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INSPECTION

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CERTIFICATION

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ASNT - NDT

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Ultrasonic Testing (UT)

ndt course in chennaiWe NTS training centre for ndt giving a best training for ndt course in chennai, tamilnadu, india. ndt courses in chennai, ndt courses in tamilnadu. Ultrasonic inspection is a non-destructive method in which high frequency sound waves are introduced into the material being inspected. Most ultrasonic inspection is done at frequencies between 0.5 and 20 MHz, well above the range of human hearing which is about 20 Hz to 20 kHz. The sound waves travel through the material with some loss of energy (attenuation) due to material characteristics. The intensity of sound waves is either measured, after reflection (pulse echo) at interfaces (or flaw) or is measured at the opposite surface of the specimen (pulse transmission).

The reflected beam is detected and analyzed to define the presence and location of flaws. The degree of reflection depends largely on the physical state of matter on the opposite side of the interface, and to a lesser extent on specific physical properties of that matter, for instance, sound waves are almost completely reflected at metal-gas interfaces. Partial reflection occurs at metal-liquid or metal-solid interfaces. Ultrasonic testing has a superior penetrating power than radiography and can detect flaws deep in the test specimen (say up to about 6 to 7 metre of steel). It is quite sensitive to small flaws and allows the precise determination of the location and size of the flaws. The basic principle of ultrasonic testing is illustrated

Ultrasonic testing method is:
  • Mostly used for detection of flaws in materials.
  • Widely used for thickness measurement.
  • Used for the determination of mechanical properties and grain structure of materials.
  • Used for the evaluation of processing variables on materials.
Some of the advantages of ultrasonic testing are:
  • It has high sensitivity which permits detection of minute defects.
  • It has high penetrating power (of the order of 6 to 7 metres in steel) which allows examination of extremely thick sections.
  • It has a high accuracy of measurement of flaw position and size.
  • It has fast response which permits rapid and automatic inspection.
  • It needs access to only one surface of the specimen.
Some of the limitations of this method are:
  • Unfavourable geometry of the test specimen causes problems during inspection.
  • Inspection of materials having undesirable internal structure is difficult.
  • It requires the use of a couplant.
  • The probe must be properly coupled during scanning.
  • Defect orientation affects defect detectability.
  • Equipment is quite expensive.
  • Highly skilled manpower is required.
  • Reference standards and calibration required.
  • Rough surfaces can be a problem and surface preparation is necessary