Acoustic Emission Testing (AET) is a nondestructive testing (NDT) method that is based on the generation of waves produced by a sudden redistribution of stress in a material. When a piece of equipment is subjected to an external stimulus, such as a change in pressure, load, or temperature, this triggers the release of energy in the form of stress waves, which propagate to the surface and are recorded by sensors. Acoustic emissions can come from natural sources, such as earthquakes or rockbursts, or from the equipment itself such as melting, twinning, and phase transformations in metals. Acoustic emission testing involves the detection and analysis of AE signals using specialized equipment and can provide information on the origin and significance of discontinuities in a material.
Acoustic emission testing is different than other NDT techniques in two major ways:
- Instead of supplying energy to the object under examination, AET listens for the energy released by the object naturally. AE tests can be, and often are, performed on structures while they are in operation since this provides adequate loading for propagating defects and triggering acoustic emissions.
- AET deals with dynamic processes in a material. This is particularly useful because only active features are highlighted during the examination. Thus, it is possible to discern between developing and stagnant defects. However, one should be aware that it is possible for flaws to go undetected if the loading isn’t high enough to cause an acoustic event that can be detected by the system.
Acoustic emission testing is most often used in a dynamic test environment, meaning that it is used to monitor for crack detection in pressure equipment when the equipment is experiencing an increase in stress. AET systems generally contain a sensor, preamplifier, filter, and amplifier, along with measurement, display, and storage equipment. Acoustic emission sensors respond to any dynamic motion caused by an acoustic emission event. This is achieved through transducers that convert mechanical movement into an electrical voltage signal. The majority of AET equipment responds to movement in a range of 30 kHz to 1 MHz. For materials with high attenuation, such as plastic composites, lower frequencies may be used to better distinguish acoustic emission signals. The inverse is true as well.
Because of its versatility, acoustic emission testing has many applications across a variety of industries. In the O&G and chemical processing industries, AET is often used to assess structural integrity, test for leaks, monitor weld quality, and detect active flaws such corrosion in the bottom of aboveground storage tanks or creep damage in high energy piping systems.
Related Topics
- Advanced Ultrasonic Backscatter Technique (AUBT)
- Eddy Current Testing (ECT)
- Electro Magnetic Acoustic Transducers (EMAT)
- Guided Wave Ultrasonics (GWUT)
- Infrared Inspection
- Liquid Penetrant Examination (LPE)
- Magnetic Flux Leakage (MFL)
- Magnetic Particle Testing (MPT)
- Meandering Winding Magnetometer Array (MWMA)
- Pulsed Eddy Current (PEC)
- Radiography
- Remote Field Eddy Current (RFEC)
- Ultrasonic Testing (UT)
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