Acoustic emission testing (AE) is a principle method of non-destructive testing (NDT). In summary, radiation of acoustic (elastic) waves occurs when a material changes because of; crack formation, deformation or external mechanical forces. The waves are of interest in structural health monitoring and quality systems.
What are the advantages and disadvantages of Acoustic Emission?
The primary advantage is the origin of the signal relating to the energy released. Testing is in situ and AE can detect a range of defects; friction, cracking, delamination and corrosion.
Extreme environment testing, including high pressures and very corrosive landscapes is a benefit. Remote locations are not a barrier, unlike in other non-destructive technical applications. The technique is used, for example, to study the formation of cracks during the welding process which is the opposite to ultrasonic testing (UT) techniques.
The disadvantage of AE leads to the fact that further, more expansive experimentation may be needed to confirm the initial AE diagnosis. AE deals with dynamic processes in a material. Only active features are highlighted and cracks or corrosion can be overlooked.
How does AE Work?
A number of sensors, convert waves into electrical signals. High pressures, loads or temperatures on the material, facilitate the signals. The component integrity decreases as the forces increase, leading to a more prominent signal.
There are two AE methods: transient and continuous. The transient method detects AE bursts that exceed a threshold offering peak amplitude, signal energy and duration of the burst. A feasible procedure in the identification of defects, such as cracks.
The continuous method captures all AE within a set time period. This is the correct method when the amplitude is low.
AE testing requires several sensors (3 acting as a triangle), by listening to the acoustic waves being emitted. Sensor response validation and logged data is recorded.
Acoustic Emission applications
AE is used across a range of applications including: faults in pressure vesselsstorage tanks and detecting creep damage in piping systems.or leakage in storage tanks, pipelines and continuous monitoring welding applications. There is extensive use in several other areas including the detection of active corrosion in the bottom of
In addition to non-destructive testing, AE monitoring has applications in process monitoring. These include detecting anomalies in fluidised beds. Additionally, analysis across rotating machinery, for example, bearings and gearboxes.
AE sensors are a fundamental component. Dependent upon the environment, testing piece material and size, sensors fall into the following categories;
Miniature sensors are ideal for smaller components or in limited access areas
High Sensitivity Integral sensors
Intrinsically Safe sensors are mainly used in dangerous areas
Acoustic emission transducers
AE transducers search for micro-fractures within rock to be tested, recorded and analysed. The analysis can give information as to the failure mechanisms.
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