspection plan then assigns PAUT to that region. If PAUT resolves a planar indication, the technician records its position and dimensions, and the governing acceptance document decides its disposition. AET found and located activity across the loaded structure; PAUT supplied local imaging and defect sizing. Treating the first result as though it were the second would skip both characterization and the separate acceptance criteria.