Visual techniques are widely used to ensure product reliability during manufacturing and to examine any gross discrepancies on the surface of operating components. These techniques involve illumination of object surface with light and examination of the reflected light using visual aids, usually at magnification.
Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials.
Magnetic particle inspection processes are non-destructive methods for the detection of surface and sub-surface defects in ferrous materials. They make use of an externally applied magnetic field or electric current through the material, and the principle that the magnetic flux will leave the part at the area of the flaw.
This technique involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray machine or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other media. The resulting shadowgraph shows the internal soundness of the part. Possible imperfections are indicated as density changes in the film in the same manner as an X-ray shows broken bones.
Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more.
Porosity is the fraction of the volume of voids/pores of a solid substance over the total volume. Porosity is the reason for which the internal surface area of a coal sample is far higher than the external surface area. The creation of pores in coal takes place throughout the process of coalification. The importance of pore spaces in coal can be seen in the processes of production of coke, gasification, liquefaction, research and development, catalyst evaluation, and the generation of high surface-area carbon for purifying water and gases. The knowledge of the presence of adsorbed gases in pores can help prevent accidents in mining operations.
Macro examination is the procedure in which a specimen is etched and evaluated macro structurally at low magnifications. Macro examination is a frequently used technique for evaluating steel products such as billets, bars, blooms, and forgings.