The Non Destructive Testing and Evaluation
The Non Destructive Testing and Evaluation (NDTE) are a set of methods that aim to characterize the physical properties of structural materials or functions (optical, magnetic, thermal, acoustic ,...) being production to optimize their use properties, and control their initial state (presence of defects) and / or in use (development and creation of defects or damage localized or diffuse) non-intrusively without degrade. For Non Destructive Testing (NDT), it is especially, after found, to determine the size of the defects and estimate their degree of harmfulness. There is also talk of NDT (Non Destructive Testing) or END (Non Destructive Examination).
Many NDTE methods are used in most industrial applications:
The automotive industry (control of engine blocks);
The oil industry (pipelines, tubes, bars, welds, tanks);
The shipbuilding industry (control of shells);
Aeronautics (beams, aircraft wings, many engine parts, landing gear, etc.).
the energy industry (reactors, boilers, piping, turbines, etc.).
the railway manufacturing and maintenance including security organs (axles, wheels, bogies);
And generally in all sectors producing:
parts to high production costs low in quantity (nuclear, petrochemical ...)
parts whose reliable operation is critical (construction, nuclear, gas line ...).
In France, workers who perform these inspections are certified by the Cofrend, French Confederation for Non Destructive Testing, according to a principle of third party and according to two standards:
French and European standard EN 473 entitled "Non-destructive testing, qualification and certification of NDT personnel." This standard was written in April 1993, revised in 2000 and 2008. Under this standard, the certification is divided into four sectoral committees: Foundry (CCF), Steel Products (CCPA), Railway Maintenance (CFCM), and Fabrication & Maintenance (METC)
European standard EN 4179 with the U.S. equivalent is the NAS 410. For parts for the aerospace industry (aeronautics and space), the CND. are considered under special procedures of EN 4179 and must be qualified as such. In France these certifications are grouped under the Sectoral Committee for Aeronautics COSAC Cofrend.
The certification is valid for 5 years (revouvelables) and in France, more than 12,000 people who are so certified, that is to say, who have passed a theoretical and practical examination. In addition, the Cofrend is accredited by the Cofrac according to ISO 17024
Whatever the method adopted, we can represent the implementation of a system according to the synoptic NDTE following:
The target is characterized by a set of parameters that we will seek to characterize and / or estimate to form a diagnostic integrity. The implementation of a system will allow NDTE adequate to produce a number of signals that are the desired settings. A step of "inversion", more or less complicated, is often necessary to find the initial parameters of the room.
Different control methods
Standards EN 473 and EN 4179 defines a number of symbols to the usual methods (see table).
These symbols are generally consistent with the abbreviation of the English name of the method, for example, the symbol for the PT bleed just Penetrant Testing.
Control Visual examination (VT)
The visual inspection is an essential technique in the nondestructive testing. The external condition of a room can give essential information on the status of this: obvious defects (such as bends, breaks, wear, corrosion, cracks open, ...) of hidden defects underlying with an irregularity on the outer surface may be an indication of more serious defect in it. choose the most suitable technique in NDT for in-depth reviews to determine the limitations of other NDT techniques selected (access, surface, etc.). Leak testing, testing tires and hydraulic tests also include a visual inspection to reveal any leaks.
The penetrant testing (PT)
This is a method to reveal the presence of discontinuities open to the surface of metal parts, mainly, but also ceramic. It is to baste (by immersion or by electrostatic spraying, sometimes but rarely, brush) the target with a fluorescent liquid or colored in red, which enters the discontinuities. After cleaning of the target, a developer is applied and by "sweated" the liquid remained in the cracks, will reveal them.
This method seems very simple to implement and it is sensitive to discontinuities open. We can highlight discontinuities 1 micron opening 100 times thinner than a human hair. By cons, it is not automated and the results are at the discretion of the operator. In addition, it requires the use of non-recoverable or contaminated after use (eg nuclear power plant: an attempt to reduce the volume of waste), but this method is invaluable for the detection of discontinuities grooved, regardless their location, regardless of their orientation.
GEMX-160: X-ray generator portable digital radiology dedicated to non destructive testing, the device is battery powered and remotely controlled by radio waves.
The primary use of X-ray non-destructive inspection is in imaging. Its advantage is to provide information directly used on the inside of objects or materials. The phase inversion can be quite small and the spatial resolution good enough. However, the interpretation of images requires a high level of expertise on the part of the operator and demand conditions for operator safety and the environment.
In heavy industry, the control by using X-ray is used particularly for welds in nuclear power plants and shipyards and oil, corrosion of pipes, the structure of composite materials or cracks in complex mechanical parts .
Other radiological methods of nondestructive testing using fluorescence and spectrometry. With the backscattered radiation, it is possible to analyze the content of atomic objects and for example to detect the presence of lead or other toxic materials in paint, or the presence of explosives in suspicious objects.
The ultrasonic (UT)
Ultrasonic testing machine. Issued and reflected waves provide information on the presence or absence of defects and their nature.
The ultrasonic testing is based on the transmission, reflection and absorption of an ultrasonic wave propagating in the test piece. The emitted wave train is reflected in the back of the room and on the defects and returns to the transducer (which often plays the role of transmitter and receiver). The interpretation of the signals used to set the default. This method has high spatial resolution and the ability to find fault at depth. The inversion step is simple, at least for parts geometrically and physically simple. By cons, it is a slow method because you have to do a thorough mechanical scanning of the room. Moreover, it is often necessary to control multiple surfaces of the room to be able to make a three-dimensional defects.
The acoustic emission (AT)
The acoustic emission testing is to collect the emission of a part or structure subject to stress, for example in a test hydraulic or pneumatic. The ultrasonic wave propagation in elastic material, detected by a network of sensors, can lead to a localization of sources of damage of the material in real time (fissuration. ..) and an assessment of their severity. It is a holistic approach (whole apparatus is controlled at the same time) and dynamic (not progressive defects are not detected).
The methods of thermal control are to excite a material or structure an input of energy (mechanical, photonic, induction heating, hot air ...). The heat diffusion in the material and its impact on the distribution of surface temperature provide information on the thermophysical properties of materials and any defects. The main advantages of all these methods lies in the possibility of a non-contact control and automation. The disadvantages are related to the slow control, investment cost and difficulty of implementation steps to reverse the diagnosis.
The magnetic particle (MT)
The VCR is a nondestructive technique of creating an intense magnetic flux inside a ferromagnetic material.
In the presence of a defect in its path, the magnetic flux is diverted and creates a leak that, by attracting the particles (colored or fluorescent) of a product developer, provides a particular signature characteristic of the defect.
The seal (LT)
Control methods involve sealing gas tracers, coupled with highly sensitive instruments to minimal concentrations of tracer gases. The most common are helium, hydrogen (hydrogenated nitrogen), the use of SF6 gas is now forbidden him by the regulations. Currently, this method is not yet codified by COFREND, but it is in many other countries1 the United States for example.
The eddy current (ET)
(ET: in English Eddy current Testing)
Eddy currents) are currents that appear in a conductive material when we vary the magnetic flux in the vicinity. They are a consequence of the law of Lenz-Faraday.
As part of the NGS is the magnetic induction B that is varied by injecting in a coil of an alternating current with different frequencies. This coil acts as a transmitter and receiver at times, the flux variation in the material creates induced currents: the eddy current (CF). In the presence of a fault, their circulation is disturbed by changes in electrical conductivity due to the geometry of the fault. This disturbance causes a change in the magnetic field created by the eddy currents that can be detected by the coil. The technique is to use a probe fitted with a coil and measure across a bridge a voltage difference generated by the change in impedance of the coil exciter / receiver.
The non-destructive testing by eddy currents can be automated which makes monitoring fast and convenient especially if the control environment is potentially dangereux.En presence of a defect complex, an additional ultrasound examination can be done for better characterize the anomaly.
Recently, coupled methods have been developed, and some are still in the research: methods electromagnetic acoustic, electromagnetic or ultrasonic magneto-optical.
non-destructive testing of aluminum castings
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