A fault detector finds faults in mechanical, electrical, optical or other systems. An example of a fault in an electrical system is an arching circuit breaker. An example of a fault in a mechanical system is a failed roller bearing. Both mechanical and electrical faults produce characteristic sounds, which can be detected using air or structure borne acoustic detection techniques.
Wet film is a layer of paint, resin, adhesive or other uncured material coating a surface. Noncontact techniques are required to measure the wet film thickness without destroying the coating.
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Instrument or systems are suitable for use in factory environments for monitoring thickness, defects or material properties during the continuous processing of primary metals or webs. Webs include plastic films, paper or paperboard, woven fabrics, metal foil or strip, nonwovens or other continuous sheet products.
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Flaws or features within a mechanical system provide specific acoustic or vibrational responses. If a break, deformation, or other failure occurs in a piece of metal or material, sensitive acoustic emission (AE) sensors can detect the high frequency elastic wave bursts given off during the event. Continuous acoustic emissions are associated with dislocation movement and the resulting strain or deformation. Bursts or short pulses of acoustic emissions signals are produced by micro-yielding, twinning and crack formation. Melting, phase transformation, thermal stresses, fiber breakage and fiber-matrix debonding in composites also result in acoustic emissions.
Monitoring acoustic emissions can also access the location and severity. This NDT technique is particularly useful in determining the structural adequacy of tanks and pressure vessels. AE is also used for the detection of faults or leakage in pressure vessels, tanks, and piping systems. Welds and stress corrosion cracking can be monitored on-line with AE techniques.
Air and structure borne detection methods are used to detect faults in electrical and mechanicals system based on detection of acoustic signals. The signals can be airborne, travel through the air, or reside only within solid structure or mechanical system. Applications of air or structure borne ultrasonic methods include the detection or inspection of:
IR, nuclear, and beta gauge instruments use the absorption of radiation to measure the thickness or basis weight of webs, sheet materials, or coatings. On nonmetallic materials such as paper or plastic films or webs, the amount of radiation is reflected back or transmitted through the material is measured to determine absorption levels. An increase in mass, density or thickness will result in increased absorption. The gauge is often calibrated with sample of known thickness, density or mass. The radiation source used can be IR (infrared electromagnetic), nuclear (beta particles) or other radiation sources (x-ray, gamma rays) and will depend on the material and inspection conditions.
Eddy current, penetrating radar, and other electromagnetic techniques are used to detect or measure flaws, bond or weld integrity, thickness, electrical conductivity, and detect the presence of rebar or metals. Eddy current is the most widely applied electromagnetic NDT technique. The eddy current method is also useful in sorting alloys and verifying heat treatment. Eddy current testing uses an electromagnet to induce an eddy current in a conductive sample. The response of the material to the induced current is sensed. Since the probe does not have to contact the work surface, eddy current testing is useful on rough surfaces or surfaces with wet films or coatings.
Electromagnetic acoustic resonance (EMAR) uses a non-contact electromagnetic transducer to impart a signal for resonant acoustic analysis. The non-contact EM induced signal produces a pure resonant response. Mechanical vibration from surrounding machinery does not influence the ultrasonic signals in the materials or part being inspected. Localized or wide acoustic field can be generated depending what features need to be isolated and measured. Small surface or subsurface flaws or anomalies can be isolated. The entire part can be resonated for elastic stiffness and structural integrity assessments.
Current flow or an external magnet magnetizes the part. Magnetic poles created at flaws, cracks or other discontinuities attract magnetic particles. The magnetic particles are fine iron oxide particles (0.125 to 60 microns) with a high permeability (easily magnetized) and low retentivity (ability to stay magnetized). Three methods are typically applied: dry nonfluorescent, wet nonfluorescent, and wet fluorescent.
Optical-based instruments using methods such as laser shearography, magneto-optical, holographic interferometry to detect flaws, residual stress or measure thickness.
In penetrant testing, penetrant is applied to the part by spray or immersion. The penetrant is pulled into surface flaws by capillary action. Next, a cleaner is used to remove residual penetrant from the surface of a part so the liquid penetrant only remains in the surface flaws or cracks that are present. Penetrant systems are available with varying sensitivity levels depending on the material and flaw type being inspected. Red dye penetrants are visible under normal light. Fluorescent penetrants or penetrant systems may require UV or backlight illumination. Developers or fluorescent powders may be required to enhance visibility of the residual or crack entrapped penetrant.
Equipment using penetrating X-rays or gamma rays to capture images of the internal structure or a part or finished product. The density and composition of the internal features will alter the intensity or density of these features in the X-ray image. Densitometers are used to quantify the density variations in the X-ray image. Penetrameters or other X-ray opaque gage references are located with the part during imaging for sizing of internal cracks, pores, defects or other features.
Ultrasonic (UT) inspection techniques are used to detect surface and subsurface flaws or to measure thickness. Beams of high frequency acoustic energy are introduced into the material and subsequently retrieved. Distance calculations are based on the speed of sound through the material being evaluated. The most widely used of all UT techniques is the pulse-echo technique. Flaws are detected and sizes estimated by comparing the amplitude of a reflected echo from an interface (flaw or back surface) with that of a reference interface of known size.
Other unlisted nondestructive techniques or technologies.
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