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Non-Destructive Tests

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Non Destructive Test (NDT)

X-Ray
Advantages of X-Ray X-rays are invisible electromagnetic energy, which is used as a way to get or make images of internal tissues, bones and organs of our body. It is by this process that an expert determines bones of a patient are intact or broken after an accident. Likewise, you can find internal injuries to organs. In addition, X-rays are used to find out whether or not a person has a cancerous tumour. With the increasing technological advances, the dose of the radiation exposure to patients has decreased (www.chem.ucla.edu). X-rays are a form of ionizing radiation which can pass through materials. The X-ray technology is an invaluable tool for medicine, industry, science and security. For example, it can be used to observe the fractured bones and swallowed objects, to monitor the blood flow of patients and to check for cavities. In addition, X-rays can be used to diagnose cancer, kill bacteria in food, detect flaws in machinery or products, analyze the structure of crystals or distant stars and inspect baggage at airports (www.chem.ucla.edu). Now there were more modern medical devices, which process image digitally. This technique automatically selects the parameters of the human organs to be examined (www.chem.ucla.edu).

Disadvantages of X-Ray The discovery and immediate use of X-rays and radioactive elements, in the late 19th century and early 20th century brought benefits to science and medicine, but also caused damage to several researchers, physicians, patients and others exposed to them. The health risks, even today, may not only be related to the dose of radiation received, but also to misdiagnosis and costs to the health system (www.chem.ucla.edu). X-rays are highly energetic and can ionize the material through which they penetrate. The ionization can damage cells or DNA in living matter. However, when used with care, the benefits of X-rays by far outweigh their risks (www.chem.ucla.edu).

Ultra Sonic
Advantages and Disadvantages of Ultra Sonic There are numerous advantages and benefits of Ultra Sonic. Ultra sonic has therapeutic use in medicine. Phonophoresis is a combining method, in which the influence of ultrasound on tissues and inputs with the help of medicinal substances (like drugs, and natural origin). Conducting materials under the action of ultrasound is due to higher penetration of the epidermis and skin glands, cell membranes and vessel walls to low molecular weight substances, especially bischofite mineral ions. Ultrasound has synergistic effect of therapeutic agents. Ultra sonic treatment is used in the phonophoresis spur, conditions after injuries of the musculoskeletal system, neuritis, neuropathy, radiculitis (Radicular pain), neuralgia, and nerve injury. In addition to wide use in diagnostic purposes, ultrasound is also used in medicine as a remedy.
Ultrasound has the following remedial actions: anti-inflammatory, resolving analgesic, antispasmodic, and cavitation increased permeability of the skin (www.eis.hu.edu.jo). Ultra sonic system is used in SONAR which is used in submarines. Ultrasound is alos employed in cutting metal. Conventional machine tools cannot be drilled in the metal on the narrow opening of complex shape, such as a five-pointed star. Using ultrasound as possible magnetostrictive vibrator can drill a hole of any shape. Ultrasound chisel completely replaces the drilling machine. Ultrasound can even make a screw thread in metal parts, in the glass, ruby, and diamond (www.eis.hu.edu.jo). Ultrasound is widely used for the preparation of homogeneous mixtures (homogenization). The ability of ultrasound to break the cell walls has been applied in biological research, such as the need to separate the cell from the enzymes. Ultrasound is also used for the destruction of intracellular structures such as mitochondria and chloroplasts to examine the relationship between their structure and function. In laboratories and in production, ultrasonic bath is applied for cleaning glassware and parts of the small particles. In the jewellery industry, ultrasonic baths are used to clean jewellery, fine particles of jewellery, and for polishing.

Magnetic Particle
Advantages and Disadvantages of Magnetic Particle The magnetic particle inspection is a type of non-destructive testing to detect surface and subsurface discontinuities in ferromagnetic materials. The principle of this method is that when a magnetic field is induced in a ferromagnetic material, it forms distortions in this field if the material contains an area where there are discontinuities perpendicular to the magnetic field lines, so that these deform or dust produced. These distortions or attract dust particles magnetitzable that are applied in the form of powder or suspension on the surface to examine and produce signs accumulation observed visually or directly using ultraviolet light. But the faults are parallel to the magnetic field lines are not appraised as just distort the magnetic field lines (www.iprt.iastate.edu). This technique is very useful when an inspection is required faster than that achieved using penetrating liquids. There are 32 variants of the method, each used for different applications and levels of sensitivity. This method is used in ferromagnetic materials such as iron, the cobalt and nickel. Because of its low magnetic permeability does not apply to materials or paramagnetic (such as aluminium, the titanium or platinum) or the diamagnetic (such as copper, the silver, the tin or zinc). UV and blue light can endanger eyes and skin, so an appropriate risk analysis and adequate protective measures is very important. UV radiation is a known risk to the eyes and skin. However, constitute the usual radiation exposure with the use of high-quality UV, which is a radiation source and easier to protect through personal protective equipment (covering clothing and protective eyewear) (www.iprt.iastate.edu).

Eddy Testing
Advantages and Disadvantages of Eddy Testing The technique of control by eddy currents is used in the industry for manufacturing and maintenance. The main applications of Eddy Testing are: monitoring health (search for defects that may affect the mechanical parts), the thickness measurement of coating layers, the sort of nuances, depth control treatment (e.g., depth tempering). There are numerous benefits and uses of the application of Eddy Testing technique. These advantages include the absence of surface preparation; absence of coupling; speed control (up to several meters per second) (www.engineersedge.com). Eddy t method is used as an alternative or extension of magnetic particle NDT, mainly being used to control pipes with external diameter not exceeding 140 mm. Sensitivity of the method is up to the maximum wall thickness of 5 mm. With increasing wall thickness, effective method of highlighting internal defects decreases; but it remains effective for highlighting surface defects and closes it. Eddy test method is used to induce eddy currents in the pipe wall control. The magnetic field of the eddy currents induced by the presence of discontinuities and non-homogeneities in the material, measuring coil impedance changes, which affect the amplitude and phase eddy currents. Amplitude, phase angle and depth of penetration of eddy currents depend on the amplitude and frequency of the excitation current, the electrical conductivity, magnetic permeability of the material, the shape of the part controlled by the relative position of the coils to the track, and material homogeneity control (www.engineersedge.com).

Disadvantages of Eddy Testing The demerits of the eddy testing technique are: the rapid attenuation of eddy current limits this technique to a shallow depth of control, only surface defects or near the surface can be detected; the interpretation of the signals can be complex (impedance plane analysis); and characterizing the depth of a defect type crack is difficult.

References

Advantages and Disadvantages of Selected Non-Destructive Inspection Methods. Data retrieved from http://www.engineersedge.com/inspection/inspection_pro_con.htm on 11th Oct 2012.
Basic Theory: Magnetic Particle Inspection. Institute for Physical Research and Technology. Iowa State University. Data retrieved from http://www.iprt.iastate.edu/nde/magparticle.html on 11th Oct 2012.
Introduction to Non-Destructive Testing Techniques. Data retrieved from http://www.eis.hu.edu.jo/Upload/38000000/Ultrasonic%20Testing.pdf on 11th Oct 2012.
X-ray Crystallography. Data retrieved from http://www.chem.ucla.edu/harding/lecsups/x-ray.pdf on 11th Oct 2012.

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