1. G.Jothinathan Project consultant C N D E . MDS
I I T M. Chennai
GJ, IIT M, Chennai

2. Overview of Ultrasonic Testing Methods
Contact Testing Through Transmission
Pulse Echo
Immersion Testing Resonance Technique
Normal Probe A Scan
Pulse Echo B Scan
Angle Probe C Scan

4.                                                                                        
Normal probe – suited for this orientation as reflected waves reach back the crystal
                                                                                                  
Normal probe – unsuitable for oriented defects as the reflected waves do not reach back the crystal
Parallel orientation results in virtually no reflection as the length is small

6. A-Scan: B-Scan and C Scan techniques and images
                      
A-Scan – point scanning – CRT gives point by information -
two information - echo position & echo amplitude
B-Scan –line scanning -CRT gives image for the line scanning
two information- probe placement &
- depth corresponding to the probe placing
C- Scan–Volume Scanning- CRT gives the image for the entire area – plan view similar to radiographic image

7. Ultrasonic Test (UT)
GJ, IIT M, Chennai

8. A,B & C Scan images .

9. Applicability of Ultrasonic Testing
Materials that allow propagation of US waves can be tested. Most engineering materials can be tested as they propagate US waves. The propagation capability can be ascertained from attenuation coefficient values, which indicate the loss of US wave energy as the waves propagate
Table of attenuation values
It can be seen low attenuation materials like fine grained materials can be easily tested . Coarse grained metals and metals having second phase particles are difficult to test.
For these reasons cast metals and composites are normally difficult to test ultrasonically

10. Applications of Ultrasonic Testing
Flaw detection and evaluation (location, size & nature)
2. Thickness measurement -(pipe lines, reactor vessels one side accessibility)
3.Material characterisation - grain size
- proportion of phases
- nodularity of cast iron
- hydrogen damage
- extent of deformation
4.Quality control tool E and  are related to
ultrasonic wave velocitiesCl and Ct  
5.Bond integrity testing - Bearings and aircraft
structures (adhesive)

11. Ultrasonic Testing (UT)
Ultrasonic waves
- sound waves of frequency more than 20 KHz
- UT frequencies of 0.5 MHz to 15 MHz (25 MHz)
choice of frequency depends on sensitivity required and attenuation (loss of US wave energy as it propagates) properties of the material.
Higher the frequency – higher the sensitivity
Higher the frequency– higher the attenuation of US waves
with the result it may not be possible to use high frequency probes with high attenuating materials settling for low sensitivity. As a corrolary wavelength and sensitivity and attenuation
Limit of defect detectability = λ/2– Smaller than this cannot be detected - why
Generation
Piezoelectric materials - presently artificially produced polarised ceramic transducers - BaTiO3, PZT, Pb meta niobate etc- mechanical vibrations to electric pulse
electrical pulse to mechanical vibrations
Magnetostrictive and electrodynamic- not normally used

12. Following guide-lines may be used for selection of the probes:
FREQUENCY APPLICATION
0.5 MHz Very coarse grained materials like C.I., S. G. Iron,
austenitic Stainless , Steel, soft plastics, rubber,
composites etc.
1.0 MHz For coarse grained materials like steel castings and
those with very high thickness.
2.0 MHz  For large sized components with fair sensitivity
requirement like testing of forgings.
4.0 MHz  For optimum sensitivity, resolution and penetration.
For inspection of fine grained material and those
involving low thickness.
6.0 MHz For very high sensitivity or checking thin walled
components used in critical space and nuclear
applications.
10.0 MHz For obtaining exceptionally high
sensitivity and resolution. For
inspection of materials like titanium,
managing steel etc.

13. Properties
1. Propagation - most engg. materials allow the propagation of USW - elastic property of the material-they allow the vibration to be transmitted
2. Reflection - Transmission
Propagating US waves get reflected/transmitted at interfaces. Large acoustic impedance mismatch between the mediums leads to reflection
similar to light reflection by mirror
Acoustic impedance = density X wave velocity
Reflection energy coefficient R= (Z2 - Z1)2 /
(Z2+Z1) 2
R = 99% for a crack interface: air interface
R = % for various inclusions
Transmission energy coefficient T = 4 Z1 Z2
(Z2+Z1) 2
Probe in direct contact with steel : T (BaTiO3-air-steel) = 0.005%
Probe in contact with couplant:T (BaTiO3-any couplant-steel) = 16%
(hence use of couplant is must in UT)
Other properties

14. Pulse Echo Technique
Almost entire UT is carried out with this technique
The principle is similar to echo hearing by bats to locate obstacles or prey
In this method, the elapsed time between the sending of the waves at the front surface and receiving of reflected waves is measured. The time information is converted into thickness information through the wave velocity in the material. The interfaces are identified- how
Wave velocity in steel is 5900 m/sec. From this it is evident that that the time of travel Ultrasonic waves in 100 mm of steel is of the order of microseconds
To measure time of this order a CRT is used

15. Ultrasonic testing
Ultrasonic waves are sent and Reflected ultrasonic waves are received and elapsed time is measured. Defect detected and located
                                                                                     
                                                                                     
                                                                                     
                                                                                     
Bats can accurately size their prey

16. GJ, IIT M, Chennai

17. Pulse Echo Method ( A-Scan) - propagation of US waves in the medium
- reflection at interfaces
measurement of elapsed time between sending and the receiving of waves-time information converted to depth information thro the velocity of USW in the medium-material .constant- from depth, location is identified ie whether backwall interface or flaw interface
- -Essentially time measurement and CRT is used--
Features of Pulse Echo A-scan Technique
1. Same probe acts as Transmitter and Receiver
2. Simultaneous application of pulse to Xal and
X-electrodes of CRT
Waves generated,get transmitted and propagating
Bright spot appears on screen at the left corner and travels left to
right- the speed of travel determined by time base setting
Time elapses
3. reflected waves reach the Xal- gets converted to an electric pulse
amplified and fed to the Y-electrodes which causes a deflection of
the moving bright spot vertically
- the point deflection in the X-axis indicates elapsed time (depth)
4. Next pulse is applied (why next pulse need be applied 50 –1200 pulses.sec

18. REPT. FREQ. AND SWEEP VOLTAGE GENERATOR BLOCK DIAGRAM OF AN ULTRASONIC
PULSE GENERATOR
AMPLIFIER
BLOCK DIAGRAM OF AN ULTRASONIC
PULSE ECHO EQUIPMENT

20. Ultrasonic wave propagation
Propagation of vibrations or oscillations – ( to and fro motion)unlike electromagentic radiation needs a medium for propagation
Wave - disturbance that travels through a
medium, transmitting energy from
one location to another location.
Medium - the material through which the
disturbance is moving – medium is
permanently displaced
GJ, IIT M, Chennai

21. Medical ultrasound- 2.5 MHz to 15 MHz
Infrasound Hz- used by elephants
Audible sound - 20 Hz to 20,000 Hz
Ultrasound - >20,000 Hz (or 20 KHz) - used by bats to locate obstacles as well as
to find prey- dolphins and cats and dogs
Medical ultrasound- 2.5 MHz to 15 MHz
Industrial Ultrasound –0.5MHz –25 MHz- 100 MHz
High energy ultrasound generated using magnetostrictive effect is widely used by process industries for mixing up, effectively cleaning using solvents
GJ, IIT M, Chennai

22. Definitions 1. Time period – time for one full oscillation-
secs, microsecs, nanosecs
2. Frequency–no. oscillations/unit time-cycles/sec Hz,
KHz, MHz
US waves above 20 KHz. 0.5 MHz – 15 MHz:25MHz
Time period and frequency are inversely related
3. Wavelength - displacement for one full oscillation
mm, cm, metre
Wave velocity is a material property dependant on ρand and μ and not thickness, distance or travel or probe frequency.
4. Wave velocity– phase velocity – different from
particle velocity velocity with which energy transferred
or the velocity with disturbance travels - C = f/λ
C being a material constant,‘λ’ is inversely proportional to ‘f’the frequecny
Guided waves are dispersive in nature- the velocity is dependant not only on material but also on thickness of the material and frequency of the probe

23. Wave velocity (contd)
Wave velocity is a material property determined by density, Youngs Modulud and Poisssons’ ratio
Wavelength contd
The ultrasonic wave interaction with obstacles or interfaces is determined by the relative sizes of the obstacle and wavelength
Defect detecability in UT = wavelength / 2
Anything below this cannot be detected - why

24. Acoustic impedance (Z)
ratio of acoustic pressure to particle velocity Z = P/V
from the above one can get an expression Z = ρ Cl or Z = ρ Ct
Z is an important property of ultrasonic waves as the entire property of reflection /transmission is determined the acoustic impedances of the two mediums Unit of Z
1.the design of ultrasonic transducers.
2.assessing absorption of sound in a medium.
The acoustic impedance (Z) of a component is the ratio of the acoustic (or AC) pressure p across it to the flow of fluid U through it. Like electrical impedance, acoustic impedance is complicated by the fact that the current and pressure are not necessarily in phase -- the maximum voltage may be ahead of the maximum current, or vice versa. As in electricity, we use complex numbers to handle this, where the real part represents the in-phase component and the imaginary part the out-of-phase component.
GJ, IIT M, Chennai

25. Pressure, Energy and Intensity: (indicative of amount of X-rays )
Sound pressure: pressure or stress oscillation in a medium with wave propagation ie x for longitudinal and xy for transverse waves.
Energy density: Intensity :
They are proportional to square of sound pressure. The above three terms denote the quantity of sound waves in a medium.
I or E  P 2
The sound pressure is the most important in UT since echo height at the screen is proportional to the sound pressure.
Intensity = Energy /unit area/unit time since the energy/time ratio is equivalent to the quantity power , intensity is simply the power/area.
Typical units for expressing the intensity of a sound wave are Watts/meter2.
GJ, IIT M, Chennai

26. Types and modes of vibration
Types of ultrasonic waves : continuous and pulsed
Modes of vibration–the relationship between particle movement direction and wave propagation direction
Modes of vibration are
Longitudinal – compressional
Transverse shear
3. Surface Rayleigh
5. Plate waves Lamb
6. Rod waves Love waves
Guided waves
dispersive
GJ, IIT M, Chennai

27. Coninuous and pulsed waves
Type of waves that could be used in Pulse echo
Through transmission &
Resonance
GJ, IIT M, Chennai

28. Modes of vibration (continued)
Topic will be dealt under the following headings
1. Definition Example Mediums of wave propagation
4. Generation Expression for wave velocity
Longitudinal waves
1.Particle movement direction is
parallel to wave propagation
direction
2. Sound in air
3. Longitudinal waves propagate in all mediums gas, liquid and solid
4.All piezoelectric materials generate longitudinal waves. Exception is Y cut quartz
5. Expression for wave velocity

29. 1. Particle movement direction is perpendicular to the wave
Transverse waves
1. Particle movement direction is
perpendicular to the wave
propagation direction
2. Rope pulled from one end
3. Propagates only in solid medium
Shear forces cannot be sustained
by fluids
4. No piezoelectric material except Y
cut quartz on its own generate
transverse waves
5. Expression for wave velocity
GJ, IIT M, Chennai

30. Longitudinal and transverse waves
For same frequency of probe in steel, which mode is sensitive – long or trans
Cl and Ct equations can be solved to get E & μ
μ = C l2 — 2 C t2
2( C l2 — C t2)
E = ρ C l C l2 — 4 C t2
C l2 — C t2
Substitute μ for steel
Cl/Ct = 91/50
Long. 91mm in steel is equivalent to 50 mm of shear
Applications :
1. good for quality control tool
2. material chracterization
GJ, IIT M, Chennai
Meaning of the above

31. Compression waves Vibration and propagation in the same direction
Travel in solids, liquids and gases
Propagation
Particle vibration
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32. Shear waves Vibration at right angles to direction of propagation
Travel in solids only
Velocity  1/2 compression (same material)
Particle vibration
Propagation
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33. GJ, IIT M, Chennai

34. Surface waves/((Rayleigh waves) x 1-
            (                             
Surface waves/((Rayleigh waves) x 1-
1. The particles move in an
elliptical path
2. Example- Earth quake
                                                   
3. Only in solids- contains transverse wave component
4. Oblique incidence of longitudinal wave: the angle corresponding to second critical angle
5. C0 = 0.9 Ct

35. Surface Waves Elliptical vibration Velocity 8% less than shear
Penetrate one wavelength deep
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36. Useful depth of penetration is limited to one wavelength
Reflected by sharp corners
Propagates along smooth curves
Damped by oil, grease & dirt
Very good candidates for complicated shapes for surface defects turbine blades curved and holes below.
Rayleigh waves are useful because they are very sensitive to surface defects and since they will follow the surface around, curves can also be used to inspect areas that other waves might have difficulty reaching.
GJ, IIT M, Chennai

37. Complicated geometry- turbine blades
GJ, IIT M, Chennai

38. GJ, IIT M, Chennai

39. Plate,Rod waves -Lamb waves & Love wavesGuided waves)
Plate thickness or dia. of rod Is equal to the wavelength pure L,T and S cannot exist.
In these cases Plate waves and Rod waves are generated.
1. Complicated motion of particles : symmetrical and assymetrical
2.They are dispersive: wave velocity not only depends on , E & 
but also on frequency and thickness of the material.
3. Sin  = Vl /VP where Vl is desired velocity
Frequency & thickness and velocity relationship-dispersion curves
As these waves involve the entire thickness for the propagation, the frequency need be so chosen that the wavelength correspond to the thickness of the plate. The velocity can be found using dispersion curves

40. Lamb and Love waves (continued)
Lamb waves are similar to longitudinal waves, with compression and rarefaction, but they are bounded by the sheet or plate surface causing a wave-guide effect.
As the entire thickness is involved, normally these waves are generated in thin plates and rod.
Velociy need be found out for frequency-thickness combination and graphs (dispersion curves)are available
GJ, IIT M, Chennai

41. Advances in NDE II – Newer UT methods
Guided waves, Phased array probe, Backscattering techniques and TOFD
Conventional UT & Guided Waves Testing
Transducer
Global inspection
Region of inspection
Transducer
Conventional ultrasonic testing
Guided wave inspection
Length of coverage limited to the probe size
Length of coverage high upto 100 mtrs
Buried pipelines and insulation coatings pose problems
Buried structures with insulation coatings can be tested

42. Generally Corroded Pipe
0.0
5.0
10.0
15.0
20.0
2.0
4.0
6.0
8.0
12.0
Distance (m)
Clean Pipe
Generally Corroded Pipe
GJ, IIT M, Chennai