Knowledge

Ultrasonic Testing (UT)

This method employs high frequency sound pulses that are emitted from a transducer; this sound wave is induced in to the material through a probe which is usually in contact with the material. These sound waves propagate through the material, and are reflected back to the probe when they reach an interface. The reflected waves are transmitted back through the probe and connecting leads to a detector which can be either analogue or digital. The sounds waves are then displayed as a series of signals on a monitor and the qualified inspector can measure, and interpret these signals to allow accurate evaluation of the internal structure of the material.


Ultrasonic testing can not only be used to indicate a surface or subsurface flaw it can also be used to determine the depth, size and type of flaw. Another advantage of using UT is the accurate measurementof the thickness of the material. The method can be applied to most materials providingthe material can transmit sound waves. UT is considered to be a fast and effectiveway of inspection providing high sensitive results.



Longitudinal wave:

The particle oscillation is parallel to the wave propagation direction. Also called as Compression wave.




Shear wave:

The particle oscillation is perpendicular to the wave propagation direction. Also called as Transverse wave.




Surface wave:

The particle oscillation is neither parallel nor perpendicular to the wave propagation direction. Also called as Rayleigh wave, Lamb wave, Plate wave, Rod wave.




Reflection Vs Refraction:




Critical angles:




Pulse Echo technique:

  • The time taken by the Ultrasonic pulse to travel from the transmitter to the back wall or flaw and return to the receiver is measured.
  • Here short pulses are regularly sent out.
  • In most cases, a single probe is used for both transmission and reception of the ultrasonic pulses.



Advantages:

  • High penetrating power, which allows the detection of flaws deep in the part.
  • High sensitivity, permitting the detection of extremely small flaws.
  • Only two nonparallel surfaces need to be accessible.
  • Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.
  • Some capability of estimating the size, orientation, shape and nature of defects.
  • Non-hazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.
  • Capable of portable or highly automated operation.
  • Results are immediate. Hence on the spot decisions can be made.

Application:

  • Plates, bars, Forging, Casting, wrought products.
  • Weld inspection of vessel, pipelines, heat exchanges, storage tanks, etc.
  • Propellers, drive shafts, engine crank shafts, hull structure, gears, crane hooks, in Ship Building industry.
  • Aerospace wings, outer body, engine shaft.
  • Wind power turbine blades, rotor shat and gears.