Defects like cracks, corrosion, composite delaminations creates sudden elastic wave events propagating through materials like ultrasonic waves. These elastic wave are called acoustic emissions (AE). Using AE we are able "listen" to defect initiations in materials via piezoceramic sensors.
AE method is fully passive and can be performed on structures loaded with internal or external stress (operational loading or pressure tests for example). Method is widelly used also for pressure vessel and pipelines leaks detections. For leak detection in pipeline system longer than 100 m, other NDT method is more cost-efficiet - Distributed Acostic Sensing (DAS) or Distributed Temperature sensing (DTS) for mediums with different leaking temperature than surrounding environment (main sensor is in this case optical fiber bounded on pipeline system).
Acoustic emission in integralk method, i.e. diagnosed object is inspected whole at once within range of acoustic emission sensors. Defects coul dbe localized, acoustic emission sources (acoustic emission event clusters) could sepparated from data flow and processed for their dynamic observation in time domain. This brings predictability of structure residual lifetime and lets you to adjust service intervals.
Acoustic Emission phenomenon are present onlyu for externaly or internaly loaded objects. This method lets you to observe active defects which are developing or propagating. Unlike conventional NDT search for all defets even those which are not sensitive to current loading mode and are not online observing the defect dynamics.
Our NDT advantages and of Structural Health Monitoring (SHM) are desctibed in our article dealing with remote NDT and SHM surveilance center.
AE is the most used NDT method for thin shell objects (pressure vessels, reactors, pipelines etc.). Objects with thick walls are better to inspect with other methods like Non-linear Elastic Wave Spectroscopy (NEWS).
Acoustic Emission is very universal NDT method for various industries::
Contatct between inspected object and sensor could be implemented in to ways. Either by direct contatc by glue (epoxy, silicons), or via waveguides for heat surface objects.Bohemian Technology Group s.r.o. produces and uses piezoceramics senzors/transducers base on resonation principle from approx 20kHz up to 2 MHz.
Our developing department is open to various other applications and we are redesign the sensors according customers needs.
Sensor mounting to measured objects is ofter realized by waveguides. The reason is increased measured object surfacet temperature or presence of thermal insulation on surface of measured object.
While using AE outside laboratory (out of in-vitro conditions) in industry you need to take into account the acoustic background noise and electromagnetic interference. Acoustic nois is present mostly at lower ultrasonic frequencies (below 70 kHz) and the frequency filtration therefore is desired. This is possible by following ways:
Amplification of amplifiers is mostly 20 and 40 dB (exceptionally 60 dB). In our portfolio you can find preamplifiers of 20 a 40 dB (custom even 60 dB) either with or without bypass which enables you to use signal path also for transmitting (higher voltage limits than in measuring mode) and not only for data acquisition.