Ultrasonic Testing


  • ut14Ultrasonic testing uses high frequency sound energy to conduct examinations and make measurements.
  • Ultrasonic examinations can be conducted on a wide variety of material forms including castings, forgings, welds, and composites.
  • A considerable amount of information about the part being examined can be collected, such as the presence of discontinuities, part or coating thickness; and acoustical properties can often be correlated to certain properties of the material.


  • Applications
  • Basic Principles of sound generation
  • Pulse echo and through transmission testing
  • Inspection applications
  • Equipment
  • Data presentation
    • Transducers
    • Instrumentation
    • Reference Standards
  • Advantages and Limitations

Ultra Sound Generation

Ultrasound is generated with a transducer.A piezoelectric element in the transducer converts electrical energy into mechanical vibrations (sound), and vice versa.The transducer is capable of both transmitting and receiving sound energy.

Basic Principles of Sound

  • The measurement of sound waves from crest to crest determines its wavelength (λ).
  • The time is takes a sound wave to travel a distance of one complete wavelength is the same amount of time it takes the source to execute one complete vibration.
  • The sound wavelength is inversely proportional to its frequency. (λ = 1/f)
  • Several wave modes of vibration are used in ultrasonic inspection. The most common are longitudinal, shear, and Rayleigh (surface) waves.
  • Ultrasonic waves are very similar to light waves in that they can be reflected, refracted, and focused.
  • Reflection and refraction occurs when sound waves interact with interfaces of differing acoustic properties.
  • In solid materials, the vibrational energy can be split into different wave modes when the wave encounters an interface at an angle other than 90 degrees.
  • Ultrasonic reflections from the presence of discontinuities or geometric features enables detection and location.
  • The velocity of sound in a given material is constant and can only be altered by a change in the mode of energy.
  • Sound is produced by a vibrating body and travels in the form of a wave.
  • Sound waves travel through materials by vibrating the particles that make up the material.
  • The pitch of the sound is determined by the frequency of the wave (vibrations or cycles completed in a certain period of time).
  • Ultrasound is sound with a pitch too high to be detected by the human ear.

Principles of Ultrasonic Inspection

  • Ultrasonic waves are introduced into a material where they travel in a straight line and at a constant speed until they encounter a surface.
  • At surface interfaces some of the wave energy is reflected and some is transmitted.
  • The amount of reflected or transmitted energy can be detected and provides information about the size of the reflector.
  • The travel time of the sound can be measured and this provides information on the distance that the sound has traveled.

Test Techniques

  • ut8Ultrasonic testing is a very versatile inspection method, and inspections can be accomplished in a number of different ways.
  • Ultrasonic inspection techniques are commonly divided into three primary classifications.
    • Pulse-echo and Through Transmission (Relates to whether reflected or transmitted energy is used)
    • Normal Beam and Angle Beam (Relates to the angle that the sound energy enters the test article)
    • Contact and Immersion (Relates to the method of coupling the transducer to the test article)

Test Techniques – Pulse-Echo

  • Digital display showing signal generated from sound reflecting off back surface.
  • Digital display showing the presence of a reflector midway through material, with lower amplitude back surface reflector.
  • The pulse-echo technique allows testing when access to only one side of the material is possible, and it allows the location of reflectors to be precisely determined.

Test Techniques – Through-Transmission

  • Two transducers located on opposing sides of the test specimen are used. One transducer acts as a transmitter, the other as a receiver.
  • Discontinuities in the sound path will result in a partial or total loss of sound being transmitted and be indicated by a decrease in the received signal amplitude.
  • Through transmission is useful in detecting discontinuities that are not good reflectors, and when signal strength is weak. It does not provide depth information.