1. NON-DESTRUCTIVE TESTING
بسمه تعالی
بررسی آزمون های غیر مخرب
NON-DESTRUCTIVE TESTING
NDT

2. NON-DESTRUCTIVE TESTING
NDT
NON-DESTRUCTIVE TESTING
Examination of materials and components in such a way that allows material to be examinated without changing or destroying their usefulness

3. NDT Most common NDT methods: Penetrant Testing (PT)
Magnetic Particle Testing (MT)
Eddy Current Testing (ET)
Mainly used for surface testing
Radiographic Testing (RT)
Ultrasonic Testing (UT)
Mainly used for Internal Testing

4. NDT Which NDT method is the best ?
Depends on many factors and conditions

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

6. History of Ultrasonic Testing (UT)
First came ‘sonic’ testing
The piezo-electric effect discovered in 1880/81
Marine ‘echo sounding’ developed from 1912
In 1929 Sokolov used vibrations in metals to find flaws
Cathode ray tubes developed in the 1930’s
Sproule made the first flaw detector in 1942

7. Ultrasonic Inspection
Sub-surface detection
This detection method uses high frequency sound waves, typically above 2MHz to pass through a material
A probe is used which contains a piezo electric crystal to transmit and receive ultrasonic pulses and display the signals on a cathode ray tube or digital display
The actual display relates to the time taken for the ultrasonic pulses to travel the distance to the interface and back
An interface could be the back of a plate material or a defect
For ultrasound to enter a material a couplant must be introduced between the probe and specimen

9. Thickness checking the material
Ultrasonic Inspection
Pulse echo signals
A scan Display
UT Set, Digital
Compression probe
Thickness checking the material

10. Ultrasonic Inspection
defect echo
Back wall echo
initial pulse
Material Thk
defect 10 20 30 40 50
Compression Probe
CRT Display

11. 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

12. 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

13.
60 mm
The depth of the defect can be read with reference to the marker on the screen

14. 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

15. Ultrasonic Inspection
UT Set
A Scan Display
Angle Probe

16. Ultrasonic Inspection
initial pulse
defect echo
Surface distance
defect
sound path 10 20 30 40 50
Angle Probe
CRT Display

17. Ultrasonic Inspection
Advantages
Rapid results
Sub-surface detection
Safe
Can detect planar defect
Capable of measuring the depth of defects
May be battery powered
Portable
Disadvantages
Trained and skilled operator required
Requires high operator skill
Good surface finish required
Difficulty on detecting volumetric defect
Couplant may contaminate
No permanent record

18. Ultrasonic Testing
Principles of Sound

19. What is Sound ? A mechanical vibration
The vibrations create Pressure Waves
Sound travels faster in more ‘elastic’ materials
Number of pressure waves per second is the ‘Frequency’
Speed of travel is the ‘Sound velocity’

20. 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)

21. Wavelength
Velocity
Frequency

22. Sound Waves
Sound waves are the vibration of particles in solids liquids or gases
Particles vibrate about a mean position
In order to vibrate they require mass and resistance to change
One cycle

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

24. 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

25. Sound travelling through a material
Velocity varies according to the material
Compression waves
Steel 5960m/sec
Water 1470m/sec
Air 344m/sec
Copper 4700m/sec
Shear waves
Steel 3245m/sec
Water NA
Air NA
Copper 2330m/sec

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

27. 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

28. 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

29. Frequency 20 KHz = 20 000 Hz 5 M Hz = 5 000 000 Hz
Pg 21
Frequency
1 Hz = 1 cycle per second
1 Kilohertz = 1 KHz = 1000Hz
1 Megahertz = 1 MHz = Hz
20 KHz = Hz
5 M Hz = Hz

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

31. 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)

32. High Frequency Sound
5MHz compression wave probe in steel

33. Frequency F  F   = v / f Which probe has the smallest 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?

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

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

36. 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

37. Sound travels in different waveforms in different conditions
Sound Waveforms
Sound travels in different waveforms in different conditions
Compression wave
Shear wave
Surface wave
Lamb wave

38. Compression / Longitudinal
Vibration and propagation in the same direction / parallel
Travel in solids, liquids and gases
Particle vibration
Propagation

39. Shear / Transverse
Vibration at right angles / perpendicular to direction of propagation
Travel in solids only
Velocity  1/2 compression (same material)
Particle vibration
Propagation

40. Compression v Shear
Frequency
0.5MHz
1 MHz
2MHz
4MHz
6MHZ
Compression
11.8
5.9
2.95
1.48
0.98
Shear
6.5
3.2
1.6
0.8
0.54
The smaller the wavelength the better the sensitivity

41. Sound travelling through a material
Velocity varies according to the material
Compression waves
Steel 5960m/sec
Water 1470m/sec
Air 344m/sec
Copper 4700m/sec
Shear waves
Steel 3245m/sec
Water NA
Air NA
Copper 2330m/sec

42. Surface Wave Elliptical vibration Velocity 8% less than shear
Penetrate one wavelength deep
Easily dampened by heavy grease or wet finger
Follows curves but reflected by sharp corners or surface cracks

43. Lamb / Plate Wave
Produced by the manipulation of surface waves and others
Used mainly to test very thin materials / plates
Velocity varies with plate thickness and frequencies
SYMETRIC
ASSYMETRIC

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

45. Sound Beam D N = 4l 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 balanced against acceptable minimum detectable defect size
N = D 4l 2

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

47. 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

48. Near Zone

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

50. 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

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

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

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

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

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

56. 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?

57. Ultrasonic Pulse
A short pulse of electricity is applied to a piezo-electric crystal
The crystal begins to vibration increases to maximum amplitude and then decays
Maximum
10% of Maximum
Pulse length

58. Natural Pulse, No Damping,
Pulse Length
Natural Pulse, No Damping,
Long "Ring Time"

59. Pulse Length The longer the pulse, the more penetrating the sound
The shorter the pulse the better the sensitivity and resolution
Short pulse, 1 or 2 cycles
Long pulse 12 cycles

60. Pulse Length
Short, Well Damped
Pulse
Long, Well Damped

61. 5 cycles for weld testing
Ideal Pulse Length
5 cycles for weld testing

62. Resolution
RESOLUTION in Pulse Echo Testing is the ability to separate echoes from two or more closely spaced reflectors.
RESOLUTION is strongly affected by Pulse Length: Short Pulse Length - GOOD RESOLUTION Long Pulse Length - POOR RESOLUTION RESOLUTION is an extremely important property in WELD TESTING because the ability to separate ROOT GEOMETRY echoes from ROOT CRACK or LACK OF ROOT FUSION echoes largely determines the effectiveness of Pulse Echo UT in the testing of single sided welds.

63. Resolution
10%
90%
> 6dB
Good resolution

64. Resolution
50%
90%
< 6dB
Poor resolution

65. Sound travelling through a material
Loses intensity
due to
Beam Spread
Attenuation
Sound beam comparable to a torch beam
Reduction differs for small and large reflectors
Energy losses due to material
Made up of absorption and scatter

66. Scatter The bigger the grain size the worse the problem
The higher the frequency of the probe the worse the problem
1 MHz
5 MHz

67. The sound beam spread out and the intensity decreases

68. Beam spread and Attenuation combined
Repeat Back-wall Echoes Beyond The Near Zone
80%
40%
20%
37%
15%
ZERO ATTENUATION
ATTENUATION 0.02 dB/mm

69. Sound at an Interface
Sound will be either transmitted across or reflected back
Reflected
How much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materials
Interface
Transmitted

70. Acoustic Impedance Definition
The Resistance to the passage of sound within a material
Formula
 = Density , V = Velocity
Steel 46.7 x 106
Water 1.48 x 106
Air x 106
Perspex 3.2 x 106
Measured in
kg / m2 x sec

71. % Sound Reflected at an Interface
% Sound Reflected + % Sound Transmitted = 100%
Therefore
% Sound Transmitted = 100% - % Sound Reflected

72. How much sound is reflected at a steel to water interface?
Z1 (Steel) = 46.7 x 106
Z2 (Water) =1.48 x 106
reflected %
88.09
100
93856 . 2 =

73. How much sound transmitted?
100 % - the reflected sound
Example : Steel to water
100 % - 88 % ( REFLECTED) = 12 % TRANSMITTED
The BIGGER the Acoustic Impedance Ratio or Difference between the two materials: More sound REFLECTED than transmitted.

74. Large Acoustic Impedance Ratio Large Acoustic Impedance Ratio
Air
Steel
Air
Steel
Large Acoustic Impedance Ratio
Large Acoustic Impedance Ratio
Aluminum
Steel
Steel
Steel
No Acoustic Impedance Difference
Small Acoustic Impedance Difference

75. Interface Behaviour
Similarly: At an Steel - Air interface 99.96% of the incident sound is reflected At a Steel - Perspex interface 75.99% of the incident sound is reflected

76. Sound Intensity

77. 2 signals at 20% and 40% FSH.
What is the difference between them in dB’s?

78. 2 signals at 10% and 100% FSH.
What is the difference between them in dB’s?

79. Amplitude ratios in decibels
2 : 1 = 6bB
4 : 1 = 12dB
5 : 1 = 14dB
10 : 1 = 20dB
100 : 1 = 40dB