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ULTRASONIC TESTING

It is a non-destructive testing (NDT) method in which beams of high frequency sound waves that are introduced into the material being tested are used to detect surface and sub-surface flaws. The sound waves travel through the materials with some attenuation of energy and are reflected at interfaces. The reflected beam is detected and analyzed to define the presence and location of flaws. Cracks, laminations, shrinkage, cavities, bursts, flakes, pores, bonding faults and other discontinuities that can act as metal-gas interfaces can be easily detected. Inclusions and other inhomogenities in the metal being inspected can also detected by causing partial reflection or scattering of the ultrasonic waves, or by producing some other detectable effect on the ultrasonic waves.

Most of the ultrasonic inspection instruments detect flaws by monitoring one or more of the following:

  • Reflection of energy from metal-gas interfaces, metal-liquid interfaces or discontinuities within the metal itself
  • Time of transit of a sound wave through the test piece from the entrance point at the sending (transmitting) transducer to the exit point at the receiving transducer, and
  • Attenuation of the beam of sound waves by absorption and scattering within the test piece.

Applicability

Ultrasonic testing or inspection (UT) is used for quality control and materials testing in all major industries. This includes Ultrasonic testing of castings, forgings, plates, extruded components, weld joints, electrical and electronic component manufacturing, production of steel, aluminum and titanium, fabrication of structures such as air frames, pressure vessels, ships, bridges, motor vehicles, machinery and jet engines. UT can also use in various in service inspections. They may be inherent in the raw materials, may result from fabrication and heat treatment, or may occur in service from fatigue, corrosion or other causes. Ultrasonic testing can also be used to measure thickness of metal sections during manufacturing and maintenance inspections.


MAGNETIC PARTICLE TESTING

Magnetic particle testing or MPT is a nondestructive testing method for locating surface and near surface discontinuities in ferromagnetic materials. It depends for its operation on the fact that when the material or part under test is magnetized, discontinuities that lie in a cause leakage field to the direction of the magnetic field will cause a leakage field to be formed at and above the surface of the part.Ferromagnetic materials include most of the iron, nickel and cobalt alloys.

Applications

The principal industrial uses of magnetic article testing are final inspection, receiving inspection, in process inspection and quality control, maintenance and overhaul in the transportation industries, plant and machinery maintenance and inspection of large components.


LIQUID PENETRANT TESTING

Liquid or dye penetrant testing is a non –destructive method for finding discontinuities that are open to the surface of solid and essentially non-porous materials. Indications of flaws can be found regardless of the size, configuration, internal structure, or chemical composition of work piece being tested and regardless of flaw orientation. The process is well suited for the detection of all types of surface cracks, laps, porosity, shrinkage areas, lamination and similar discontinuities in casting, forgings, welds and other product forms. Dye penetrant inspection is used extensively for the testing of wrought and cast products of ferrous and non-ferrous metals, powder metallurgy parts, and ceramics and glass objects.


VISUAL TESTING

Visual inspection is one of the most common and most powerful means of non-destructive testing. Visual testing requires adequate illumination of the test surface and proper eye-sight of the tester. To be most effective visual inspection does however, merit special attention because it requires training (knowledge of product and process, anticipated service conditions, acceptance criteria, record keeping, for example) and it has its own range of equipment and instrumentation. It is also a fact that all defects found by other NDT methods ultimately must be substantiated by visual inspection.