Presentation on theme: "NON-DESTRUCTIVE TESTING"— Presentation transcript:
1 NON-DESTRUCTIVE TESTING بسمه تعالیبررسی آزمون های غیر مخربNON-DESTRUCTIVE TESTINGNDT
2 NON-DESTRUCTIVE TESTING NDTNON-DESTRUCTIVE TESTINGExamination of materials and components in such a way that allows material to be examinated without changing or destroying their usefulness
3 NDT Most common NDT methods: Penetrant Testing (PT) Magnetic Particle Testing (MT)Eddy Current Testing (ET)Mainly used for surface testingRadiographic Testing (RT)Ultrasonic Testing (UT)Mainly used for Internal Testing
4 NDT Which NDT method is the best ? Depends on many factors and conditions
5 Basic Principles of Ultrasonic Testing To understand and appreciate the capability and limitation of UT
6 History of Ultrasonic Testing (UT) First came ‘sonic’ testingThe piezo-electric effect discovered in 1880/81Marine ‘echo sounding’ developed from 1912In 1929 Sokolov used vibrations in metals to find flawsCathode ray tubes developed in the 1930’sSproule made the first flaw detector in 1942
7 Ultrasonic Inspection Sub-surface detectionThis detection method uses high frequency sound waves, typically above 2MHz to pass through a materialA probe is used which contains a piezo electric crystal to transmit and receive ultrasonic pulses and display the signals on a cathode ray tube or digital displayThe actual display relates to the time taken for the ultrasonic pulses to travel the distance to the interface and backAn interface could be the back of a plate material or a defectFor ultrasound to enter a material a couplant must be introduced between the probe and specimen
11 Basic Principles of Ultrasonic Testing The distance the sound traveled can be displayed on the Flaw DetectorThe screen can be calibrated to give accurate readings of the distanceSignal from the backwallBottom / Backwall
12 Basic Principles of Ultrasonic Testing The presence of a Defect in the material shows up on the screen of the flaw detector with a less distance than the bottom of the materialThe BWE signalDefect signalDefect
13 60 mmThe depth of the defect can be read with reference to the marker on the screen
14 Thickness / depth measurement The closer the reflector to the surface, the signal will be more to the left of the screenCBA304668The thickness is read from the screenThe THINNER the material the less distance the sound travelCBA
15 Ultrasonic Inspection UT SetA Scan DisplayAngle Probe
17 Ultrasonic Inspection AdvantagesRapid resultsSub-surface detectionSafeCan detect planar defectCapable of measuring the depth of defectsMay be battery poweredPortableDisadvantagesTrained and skilled operator requiredRequires high operator skillGood surface finish requiredDifficulty on detecting volumetric defectCouplant may contaminateNo permanent record
19 What is Sound ? A mechanical vibration The vibrations create Pressure WavesSound travels faster in more ‘elastic’ materialsNumber of pressure waves per second is the ‘Frequency’Speed of travel is the ‘Sound velocity’
20 Sound Wavelength : The distance required to complete a cycle Measured in Meter or mmFrequency :The number of cycles per unit timeMeasured in Hertz (Hz) or Cycles per second (cps)Velocity :How quick the sound travelsDistance per unit timeMeasured in meter / second (m / sec)
22 Sound WavesSound waves are the vibration of particles in solids liquids or gasesParticles vibrate about a mean positionIn order to vibrate they require mass and resistance to changeOne cycle
23 Properties of a sound wave Sound cannot travel in vacuumSound energy to be transmitted / transferred from one particle to anotherSOLIDLIQUIDGAS
24 Velocity The velocity of sound in a particular material is CONSTANT It is the product of DENSITY and ELASTICITY of the materialIt will NOT change if frequency changesOnly the wavelength changesExamples:V Compression in steel : 5960 m/sV Compression in water : 1470 m/sV Compression in air : m/s5 M HzSTEELWATERAIR
25 Sound travelling through a material Velocity varies according to the materialCompression wavesSteel 5960m/secWater 1470m/secAir 344m/secCopper 4700m/secShear wavesSteel 3245m/secWater NAAir NACopper 2330m/sec
26 Ultrasonic Sound : mechanical vibration What is Ultrasonic? Very High Frequency sound – above 20 KHz20,000 cps
27 Acoustic Spectrum Sonic / Audible Human Ultrasonic 16Hz - 20kHz > 20kHz = 20,000HzK K 100K 1M 10M 100mUltrasonic Testing0.5MHz - 50MHzUltrasonic : Sound with frequency above 20 KHz
28 THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH Frequency : Number of cycles per second1 second1 second1 second1 cycle per 1 second = 1 Hertz3 cycle per 1 second = 3 Hertz18 cycle per 1 second = 18 HertzTHE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH
30 ULTRASONIC TESTING Very High Frequency 5 M Hz GlassHigh Frequency5 K HzDRUM BEATLow Frequency Sound40 Hz
31 Wavelength and frequency The higher the frequency the smaller the wavelengthThe smaller the wavelength the higher the sensitivitySensitivity : The smallest detectable flaw by the system or techniqueIn UT the smallest detectable flaw is ½ (half the wavelength)
32 High Frequency Sound5MHz compression wave probe in steel
33 Frequency F F = v / f Which probe has the smallest wavelength? 1 M Hz5 M Hz10 M Hz25 M HzLONGESTSMALLEST = v / fFFWhich probe has the smallest wavelength?Which probe has the longest wavelength?
34 Which of the following compressional probe has the highest sensitivity? 1 MHz2 MHz5 MHz10 MHz10 MHz
35 Very high frequency = Very small wavelength Acoustic SpectrumSonic / AudibleHuman16Hz - 20kHzTesting 0.5MHz - 50MHzUltrasonic> 20kHz = 20,000HzK K 100K 1M 10M 100mUltrasonic : Sound with frequency above 20 KHzVery high frequency = Very small wavelength
36 What is the velocity difference in steel compared with in water? 4 timesIf the frequency remain constant, in what material does sound has the highest velocity, steel, water, or air?SteelIf the frequency remain constant, in what material does sound has the shortest wavelength, steel, water, or air?AirRemember the formula = v / f
37 Sound travels in different waveforms in different conditions Sound WaveformsSound travels in different waveforms in different conditionsCompression waveShear waveSurface waveLamb wave
38 Compression / Longitudinal Vibration and propagation in the same direction / parallelTravel in solids, liquids and gasesParticle vibrationPropagation
39 Shear / TransverseVibration at right angles / perpendicular to direction of propagationTravel in solids onlyVelocity 1/2 compression (same material)Particle vibrationPropagation
40 Compression v ShearFrequency0.5MHz1 MHz2MHz4MHz6MHZCompression184.108.40.2061.480.98Shear220.127.116.11.80.54The smaller the wavelength the better the sensitivity
41 Sound travelling through a material Velocity varies according to the materialCompression wavesSteel 5960m/secWater 1470m/secAir 344m/secCopper 4700m/secShear wavesSteel 3245m/secWater NAAir NACopper 2330m/sec
42 Surface Wave Elliptical vibration Velocity 8% less than shear Penetrate one wavelength deepEasily dampened by heavy grease or wet fingerFollows curves but reflected by sharp corners or surface cracks
43 Lamb / Plate WaveProduced by the manipulation of surface waves and othersUsed mainly to test very thin materials / platesVelocity varies with plate thickness and frequenciesSYMETRICASSYMETRIC
44 The Sound Beam Dead Zone Near Zone or Fresnel Zone Far Zone or Fraunhofer Zone
45 Sound Beam D N = 4l Near Zone Thickness measurement Detection of defectsSizing of large defects onlyFar ZoneThickness measurementDefect detectionSizing of all defectsNear zone length as small as possible balanced against acceptable minimum detectable defect sizeN =D4l2
46 The Sound Beam FZ NZ Intensity varies Exponential Decay Distance Main BeamIntensity variesExponential DecayDistance
47 Near Zone The side lobes has multi minute main beams Two identical defects may give different amplitudes of signalsNear ZoneSide LobesThe main beam or the centre beam has the highest intensity of sound energyAny reflector hit by the main beam will reflect the high amount of energyMain LobeMain Beam
49 Near ZoneWhat is the near zone length of a 5MHz compression probe with a crystal diameter of 10mm in steel?
50 Near Zone The bigger the diameter the bigger the near zone The higher the frequency the bigger the near zoneThe lower the velocity the bigger the near zone
51 Which of the above probes has the longest Near Zone ? 1 M Hz5 M Hz
52 Beam SpreadIn the far zone sound pulses spread out as they move away from the crystal/2
53 Beam SpreadEdge,K=1.2220dB,K=1.086dB,K=0.56Beam axis or Main Beam
54 Beam SpreadWhat is the beam spread of a 10mm,5MHz compression wave probe in steel?
55 Which of the above probes has the Largest Beam Spread ? 1 M Hz5 M Hz
56 Beam Spread The bigger the diameter the smaller the beam spread The higher the frequency the smaller the beam spreadWhich has the larger beam spread, a compression or a shear wave probe?
57 Ultrasonic PulseA short pulse of electricity is applied to a piezo-electric crystalThe crystal begins to vibration increases to maximum amplitude and then decaysMaximum10% of MaximumPulse length
58 Natural Pulse, No Damping, Pulse LengthNatural Pulse, No Damping,Long "Ring Time"
59 Pulse Length The longer the pulse, the more penetrating the sound The shorter the pulse the better the sensitivity and resolutionShort pulse, 1 or 2 cyclesLong pulse 12 cycles
60 Pulse LengthShort, Well DampedPulseLong, Well Damped
61 5 cycles for weld testing Ideal Pulse Length5 cycles for weld testing
62 ResolutionRESOLUTION in Pulse Echo Testing is the ability to separate echoes from two or more closely spaced reflectors.RESOLUTION is strongly affected by Pulse Length: Short Pulse Length - GOOD RESOLUTION Long Pulse Length - POOR RESOLUTION RESOLUTION is an extremely important property in WELD TESTING because the ability to separate ROOT GEOMETRY echoes from ROOT CRACK or LACK OF ROOT FUSION echoes largely determines the effectiveness of Pulse Echo UT in the testing of single sided welds.
65 Sound travelling through a material Loses intensitydue toBeam SpreadAttenuationSound beam comparable to a torch beamReduction differs for small and large reflectorsEnergy losses due to materialMade up of absorption and scatter
66 Scatter The bigger the grain size the worse the problem The higher the frequency of the probe the worse the problem1 MHz5 MHz
67 The sound beam spread out and the intensity decreases
68 Beam spread and Attenuation combined Repeat Back-wall Echoes Beyond The Near Zone80%40%20%37%15%ZERO ATTENUATIONATTENUATION 0.02 dB/mm
69 Sound at an InterfaceSound will be either transmitted across or reflected backReflectedHow much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materialsInterfaceTransmitted
70 Acoustic Impedance Definition The Resistance to the passage of sound within a materialFormula = Density , V = VelocitySteel 46.7 x 106Water 1.48 x 106Air x 106Perspex 3.2 x 106Measured inkg / m2 x sec
72 How much sound is reflected at a steel to water interface? Z1 (Steel) = 46.7 x 106Z2 (Water) =1.48 x 106reflected%88.0910093856.2=
73 How much sound transmitted? 100 % - the reflected soundExample : Steel to water100 % - 88 % ( REFLECTED) = 12 % TRANSMITTEDThe BIGGER the Acoustic Impedance Ratio or Difference between the two materials: More sound REFLECTED than transmitted.
74 Large Acoustic Impedance Ratio Large Acoustic Impedance Ratio AirSteelAirSteelLarge Acoustic Impedance RatioLarge Acoustic Impedance RatioAluminumSteelSteelSteelNo Acoustic Impedance DifferenceSmall Acoustic Impedance Difference
75 Interface BehaviourSimilarly: At an Steel - Air interface 99.96% of the incident sound is reflected At a Steel - Perspex interface 75.99% of the incident sound is reflected
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