1. TWI
Ultrasonic Testing
Part 1

2. NDT Training & Certification
Ultrasonic Testing

3. Basic Principles of Ultrasonic Testing
To understand and appreciate the capability and limitation of UT

4. Basic Principles of Ultrasonic Testing
Sound is transmitted in the material to be tested
The sound reflected back to the probe is displayed on
the Flaw Detector

5. Basic Principles of Ultrasonic Testing
The distance the sound traveled can be displayed on the Flaw Detector
The screen can be calibrated to give accurate readings of the distance
Signal from the backwall
Bottom / Backwall

7. Basic Principles of Ultrasonic Testing
The presence of a Defect in the material shows up on the screen of the flaw detector with a less distance than the bottom of the material
The BWE signal
Defect signal
Defect

8.
60 mm
The depth of the defect can be read with reference to the marker on the screen

9. Thickness / depth measurement
The closer the reflector to the surface, the signal will be more to the left of the screen C B A 30 46 68
The thickness is read from the screen
The THINNER the material the less distance the sound travel C B A

10. Ultrasonic Testing
Principles of Sound

11. Sound Wavelength : The distance required to complete a cycle
Measured in Meter or mm
Frequency :
The number of cycles per unit time
Measured in Hertz (Hz) or Cycles per second (cps)
Velocity :
How quick the sound travels
Distance per unit time
Measured in meter / second (m / sec)

12. Properties of a sound wave
Sound cannot travel in vacuum
Sound energy to be transmitted / transferred from one particle to another
SOLID
LIQUID
GAS

13. Velocity The velocity of sound in a particular material is CONSTANT
It is the product of DENSITY and ELASTICITY of the material
It will NOT change if frequency changes
Only the wavelength changes
Examples:
V Compression in steel : 5960 m/s
V Compression in water : 1470 m/s
V Compression in air : m/s
5 M Hz
STEEL
WATER
AIR

14. What is the velocity difference in steel compared with in water?
4 times
If the frequency remain constant, in what material does sound has the highest velocity, steel, water, or air?
Steel
If the frequency remain constant, in what material does sound has the shortest wavelength, steel, water, or air?
Air
Remember the formula
 = v / f

15. ULTRASONIC TESTING Very High Frequency 5 M Hz
Glass
High Frequency
5 K Hz
DRUM BEAT
Low Frequency Sound
40 Hz

16. Ultrasonic Sound : mechanical vibration What is Ultrasonic?
Very High Frequency sound – above 20 KHz
20,000 cps

17. Acoustic Spectrum Sonic / Audible Human Ultrasonic 16Hz - 20kHz
> 20kHz = 20,000Hz
K K 100K 1M 10M 100m
Ultrasonic Testing
0.5MHz - 50MHz
Ultrasonic : Sound with frequency above 20 KHz

18. THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH
Frequency : Number of cycles per second
1 second
1 second
1 second
1 cycle per 1 second = 1 Hertz
3 cycle per 1 second = 3 Hertz
18 cycle per 1 second = 18 Hertz
THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH

19. Frequency 20 KHz = 20 000 Hz 5 M Hz = 5 000 000 Hz
1 Hz = 1 cycle per second
1 Kilohertz = 1 KHz = 1000Hz
1 Megahertz = 1 MHz = Hz
20 KHz = Hz
5 M Hz = Hz

20. Wavelength
Wavelength is the distance required to complete a cycle.
Sound waves are the vibration of particles in solids, liquids or gases.
Particles vibrate about a mean position.
wavelength
Displacement 
The distance taken to complete one cycle
wavelength
One cycle

21. Wavelength
Velocity
Frequency

22. Frequency & Wavelength
1 M Hz
5 M Hz
10 M Hz
25 M Hz
LONGEST
SMALLEST
 = v / f F  F 
Which probe has the smallest wavelength?
Which probe has the longest wavelength?

23. Wavelength is a function of frequency and velocity.
Therefore: f V = l V l = f V = f l or or
5MHz compression wave probe in steel

24. Which of the following compressional probe has the highest sensitivity?
1 MHz
2 MHz
5 MHz
10 MHz
10 MHz

25. Wavelength and frequency
The higher the frequency the smaller the wavelength
The smaller the wavelength the higher the sensitivity
Sensitivity : The smallest detectable flaw by the system or technique
In UT the smallest detectable flaw is ½  (half the wavelength)

26. The Sound Beam Dead Zone Near Zone or Fresnel Zone
Far Zone or Fraunhofer Zone

27. The Sound Beam FZ NZ Intensity varies Exponential Decay Distance
Main Beam
Intensity varies
Exponential Decay
Distance

28. Near Zone The side lobes has multi minute main beams
Two identical defects may give different amplitudes of signals
Near Zone
Side Lobes
The main beam or the centre beam has the highest intensity of sound energy
Any reflector hit by the main beam will reflect the high amount of energy
Main Lobe
Main Beam

29. Sound Beam Near Zone Thickness measurement Detection of defects
Sizing of large defects only
Far Zone
Thickness measurement
Defect detection
Sizing of all defects
Near zone length as small as possible

30. Near Zone

31. Near Zone
What is the near zone length of a 5MHz compression probe with a crystal diameter of 10mm in steel?

32. Near Zone The bigger the diameter the bigger the near zone
The higher the frequency the bigger the near zone
The lower the velocity the bigger the near zone
Should large diameter crystal probes have a high or low frequency?

33. Which of the above probes has the longest Near Zone ?
1 M Hz
5 M Hz

34. Near Zone The bigger the diameter the bigger the near zone
The higher the frequency the bigger the near zone
The lower the velocity the bigger the near zone
Should large diameter crystal probes have a high or low frequency?

35. Beam Spread
In the far zone sound pulses spread out as they move away from the crystal
/2 

36. Beam Spread
Edge,K=1.22
20dB,K=1.08
6dB,K=0.56
Beam axis or Main Beam

37. Beam Spread The bigger the diameter the smaller the beam spread
The higher the frequency the smaller the beam spread
Which has the larger beam spread, a compression or a shear wave probe?

38. Beam Spread
What is the beam spread of a 10mm,5MHz compression wave probe in steel?

39. Which of the above probes has the Largest Beam Spread ?
1 M Hz
5 M Hz

40. Beam Spread The bigger the diameter the smaller the beam spread
The higher the frequency the smaller the beam spread
Which has the larger beam spread, a compression or a shear wave probe?

41. Testing close to side walls