asnt level-ii ut

DAY 1 ---------->>>

TOPICS

• INRODUCTION

• HISTORY

• BASICS

INRODUCTION:

• Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements.

• Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more.

• The sound energy is introduced and propagates through the materials in the form of waves.

• When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface.

• The reflected wave signal is transformed into electrical signal by the transducer and is displayed on a screen.

See below fig

delaminationplate0 2 4 6 8 10

Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of ultrasonic inspection that are often

cited include:

• It is sensitive to both surface and subsurface discontinuities.

• The depth of penetration for flaw detection or measurement is superior to other NDT methods.

• Only single-sided access is needed when the pulse-echo technique is used.

• It is 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.

• It has other uses such as thickness measurements, in addition to flaw detection.

As with all NDT methods, ultrasonic inspection also has its limitations, which include:

• Surface must be accessible to transmit ultrasound. • Skill and training is more extensive than with some other

methods.

• It 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.

Applications:• Ultrasonic inspection is used for quality control and

materials inspection in all major industries.

• Ultrasonic inspection is used for finding flaws in production of metallic and composite materials.

• It is used in fabrication of structures such as airframes, piping and pressure vessels, ships, motor vehicles, machinery , jet engines and submarines.

• In-service ultrasonic inspection for preventive maintenance is used for detecting the impending failure of rails, rolling-stock axils, mill rolls, mining equipment and nuclear systems.

• And also used for thickness measurement in refinery and chemical pressure vessels

• And many more in medical , rail track inspection, liquid height measurements, material analysis.

• Etc…..

HISTORY:

UT is the discovery of Curie the brothers in 1880 that the quartz crystal cut in a certain way produces an electric potential subjected to pressure.

In 1881 Lippmann theorized that the effect might work in reverse.

In 1929 Russian physicist sokolov experimented with the techniques of passing the vibration to metals to find the flaws.

The first flaw detector was made by D O Sproule in 1942.

• Prior to World War II, sonar, the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects, inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis.

• in 1931, obtained a patent for using ultrasonic waves, using two transducers to detect flaws in solids. Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique.

• Shortly after the close of World War II, researchers in Japan began to explore medical diagnostic capabilities of ultrasound. The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen. That was followed by a B-mode presentation with a two dimensional, gray scale imaging.

• Japan was also the first country to apply Doppler ultrasound, an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation.

BASICS:

WHAT IS ULTRASONIC:

• It is a High frequency Sound.

• We generate the Ultrasonic Sound sound by using piezo electric crystals

What is sound, frequency

• Sound is a mechanical vibration (oscillation) of particles in a medium.

• Sound travels in a medium(where particles are present) but not in vacuum.

• Particles are oscillating and comes in contact with another particles and form a wave form.

Examples of oscillation

ball ona spring

pendulum rotatingearth

Oscillation

In vibratory motion the motion in which a body moves to and fro repeatedly in a fixed interval of time about a fixed point is called mean position.Mean position is also called equilibrium position or zero position.

• The deviation of a vibrating or oscillating body from the mean position of oscillation with time is called displacement.

gas liquid solid

Atomic structures

• low density• weak bonding forces

• medium density• medium bonding

forces

• high density • strong bonding forces• crystallographic structure

Understanding wave propagation:

Spring = elastic bonding forceBall = atom

distance travelled

start of oscillation

Frequency:

• Number of oscillations for second• Its measured in Hertz(Hz)• 1 OSCILATION 2 OSILATIONS

• FREQUENCYIn 1second 1 oscillation so frequency 1 Hz In 1 second 2 oscillation frequency 2 Hz

1sec 1sec> 2cycles=2Hz frequency1 cycle=1Hz

• One vibration in one second is called One Hertz• Ten vibration in one second is called Ten Hertz• One thousand vibrations in one second is called

One Kilohertz( kHz)• One million vibrations in one second is called One

Megahertz ( MHz)

• The distance travelled by a wave at one complete cycle is called wave length.

• Wave length is denoted by lambda(λ).

• The minimum time taken to complete one complete vibration is called time period.

• Time period is denoted by ‘T’.

• The force which tends the vibrating particles towards its mean position is called restoring force of vibrating particles.

DISPLACEMENT(λ)• VELOCITY = _______________ (mts/sec) TIME PERIOD(T)

VELOCITY= λ*F

WHERE FREQUENCY (F) = 1/T • c = λ × f ; λ = c / f = c × T ; f = c / λ

Wavelength = Velocity Frequency

or = V FIf we want to know the wavelength of a 2 Megahertz compression wave traveling through steel, we can use the formulae as we know compression sound speed of sound in steel is, 5920 meters per second. = 5,920 2,000,000 = 2.96 mm

TOPICS1. PROPERTIES OF ULTRASONIC WAVES

2.MODES OF SOUND ENERGY

3.PRINCIPAL OF UT

4.REFLECTION ,TRANMISION , RAREFRACTION , DIFRACTION

5.SNELLS LAW

SPECTROM OF SOUND:

Frequency range Hz Description Example

0 - 20 Infrasound Earth quake

20 - 20.000 Audible sound Speech, music

> 20.000 Ultrasound Bat, Quartz crystal

General we are using 0.5 M Hz to 10 M Hz Ultrasonic Frequencies.

In special testing's we go for up to 25 M Hz also(Immersion Testing)

For high thickness, high grain size materials we are using low frequencies bcoz low frequencies travels more distances and less attenuation.

• High frequencies are give good sensitivity and resolution

• But these high frequencies are more attenuated due to high grain sizes and more thickness.

• High frequency low frequency

Factors Affecting the propagation of ultra sound:

The propagation of ultrasound in a material I depend on the density elastic properties of the material and type of the wave transmitted.

The test material grain sizeAttenuation( scattering, absorption)Acoustic impedance of the materialCharacteristic impedance of inclusionDiffractionLack of homogeneityAnisotropic material

Attenuation of Sound Wave o When sound travels through a medium, its

intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave.

o Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from two basic causes,

o which are scattering and absorption.

• Scatter:

This is the major cause of attenuation and is the redirection of the sound waves reflecting off grain boundaries, porosity and non-metallic inclusions, etc.,

And becomes more apparent on the inspection when the size of grain become of the wavelength of the search unit being employed.

• ABSORPTION:-• As the sound travel through a material a small amount of the

energy is used up by the interaction of the particles, as they vibrate, causing friction which is dissipated as heat.

• As the frequency of the sound is increased the attenuation increases due to more particle vibration and increased sensitivity to small reflectors which is related to the wavelength of the sound.

• Materials such as castings and austenitic stainless steel are highly attenuative due to their coarse grain structures, etc.,

• The attenuation factor of material can be measured and is expressed in db/mm.

• Natural attenuation also occurs due to the divergence of the beam in the far zone, i.e. assuming compression probe use, the amplitude of the backwall echo will be halved(-6db) every time the distance from the probe is doubled.

• Materials such as castings and austenitic stainless steel are highly attenuative due to their coarse grain structures, etc.,

• The attenuation factor of material can be measured and is expressed in db/mm. natural attenuation also occurs due to the divergence of the beam in the far zone, i.e. assuming compression probe use, the amplitude of the backwall echo will be halved(-6db) every time the distance from the probe is doubled.

α=αs+αa

where α is attenuation constant αs scattering constant

αa absorption constant

Reflection, Transmission:

• Reflection: How much sound energy coming back while

hitting an interface.

• Transmission: How much energy transmitted from one medium

to another medium.

Reflection and Transmission Coefficients

• Ultrasonic waves are reflected at boundaries where there is a difference in acoustic impedances (Z) of the materials on each side of the boundary. (See preceding page for more information on acoustic impedance.)

• This difference in Z is commonly referred to as the impedance mismatch. The greater the impedance mismatch, the greater the percentage of energy that will be reflected at the interface or boundary between one medium and another.

T= 1-RR= Parentage of reflection coefficient

T= Percentage of Transmission coefficient

Where Z= pVp= Density of material

V=Sound velocity in that material

As soon as a sound wave comes to a change in material characteristics e.g. the surface of a workpiece, or an internal inclusion, wave propagation will change too:

Behaviour at an interface

Medium 1 Medium 2

Interface

Incoming wave Transmitted wave

Reflected wave

Reflection + Transmission: Perspex - Steel

Reflected wave

Perspex Steel

1,00,87

Reflection + Transmission: Steel - Perspex

Perspex Steel

Reflected wave

Amplitude of sound transmissions:

• Strong reflection• Double transmission

• Less reflection• Single transmission

• Strong reflection with inverted phase

• No transmission

Water - Steel Copper - Steel Steel - Air

UT Principle (Acoustic impedance mismatch)

• Acoustic Impedance• Sound travels through materials under the influence of

sound pressure. • Because molecules or atoms of a solid are bound

elastically to one another, the excess pressure results in a wave propagating through the solid.

• The acoustic impedance (Z) of a material is defined as the product of density (p) and acoustic velocity (V) of that material.

Z = pV

• Acoustic impedance is important in• The determination of acoustic transmission and

reflection at the boundary of two materials having different acoustic impedance

• The design of ultrasonic transducers. • Assessing absorption of sound in a medium.

TRANSDUCER

MATERIAL DISCONTINIUITY BACK WALL REFLECTIONREFLECTION FROM DICONTINUITY

AMPLITUDE

INITIAL PULSE

DISCONTINUITY INDICATION

BACK WALL ECHO

HORIZONTAL SWEEP

PRINCIPLE OF ULTRASONIC TESTING

Modes of sound waves: • In solids, sound waves can propagate in four principle

modes that are based on the way the particles oscillate.

• Sound can propagate as longitudinal waves, shear waves, surface waves, and in thin materials as plate waves.

• Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing

Wave Types in SolidsParticle Vibrations

Longitudinal Parallel to wave direction

Transverse (Shear) Perpendicular to wave direction

Surface - Rayleigh Elliptical orbit - symmetrical mode

Plate Wave – Lamb Component perpendicular to surface (extensional

Plate Wave – Love Parallel to plane layer, perpendicular to wave

direction

Stoneley (Leaky Rayleigh

Waves)

Wave guided along interface

Sezawa Antisymmetric mode

Reflection ,Rarefaction

• When an ultrasound wave passes through an interface between two materials at an oblique angle, and the materials have different indices of refraction, it produces both reflected and refracted waves.

• Refraction takes place at an interface due to the different velocities of the acoustic waves within the two materials.

Angle of incidence=angle of reflection

Snell law, mode conversion:

• Snell's Law describes the relationship between the angles and the velocities of the waves.

• Snell's law equates the ratio of material velocities V1 and V2 to the ratio of the sine's of incident (Q1) and refraction (Q2) angles, as shown in the following equation.

Where:VL1 is the longitudinal wave velocity in material 1.VL2 is the longitudinal wave velocity in material 2.

Mode Conversion• When sound travels in a solid material, one form of wave

energy can be transformed into another form.

• For example, when a longitudinal waves hits an interface at an angle, some of the energy can cause particle movement in the transverse direction to start a shear (transverse) wave.

• Mode conversion, occurs when a wave encounters an interface between materials of different acoustic impedance and the incident angle is not normal to the interface.

VL = VS = CL = CS

Sin1 Sin3 Sin4 Sin2

TRANSMISSION, REFLECTION & MODE CONVERSION OF LONGITUDINAL WAVES AT AN INTERFACE

INCIDENT LONGITUDINAL WAVEVELOCITY = VL

REFLECTED LONGITUDINAL WAVEVELOCITY = VL

REFLECTED SHEAR WAVEVELOCITY = VS

TRANSMITTED SHEAR WAVEVELOCITY = CS

TRANSMITTED LONGITUDINAL WAVEVELOCITY = CL

MEDIUM - 1

MEDIUM - 2

INTERFACE

SNELL’S LAW

Where: VL1 is the longitudinal wave velocity in material 1. VL2 is the longitudinal wave velocity in material 2.

VS1 is the shear wave velocity in material 1. VS2 is the shear wave velocity in material 2.

• Diffraction: This occurs when sound waves pass the tip of a narrow

reflector. Some of the sound scatters off tip causing waves in different directions that reinforce or cancel out the original waves. This results in a series of high and low intensity waves radiating out from the tips, gives imperfection of sound bending around the edges of the defect.

• LONGITUDINAL WAVES:

• In longitudinal waves, the oscillations occur in the longitudinal direction or the direction of wave propagation.

• In compression and dilatational forces are active in these waves.

• They are also called pressure or compression waves. They are also sometimes called density waves because their particle density fluctuates as they move.

• Compression waves can be generated in liquids, as well as solids because the energy travels through the atomic structure by a series of compression and expansion (rarefaction) movements.

• These waves are high velocities compare to other waves, less sensitive and less attenuated.

• Compression waves can be generated in liquids, as well as solids because the energy travels through the atomic structure by a series of compression and expansion (rarefaction) movements.

• These waves are high velocities compare to other waves, less sensitive and less attenuated.

Direction of oscillation

Direction of propagationLongitudinal wave

Sound propagation

SHEAR WAVES:

• In the transverse or shear wave, the particles oscillate at a right angle or transverse to the direction of propagation.

• shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses.

• Shear wave are relatively weak when compared to longitudinal waves in fact, shear waves are usually generated in materials using some of the energy from longitudinal waves.

Direction of propagationTransverse waveDirection of oscillation

Sound propagation

Surface or Rayleigh waves:

• Surface or Rayleigh waves travel the surface of a relative thick solid material penetrating to a depth of one wavelength.

• The particle movement has an elliptical orbit as shown in the image and animation 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.

• These waves are high sensitive compare to all other waves.

• These wave velocities are approximately 90% of shear waves in solids.

• Surface waves are formed when shear waves refract to 90 degrees.

• Particle vibration is elliptical motion by changing direction at the interface with surface.

• Penetration depth is 1 wave length only.• Their velocity is approximately 90% of shear waves

of that material.• These are high sensitive .

• Plate waves can be propagated only in very thin metals.

• Lamb waves are the most commonly used plate waves in NDT.

• Lamb waves are a complex vibrational wave that travels through the entire thickness of a material.

• Propagation of Lamb waves depends on density, elastic, and material properties of a component, and they are influenced by a great deal by selected frequency and material thickness.

With Lamb waves, a number of modes of particle vibration are possible, but the two most common are symmetrical and asymmetrical

Typical Sound Velocities (m/sec)

Material Compression ShearAir 332 N/AWater 1480 N/ASteel 5920 3250Aluminum 6320 3130Perspex 2730 1430Copper 4700 2260Brass 4430 2120

N/A= not applicable i.e. not travelling

Direction of oscillation

WaterSteel, longSteel, trans

330 m/s

1480 m/s

3250 m/s

5920 m/s

• Topics• Ultra sonic Sound generation• Piezo electric materials• Types of probes • UT equipment

ULTRAONIC SOUND GENERATION:

• Piezo electric crystals generates ultra sonic sound.• Piezo electric crystals generates ultrasonic sounds

when we are giving electrical signal to them.

Natural Artificial Grown Manufactured Ceramics

Quartz Crystals Lithium Sulphate Barium Titanate

Lead Zirconate

Lead Metaniobate

Lead Zirconate Titanate

Crystal material Advantages Limitations

Quartz Stable ,Good Wear Resistance

Poor piezo electric properties

Lithium Sulphate Best Receiver and Easily Damped

Soluble in water

Barium Titanate Best Transmitter good piezo electric properties and may used as Focused beam

Less critical temperature

Lead Zirconate Good piezo electric properties

Lead Zirconate Titanate Good transmitter and Round properties

Poor silvering

• Lead zerconate titanate crystal lattice:

Crystal Thickness

Frequency depends on the thickness of the crystal, according to the formula :

t = v 2f

Where t=crystal thickness, v= sound velocity in crystal, f= frequency

• The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing.

• The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa.

• The active element is basically a piece polarized material

Piezoelectric Effect

Piezoelectrical Crystal (Quartz)

Battery

The crystal gets thicker, due to a distortion of the crystal lattice

The effect inverses with polarity change

An alternating voltage generates crystal oscillations at the frequency f

Sound wave with

frequency f

A short voltage pulse generates an oscillation at the crystal‘s resonantfrequency f0

Short pulse ( < 1 µs )

Reception of ultrasonic waves

A sound wave hitting a piezoelectric crystal, induces crystal vibration which then causes electrical voltages at the crystal surfaces.

Electrical energy

Piezoelectrical crystal Ultrasonic wave

Probe frequency , bandwidth & damping:

• UT probe transmits range of frequencies, this I know as bandwidth.• For example 5 M Hz • probe trans mitts 4 t0 6 M Hz

Broad band probes Narrow band probe

Highly damped Low damping

Short pulse length Longer pulse length

Less dead zone More dead zone

Good resolution Poor resolution

Poor penetration Good penetration

Near zone, Far zone, Dead zone, Beam divergence

Near field Far field

Focus Angle of divergenceCrystalAccoustical axis

• Since the ultrasound originates from a number of points along the transducer face, the ultrasound intensity along the beam is affected by constructive and destructive wave interference

• These are sometimes also referred to as diffraction effects in the NDT world.

• This wave interference leads to extensive fluctuations in the sound intensity near the source, known as the near field.

• Because of acoustic variations within a near field, it can be extremely difficult to accurately evaluate flaws in materials when they are positioned within this area.

• The pressure waves combine to form a relatively uniform front at the end of the near field.

• The area beyond the near field where the ultrasonic beam is more uniform is called the far field.

• In the far field, the beam spreads out in a pattern originating from the center of the transducer

Transducer Beam Spread

• The energy in the beam does not remain in a cylinder, but instead spread out as it propagates through the material.

• The phenomenon is usually referred to as beam spread but is sometimes also referred to as beam divergence or ultrasonic diffraction.

Where:θ = Beam divergence angle from centerline to point

where signal is at half strength.

V = Sound velocity in the material. (inch/sec or cm/sec)

a = Radius of the transducer. (inch or cm)

D= Dia of probe=2a

F = Frequency of the transducer. (cycles/second)

Full beam angle Half beam angle (Beam spread) (Beam divergence)

Low frequency HIGH FREQUENCY

Long wavelength Short wavelength

More beam spread Less beam spread

Shorter near zone Longer near zone

Better penetration Less penetration

Less attenuation More attenuation

Longer dead zone Shorter dead zone

Less sensitivity Higher sensitivity

Transducers:

• The conversion of electrical pulses to mechanical vibrations and the conversion of returned mechanical vibrations back into electrical energy is the basis for ultrasonic testing.

• The active element is the heart of the transducer as it converts the electrical energy to acoustic energy, and vice versa. The active element is basically a piece polarized material

• Contact transducers are used for direct contact inspections, and are generally hand manipulated.

• They have elements protected in a rugged casing to withstand sliding contact with a variety of materials. These transducers have an ergonomic design so that they are easy to grip and move along a surface.

• They also often have replaceable wear plates to lengthen their useful life.

• Coupling materials of water, grease, oils, or commercial materials are used to remove the air gap between the transducer and the component inspected.

Ultrasonic Probes

socketcrystalDamping

Delay / protecting faceElectrical matchingCable

Straight beam probe Angle beam probeTR-probe

• Delay line transducers provide versatility with a variety of replaceable options.

• Removable delay line, surface conforming membrane, and protective wear cap options can make a single transducer effective for a wide range of applications.

• As the name implies, the primary function of a delay line transducer is to introduce a time delay between the generation of the sound wave and the arrival of any reflected waves.

• This allows the transducer to complete its "sending" function before it starts it "listening" function so that near surface resolution is improved.

Dual element transducers contain two independently operating elements in a single housing. One of the elements transmits and the other receives.

Active elements can be chosen for their sending and receiving capabilities providing a transducer with a cleaner signal, and transducers for special applications, such as inspection of course grain material.

Dual element transducers are especially well suited for making measurements

• Angle beam transducers and wedges are typically used to introduce a refracted shear wave into the test material.

• Transducers can be purchased in a variety of fixed angles or in adjustable versions where the user determines the angles of incident and refraction.

• In the fixed angle versions, the angle of refraction that is marked on the transducer is only accurate for a particular material, which is usually steel.

• The angled sound path allows the sound beam to be reflected from the back wall to improve delectability of flaws in and around welded areas.

• They are also used to generate surface waves for use in detecting defects on the surface of a component

• Normal incidence shear wave transducers are unique because they allow introduction of shear waves directly into a test piece without the use of an angle beam wedge.

• Careful design has enabled manufacturing of transducers with minimal longitudinal wave contamination.

• Paint brush transducers are used to scan wide areas. These long and narrow transducers are made up of an array of small crystals that are carefully matched to minimize variation of performance and maintain uniform sensitivity over the entire area of the transducer.

• Paint brush transducers make it possible to scan a larger area more rapidly for discontinuities.

SELECTION OF TEST FREQUENCIES

TEST PARPMETERS RECOMMENDED FREQUENCY RANGE

CAST IRON & COARSE GRAIN MATERIALS 0.5 MHz

REFINED GRAIN STEELS, SMALL DISCONTINUITIES, (BURST,FLAKING,PIPE)LARGE FORGINGS

2.25 TO 5.0 MHz

SMALL FORGINGS 5.0 - 10.0 MHz

MICROSCOPIC DEFECTS,

FATIGUE CRACKS ETC.10.0 MHz

TYPE OF PROBE SIZE APPLICATION / ADVANTAGE

NORMAL BEAM PROBE

LARGE DIAMETERUSED FOR THICKER SECTION

MAXIMUM BEAM COVERAGE

MINIMUM NUMBER OF SCANNING

PASSES

LOW BEAM SPREAD

SMALL DIAMETER

LESS THICK SECTION

BEAM SPREAD IS MORE

DESIRABLE FOR RANDOMLY

ORIENTED FLAW

SELECTION OF PROBES

Couplant:

• A couplant is a material (usually liquid) that facilitates the transmission of ultrasonic energy from the transducer into the test specimen.

• Couplant is generally necessary because the acoustic impedance mismatch between air and solids, such as the test specimen, is large and, therefore, nearly all of the energy is reflected and very little is transmitted into the test material

• The couplant displaces the air and makes it possible to get more sound energy into the test specimen so that a usable ultrasonic signal can be obtained.

• In contact ultrasonic testing a thin film of oil, glycerin or water is generally used between the transducer and the test surface.

Ultrasonic Flaw Detector:

amplifier

work piece

horizontal sweep

pulser

screen

The pulse generator:- It is also known as clock or timer. It generates electrical signal frequencies.

The time base generator:- It is also known as sweep generator. It controls the voltage or charge on the X-plate causing beam on the CRT to sweep across in a linear motion.

• The pulse transmitter:- It is also called a pulsar circuit. This circuit burst the electrical energy to activate the probe.

• The receiving amplifier:- This circuit amplifies the incoming electrical signal.

• The attenuator:- It is also called a gain control circuit. It reduces the amplification from the amplifier by controlling the voltage on the Y-plate in CRT , which will control the signal heights

CATHODE RAY TUBE(CRT)

• Cathode is an out put device which shows the flaws of the job material.

• Let us see the cross sectional view of CRT.

Cathode ray tube : CRT

0 2 4 8 106

Modes of displays:

• Ultrasonic data can be collected and displayed in a number of different formats. The three most common formats are know in the NDT world as

• A-scan• B-scan • C-scan

A-Scan Presentation• The A-scan presentation displays the amount of received

ultrasonic energy as a function of time.

• The relative amount of received energy is plotted along the vertical axis and elapsed time .

• In the A-scan presentation, relative discontinuity size can be estimated by comparing the signal amplitude obtained from an unknown reflector to that from a known reflector.

• Reflector depth can be determined by the position of the signal on the horizontal sweep

B-Scan Presentation• The B-scan presentations is a profile (cross-sectional)

view of the a test specimen.

• In the B-scan, the time-of-flight (travel time) of the sound energy is displayed along the vertical and the linear position of the transducer is displayed along the horizontal axis.

• From the B-scan, the depth of the reflector and its approximate linear dimensions in the scan direction can be determined.

C-Scan Presentation

• The C-scan presentation provides a plan-type view of the location and size of test specimen features.

• The plane of the image is parallel to the scan pattern of the transducer.

• C-scan presentations are produced with an automated data acquisition system, such as a computer controlled immersion scanning system.

Cables and Connectors:

• For Ultrasonic testing Coaxial cables are used for connecting transducer and UT flaw detector.

• Because coaxial cables are S/N ratio is good.

• Ultrasonic Testing Techniques

• Calibration blocks

• Weld scan

Ultrasonic Testing Techniques:

A. Contact Testing 1.Pulse echo Testing 2.Through Transmission TestingB. Immersion Testing

C. Through Transmission Testing

D. Air Coupling Testing

Contact Testing:

• In Contact Testing the Transducer is on contact with testing object with the help of couplet.

Pulse Echo Testing:.In which single Transducer is used.From the reflected echo I to be considered..It is mostly used industrial UT technique.. In which avoid lack of coupulant, which causes

improper contact .

CONTACT TESTING

SIDE - 1 SIDE - 2

SIDE - 3 SIDE - 4

DOUBLE “V” BUTT JOINTSCANNING FROM ALL FOUR SIDES

ADVANTAGES IT IS PORTABLE.

SYSTEM DOES NOT REQUIRE LARGE AMOUNT OF ACCESSORIES

0.5 TO 6 MHz COMMONLY USED FREQUENCY FOR CONTACT TESTING

10 TO 25 MHz IMMERSION TESTING

PULSE ECHO METHOD

NORMAL PROBE

ANGLE PROBE

T.R. PROBE

CONTACT TESTING

NORMAL PROBE

ANGLE PROBE

IMMERSION TESTING

AMPLIFIER

TRANSMITTER

RECEIVER

HIGH FREQUENCY GENERATOR

METHODS OF ULTRASONIC TESTING OF MATERIALS

PULSE ECHO METHOD

• Depth of defect is possible.

• Near zone and Dead zone are major draw backs in this technique.

• In which from the reflected echo we will estimate depth, size, shape and type of defect.

• For weld scanning angle beams are used in this technique.

• Through Transmission technique:

• In which separate Transducer and Receiver is used.• In which both side accessible is important.• Tx, Rx are in same axis.• It mostly used for less thickness plate scanning.• Only normal probes and delay line probes are used.• Depth of defect is not possible.• Initial pulse is not appear, dead zone and near field effects

are eliminated.

• CAPABILITY OF TESTING THICKER TEST SPECIMENS• DEFECTS VERY NEAR TO THE SURFACE CAN BE DETECTED

100% INTENSITY

HIGH FREQUENCY GENERATOR AMPLIFIER

AMPLIFIER

INTENSITY METERTRANSMITTING PROBE RECEIVING PROBE

DISCONTINUITY

25% intensity due to partial energy being received because of the discontinuity

METHODS OF ULTRASONIC TESTING OF MATERIALS

2. THROUGH TRANSMISSION METHOD

INTENSITY OF ULTRASOUND IS MEASURED AFTER IT HAS PASSED THROUGH THE TEST PIECE

ADVANTAGES

LIMITATIONS• DEFECT LOCATION IS NOT POSSIBLE.• BOTH SIDES SHOULD BE ACCESSIBLE.

AIR COUPLING METHOD

• In this we used air as a couplent

• This method is used when we test heated objects.

Straight beam inspection techniques:Direct contact,

single element probeDirect contact,

dual element probeFixed delay

Immersion testingThrough transmission

Sound reflection at a flaw

Flaw Sound travel path

Work piece

Plate testing

delaminationplate 0 2 4 6 8 10

IP = Initial pulseF = FlawBE = Backwall echo

0 2 4 6 8 10

Wall thickness measurement

Corrosion

Through transmission testing

0 2 4 6 8 10

Through transmission signal

surface = sound entry

backwall flaw

water delay

0 2 4 6 8 10 0 2 4 6 8 10

IE IEIP IP

BE BEF

Immersion testing

IMMERSION TESTING METHOD

• In this case near field is minimize in water

• velocity of water min water path= --------------------- X thickness velocity of job material

• The main disadvantage of this method is shocking problem.

• The main advantage of this method is near field is minimized.

• In this we use high frequency probes are used around 25 Mhz.

• In this object we can generate all type of incident angles, generally it is used in automatic testing or hydro testing.

Automated Immersion scanning:

Weld inspection

0 20 40 60 80 100

a = s sinßa = s sinß

a' = a - xa' = a - x

d' = s cosßd' = s cosß

d = 2T - t'd = 2T - t'

Lack of fusionWork piece with welding

Fß = probe angles = sound patha = surface distancea‘ = reduced surface distanced‘ = virtual depthd = actual depthT = material thickness

Shear Wave Propagation

Transmitter / Receiver

No reflected echo

Propagate at same angle through part

Time (distance)

Shear Wave Beam Spread

Transmitter / Receiver

ReflectionTransmitter / Receiver

Reflected echo

Wave reflected from acoustic interface

Time (distance)

Strong reflected echo

Scattered reflected echo

No reflected echo

Raster ScanTransducer moved into and away from weld while being

indexedManual or automated (encoded for position)Slow

Line ScanTransducer moved along the weldFixed distance from weldManual or automated, encoded for positionFast

Different types of probe movement:

Calibration Methods

• Calibration refers to the act of evaluating and adjusting the precision and accuracy of measurement equipment. In ultrasonic testing, several forms of calibration must occur

• 1. The electronics of the equipment must be calibrated to assure that they are performing as designed. This operation is usually performed by the equipment manufacturer .

• 2.This user calibration is necessary because most ultrasonic equipment can be reconfigured for use in a large variety of applications.

• The user must "calibrate" the system, which includes the equipment settings, the transducer, and the test setup, to validate that the desired level of precision and accuracy are achieved.

• In ultrasonic testing, there is also a need for reference standards. Reference standards are used to establish a general level of consistency in measurements and to help interpret and quantify the information contained in the received signal.

• Reference standards are used to validate that the equipment and the setup provide similar results from one day to the next and that similar results are produced by different systems.

• Reference standards also help the inspector to estimate the size of flaws. In a pulse-echo type setup, signal strength depends on both the size of the flaw and the distance between the flaw and the transducer.

• The inspector can use a reference standard with an artificially induced flaw of known size and at approximately the same distance away for the transducer to produce a signal.

• By comparing the signal from the reference standard to that received from the actual flaw, the inspector can estimate the flaw size.

SENSITIVITY

CHARACTERISTIC OF ULTRASONIC PROBES

• ABILITY OF THE PROBE TO DETECT SMALLEST DISCONTINUITY

• MEASURED BY THE AMPLITUDE OF ITS RESPONSE TO ENERGY REFLECTED FROM A STANDARD DISCONTINUITY

SAME REFLECTOR, SAME DISTANCE & GAIN SETTING PROBE N0 - 2 IS MORE SENSITIVE

0 2 4 6 8 10

FLAT BOTTOM HOLE

PROBE NO. - 1

FLAT BOTTOM HOLE

PROBE NO. - 2

HIGHER THE FREQUENCY, MORE THE SENSITIVITY

IIW V1 Block:

1). Material: carbon steel 2). Dimensions: 300mmL*100mmW*25mmT.

3). Application: Used for calibration of shear , longitudinal transducers, verification of shear wedge exit point and refracted angle. Can also be used for resolution and sensitivity checking. Includes a 100mm radius on one end . Also includes a 50mm diameter

and a 1.5mm diameter hole. In accordance with International Institute of Welding and ASTM E164

RESOLUTION

ABILITY TO SEPARATE ECHOES FROM TWO OR MORE DISCONTINUITIES LOCATED CLOSE TOGETHER IN DEPTH

HIGHER THE FREQUENCY, BETTER WILL BE RESOLUTION

0 2 4 6 8 10

GOOD RESOLUTION POOR RESOLUTION

• MINIMUM TWO REFERENCE POINTS ARE NECESSARY

• FIRST REFERENCE ALWAYS CONTROLLED WITH THE HELP OF DELAY CONTROL KNOB

• SECOND REFERENCE POINT ALWAYS CONTROLLED WITH THE HELP OF RANGE CONTROL KNOB

IIW “V1” BLOCK

CALIBERATION OF ULTRASONIC EQUIPEMENT

GENERAL RULES

0 2 4 6 8 10

INITIAL ECHO 1ST BACK WALL ECHO(BWE)

IIW “V1” BLOCK

CALIBERATION OF ULTRASONIC EQUIPEMENTRANGE CALIBERATION BY NORMAL PROBE

0 2 4 6 8 10

INITIAL ECHO 1ST BACK WALL ECHO(BWE)

0 2 4 6 8 10

INITIAL ECHO

1ST BWE2ND BWE

0 2 4 6 8 10

INITIAL ECHO 1ST BWE

2ND BWE

IIW:V-2: OR Miniature Aperture Block

Description: 12.5mm thick, small calibration block • For on-site checking of miniature shear wave probe

index, time base, beam angle , Sensitivity(1.5 mm)• Includes a 25mm and 50 mm radius, 1.5mm hole

engraved reference mark scales from 35 to 75 degrees. • In accordance with BS EN 27963:1992, ISO 7963 Cal

block No. 2, Fig. 1.

ASME Angle Beam Calibration Blocks:

• Meet the requirements of ASME Section V, Article 5, Fig. T-542.8.1.1 and contain EDM notches at 10% of nominal wall on both OD and ID oriented longitudinally and transversely.

AWS Resolution Calibration (RC) Block

• The RC Block is used to determine the resolution of angle beam transducers per the requirements of AWS

• Engraved Index markers are provided for 45, 60, and 70 degree refracted angle beams.

Step and Tapered Calibration Wedges

• Step and tapered calibration wedges come in a large variety of sizes and configurations.

• Step wedges are typically manufactured with four or five steps but custom wedge can be obtained with any number of steps.

• Tapered wedges have a constant taper over the desired thickness range.

Distance/Area-Amplitude Blocks

• Distance/area amplitude correction blocks typically are purchased as a ten-block set, as shown above.

• Aluminum sets are manufactured per the requirements of ASTM E127 and steel sets per ASTM E428.

• Sets can also be purchased in titanium. Each block contains a single flat-bottomed, plugged hole.

• The hole sizes and metal path distances are as follows: 3/64" at 3" 5/64" at 1/8", 1/4", 1/2", 3/4", 11/2", 3", and 6" 8/64" at 3" and 6"

• DAC CURVE

• DGS CURVE

• 6dB,20dB DROP METHODS

• DISCONTINUTIES

• Accept and Rejection criteria

DAC Curve:

• Acoustic signals from the same reflecting surface will have different amplitudes at different distances from the transducer.

• Distance amplitude correction (DAC) provides a means of establishing a graphic ‘reference level sensitivity’ as a function of sweep distance on the A-scan display.

• The use of DAC allows signals reflected from similar discontinuities to be evaluated where signal attenuation as a function of depth has been correlated.

• Most often DAC will allow for loss in amplitude over material depth (time), graphically on the A-scan display but can also be done electronically by certain instruments

• A distance amplitude correction curve is constructed from the peak amplitude responses from reflectors of equal area at different distances in the same material.

• Reference standards which incorporate side drilled holes (SDH), flat bottom holes (FBH), or notches whereby the reflectors are located at varying depths are commonly used

• While drawing DAC 1st echo set to 80% FSH, and note down the gain . Which is Actual gain or Actual dB.

• And trace the next 2 or 3 indications, and make a curve.

• While scanning on job increase gain to(DAC+6dB), which is called as scanning dB.

• If any echo touches DAC curve reduce gain by 6dB, still it is touches then mark as defect at that place.

DGS curve:

• DGS – Distance Gain Size is a method of setting sensitivity or assessing the signal from an unknown reflector based on the theoretical response of a flat-bottomed hole reflector perpendicular to the beam axis.

• The DGS system was introduced by Krautkramer in 1958 and is referred to in German as AVG.

• A schematic of a general DGS diagram is shown in the Figure. The Y-axis shows the Gain and X-axis shows the Distance from the probe.

• In a general DGS diagram the distance is shown in units of Near Field and the scale is logarithmic to cover a wide range.

The blue curves plotted show how the amplitudes obtained from different sizes of disc shaped reflector (equivalent to a FBH) decrease as the distance between the probe and the reflector increases.

Finding Length of defects:

• Length of defect by 2 techniques. 1. 6dB Drop method 2.20 dB drop method

DISCONTINUTIES

DEFECTS IN PLATE MATERIAL

• LAMINATIONS

• INCLUSIONS > LINEAR INCLUSIONS > SCATERED INCLUSIONS

• STRINGERS

• A ROLLING LAP

DEFECTS IN WELDS

• ROOT DEFECTS:-

>LACK OF PENETRATION >LACK OF ROOT FUSION >ROOT CRACK >ROOT UNDER CUT >OVER PENETRATION >ROOT CONCAVITY

DEFECTS IN PLATE MATERIALS

LAMINATIONS:

THESE ARE FORMED WHEN A BILLET IS FLATTENED AND SPREAD OUTMAY CAUSES LAMINATION.PIPE AND POROSITY ALSO MAY CAUSES LAMINATION.

0 2 4 6 8 10

INITIAL ECHO 1ST BWE 2ND BWE

APPLICATIONS OF ULTRASONIC TESTING

TESTING OF LAMINATION IN PLATES

LAMINATION IN THE PLATEPLATE

NO DEFECT

0 2 4 6 8 10

INITIAL ECHO 1ST BWEFROM DEFECT

2ND BWEFROM DEFECT

3RD BWEFROM DEFECT

4TH BWEFROM DEFECT

DEFECT INDICATION

BOND TESTING

0 2 4 6 8 10

2ND BWEFROM DEFECT

DEFECT INDICATION

0 2 4 6 8 10

INITIAL ECHOFIRST ECHO FROM INTERFACE 1ST BWE

NO DEFECT

DEFECT IN BONDING AT INTERFACE CALLED “DISBONDING”

BEARING CASTING PORTION

BABBIT METAL

INTERFACE

BOND TESTING

0 2 4 6 8 10

2ND BWEFROM DEFECT

DEFECT INDICATION

0 2 4 6 8 10

INITIAL ECHOFIRST ECHO FROM INTERFACE 1ST BWE

NO DEFECT

DEFECT IN BONDING AT INTERFACE CALLED “DISBONDING”

BEARING CASTING PORTION

BABBIT METAL

INTERFACE

INCULUSIONS

• LINEAR INCLUSIONS:

SCATTERED INCLUSIONS:

0 2 4 6 8 10

INITIAL ECHO

INDICATION FROM SPHERICAL FLAW

SCREEN PRESENTATIONWHEN PROBE IS AT 1 OR 2 OR 3 OR 4

INTERPRETATION OF ULTRASONIC FLAW - ECHO INDICATIONS

SPHERICAL FLAW (POROSITY)

• REFLECT ONLY A SMALL AMOUNT OF SOUND• ECHO HEIGHT SMALL• ECHO HEIGHT REMAINS UNCHANGED WHEN ANGLE OF APPROACH IS CHANGED

SPHERICALFLAW

STRINGERS:

• These are formed when the non metallic inclusions in the ingot.

The signal responseIs like the linearInclusion signal

In the rolling directionThe BWE is still presentBut the signal can be Maintained along the Defects length

A ROLLING LAP:

• This defect occurs in the rolling process.

DEFECTS IN WELDS

ROOT DEFECTS• LACK OF PENETRATIN:

• High amplitude corner signals both sides of the weld, rapidly decreasing in amplitude on rotational path.

• Plotting at plate thickness depth, the width of the root gap apart, with no cross over.

0 2 4 6 8 10

INITIAL ECHOINDICATION FROM CORNER

SCREEN PRESENTATIONWHEN PROBE IS AT 1 OR 2

LACK OF PENETRATION

ANGLE PROBE WELD

WELD TESTING - INTERPRETATION OF ULTRASONIC INDICATIONS

LACK OF PENETRATION

• SHARP ECHO FROM BOTH SIDES OF WELD

• INDICATION REMAINS AT THE SAME POSITION WHEN PROBE IS MOVED ALONG THE LENGTH

ROOT CRACK

• It would be normal to expect a high amplitude, multi-faceted reflector probably from both sides of the weld.

• The vertical height of the crack was substantial, a characteristic running signal on the time base would be noted on depth scan with the angle probe.

• The response would raise and fall on rotational or lateral probe moments due to crack irregularity.

ROOT CRACK

ROOT UNDERCUT

• Depend on how severe the undercut is will determine the type of amplitude received.

• However, associated with the undercut echo will be as signal from the root bead as well.

• If the undercut is only one side of the weld the root bead is examined from the opposite side.

ROOT UNDERCUT

EXCESS ROOT PENETRATION

• Root bead type signals on both side of the welds are plotting beyond expected beam path length to the bead and crossing over.

• Steeper angle probe(i.e., 38 and 45 degrees), access permitting will give best results.

• It is also called over penetration.

0 2 4 6 8 10

INITIAL ECHOINDICATION FROM EXCESS PENETRATION

SCREEN PRESENTATION WHEN PROBE IS AT 1

ECHO MAY BE ABSENT WHEN PROBE AT 2 DEPENDING ON SURFACE CONTOUR

EXCESS PENETRATION

• SHARP ECHO DEPENDS ON SHAPE OF ROOT SURFACE

EXCESS PENETRATION

ANGLE PROBE WELD

ROOT CONCAVITY

• Low amplitude signals on both sides of the weld are plotting short of plate thickness and no cross over.

• If only slight concavity it is likely that it will not be observed ultrasonically.

0 2 4 6 8 10

INITIAL ECHOINDICATION FROM ROOT CONCAVITY

SCREEN PRESENTATION WHEN PROBE IS AT 1 OR 2

ROOT CONCAVITY

ANGLE PROBE WELD

DEFECTS IN WELD REGION

• High amplitude signal from “a” on full skip and “c” on half skip.

• Low amplitude signal from “c” and “d”.

A B C D

SLAG INCLUSION

• Detectable from all accessible positions and directions due to volumetric nature.

• Signal contains numerous half cycles and have a rounded peak.

• It should be detected with any angle probe.

SLAG INCLUSION

CLUSTER POROSITY

• Detectable from all accessible positions and directions due to volumetric nature.

• Very low amplitude response due to signal attenuation giving multiple signal with a wide time base.

• It is also called as multiple small inclusions.

CLUSTER POROSITY

0 2 4 6 8 10

INITIAL ECHOINDICATION FROM MISMATCH

SCREEN PRESENTATION WHEN PROBE IS AT 2

ECHO MAY BE ABSENT WHEN PROBE AT 1 DEPENDING ON SURFACE CONTOUR

MISMATCH

• STRONG ECHO INDICATION WHEN SCANNED FROM LOWER SIDE OF THE WELD

• NO INDICATION FROM OTHER SIDE

MISMATCH

ANGLE PROBE WELD

Accept and Rejection criteria:

• According to CODES and STANDARDS we will interpitation the results.

• Codes and standards are intended to enhance the safety of workers and the public

• CODE: A systematic collection of regulations and rules of

procedure or conduct

• A standard is a set of "how to" instructions for designers, manufacturers, and/or users of the equipment covered.

• It can run from a few paragraphs to hundreds of pages. Standards are considered voluntary because they serve as guidelines only, without the force of law.

• Organizations such as ASME that develop standards can publish them, and can certify manufacturers

• Some of the codes used in NDT

• API 650 Oil and Storage Tanks.• API 1104 Cross Country or Long Pipe Lines.• ASME Sec V Preparation of NDT Procedures.• ASME Sec VIII Div 1&2 Boiler and Pressure Vessels .• ASME Sec IX Welder Qualification Tests.• ASME B31.1 Power Piping.• ASME B31.4 Liquid Transportation system for hydro carbons.ASME B31.8 Gas Transmission & piping system.AWS D1.1 Structural Welding.

asnt level-ii ut

materials inspection

flaw surface

ultrasonic testing ut

rail track inspection

transfer of sound energy

high frequency sound

sound beam

flaw detectionevaluation

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