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TWI Ultrasonic Testing Part 1.

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Presentation on theme: "TWI Ultrasonic Testing Part 1."— Presentation transcript:

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

6

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


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