Definition and importance of NDT<br /><ul><li>Non-destructive testing is the use of physical methods to test materials, components and assemblies for flaws in </li></ul>their structure without damaging their future usefulness.<br /><ul><li>NDT is concerned with revealing flaws in the structure of a product. It cannot predict where flaws will develop due to the design itself.
NDT plays an important role in the quality control of a product. It is used during all the stages of manufacturing of a product.</li></li></ul><li>Common characteristics of all NDT methods :<br />The application of a testing medium on the product to be tested.<br />To observe changes in the testing medium due to the defects in <br /> the structure of the product.<br />(c) An instrument which it detects these changes.<br />(d) Interpretation of these changes to obtain information <br /> about the flaws in the structure of the product.<br />
TYPES OF METHODS:<br /><ul><li>Visual testing (VT)</li></ul>*Liquid penetrant testing (LPT)<br />*Magnetic particle testing (MT)<br /><ul><li>Eddy current testing (ET)
Ultrasonic testing (UT)</li></li></ul><li>Applications:<br />Flaw Detection and Evaluation<br />Leak Detection <br />Location Determination<br />Dimensional Measurements <br />Structure and Microstructure Characterization <br />Estimation of Mechanical and Physical Properties <br />Material Sorting and Chemical Composition Determination <br />Fluorescent penetrant indication<br />
Liquid penetranttesting (PT)<br /><ul><li>This is a method which can be employed for the detection of</li></ul> open-surface discontinuities in any industrial product which <br /> is made from a non-porous material.<br /><ul><li> This method is widely used for testing of non-magnetic </li></ul> materials.<br /><ul><li>STAGES:</li></li></ul><li>
Subdivision according to the method of washing of the specimen:<br />(i) Water-washable<br />(ii) Post emulsifiable: An emulsifier is added to the excess penetrant on surface of the specimen to make it water-washable<br />(iii) Solvent removable: Excess penetrant is needed to be dissolved in a solvent to remove it from the test specimen surface.<br />
The order of decreasing sensitivity and decreasing cost: <br />(1) Post emulsifiable fluorescent dyepenetrant.<br />(2) Solvent removable fluorescent dye penetrant.<br />(3) Water washable fluorescent dye penetrant.<br />(4) Post emulsifiable visible dyepenetrant.<br />(5) Solvent removable visible dye penetrant.<br />(6) Water washable visible dye penetrant.<br />
All surface discontinuities are detected in one operation, regardless of orientation.</li></li></ul><li>LIMITATIONS:-<br /><ul><li>Test surface must be free of all contaminants (dirt,oil, grease, paint, rust, etc.).
Cannot be used on porous specimens and is difficult to use on very rough surfaces.
Removal of all penetrant materials, following the test, is often required.
It is not easy method to produce permanent record.</li></li></ul><li>MAGNETIC PARTICLE METHOD<br /><ul><li>Magnetic particle testing is used for the testing of materials which can be easily magnetized.
This method is capable of detecting open to surface and just below the surface flaws.
In this method the test specimen is first magnetized either by using a permanent or an electromagnet or by passing electric current through or around the specimen.</li></li></ul><li>Basic principle of magnetic particle testing:<br />