Shokoh manesh asghar & Hammori amin supervisor: Dr Moeinifar دانشگاه آزادواحداهواز دانشکده فنی ومهندسی Ultrasonic Testing Shokoh manesh asghar & Hammori amin supervisor: Dr Moeinifar

Introduction to Nondestructive Testing

Six Most Common NDT Methods Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current X-ray

آزمون فرا صوتي Ultrasonic Test

آزمون‌هاي فرا صوتي كاربرد بسيار گسترده‌اي در تعيين نقص‌هاي دروني مواد دارند. از اين روش مي‌توان براي تعيين ترك‌هاي زير سطحي نيز استفاده كرد. آزمون‌هاي فرا صوتي علاوه بر بازرسي قطعات تكميل شده براي بازرسي كنترل كيفيت مراحل مختلف توليد قطعاتي همچون ورقهاي نورد شده نيز بكار مي‌روند. مباني آزمون فرا صوتي از ايجاد موج‌هاي صوتي توسط يك ضربان سنج استخراج شده است. روش مدرن بكار گرفته شده امروزي، التراسونيك ناميده مي‌شود كه علت اين نامگذاري كلمه Sona مي‌باشد كه در لاتين به معني صوت است.

سرعت موج : در حالت كلي هر چه محيط مادي فشرده‌تر باشد، سرعت حركت موج صوتي در آن بيشتر است. بنابراين سرعت حركت امواج صوتي در جامدات بيشتر از سيالات مي‌باشد.

Sound Wavelength : The distance required to complete a cycle Measured in Meter or mm Frequency : The number of cycles per unit time Measured in Hertz (Hz) or Cycles per second (cps) Velocity : How quick the sound travels Distance per unit time Measured in meter / second (m / sec)

Wavelength Velocity Frequency

Sound Waves Sound waves are the vibration of particles in solids liquids or gases Particles vibrate about a mean position In order to vibrate they require mass and resistance to change One cycle

Properties of a sound wave Sound cannot travel in vacuum Sound energy to be transmitted / transferred from one particle to another SOLID LIQUID GAS

Velocity The velocity of sound in a particular material is CONSTANT It is the product of DENSITY and ELASTICITY of the material It will NOT change if frequency changes Only the wavelength changes Examples: V Compression in steel : 5960 m/s V Compression in water : 1470 m/s V Compression in air : 330 m/s 5 M Hz STEEL WATER AIR

ساختمان پروب : چندين نوع پروب فرستنده وجود دارد، اما همه انواع آنها داراي كريستالي است كه مستقيماً يا از طريق پوشش محافظ با ماده مورد آزمايش در تماس است. جنس بلور معمولاً از كوارتز طبيعي، تيتانات باريم، نيوبات سرب و سولفات ليتيم مي‌باشد. ولتاژ پله‌اي كوتاه مدتي به كريستال اعمال مي‌شود. پروب‌ها ممكن است قائم يا زاويه‌دار باشند.

پروب‌هاي زاويه‌دار : پروب‌هاي زاويه‌دار براي فرستادن موج‌هاي برشي يا موج‌هاي ريلي به درون قطعه تحت بازرسي طراحي شده‌اند. ساختمان كلي پروب زاويه‌اي همانند پروب عمودي است با اين تفاوت كه بلور در قطعه پرسپكسي جاسازي شده است. موج طولي بازگشتي كه در فصل مشترك پرسپكسي - فلز توليد مي‌شود، ممكن است به كريستال برگردد و علائم گمراه كننده‌اي به وجود آورد. براي جلوگيري از اين كار ماده جذب كننده‌اي همچون لاستيك در پروب جاسازي مي‌شود. روش ديگر اين است كه قطعه پرسپكس به گونه‌اي شكل داده شود كه موج برگشتي چندين بار بازتاب شود و انرژي خود را از دست بدهد و از آنجا كه ضريب جذب پرسپكس بالا است، اين امكان وجود خواهد داشت.

پروبهای قائم امواج را با زاویه صفر درجه و به صورت عمود وارد قطعه میکنند .

Sound travels in different waveforms in different conditions Sound Waveforms Sound travels in different waveforms in different conditions Compression wave Shear wave Surface wave Lamb wave

Compression / Longitudinal Vibration and propagation in the same direction / parallel Travel in solids, liquids and gases Particle vibration Propagation

Shear / Transverse Particle vibration Propagation Vibration at right angles / perpendicular to direction of propagation Travel in solids only Velocity  1/2 compression (same material) Particle vibration Propagation

Compression v Shear Frequency 0.5MHz 1 MHz 2MHz 4MHz 6MHZ Compression 11.8 5.9 2.95 1.48 0.98 Shear 6.5 3.2 1.6 0.8 0.54 The smaller the wavelength the better the sensitivity

Sound travelling through a material Velocity varies according to the material Compression waves Steel 5960m/sec Water 1470m/sec Air 344m/sec Copper 4700m/sec Shear waves Steel 3245m/sec Water NA Air NA Copper 2330m/sec

Surface Wave Elliptical vibration Velocity 8% less than shear Penetrate one wavelength deep Easily dampened by heavy grease or wet finger Follows curves but reflected by sharp corners or surface cracks

Lamb / Plate Wave Produced by the manipulation of surface waves and others Used mainly to test very thin materials / plates Velocity varies with plate thickness and frequencies SYMETRIC ASSYMETRIC

Ultrasonic Sound : mechanical vibration What is Ultrasonic? Very High Frequency sound – above 20 KHz 20,000 cps

Acoustic Spectrum Sonic / Audible Human Ultrasonic 16Hz - 20kHz > 20kHz = 20,000Hz 0 10 100 1K 10K 100K 1M 10M 100m Ultrasonic Testing 0.5MHz - 50MHz Ultrasonic : Sound with frequency above 20 KHz

THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH Frequency : Number of cycles per second 1 second 1 second 1 second 1 cycle per 1 second = 1 Hertz 3 cycle per 1 second = 3 Hertz 18 cycle per 1 second = 18 Hertz THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH

Frequency 20 KHz = 20 000 Hz 5 M Hz = 5 000 000 Hz Pg 21 Frequency 1 Hz = 1 cycle per second 1 Kilohertz = 1 KHz = 1000Hz 1 Megahertz = 1 MHz = 1000 000Hz 20 KHz = 20 000 Hz 5 M Hz = 5 000 000 Hz

Ultrasonic Inspection defect echo Back wall echo initial pulse Material Thk defect 10 20 30 40 50 Compression Probe CRT Display

Basic Principles of Ultrasonic Testing The distance the sound traveled can be displayed on the Flaw Detector The screen can be calibrated to give accurate readings of the distance Signal from the backwall Bottom / Backwall

Basic Principles of Ultrasonic Testing The presence of a Defect in the material shows up on the screen of the flaw detector with a less distance than the bottom of the material The BWE signal Defect signal Defect

0 10 20 30 40 50 60 60 mm The depth of the defect can be read with reference to the marker on the screen

Thickness / depth measurement The closer the reflector to the surface, the signal will be more to the left of the screen C B A 30 46 68 The thickness is read from the screen The THINNER the material the less distance the sound travel C B A

Ultrasonic Inspection initial pulse defect echo Surface distance defect sound path 10 20 30 40 50 Angle Probe CRT Display

The Sound Beam Dead Zone Near Zone or Fresnel Zone Far Zone or Fraunhofer Zone MMZ02

The Sound Beam FZ NZ Intensity varies Exponential Decay Distance Main Beam Intensity varies Exponential Decay Distance MMZ02

Near Zone The side lobes has multi minute main beams Two identical defects may give different amplitudes of signals Near Zone Side Lobes The main beam or the centre beam has the highest intensity of sound energy Any reflector hit by the main beam will reflect the high amount of energy Main Lobe Main Beam

Sound Beam Near Zone Thickness measurement Detection of defects Sizing of large defects only Far Zone Thickness measurement Defect detection Sizing of all defects Near zone length as small as possible balanced against acceptable minimum detectable defect size N = D 4l 2

Near Zone MMZ02

Near Zone What is the near zone length of a 5MHz compression probe with a crystal diameter of 10mm in steel? MMZ02

Near Zone The bigger the diameter the bigger the near zone The higher the frequency the bigger the near zone The lower the velocity the bigger the near zone MMZ02

Which of the above probes has the longest Near Zone ? 1 M Hz 5 M Hz MMZ02

Beam Spread In the far zone sound pulses spread out as they move away from the crystal /2  MMZ02

Beam Spread Edge,K=1.22 20dB,K=1.08 6dB,K=0.56 Beam axis or Main Beam MMZ02

Beam Spread What is the beam spread of a 10mm,5MHz compression wave probe in steel? MMZ02

Which of the above probes has the Largest Beam Spread ? 1 M Hz 5 M Hz MMZ02

Beam Spread The bigger the diameter the smaller the beam spread The higher the frequency the smaller the beam spread Which has the larger beam spread, a compression or a shear wave probe? MMZ02

Ultrasonic Pulse A short pulse of electricity is applied to a piezo-electric crystal The crystal begins to vibration increases to maximum amplitude and then decays Maximum 10% of Maximum Pulse length MMZ02

Natural Pulse, No Damping, Pulse Length Natural Pulse, No Damping, Long "Ring Time"

Pulse Length The longer the pulse, the more penetrating the sound The shorter the pulse the better the sensitivity and resolution Short pulse, 1 or 2 cycles Long pulse 12 cycles MMZ02

Pulse Length Short, Well Damped Pulse Long, Well Damped

5 cycles for weld testing Ideal Pulse Length 5 cycles for weld testing

Resolution RESOLUTION 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.

Resolution 10% 90% > 6dB Good resolution

Resolution 50% 90% < 6dB Poor resolution

Scatter The bigger the grain size the worse the problem The higher the frequency of the probe the worse the problem 1 MHz 5 MHz MMZ02

Inclined incidence(not at 0o) REFRACTION a = b a b Material A Material B r Sin = v A B Snell's Law The sound is refracted due to differences in sound velocity in the 2 materials

Snell’s Law C 20 Perspex Steel 48.3 C

Snell’s Law C 15 Perspex Steel 34.4 C

Snell’s Law C 20 Perspex Steel 48.3 C 24 S

1st Critical Angle C 27.4 Compression wave refracted at 90 degrees C 33 S

2nd Critical Angle C C 57 S (Surface Wave) 90 Shear wave refracted at 90 degrees Shear wave becomes a surface wave

1st Critical Angle Calculation 27.2 Perspex C Steel S

2nd Critical Angle Calculation 57.4 Perspex S Steel

Sound at an Interface Sound will be either transmitted across or reflected back Reflected How much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materials Interface Transmitted MMZ02

Acoustic Impedance Steel 46.7 x 106 Measured in Water 1.48 x 106 Definition The Resistance to the passage of sound within a material Formula  = Density , V = Velocity Steel 46.7 x 106 Water 1.48 x 106 Air 0.0041 x 106 Perspex 3.2 x 106 Measured in kg / m2 x sec MMZ02

% Sound Reflected at an Interface % Sound Reflected + % Sound Transmitted = 100% Therefore % Sound Transmitted = 100% - % Sound Reflected MMZ02

How much sound is reflected at a steel to water interface? Z1 (Steel) = 46.7 x 106 Z2 (Water) =1.48 x 106 reflected % 88.09 100 93856 . 2 = ´ MMZ02

How much sound transmitted? 100 % - the reflected sound Example : Steel to water 100 % - 88 % ( REFLECTED) = 12 % TRANSMITTED The BIGGER the Acoustic Impedance Ratio or Difference between the two materials: More sound REFLECTED than transmitted.

Large Acoustic Impedance Ratio Large Acoustic Impedance Ratio Air Steel Air Steel Large Acoustic Impedance Ratio Large Acoustic Impedance Ratio Aluminum Steel Steel Steel No Acoustic Impedance Difference Small Acoustic Impedance Difference

Interface Behaviour Similarly: 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

What is the difference between them in dB’s? 2 signals at 20% and 40% FSH. What is the difference between them in dB’s? MMZ02

What is the difference between them in dB’s? 2 signals at 10% and 100% FSH. What is the difference between them in dB’s? MMZ02

Amplitude ratios in decibels 2 : 1 = 6bB 4 : 1 = 12dB 5 : 1 = 14dB 10 : 1 = 20dB 100 : 1 = 40dB MMZ02

SIZING METHODS 0O PROBE There are four main sizing techniques used with 0o probes: 6 dB drop Maximum Amplitude Equalisation DGS

For sizing large planar reflectors only 6 dB Drop For sizing large planar reflectors only Signal / echo reduced to half the height Example: 100% to 50% 80% to 40% 70% to 35% 20% to 10% Centre of probe marked representing the edge of defect.

6 dB Drop Defect BWE Plan View The back wall echo reduced as some part of the beam now striking the defect The echo of the defect has NOT yet maximise as the whole beam Not yet striking the defect

6 dB Drop Defect Now the whole beam is on the defect Plan View Defect Now the whole beam is on the defect Back wall echo is now may be reduced or disappeared

6 dB Drop Defect BWE Plan View The probe is moved back until the echo is reduced by half of it’s original height At this point the probe centre beam is directly on the edge of the defect The probe is then removed and the centre is marked, and repeat to size the whole defect

Maximum Amplitude Technique For sizing multifaceted defect – eg. crack Not very accurate Small probe movement

Maximum Amplitude Multifaceted defect : crack The whole probe beam is on the defect At this point, multipoint of the defect reflect the sound to the probe The echo (signal) show as a few peaks

Maximum Amplitude Multifaceted defect : crack If the probe is moved into the defect, the signals height increase The probe is moved out of the defect, the signal disappeared One of the peak maximised If the edge of the beam strike the edge of the defect, a very small echo appears At this point the MAIN BEAM is directly at the edge of the defect

Maximum Amplitude Remember: The peak which maximised does not have to be the tallest or the first one Length The probe is to be moved to the other end of the defect Mark the point under the centre of the probe which indicates the edge of the defect The signals will flactuate as the beam hits the different faces of the defects The length of the defect is measured The probe is moved back into the defect and to observe a peak of the signal maximises

Equalization Technique The equalization technique can ONLY be used if the defect is halfway the thickness Defect BWE At this point the whole beam is on the back wall The BWE is at it maximum At this point the whole beam is on the defect The Defect echo is at it maximum At the edge of the defect, half of the beam is on the defect, and another half is on the back wall The defect echo is at equal height as the back wall The point is marked as the edge of defect

Ultrasonic Displays A scan The CRT (Cathode Ray Tube) display The Horizontal axis : Represents time base / beam path length / distance / depth The Vertical axis : Represent the amount of sound energy returned to the crystal

Ultrasonic Displays B scan The End View Display B

Ultrasonic Displays C scan The Plan View Display C

Ultrasonic Displays D scan The Side View Display D

Ultrasonic Test Methods Pulse Echo Through Transmission Transmission with Reflection (pulse echo techniques where the transmitter is separate from the receiver - e.g. tandem testing, time of flight)

Pulse Echo Technique Single probe sends and receives sound Gives an indication of defect depth and dimensions

Using Ultrasound for Testing: PULSE ECHO Probe Time

Using Ultrasound for Testing: PULSE ECHO Probe Time

Using Ultrasound for Testing: PULSE ECHO Probe Time

Using Ultrasound for Testing: PULSE ECHO Probe Time

Defect Position B B A No indication from defect A (wrong orientation)

Through Transmission Testing Transmitting and receiving probes on opposite sides of the specimen Pulsed or Continuous sound Presence of defect indicated by reduction in transmission signal No indication of defect location Easily automated Commonly integrated into plate rolling mills - lamination testing

Through Transmission Technique Tx Rx Transmitting and receiving probes on opposite sides of the specimen Presence of defect indicated by reduction in transmission signal No indication of defect location

Transmission with Reflection Also known as: Tandem Technique or Pitch and Catch Technique

Transmission with Reflection TANDEM TESTING

Gap Scanning Probe held a fixed distance above the surface (1 or 2mm) Couplant is fed into the gap

Immersion Testing Component is placed in a water filled tank Item is scanned with a probe at a fixed distance above the surface

Immersion Testing PROBE Front Surface Defect Back

Immersion Testing Water path distance Front surface Back surface Defect Water path distance

Using Ultrasound for Testing Amplifier Transmit Receive Probe (transducer) Gain Control Pulse Generator Timebase Range Delay Cathode Ray Tube Backwall Echo PULSE ECHO

ULTRASONIC EXAMINATION OF WELDS 40 450 450 BACK GOUGE 40 DOUBLE SIDED “T” JOINT

ULTRASONIC EXAMINATION OF WELDS COVERAGE OF FUSION FACES 00 100 (approx.) COVERAGE OF WELD VOLUME

ULTRASONIC EXAMINATION OF WELDS COVERAGE OF FUSION FACES 450 COVERAGE OF WELD VOLUME

SCANNING FOR TRANSVERSE IMPERFECTIONS 450

SCANNING FOR TRANSVERSE IMPERFECTIONS

THREADLIKE DEFECTS, POINT DEFECTS AND FLAT PLANAR DEFECTS ORIENTATED NEAR-NORMAL TO THE BEAM AXIS ALL PRODUCE AN ECHO RESPONSE WHICH HAS A SINGLE PEAK:

PLANAR (NEAR NORMAL INCIDENCE) THESE DEFECTS CAN BE DIFFERENTIATED BETWEEN BY OBSERVING THE ECHO DYNAMIC BEHAVIOUR IN LENGTH AND DEPTH SCANS: POINT THREADLIKE PLANAR (NEAR NORMAL INCIDENCE) DEPTH SCAN LENGTH SCAN NOTE: THE RESPONSE FROM A PLANAR DEFECT WILL BE STRONGLY AFFECTED BY PROBE ANGLE WHILE THAT FROM A THREADLIKE REFLECTOR WILL REMAIN ALMOST UNCHANGED IF A DIFFERENT PROBE ANGLE IS USED.

THE ECHO RESPONSE FROM A LARGE SLAG INCLUSION OR A ROUGH CRACK IS LIKELY TO HAVE MULTIPLE PEAKS:

SOMETIMES IT WILL BE POSSIBLE TO DIFFERENTIATE BETWEEN THESE 2 DEFECTS SIMPLY BY PLOTTING THEIR POSITION WITHIN THE WELD ZONE: A. PROBABLE SLAG, POSSIBLE CENTRELINE CRACK B. PROBABLE HAZ CRACK

“ROTATIONAL” OR “ORBITAL” PROBE MOVEMENTS MAY HELP: IN CASE “A” IT WILL BE DIFFICULT TO DETERMINE WHETHER THE DEFECT IS SLAG OR A CRACK. “ROTATIONAL” OR “ORBITAL” PROBE MOVEMENTS MAY HELP: ORBITAL ROTATIONAL

TYPICAL ECHO DYNAMIC PATTERNS CRACK SLAG ORBITAL SCAN ROTATIONAL SCAN

Calibration Blocks and Their Usage I.I.W (International Institute of Welding) Block / V1 / A2 Block 300mm 91mm 85mm 200mm 50mm Dia Perspex 5mm 10mm 15mm 35mm 1.5mm Dia 100mm 100mm 23mm 25mm USES Compressional Shear

A4 / V2 / DIN 54/122 / KIDNEY BLOCK R50 R25 12.5mm or 20mm PLAN VIEW 1.5 OR 5mm dia. hole USES a) Compressional Probes Calibration This block can be purchased having a thickness of either 12.5mm or 20mm. Shear Probes Calibration When aiming at 25mm radius, signals occur at 25, 100, 175, 250, etc. When aiming at 50mm radius, signals occur at 50, 125, 200, 275, etc. Index Point Aiming at 25mm or 50mm radius, maximise signal and mark index. Probe Angle By maximising echo from either 1.5mm or 5mm diameter hole and reading off engraved on side of test block.