NON DESTRUCTIVE TESTING ##HOT##
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.[1]The terms nondestructive examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are also commonly used to describe this technology.[2]Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. The six most frequently used NDT methods are eddy-current, magnetic-particle, liquid penetrant, radiographic, ultrasonic, and visual testing.[3] NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art.[1] Innovations in the field of nondestructive testing have had a profound impact on medical imaging, including on echocardiography, medical ultrasonography, and digital radiography.
NON DESTRUCTIVE TESTING
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Analyzing and documenting a nondestructive failure mode can also be accomplished using a high-speed camera recording continuously (movie-loop) until the failure is detected. Detecting the failure can be accomplished using a sound detector or stress gauge which produces a signal to trigger the high-speed camera. These high-speed cameras have advanced recording modes to capture some non-destructive failures.[4] After the failure the high-speed camera will stop recording. The captured images can be played back in slow motion showing precisely what happened before, during and after the nondestructive event, image by image.
NDT is used in a variety of settings that covers a wide range of industrial activity, with new NDT methods and applications, being continuously developed. Nondestructive testing methods are routinely applied in industries where a failure of a component would cause significant hazard or economic loss, such as in transportation, pressure vessels, building structures, piping, and hoisting equipment.
Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current. In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.
Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials.[5] In the case of high stress or safety critical welds, weld monitoring will be employed to confirm the specified welding parameters (arc current, arc voltage, travel speed, heat input etc.) are being adhered to those stated in the welding procedure. This verifies the weld as correct to procedure prior to nondestructive evaluation and metallurgy tests.
Several NDT methods are related to clinical procedures, such as radiography, ultrasonic testing, and visual testing. Technological improvements or upgrades in these NDT methods have migrated over from medical equipment advances, including digital radiography (DR), phased array ultrasonic testing (PAUT), and endoscopy (borescope or assisted visual inspection).
The certification covers proficiency in one or more of the following methods: a) acoustic emission testing; b) eddy current testing; c) infrared thermographic testing; d) leak testing (hydraulic pressure tests excluded); e) magnetic testing; f) penetrant testing; g) radiographic testing; h) strain gauge testing; i) ultrasonic testing; j) visual testing (direct unaided visual tests and visual tests carried out during the application of another NDT method are excluded).
NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques. The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore, choosing the right method and technique is an important part of the performance of NDT.
Successful and consistent application of nondestructive testing techniques depends heavily on personnel training, experience and integrity. Personnel involved in application of industrial NDT methods and interpretation of results should be certified, and in some industrial sectors certification is enforced by law or by the applied codes and standards.[19]
NDT professionals and managers who seek to further their growth, knowledge and experience to remain competitive in the rapidly advancing technology field of nondestructive testing should consider joining NDTMA, a member organization of NDT Managers and Executives who work to provide a forum for the open exchange of managerial, technical and regulatory information critical to the successful management of NDT personnel and activities. Their annual conference at the Golden Nugget in Las Vegas is a popular for its informative and relevant programming and exhibition space
Central certification is more widely used in the European Union, where certifications are issued by accredited bodies (independent organizations conforming to ISO 17024 and accredited by a national accreditation authority like UKAS). The Pressure Equipment Directive (97/23/EC) actually enforces central personnel certification for the initial testing of steam boilers and some categories of pressure vessels and piping.[31] European Standards harmonized with this directive specify personnel certification to EN 473. Certifications issued by a national NDT society which is a member of the European Federation of NDT (EFNDT) are mutually acceptable by the other member societies [32] under a multilateral recognition agreement.
Probability of detection (POD) tests are a standard way to evaluate a nondestructive testing technique in a given set of circumstances, for example "What is the POD of lack of fusion flaws in pipe welds using manual ultrasonic testing?" The POD will usually increase with flaw size. A common error in POD tests is to assume that the percentage of flaws detected is the POD, whereas the percentage of flaws detected is merely the first step in the analysis. Since the number of flaws tested is necessarily a limited number (non-infinite), statistical methods must be used to determine the POD for all possible defects, beyond the limited number tested. Another common error in POD tests is to define the statistical sampling units (test items) as flaws, whereas a true sampling unit is an item that may or may not contain a flaw.[39][40] Guidelines for correct application of statistical methods to POD tests can be found in ASTM E2862 Standard Practice for Probability of Detection Analysis for Hit/Miss Data and MIL-HDBK-1823A Nondestructive Evaluation System Reliability Assessment, from the U.S. Department of Defense Handbook.
This frequently asked question has been created to provide a breakdown of what NDT is, an introduction to each of the methods, the difference between NDT and destructive testing and the advantages of using this analysis technique.
This is a passive NDT technique, which relies on detecting the short bursts of ultrasound emitted by active cracks under a load. Sensors dispersed over the surface the structure detect the AE. It is even possible to detect AE from plasticisation in highly stressed areas before a crack forms. 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. Leaks and active corrosion are detectable AE sources too.
This testing method uses an electric current or magnetic field which is passed through a conductive part. There are three types of electromagnetic testing, including eddy current testing, alternating current field measurement (ACFM) and remote field testing (RFT).
Eddy 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.
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. The results are then compared to an undamaged reference sample to show defects.
Only used on closed systems, pressure change testing uses either pressure or a vacuum to monitor the test piece. A loss of pressure or vacuum over a set time span will show that there is a leak in the system.
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.
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. 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.
Liquid penetrant testing involves the application of a fluid with low viscosity to the material to be tested. This fluid seeps into any defects such as cracks or porosity before a developer is applied which allows the penetrant liquid to seep upwards and create a visible indication of the flaw. Liquid penetrant tests can be conducted using solvent removable penetrants, water washable penetrants or post-emulsifiable penetrants.
Radiographic testing uses radiation passed through a test piece to detect defects. X-rays are commonly used for thin or less dense materials while gamma rays are used for thicker or denser items. The results can be processed using film radiography, computed radiography, computed tomography or digital radiography. Whichever method is used, the radiation will show discontinuities in the material due to the strength of the radiation. 041b061a72