ULTRASONIC TESTING (UT) - NDT

ME367 NON-DESTRUCTIVE TESTING MODULE-4 UT Sukesh O P, AP-ME, JECC 16-Oct-18 SUKESH O P/ APME/JECC 1

ME357 Non-Destructive Testing 16-Oct-18 SUKESH O P/ APME/JECC 2 Introduction to NDT- Visual Inspection- Liquid Penetrant Inspection- Magnetic Particle Inspection- Ultrasonic Testing - Radiography Testing- Eddy Current Testing.

MODULE-4 16-Oct-18 SUKESH O P/ APME/JECC 3

16-Oct-18 SUKESH O P/ APME/JECC 4

INTRODUCTION 16-Oct-18 SUKESH O P/ APME/JECC 5  Ultrasonic testing(UT) which is applicable to most materials, metallic or non-metallic.  Ultrasonic testing uses high frequency sound energy to conduct examinations and make measurements.  Ultrasonic examinations can be conducted on a wide variety of material forms including castings, forgings, welds, and composites.  By this method, surface and internal discontinuities such as laps, seams, voids, cracks, blow holes, inclusions and lack of bond can be accurately evaluated from one side. Frequencies from 1-10 Mega Hertz(MHz) are typically used.

Basic Principle of UT 16-Oct-18 SUKESH O P/ APME/JECC 11  In ultrasonic testing, ultrasound transducer connected to a diagnostic machine is passed over the object being inspected.  The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing. However, when ultrasonic testing is conducted with an Electromagnetic Acoustic Transducer (EMAT) the use of couplant is not required.  There are two methods of receiving the ultrasound waveform: reflection and attenuation

SOUND 16-Oct-18 SUKESH O P/ APME/JECC 13 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)

Basic Principles of Sound  Sound is produced by a vibrating body and travels in the form of a wave.  Sound waves travel through materials by vibrating the particles that make up the material.  The pitch of the sound is determined by the frequency of the wave (vibrations or cycles completed in a certain period of time).  Ultrasound is sound with a pitch too high to be detected by the human ear. 16-Oct-18SUKESH O P/ APME/JECC14

Properties of a sound wave 16-Oct-18 SUKESH O P/ APME/JECC 15  Sound cannot travel in vacuum  Sound energy to be transmitted / transferred from one particle to another

Sound waves 16-Oct-18 SUKESH O P/ APME/JECC 16  All sound waves, whether audible or ultrasonic, are mechanical vibrations involving movement of the medium in which they are travelling.  A sound wave may be transmitted through any material which behaves in an elastic manner.  Longitudinal waves  Transverse or shear waves  Surface or Rayleigh waves

Ultrasonic waves  Ultrasonic waves are very similar to light waves in that they can be reflected, refracted, and focused.  Reflection and refraction occurs when sound waves interact with interfaces of differing acoustic properties.  In solid materials, the vibrational energy can be split into different wave modes when the wave encounters an interface at an angle other than 90 degrees.  Ultrasonic reflections from the presence of discontinuities or geometric features enables detection and location.  The velocity of sound in a given material is constant and can only be altered by a change in the mode of energy. 16-Oct-18SUKESH O P/ APME/JECC17

Longitudinal waves 16-Oct-18 SUKESH O P/ APME/JECC 18  Longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave.  Mechanical longitudinal waves are also called compressional or compression waves, because they produce compression and rarefaction when traveling through a medium, and pressure waves, because they produce increases and decreases in pressure.

Transverse or shear wave 16-Oct-18 SUKESH O P/ APME/JECC 20  A transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave).  If a transverse wave is moving in the positive x- direction, its oscillations are in up and down directions that lie in the y–z plane.  Light is an example of a transverse wave, while sound is a longitudinal wave. A ripple in a pond and a wave on a string are easily visualized as transverse waves.

Surface or Rayleigh waves 16-Oct-18 SUKESH O P/ APME/JECC 22  This type of waves can travel only along surface bounded on one side by strong elastic forces of the solid and on the other by nearly nonexistent elastic forces between gas molecules.  Surface waves therefore are essentially nonexistent in a solid immersed in liquid, unless the liquid covers the solid surface only as a very thin layer.

Plate or Lamp waves 16-Oct-18 SUKESH O P/ APME/JECC 24

VELOCITY 16-Oct-18 SUKESH O P/ APME/JECC 27  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

FREQUENCY 16-Oct-18 SUKESH O P/ APME/JECC 32 the minimum size of defect, which is to be detected and the medium in which such a defect is situated.  Generally the choice of test frequency depends upon two factors : the minimum size of defect, which is to be detected and the medium in which such a defect is situated.

Reflection 16-Oct-18 SUKESH O P/ APME/JECC 36  Light can bend and move through the material, which is called refraction. Or, light can bounce off the material, which is called reflection.  When sound travels in a given medium, it strikes the surface of another medium and bounces back in some other direction, this phenomenon is called the reflection of sound. The waves are called the incident and reflected sound waves. SUKESH O P/ APME/JECC

Divergence 16-Oct-18 SUKESH O P/ APME/JECC 37  A term used to describe the spreading of ultrasonic waves beyond the near field. It is a function of the transducer diameter and wave length in the medium.  Divergence angle, angle within the far field between the beam axis and the beam edge at which the amplitude has fallen by a defined level

16-Oct-18 SUKESH O P/ APME/JECC 38  Scattering : it is the reflection of sound beam from its original direction of propagation.  Absorption : it is conversion of sound energy from one form to some another form.

Attenuation of sound waves 16-Oct-18 SUKESH O P/ APME/JECC 39  It is a combined effect of scattering and absorption. Which states that when a sound beam travels through any medium, its intensity gradually reduces due to scattering and absorption.  Attenaution defines the decay rate of propagated sound wave.

TEST TECHNIQUES 16-Oct-18 SUKESH O P/ APME/JECC 40  Ultrasonic testing is a very versatile inspection method, and inspections can be accomplished in a number of different ways.  Ultrasonic inspection techniques are commonly divided into three primary classifications.  Pulse-echo and Through Transmission - (Relates to whether reflected or transmitted energy is used)  Normal Beam and Angle Beam - (Relates to the angle that the sound energy enters the test article)  Contact and Immersion - (Relates to the method of coupling the transducer to the test article)

Pulse Echo Method 16-Oct-18 SUKESH O P/ APME/JECC 41  This is the method most commonly utilized in the ultrasonic testing of materials. The transmitter and receiver probes are on the same side of the specimen and the presence of a defect is indicated by the reception of an echo before that of the back wall echo.  The CRT screen is calibrated to show the separation in distance between the time of arrival of a defect echo as against that of the back wall echo of the specimen, therefore, the location of a defect can be assessed accurately.

Pulse Echo Technique 16-Oct-18 SUKESH O P/ APME/JECC 42

Pulse Echo Technique 16-Oct-18 SUKESH O P/ APME/JECC 43  Single probe sends and receives sound  Gives an indication of defect depth and dimensions  Not fail safe

Through Transmission Method 16-Oct-18 SUKESH O P/ APME/JECC 44  In this method two ultrasonic probes are used.  One is the transmitter probe and the other is the receiver probe.

16-Oct-18 SUKESH O P/ APME/JECC 45  In this method the presence of an internal defect is indicated by a reduction in signal amplitude, or in the case of gross defects, complete loss of the transmitted signal. SUKESH O P/ APME/JECC

Through transmission testing 0246810 Through transmission signal 1 2 1 2 T T R R Flaw 16-Oct-18 SUKESH O P/ APME/JECC 46

Through Transmission Technique 16-Oct-18 SUKESH O P/ APME/JECC 47

Through Transmission Technique 16-Oct-18 SUKESH O P/ APME/JECC 48  Advantages  Less attenuation  No probe ringing  No dead zone  Orientation does not matter  Disadvantages  Defect not located  Defect can’t be identified  Vertical defects don’t show  Must be automated  Need access to both surfaces

Resonance Method 16-Oct-18 SUKESH O P/ APME/JECC 50  A condition of resonance exists whenever the thickness of a material equals half the wavelength of sound or any multiple thereof in that material.  Control of wavelength in ultrasonics is achieved by control of frequency.

Resonance Method 16-Oct-18 SUKESH O P/ APME/JECC 51  Knowing the resonance or fundamental frequency f and velocity V of ultrasound in the specimen the thickness ‘t’ of the specimen under test can be calculated from the equation : -  Since it is difficult to recognize the fundamental mode of vibration, the fundamental frequency is usually calculated from the difference of two adjacent harmonics which are depicted by two adjacent rises in the pulse amplitude.

Resonance Method 16-Oct-18 SUKESH O P/ APME/JECC 52  This method is used for the inspection of large ingots and castings particularly when the attenuation is high and gross defects are present. does not give the size and location of the defect.  The method does not give the size and location of the defect. In addition good mechanical coupling and alignment of the two probes is essential.

16-Oct-18 SUKESH O P/ APME/JECC 53  Techniques of ultrasonic testing are either of the contact type or the immersion type.  In the contact type  In the contact type, the probe is placed in direct contact with the test specimen with a thin liquid film used as a couplant for better transmission of ultrasonic waves in to the test specimen.  In the immersion type  In the immersion type, a waterproof probe is used at some distance from the test specimen and the ultrasonic beam is transmitted in to the material through a water path or water column.

Contact Type Techniques 16-Oct-18 SUKESH O P/ APME/JECC 54 Normal Beam Techniques:  In the normal beam technique the ultrasonic beam is projected perpendicularly in to the test specimen. This technique may use either single, double or SE normal beam probes.  With the single probe, the transducer of the probe acts as both transmitter and receiver.

Straight beam inspection techniques: Direct contact, single element probe Direct contact, dual element probe Fixed delay Immersion testingThrough transmission 16-Oct-18 SUKESH O P/ APME/JECC 55

16-Oct-18 SUKESH O P/ APME/JECC 56  Angle Beam Techniques predetermined angle to the test surface.  The angle beam technique is used to transmit ultrasonic waves in to a test specimen at a predetermined angle to the test surface.  Transverse waves 35° and 80°  Transverse waves at various angles of refraction between 35° and 80° are used to locate defects whose orientation is not suitable for detection by normal beam techniques.

16-Oct-18 SUKESH O P/ APME/JECC 57  Surface Wave Techniques  Surface wave techniques have been used very successfully for a great number of applications, particularly in the Aircraft Industry.  The main advantage of surface waves is that they follow gentle contours and are reflected sharply only by sudden changes in contour, thus making it a very useful tool for the examination of complex shaped components.  The main limitation of these waves is that they are almost immediately attenuated if the surface finish is rough, is covered in scale or a liquid (such as the couplant), or if any pressure is applied by another object (such as the hand of the operator ).

Immersion Testing Techniques 16-Oct-18 SUKESH O P/ APME/JECC 58 laboratory and for large installations doing automatic ultrasonic testing. longitudinal and transverse waves can be generated with the same probe simply by changing the incident beam angle.  Immersion testing techniques are mainly used in the laboratory and for large installations doing automatic ultrasonic testing. It has the advantage that uniform couplant conditions are obtained and longitudinal and transverse waves can be generated with the same probe simply by changing the incident beam angle.  In the immersion technique both the probe and the test specimen are immersed in water. The ultrasonic beam is directed through the water in to the test specimen, using either a normal beam technique for generating longitudinal waves or an angle beam technique for generating transverse waves.

surface = sound entry backwall flaw 12 water delay 0 246810 0 2468 IE IP BE F 1 2 Immersion testing 16-Oct-18 SUKESH O P/ APME/JECC 59

Immersion testing 16-Oct-18 SUKESH O P/ APME/JECC 61  In the bubbler or squirter technique, the ultrasonic beam is directed through a water column in to the test specimen.  This technique is usually used with an automated system for high speed scanning of plate, sheet, strip, cylindrical forms and other regularly shaped forms.

Immersion testing 16-Oct-18 SUKESH O P/ APME/JECC 62

Immersion testing 16-Oct-18 SUKESH O P/ APME/JECC 63  In the wheel transducer technique the ultrasonic beam is projected through a water-filled tire in to the test specimen.  The probe, mounted on the wheel axle, is held in a fixed position while the wheel and tire rotate freely.

Equipment Equipment for ultrasonic testing is very diversified. Proper selection is important to insure accurate inspection data as desired for specific applications. In general, there are three basic components that comprise an ultrasonic test system: - Instrumentation - Transducers - Calibration Standards 16-Oct-18 SUKESH O P/ APME/JECC 64

1. TRANSDUCERS Transducers are manufactured in a variety of forms, shapes and sizes for varying applications. Transducers are categorized in a number of ways which include: - Contact or immersion - Single or dual element - Normal or angle beam In selecting a transducer for a given application, it is important to choose the desired frequency, bandwidth, size, and in some cases focusing which optimizes the inspection capabilities. 16-Oct-18 SUKESH O P/ APME/JECC 65

Contact Transducers Contact transducers are designed to withstand rigorous use, and usually have a wear plate on the bottom surface to protect the piezoelectric element from contact with the surface of the test article. Many incorporate ergonomic designs for ease of grip while scanning along the surface. 16-Oct-18SUKESH O P/ APME/JECC66

Contact Transducers (cont.)  Contact transducers are available with two piezoelectric crystals in one housing. These transducers are called dual element transducers.  One crystal acts as a transmitter, the other as a receiver.  This arrangement improves near surface resolution because the second transducer does not need to complete a transmit function before listening for echoes.  Dual elements are commonly employed in thickness gauging of thin materials. 16-Oct-18SUKESH O P/ APME/JECC67

Angle beam Transducers  Angle beam transducers incorporate wedges to introduce a refracted shear wave into a material.  The incident wedge angle is used with the material velocity to determine the desired refracted shear wave according to Snell’s Law)  Transducers can use fixed or variable wedge angles.  Common application is in weld examination. 16-Oct-18SUKESH O P/ APME/JECC68 SUKESH O P/ APME/JECC

Immersion Transducers  Immersion transducers are designed to transmit sound whereby the transducer and test specimen are immersed in a liquid coupling medium (usually water).  Immersion transducers are manufactured with planar, cylindrical or spherical acoustic lenses (focusing lens). 16-Oct-18SUKESH O P/ APME/JECC69

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2. INSTRUMENTATION  Ultrasonic equipment is usually purchased to satisfy specific inspection needs, some users may purchase general purpose equipment to fulfill a number of inspection applications.  Test equipment can be classified in a number of different ways, this may include portable or stationary, contact or immersion, manual or automated.  Further classification of instruments commonly divides them into four general categories: D-meters, Flaw detectors, Industrial and special application. 16-Oct-18 SUKESH O P/ APME/JECC 72

D-meters or digital thickness gauge  D-meters or digital thickness gauge instruments provide the user with a digital (numeric) readout.  They are designed primarily for corrosion/erosion inspection applications. Some instruments provide the user with both a digital readout and a display of the signal. A distinct advantage of these units is that they allow the user to evaluate the signal to ensure that the digital measurements are of the desired features. 16-Oct-18SUKESH O P/ APME/JECC73

3. CALIBRATION STANDARDS  Calibration is a operation of configuring the ultrasonic test equipment to known values. This provides the inspector with a means of comparing test signals to known measurements.  Calibration standards come in a wide variety of material types, and configurations due to the diversity of inspection applications.  Calibration standards are typically manufactured from materials of the same acoustic properties as those of the test articles. 16-Oct-18 SUKESH O P/ APME/JECC 74

Calibration Standards (cont.) Thickness calibration standards may be flat or curved for pipe and tubing applications, consisting of simple variations in material thickness. Distance/Area Amplitude standards utilize flat bottom holes or side drilled holes to establish known reflector size with changes in sound path form the entry surface. ASTM Distance/Area Amplitude NAVSHIPS 16-Oct-18 SUKESH O P/ APME/JECC 75

Calibration Standards (cont.) There are also calibration standards for use in angle beam inspections when flaws are not parallel to entry surface. These standards utilized side drilled holes, notches, and geometric configuration to establish time distance and amplitude relationships. IIW DSC DC Rhompas SC ASME Pipe Sec. XI 16-Oct-18 SUKESH O P/ APME/JECC 76

Qualification Standards Qualification standards differ from calibration standards in that their use is for purposes of varying proper equipment operation and qualification of equipment use for specific codes and standards. AWS Resolution IOW Beam Profile DC-dB Accuracy 16-Oct-18 SUKESH O P/ APME/JECC 77

DATA PRESENTATION  Information from ultrasonic testing can be presented in a number of differing formats.  Three of the more common formats include:  A-scan  B-scan  C-scan 16-Oct-18 SUKESH O P/ APME/JECC 78

Data Presentation - A-scan  A-scan presentation displays the amount of received ultrasonic energy as a function of time.  Relative discontinuity size can be estimated by comparing the signal amplitude to that from a known reflector.  Reflector depth can be determined by the position of the signal on the horizontal sweep. Time Signal Amplitude Time 16-Oct-18SUKESH O P/ APME/JECC79

Data Presentation - B-scan  B-scan presentations display a profile view (cross-sectional) of a test specimen.  Only the reflector depth in the cross-section and the linear dimensions can be determined.  A limitation to this display technique is that reflectors may be masked by larger reflectors near the surface. 16-Oct-18 SUKESH O P/ APME/JECC 80

Data Presentation - C-scan  The C-scan presentation displays a plan type view of the test specimen and discontinuities.  C-scan presentations are produced with an automated data acquisition system, such as in immersion scanning.  Use of A-scan in conjunction with C-scan is necessary when depth determination is desired. Photo of a Composite Component C-Scan Image of Internal Features 16-Oct-18 SUKESH O P/ APME/JECC 81

ADVANTAGE OF ULTRASONIC TESTING  Sensitive to small discontinuities both surface and subsurface.  Depth of penetration for flaw detection or measurement is superior to other methods.  Only single-sided access is needed when pulse-echo technique is used.  High accuracy in determining reflector position and estimating size and shape.  Minimal part preparation required.  Electronic equipment provides instantaneous results.  Detailed images can be produced with automated systems.  Has other uses such as thickness measurements, in addition to flaw detection. 16-Oct-18 SUKESH O P/ APME/JECC 82

LIMITATIONS OF ULTRASONIC TESTING  Surface must be accessible to transmit ultrasound.  Skill and training is more extensive than with some other methods.  Normally requires a coupling medium to promote transfer of sound energy into test specimen.  Materials that are rough, irregular in shape, very small, exceptionally thin or not homogeneous are difficult to inspect.  Cast iron and other coarse grained materials are difficult to inspect due to low sound transmission and high signal noise.  Linear defects oriented parallel to the sound beam may go undetected.  Reference standards are required for both equipment calibration, and characterization of flaws. 16-Oct-18 SUKESH O P/ APME/JECC 83 SUKESH O P/ APME/JECC

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