Ultrasonic Testing Part 1
NDT Training Training & Certification
Ultrasonic Testing
NDT Training Training & Certification
Ultrasonic Testing
Course Layout •
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Duration : 9.5 Days (Mon Fri) Start : 8:30 am Coffee Break : 10:00 10:30 am Lunch : 12:30 1:30 pm Tea Break : 3:00 3:30 pm Day End : 5:00 pm Course Objective: To train and prepare participants to obtain required skill and knowledge in Ultrasonic Testing and to meet the examination schemes requirements. –
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NDT Most common NDT methods: Penetrant Penetran t Testing Testing (PT) Magnetic Particle Testing (MT)
Mainly used for surface testing
Eddy Current Testing (ET) Radiographic Testing (RT) Ultrasonic Testing (UT)
Mainly used for Internal Testing
NDT •
Which method is the best ? Depends on many factors and conditions
Basic Principles of Ultrasonic Testing •
To understand and appreciate the capability and limitation of UT
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
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
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
0
10
20
30
40
50
60
60 mm
The depth of the defect can be read with reference to the marker on the screen
Thickness / depth measurement The closer the reflector to the surface, the signal will be more to the left of the screen
B
C
30
A
46
68
The thickness is read from the screen
C B A
The THINNER the material the less distance the sound travel
Ultrasonic Testing
Principles of Sound
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)
Properties of a sound wave •
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Sound cannot travel in vacuum Sound energy to be transmitted / transferred from one particle to another
SOLID
LIQUID
GAS
Velocity •
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•
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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 : 330 m/s
5 M Hz
STEEL
WATER
AIR
Velocity 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
ULTRASONIC TESTING Very High Frequency 5 M Hz
Glass High Frequency 5 K Hz DRUM BEAT Low Frequency Sound 40 Hz
Ultrasonic •
Sound : mechanical vibration
What is Ultrasonic? Very High Frequency sound above 20 KHz –
20,000 cps
Acoustic Spectrum Sonic / Audible Human 16Hz - 20kHz
0
10
100
1K
Ultrasonic > 20kHz = 20,000Hz
10K 100K 1M 10M 100m Ultrasonic Testing 0.5MHz - 50MHz
Ultrasonic : Sound with frequency above 20 KHz
Frequency •
Frequency
1 second 1 cycle per 1 second = 1 Hertz
:
Number of cycles per second
1 second 3 cycle per 1 second = 3 Hertz
1 second 18 cycle per 1 second = 18 Hertz
THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH
Frequency •
1 Hz
=
1 cycle per second
•
1 Kilohertz
=
1 KHz
=
•
1 Megahertz =
1 MHz
= 1000 000Hz
20 KHz =
20 000 Hz
5 M Hz =
5 000 000 Hz
1000Hz
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
wavelength
One cycle
The distance taken to complete one cycle
Wavelength
Velocity
V
f Frequency
Frequency & Wavelength
1 M Hz
5 M Hz
LONGEST
F
10 M Hz
=v/f
25 M Hz SMALLEST
F
Which probe has the smallest wavelength? Which probe has the longest wavelength?
Wavelength is a function of frequency and velocity. Therefore:
V or f V f
or V
5MHz compression wave probe in steel
5,900 ,000
5,000 ,000
1.18 mm
f
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Which of the following compressional probe has the highest sensitivity?
•
1 MHz
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2 MHz
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5 MHz
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10 MHz
10 MHz
Wavelength and frequency •
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The higher the frequency the smaller the wavelength The smaller the wavelength the higher the sensitivity
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Sensitivity
:
The smallest detectable flaw by the system or technique
•
In UT the smallest detectable flaw is ½
(half the wavelength)
The Sound Beam •
Dead Zone
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Near Zone or Fresnel Zone
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Far Zone or Fraunhofer Zone
The Sound Beam NZ
FZ
Main Beam
Intensity varies Exponential Decay
Distance
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 Main Lobe
Main Beam
Any reflector hit by the main beam will reflect the high amount of energy
Sound Beam Near Zone •
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Thickness measurement Detection of defects Sizing of large defects only
Far Zone •
Thickness measurement
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Defect detection
•
Sizing of all defects
Near zone length as small as possible
Near Zone Near Zone
D
2
4
V f 2
Near Zone
D f 4V
Near Zone •
What is the near zone length of a 5MHz compression probe with a crystal diameter of 10mm in steel? 2
Near Zone
10
2
D f 4V
5,000,000
4 5,920,000
21.1mm
Near Zone Near Zone •
•
•
D
2
4
2
D f 4V
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?
Which of the above probes has the longest Near Zone ?
1 M Hz 1 M Hz
5 M Hz
5 M Hz
Near Zone Near Zone •
•
•
D
2
4
2
D f 4V
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?
Beam Spread •
In the far zone sound pulses spread out as they move away from the crystal /2
Sine
K
2
D
or
KV Df
Beam Spread
Sine
K
2
D
or
KV Df
Edge,K=1.22 20dB,K=1.08 6dB,K=0.56 Beam axis or Main Beam
Beam Spread
Sine •
•
K
2
D
or
KV Df
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?
Beam Spread •
What is the beam spread of a 10mm,5MHz compression wave probe in steel?
Sine
2
KV Df
1.08 5920 5000 10 0.1278
7.35
o
Which of the above probes has the Largest Beam Spread ? 1 M Hz 1 M Hz
5 M Hz
5 M Hz
Beam Spread
Sine •
•
K
2
D
or
KV Df
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?
