Ultrasonic Testing.pdf

Ultrasonic Testing Part 1

Course Layout • • • • • • •

Duration : 9.5 Days (Mon – Fri) Start : 8:30 am Coffee Break : 10:00 – 10:30 am Lunch : 12:30 – 1:30 pm Tea Break : 3:00 – 3:15 pm Day End : 4:30 pm Course Objective: To train and prepare participants to obtain required skill and knowledge in Ultrasonic Testing and to meet the examination schemes requirements.

NON-DESTRUCTIVE TESTING Examination of materials and components in such a way that allows material to be examinated without changing or destroying their usefulness

NDT Most common NDT methods: Penetrant Testing (PT) Magnetic Particle Testing (MT)

Mainly used for surface testing

Eddy Current Testing (ET) Radiographic Testing (RT) Ultrasonic Testing (UT)

Mainly used for Internal Testing

NDT • Which NDT method is the best ? Depends on many factors and conditions

Basic Principles of Ultrasonic Testing • To understand and appreciate the capability and limitation of UT

History of Ultrasonic Testing (UT) • First came ‘sonic’ testing • The piezo-electric effect discovered in 1880/81 • Marine ‘echo sounding’ developed from 1912 • In 1929 Sokolov used vibrations in metals to find flaws • Cathode ray tubes developed in the 1930’s • Sproule made the first flaw detector in 1942

Ultrasonic Inspection

 Sub-surface detection

 This detection method uses high frequency sound waves, typically above 2MHz to pass through a material  A 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 display  The actual display relates to the time taken for the ultrasonic pulses to travel the distance to the interface and back  An interface could be the back of a plate material or a defect  For ultrasound to enter a material a couplant must be introduced between the probe and specimen

Ultrasonic Inspection

Pulse echo signals A scan Display

Compression probe

UT Set, Digital

Thickness checking the material

Ultrasonic Inspection defect echo

initial pulse

Material Thk

defect

0

Compression Probe

Back wall echo

10

20

30

40

CRT Display

50

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

A

B

C

30

46

68

The thickness is read from the screen

C B A

The THINNER the material the less distance the sound travel

Ultrasonic Inspection A Scan Display

Angle Probe

UT Set

Ultrasonic Inspection initial pulse

defect echo

Surface distance

defect

sound path

Angle Probe

0

10

20

30

40

CRT Display

50

Ultrasonic Inspection 

Advantages



Disadvantages

 Trained and skilled Rapid results operator required  Sub-surface detection  Requires high operator  Safe skill  Can detect planar defect  Good surface finish  Capable of measuring the required depth of defects  Difficulty on detecting  May be battery powered volumetric defect  Portable  Couplant may 

contaminate  No permanent record

Ultrasonic Testing Principles of Sound

What is Sound ? • A mechanical vibration • The vibrations create Pressure Waves • Sound travels faster in more ‘elastic’ materials • Number of pressure waves per second is the ‘Frequency’ • Speed of travel is the ‘Sound velocity’

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

V λ= f 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

Sound travelling through a material • Velocity varies according to the material Compression waves

Shear waves

• Steel

5960m/sec

• Steel

3245m/sec

• Water

1470m/sec

• Water

NA

• Air

344m/sec

• Air

NA

• Copper

4700m/sec

• Copper

2330m/sec

Ultrasonic • Sound : mechanical vibration

What is Ultrasonic? Very High Frequency sound – above 20 KHz 20,000 cps

Acoustic Spectrum Sonic / Audible Human 16Hz - 20kHz

0

10

100

1K

Ultrasonic > 20kHz = 20,000Hz

10K 100K 1M 10M 100m Ultrasonic Testing

0.5MHz - 50MHz Ultrasonic : Sound with frequency above 20 KHz

Frequency • Frequency

1 second 1 cycle per 1 second = 1 Hertz

:

Number of cycles per second

1 second 3 cycle per 1 second = 3 Hertz

1 second 18 cycle per 1 second = 18 Hertz

THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH

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 TESTING Very High Frequency 5 M Hz

Glass High Frequency 5 K Hz DRUM BEAT Low Frequency Sound 40 Hz

Wavelength and frequency • The higher the frequency the smaller the wavelength • The smaller the wavelength the higher the sensitivity • Sensitivity : The smallest detectable flaw by the system or technique • In UT the smallest detectable flaw is ½ λ

(half the wavelength)

High Frequency Sound

V λ= f 5MHz compression wave probe in steel

5,900,000 = 1.18mm λ= 5,000,000

Frequency

1 M Hz

5 M Hz

LONGEST

F

10 M Hz

25 M Hz SMALLEST

λ=v/f

λ

F

λ

Which probe has the smallest wavelength? Which probe has the longest wavelength?

• Which of the following compressional probe has the highest sensitivity? • 1 MHz • 2 MHz • 5 MHz • 10 MHz

10 MHz

What is the velocity difference in steel compared with in water? 4 times If the frequency remain constant, in what material does sound has the highest velocity, steel, water, or air? Steel If the frequency remain constant, in what material does sound has the shortest wavelength, steel, water, or air? Air Remember the formula λ=v/f

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

• 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

Shear waves

• Steel

5960m/sec

• Steel

3245m/sec

• Water

1470m/sec

• Water

NA

• Air

344m/sec

• Air

NA

• Copper

4700m/sec

• 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 Testing Part 2

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

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

The Sound Beam NZ

FZ

Main Beam

Intensity varies Exponential Decay

Distance

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 Main Lobe Main Beam

Any reflector hit by the main beam will reflect the high amount of energy

Near Zone 2

D Near Zone = 4λ V λ= f

2

D f Near Zone = 4V

Near Zone • What is the near zone length of a 5MHz compression probe with a crystal diameter of 10mm in steel? 2

D f Near Zone = 4V 2 10 × 5,000,000 = 4 × 5,920,000 = 21.1mm

Near Zone 2

D Near Zone = 4λ

2

D f = 4V

• 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

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

5 M Hz

5 M Hz

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

θ Kλ KV Sine = or 2 D Df

Beam Spread

θ Kλ KV Sine = or 2 D Df Edge,K=1.22

20dB,K=1.08 6dB,K=0.56 Beam axis or Main Beam

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

θ

KV Sine = Df 2 1.08 × 5920 = 5000 × 10 o = 0.1278 = 7.35

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

5 M Hz

5 M Hz

Beam Spread

θ Kλ KV Sine = or 2 D Df • 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?

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

•

Pulse Length

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

•

Pulse Length

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

Good resolution

Resolution

Poor resolution

Sound travelling through a material Loses intensity due to

Beam Spread

Attenuation

• Sound beam comparable to a torch beam

• Energy losses due to material

•Reduction differs for small and large reflectors

•Made up of absorption and scatter

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

Beam Spread The sound beam spread out and the intensity decreases

Beam spread and Attenuation combined

Repeat Back-wall Echoes Beyond The Near Zone

ZERO ATTENUATION

ATTENUATION 0.02 dB/mm

Sound at an Interface • Sound will be either transmitted across or reflected back Reflected

Interface

Transmitted

How much is reflected and transmitted depends upon the relative acoustic impedance of the 2 materials

Acoustic Impedance • Definition The Resistance to the passage of sound within a material • Measured in kg / m2 x sec

• Formula

Z = ρ ×V ρ = Density , V = Velocity

• • • •

Steel Water Air Perspex

46.7 x 106 1.48 x 106 0.0041 x 106 3.2 x 106

% Sound Reflected at an Interface 2

 Z1 − Z 2    × 100 = % reflected  Z1 + Z 2  % Sound Reflected + % Sound Transmitted = 100% Therefore % Sound Transmitted = 100% - % Sound Reflected

How much sound is reflected at a steel to water interface? • Z1 (Steel) = 46.7 x 106 • Z2 (Water) =1.48 x 106 2

 46.7 − 1.48  × = 100 % reflected  46.7 + 1.48  2

 45.22   48.18  × 100 = % reflected

0. 93856 ×100 = 88.09% reflected 2

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.

Air

Steel Steel

Large Acoustic Impedance Ratio

Air 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

Sound Intensity

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

dB = 20 Log..10

H0 H1

40 dB = 20 Log..10 = 20 Log ..10 2 20 dB = 20× 0.3010 dB = 6dB

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

dB = 20 Log..10

H0 H1

100 dB = 20 Log..10 = 20 Log ..1010 10 dB = 20× 1 dB = 20dB

Amplitude ratios in decibels • • • • •

2:1 4:1 5:1 10 : 1 100 : 1

= = = = =

6bB 12dB 14dB 20dB 40dB

Ultrasonic Testing Part 3

The Phenomenon of Sound REFLECTION REFRACTION DIFFRACTION

Law of Reflection • Angle of Incidence = Angle of Reflection

60o

60o

Inclined incidence(not at

o 90 )

Incident

Transmitted The sound is refracted due to differences in sound velocity in the 2 DIFFERENT materials

REFRACTION • Only occurs when:

The incident angle is other than 0° 30°

Water

Steel

Water

Steel

Steel

Steel Refracted

REFRACTION • Only occurs when:

The incident angle is other than 0° The Two Materials has different VELOCITIES 30°

30°

Steel

Water

Steel

Steel 65° 30°

No Refraction

Refracted

Snell’s Law Normal

Incident

Material 2

I

Material 1

R

Refracted

Sine I Vel in Material 1 = Sine R Vel in Material 2

Snell’s Law C

C

When an incident beam of sound approaches an interface of two different materials: REFRACTION occurs

Perspex Steel

There may be more than one waveform transmitted into the second material, example: Compression and Shear

C C

SS

When a waveform changes into another waveform: MODE CHANGE

Snell’s Law C

If the angle of Incident is increased the angle of refraction also increases

Perspex Steel

90°

C

S

Up to a point where the Compression Wave is at 90° from the Normal This happens at the FIRST CRITICAL ANGLE

1st Critical Angle C 27.4

Compression wave refracted at 90 degrees C

33 S

1st Critical Angle Calculation C 27.2

Sine I 2730 = Sine 90 5960 Perspex

C

Steel

S

Sin90 = 1 2730 SinI = 5960

SinI = 0.458 I = 27.26

Snell’s Law • Calculate the 1st critical angle for a perspex/copper interface • V Comp perspex : 2730m/sec • V Comp copper : 4700m/sec

2730 SinI = = 0.5808 = 35.5 4700

2nd Critical Angle C

C

57

S (Surface Wave) 90 Shear wave refracted at 90 degrees Shear wave becomes a surface wave

2nd Critical Angle Calculation C 57.4

Sine I 2730 = Sine 90 3240

C

Perspex Steel

S

Sin90 = 1 2730 SinI = 3240

SinI = 0.8425 I = 57.4

Snell’s Law C

Sine I Vel in Material 1 = Sine R Vel in Material 2

20 Perspex

2730 Sine 20 = Sine 48.3 5960

Steel

0.4580 = 0.4580

48.3 C

Snell’s Law C

Sine I Vel in Material 1 = Sine R Vel in Material 2

15

Sine 15 2730 = Sine R 5960

Perspex Steel 34.4 C

5960 SinR = Sin15 2730

SinR = 0.565 R = 34.4

Snell’s Law C

20 Perspex

Steel

48.3 24

C S

1st. 2nd.

C

Before the 1st. Critical Angle: There are both Compression and Shear wave in the second material At the FIRST CRITICAL ANGLE Compression wave refracted at 90° Shear wave at 33 degrees in the material

90° Beyond the 2nd. Critical Angle: All waves are reflected out of the material. NO wave in the material.

S C

33°

Between the 1st. And 2nd. Critical Angle: Only SHEAR wave in the material. Compression is reflected out of the material.

At the 2nd. Critical Angle: Shear is refracted to 90° and become SURFACE wave

Summary • Standard angle probes between 1st and 2nd critical angles (45,60,70) • Stated angle is refracted angle in steel • No angle probe under 35, and more than 80: to avoid being 2 waves in the same material. One Defect Two Echoes C C S

S

Sound Generation • • • •

Hammers (Wheel tapers) Magnetostrictive Lasers Piezo-electric

magnetostrictive

Piezo-Electric Effect • When exposed to an alternating current a crystal expands and contracts • Converting electrical energy into mechanical

-

+

+

-

-

+

Piezo-Electric Materials QUARTZ • Resistant to wear • Insoluble in water • Resists ageing • Inefficient converter of energy • Needs a relatively high voltage Very rarely used nowadays

LITHIUM SULPHATE • Efficient receiver • Low electrical impedance • Operates on low voltage • Water soluble • Low mechanical strength • Useable only up to 30ºC Used mainly in medical

Polarized Crystals • Powders heated to high temperatures • Pressed into shape • Cooled in very strong electrical fields

Examples • Barium titanate (Ba Ti O3) • Lead metaniobate (Pb Nb O6) • Lead zirconate titanate (Pb Ti O3 or Pb Zr O3)

Most of the probes for conventional usage use

PZT : Lead Zirconate Titanate

Probes

Z

Probes

• The most important part of the probe is the crystal • The crystal are cut to a particular way and thickness to give the intended properties • Most of the conventional crystal are X – cut to produce Y Compression wave X

X

X

Probes • The frequency of the probe depends on the THICKNESS of the crystal • Formula for frequency: Ff = V / 2t Where

Ff = the Fundamental frequency

V = the velocity in the crystal t = the thickness of the crystal Fundamental frequency is the frequency of the material ( crystal ) where at that frequency the material will vibrate.

Probes • The Thinner the crystal the Higher the frequency • Which of the followings has the Thinnest crystal ? 1 MHz Compression probe 5 MHz Compression probe 10 MHz Shear probe 25 MHz Shear probe

25 MHz Shear Probe

Probe Design • Compression Probe – Normal probe – 0°

Housing

Electrical connectors

Damping Transducer

Probe Design • Shear Probe – Angle probe

Damping

Backing medium

Transducer

Probe Shoe

Perspex wedge

Probe Design Twin Crystal

Transmitter Receiver

Separator / Insulator

Focusing lens

Advantages • Can be focused • Measure thin plate • Near surface resolution Disadvantages • Difficult to use on curved surfaces • Sizing small defects • Signal amplitude / focal spot length

Ultrasonic Displays • • • •

A-Scan B-Scan End View C-Scan Plan View D-Scan Side View

• P-Scan or “projection scan” collects and combines A, B, C & D Scan information

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

Defect Orientation

ONLY DEFECTS HAVING A SUITABLY ORIENTATED REFLECTING SURFACE CAN BE DETECTED BY PULSE ECHO METHODS!!

Orientation favourable, sound reflected back to point of origin

Orientation unfavourable, sound not reflected back to point of origin

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

Tx

Rx

Through Transmission Technique 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

Transmission with Reflection T

Also known as: Tandem Technique or Pitch and Catch Technique

R

Transmission with Reflection T

R

TANDEM TESTING

Transmission with Reflection T

R

TANDEM TESTING

Automated Inspections • Pulse Echo • Through Transmission • Transmission with Reflection • Contact scanning • Gap scanning • Immersion 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

Immersion Testing Water path distance Front surface Defect

Water path distance

Back surface

Ultrasonic Testing Part 4

DEFECT LOCATION DEFECT LOCATION IN ULTRASONIC TESTING IS BASED UPON THE PREMISE THAT A “MAXIMISED ECHO RESPONSE” CAN ONLY COME FROM A REFLECTOR WHICH IS LYING ON THE BEAM AXIS. THIS PREMISE CAN BE ASSUMED BECAUSE THE GREATEST SOUND INTENSITY OR PRESSURE IS CONCENTRATED IN A SMALL VOLUME AROUND THE BEAM AXIS.

DEFECT LOCATION IN FUSION WELDS S

600

S = STAND OFF DISTANCE FROM ANY CONVENIENT DATUM POINT (IN THIS CASE THE WELD CENTRELINE) R=

RANGE READ FROM THE FLAWDETECTOR SCREEN

DEFECT LOCATION IN FUSION WELDS 450 S S = STAND OFF DISTANCE FROM ANY CONVENIENT DATUM POINT R=

RANGE READ FROM THE FLAWDETECTOR SCREEN

DEFECT LOCATION IN FUSION WELDS TO ACCURATELY LOCATE DEFECTS IN A BUTT WELD THE FOLLOWING CRITERIA MUST BE MET: 1.

THE PROBE EXIT POINT MUST BE ACCURATELY KNOWN.

2.

THE BEAM ANGLE MUST BE ACCURATELY KNOWN.

3.

THE WELD CENTRELINE MUST BE ACCURATELY KNOWN.

4.

THE MATERIAL THICKNESS MUST BE ACCURATELY KNOWN.

5.

THE FLAWDETECTOR MUST BE ACCURATELY CALIBRATED.

DEFECT SIZING TECHNIQUES 1.

6 dB DROP TECHNIQUE (SOMETIMES CALLED HALF AMPLITUDE OR BEAM SPLITTING TECHNIQUE).

2.

20 dB DROP TECHNIQUE (SOMETIMES CALLED BEAM BOUNDARY TECHNIQUE).

3.

MAXIMUM AMPLITUDE TECHNIQUE.

6 dB DROP LENGTH

6 dB DROP 1.

THE DIMENSION OF THE REFLECTOR WHICH IS BEING MEASURED MUST EXCEED THE BEAM WIDTH.

2.

THE ULTRASONIC BEAM MUST BE SYMMETRICAL IN THE DIRECTION OF PROBE MOVEMENT.

3.

WORKS BEST ON UNIFORM REFLECTORS WITH RELATIVELY STRAIGHT EDGES

20 dB DROP

LENGTH

20 dB DROP 1.

THE DIMENSION OF THE REFLECTOR WHICH IS BEING MEASURED MAY BE EITHER LARGER OR SMALLER THAN THE BEAM WIDTH.

2.

THE ULTRASONIC BEAM NEED NOT BE SYMMETRICAL IN THE DIRECTION OF PROBE MOVEMENT.

3.

THE BEAM SPREAD PARALLEL TO THE DIRECTION OF PROBE MOVEMENT MUST BE KNOWN.

4.

WORKS BEST ON UNIFORM REFLECTORS WITH RELATIVELY STRAIGHT EDGES.

MAXIMUM AMPLITUDE 1.

THE MAXIMUM AMPLITUDE TECHNIQUE IS AN EXTENSION OF THE TECHNIQUE USED IN UT FOR DEFECT LOCATION.

2.

IT WORKS ON THE PREMISE THAT A MAXIMISED RESPONSE COULD ONLY COME FROM A POINT ON A REFLECTOR WHICH IS ON THE SOUND BEAM AXIS.

4.

VOLUMETRIC REFLECTORS CAN BE SIZED VERY ACCURATELY IF THEY CAN BE APPROACHED FROM A VARIETY OF ANGLES.

3.

PLANAR REFLECTORS CAN OFTEN BE SIZED USING THIS TECHNIQUE DUE TO THE PRESENCE OF TIP MAXIMA.

MAXIMUM AMPLITUDE

MAXIMUM AMPLITUDE LACK OF FUSION

700

700

AMPLITUDE

TIP MAXIMA

ECHO DYNAMIC PATTERN RANGE

MAXIMUM AMPLITUDE 1.

THE DIMENSION OF THE REFLECTOR WHICH IS BEING MEASURED MAY BE EITHER LARGER OR SMALLER THAN THE BEAM WIDTH.

2.

WILL WORK WITH ALMOST ANY REFLECTOR.

ULTRASONIC EXAMINATION OF WELDS PRIMARY OBJECTIVES: 1.

TO SCAN ALL FUSION FACES AT AN ANGLE OF INCIDENCE = 00 +/- 200 (00 +/- 100 FOR CRITICAL EXAMINATIONS).

2.

TO SCAN THE ENTIRE WELD VOLUME INCLUDING THE HEAT AFFECTED ZONE WITH A MINIMUM OF TWO PROBE ANGLES.

3.

TO SCAN FOR POSSIBLE TRANSVERSE IMPERFECTIONS

ULTRASONIC EXAMINATION OF WELDS

20

2

600

4

SINGLE SIDED BUTT WELD

ULTRASONIC EXAMINATION OF WELDS 450

THE 450 PROBE CAN NOT BE USED TO SCAN THE WELD ROOT AT HALF SKIP, THEREFORE THE 700 PROBE MUST BE USED: 57

700

57

700

FIXED STAND-OFF SCAN OF WELD ROOT USING THE 700 PROBE

ULTRASONIC EXAMINATION OF WELDS 600 SCAN OF WELD VOLUME AND FUSION ZONES 80

80 23

600

23

600

600

COVERED AT FULL SKIP COVERED AT FULL & HALF SKIP COVERED AT HALF SKIP

600

SCANNING FOR TRANSVERSE IMPERFECTIONS

SCAN

ULTRASONIC EXAMINATION OF WELDS 40

450

BACK GOUGE

DOUBLE SIDED “T” JOINT

40

450

ULTRASONIC EXAMINATION OF WELDS

COVERAGE OF FUSION FACES

COVERAGE OF WELD VOLUME

100 (approx.)

00

00

ULTRASONIC EXAMINATION OF WELDS

COVERAGE OF FUSION FACES

450

450

450

450

COVERAGE OF WELD VOLUME

SCANNING FOR TRANSVERSE IMPERFECTIONS

SCANNING FOR TRANSVERSE IMPERFECTIONS

RECOGNITION OF DEFECT TYPE DEFECT TYPES SUCH AS CRACK, LACK OF FUSION, SLAG INCLUSION etc WHICH ARE DETECTED BY UT CAN OFTEN BE RECOGNISED AS SUCH BY: 1. OBSERVATION OF THE SHAPE OF THE ECHO RESPONSE AND IT’S BEHAVIOUR WHEN THE PROBE IS MOVED IN VARIOUS DIRECTIONS. 2. OBSERVING THE SIZE OF THE ECHO RESPONSE. 3. OBSERVING THE POSITION OF THE REFLECTOR. 4. MEASURING THE SIZE OF THE REFLECTOR. 5. TAKING INTO CONSIDERATION THE TYPES OF DEFECT WHICH ARE MOST LIKELY TO BE PRESENT.

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:

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

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 ORBITAL SCAN

ROTATIONAL SCAN

SLAG