The test probe detects changes in dielectric properties, such as shrinkage cavities, pores, foreign materials or cracks and displays the results as B or C scans. This method is restricted to use on dielectric materials and uses microwave frequencies transmitted and received by a test probe. A sensor is then used to detect changes in magnetic flux density which show any reduction in material due to pitting, erosion or corrosion. This method uses a powerful magnet to create magnetic fields which saturate steel structures such as pipelines and storage tanks. Alternatively, a vacuum can be used, in which case the mass spectrometer will sample the vacuum chamber to detect ionised helium, which will show that there has been a leak. Mass spectrometer testing uses helium or a helium and air mix inside a test chamber with a 'sniffer' to detect any changes in the air sample, which would indicate a leak. Halogen diode testing also uses pressure to find leaks, except in this case air and a halogen-based tracer gas are mixed together and a halogen diode detection unit (or 'sniffer') is used to locate any leaks. A loss of pressure or vacuum over a set time span will show that there is a leak in the system. Only used on closed systems, pressure change testing uses either pressure or a vacuum to monitor the test piece. Leak testing can be broken down into four different methods - bubble leak testing, pressure change testing, halogen diode testing and mass spectrometer testing.īubble leak testing uses a tank of liquid, or a soap solution for larger parts, to detect gas (usually air) leaking from the test piece in the form of bubbles. These images are compared to one another to determine if any defects are present. Laser shearography uses laser light to create an image before the surface is stressed and a new image is created. Laser profilometry uses a high speed rotating laser light source and miniature optics to detect corrosion, pitting, erosion and cracks by detecting changes in the surface via a 3D image generated from the surface topography. The results are then compared to an undamaged reference sample to show defects. Holographic testing uses a laser to detect changes in the surface of the material which has been subjected to stress such as heat, pressure or vibration. Laser testing falls into three categories including holographic testing, laser profilometry and laser shearography. The waves are reflected or refracted when they encounter a buried object or material boundary with different electromagnetic properties. This geophysical NDT method sends radar pulses through the surface of a material or subsurface structure, such as rock, ice, water or soil. There are three types of electromagnetic testing, including eddy current testing, alternating current field measurement (ACFM) and remote field testing (RFT).Įddy current testing uses an alternating current coil to induce an electromagnetic field into the test piece, alternating current field measurement and remote field testing both use a probe to introduce a magnetic field, with RFT generally used to test pipes. This testing method uses an electric current or magnetic field which is passed through a conductive part.
Leaks and active corrosion are detectable AE sources too.
Frequently a method for use during proof tests of a pressure vessel, AE testing is also a continuous Structural Health Monitoring (SHM) method, for example on bridges.
PARTICLE PLAYGROUND EMIT OVER DISTANCE CRACK
It is even possible to detect AE from plasticisation in highly stressed areas before a crack forms. Sensors dispersed over the surface the structure detect the AE. This is a passive NDT technique, which relies on detecting the short bursts of ultrasound emitted by active cracks under a load. National Structural Integrity Research CentreĬurrent NDT test methods include: Acoustic Emission Testing (AE).Structural Integrity Research Foundation.
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