What Is Acoustic Emission Testing?
Acoustic Emission (AE) testing is a passive NDT technique that detects and analyses the
transient elastic waves — acoustic emissions — generated when a material undergoes localised
deformation, cracking, leaking, or other active damage processes. Unlike most NDT methods
that interrogate a component from outside using an introduced energy source, AE listens for the
energy released by the material or component itself in response to an applied stimulus —
typically pressure, load, or temperature change.
AE sensors (piezoelectric transducers) are attached to the external surface of the component at
defined positions. When an active source — a propagating crack, a corroding pit, a leaking joint,
or a high-stress zone — emits an acoustic wave, multiple sensors detect the signal at slightly
different times. The difference in arrival times between sensors enables triangulation of the
source location — pinpointing the active zone on the structure without scanning every surface.
Key AE capabilities:
- Detection of active defects under load — cracks that are opening and propagating, not just
dormant
- Global monitoring of large structures from a limited number of sensor positions
- In-service inspection — equipment remains in operation during monitoring
- Leak detection — high-frequency AE signal from pressurised leaks is detectable through
the structure
- Source location — triangulation identifies the position of active AE sources
- Source characterisation — signal parameters differentiate crack growth, friction, leak, and
impact sources