ultrasonic

• Ultrasonic Testing


  NDT method that uses high-frequency sound energy to conduct examinations and make measurements
• Ultrasonic testing


  • Can be conducted on a wide variety of material forms including castings, forgings, welds, and composites
  • Can collect information about the part being examined such as the presence of discontinuities, part or coating thickness, and acoustical properties that can be correlated to certain properties of the material
• Sound


  Mechanical vibration of particles in a medium (solid, liquid, or gaseous)
• Wave characteristics


  • Amplitude - height of the wave from the zero axis
  • Crest - portion above the zero axis
  • Trough - portion below the zero axis
  • Wavelength (λ) - length of one cycle
  • Frequency (f) - number of cycles per second
  • Velocity (v) - distance covered per second
• In the case of an electromagnetic wave, the velocity of the wave is the same as the speed of light which is 300,000 km/sec
• Sound


  • Produced by a vibrating body and travels in the form of a wave
  • Travels through materials by vibrating the particles that make up the material
  • Pitch is determined by the frequency of the wave
  • Ultrasound is a sound with a pitch too high to be detected by the human ear
• Wavelength (λ)


  Measurement from crest to crest of a sound wave
• The time it takes a sound wave to travel a distance of one complete wavelength is the same amount of time it takes the source to complete one vibration
• Sound wavelength is inversely proportional to its frequency (λ = 1/f)
• Wave modes of vibration used in ultrasonic inspection

  • Longitudinal
  • Shear
  • Rayleigh (surface)
• Acoustic impedance (Z)


  Z=ρ*V, where ρ is density and V is velocity
• Piezoelectric effect


  Generation of electricity or electric polarity in ceramic dielectric crystals subjected to mechanical stress, or the generation of stress in such ceramic crystals subjected to an applied voltage
• Ultrasonic waves


  • 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
• Ultrasonic testing techniques


  • Pulse-echo
  • Through Transmission
  • Normal Beam
  • Angle Beam
  • Contact
  • Immersion
• Pulse-echo testing


  A transducer sends out a pulse of energy and the same or a second transducer listens for reflected energy (an echo)
• Through transmission testing


  Two transducers are used, one to send the ultrasonic signal and one to receive it on the opposite side of the test piece
• Normal beam testing


  The sound beam is introduced into the test article at 90 degrees to the surface
• Angle beam testing


  The sound beam is introduced into the test article at some angle other than 90 degrees
• Contact testing


  A couplant such as water, gel, or oil is applied between the probe and the surface of the test specimen
• Immersion testing


  The test specimen and the transducer probe are immersed in a water bath
• Couplant


  A material (usually liquid) that facilitates the transmission of ultrasonic energy from the transducer into the test specimen
• Applications of ultrasonic testing

  • Flaw detection (cracks, inclusions, porosity, etc.)
  • Erosion & corrosion thickness gauging
  • Assessment of bond integrity in adhesively joined and brazed components
  • Estimation of void content in composites and plastics
  • Measurement of case hardening depth in steels
  • Estimation of grain size in metals
• Thickness gauging


  • Routinely utilized in the petrochemical and utility industries to determine various degrees of corrosion/erosion in piping systems, storage and containment facilities, and pressure vessels
• Flaw detection in welds

  • One of the most widely used methods of inspecting weldments is ultrasonic inspection, particularly for full penetration groove welds using angle beam shear wave
• Components of an ultrasonic test system

  • Instrumentation
  • Transducers
  • Calibration standards
• Transducers


  • Manufactured in a variety of forms, shapes, and sizes for varying applications
  • Categorized by contact or immersion, single or dual element, normal or angle beam
• In selecting a transducer for a given application, it is important to choose the desired characteristics to ensure accurate inspection data
• Includes


  • Piping systems
  • Storage and containment facilities
  • Pressure vessels
• Flaw Detection in Welds

  • One of the most widely used methods of inspecting weldments is ultrasonic inspection
  • Full penetration groove welds lend themselves readily to angle beam shear wave
• Components of an ultrasonic test system

  • Instrumentation
  • Transducers
  • Calibration Standards
• Transducers


  • Manufactured in a variety of forms, shapes, and sizes for varying applications
  • Categorized by: contact or immersion, single or dual element, normal or angle beam
  • Selection is important to optimize inspection capabilities
• Contact transducers


  • Designed to withstand rigorous use, usually have a wear plate on the bottom surface
  • Many incorporate ergonomic designs for ease of grip
  • Delay line transducers have a plastic piece that provides a time delay
• Data presentation formats


  • A-scan
  • B-scan
  • C-scan
• 1. scan


  • Displays the amount of received ultrasonic energy as a function of time
  • Relative discontinuity size can be estimated by comparing signal amplitude
  • Reflector depth can be determined by the position of the signal on the horizontal sweep
• 1. scan


  • Provides a profile (cross-sectional) view of the test specimen
  • Time-of-flight (travel time) of the sound energy is displayed along the vertical axis, linear position of the transducer is displayed along the horizontal axis
  • Depth of the reflector and its approximate linear dimensions in the scan direction can be determined
• 1. scan


  • Provides a plan-type view of the location and size of test specimen features
  • Produced with an automated data acquisition system
  • Relative signal amplitude or the time-of-flight is displayed as a shade of gray or a color for each data collection position