آزادواحداهواز دانشگاهومهندسی فنی دانشکده

Ultrasonic Testing

Shokoh manesh asghar&

Hammori aminsupervisor: Dr Moeinifar

Introduction to Nondestructive Testing

Six Most Common NDT Methods

• Visual• Liquid

Penetrant • Magnetic • Ultrasonic• Eddy Current• X-ray

آزمون فرا صوتيUltrasonic Test

آزمون هاي فرا صوتي كاربرد بسيار گسترده اي درتعيين نقص هاي دروني مواد دارند.

از اين روش مي توان براي تعيين ترك هاي زيرسطحي نيز استفاده كرد.

آزمون هاي فرا صوتي عالوه بر بازرسي قطعاتتكميل شده براي بازرسي كنترل كيفيت مراحل

مختلف توليد قطعاتي همچون ورقهاي نورد شده نيز بكار مي روند.

مباني آزمون فرا صوتي از ايجاد موج هاي صوتي توسط يك ضربان سنج استخراج شده است.

روش مدرن بكار گرفته شده امروزي، التراسونيك Sonaناميده مي شود كه علت اين نامگذاري كلمه

مي باشد كه در التين به معني صوت است.

: سرعت موج

در حالتكلي هر چه

محيط مادي

فشرده تر باشد،

سرعت حركت موج

صوتي در آن بيشتر

است. بنابراين سرعت حركت امواج

صوتي در جامدات

بيشتر از سياالت

مي باشد.

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)

f

V

Velocity

Frequency

Wavelength

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

Sound WavesSound Waves

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/sV Compression in water : 1470 m/sV Compression in air : 330 m/s

STEEL WATER AIR

5 M Hz

ساختمان : پروب

چندين نوع پروب فرستنده وجوددارد، اما همه انواع آنها داراي

� يا از كريستالي است كه مستقيماطريق پوشش محافظ با ماده مورد

آزمايش در تماس است. ،از كوارتز طبيعي � جنس بلور معموال

تيتانات باريم، نيوبات سرب و سولفات ليتيم مي باشد. ولتاژ پله اي

كوتاه مدتي به كريستال اعمال مي شود.

پروب ها ممكن است قائم يازاويه دار باشند.

: پروب هاي زاويه دار پروب ه�اي زاويه دار ب�راي فرس�تادن موج ه�اي برش�ي ي�ا

موج ه�اي ريلي ب�ه درون قطع�ه تحت بازرس�ي ط�راحي شده اند.

پ�روب همانن�د زاويه اي پ�روب كلي س�اختمان عم�ودي اس�ت ب�ا اين تف�اوت ك�ه بل�ور در قطع�ه

پرسپكسي جاسازي شده است. در فص�ل مش�ترك ك�ه بازگش�تي م�وج ط�ولي

پرسپكس�ي - فل�ز تولي�د مي ش�ود، ممكن اس�ت ب�ه كريس�تال برگ�ردد و عالئم گم�راه كنن�ده اي ب�ه م�اده ك�ار اين از جلوگ�يري ب�راي آورد. وج�ود پ�روب در الس�تيك همچ�ون كنن�ده اي ج�ذب ك�ه اس�ت اين ديگ�ر روش جاس�ازي مي ش�ود. قطع�ه پرس�پكس ب�ه گ�ونه اي ش�كل داده ش�ود ك�ه م�وج برگش�تي چن�دين ب�ار بازت�اب ش�ود و ان�رژي ض�ريب ك�ه آنج�ا از و بده�د دس�ت از را خ�ود وج�ود امك�ان اين اس�ت، ب�اال پرس�پكس ج�ذب

خواهد داشت.

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

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

Propagation

Particle vibration

Shear / Transverse Vibration at right angles / perpendicular

to direction of propagation Travel in solids only Velocity 1/2 compression (same

material)

Propagation

Particle vibration

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 fingerFollows 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

0 10 100 1K 10K 100K 1M 10M 100m

Sonic / Audible

Human

16Hz - 20kHz

Ultrasonic

> 20kHz = 20,000Hz

Ultrasonic Testing

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

Frequency Frequency : Number of cycles

per second

1 second

1 cycle per 1 second = 1 Hertz

18 cycle per 1 second = 18 Hertz

3 cycle per 1 second = 3 Hertz

1 second 1 second

THE HIGHER THE FREQUENCY THE SMALLER THE WAVELENGTH

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

Pg 21

Ultrasonic Inspection

defect

0 10 20 30 40 50

defect echo

Back wall echo

CRT DisplayCompression Probe

Material Thk

initial pulse

Basic Principles of Ultrasonic TestingThe distance the sound traveled can be displayed on the

Flaw DetectorThe screen can be calibrated to give accurate readings of the distance

Bottom / Backwall

Signal from the backwall

Basic Principles of Ultrasonic TestingThe 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

The depth of the defect can be read with reference to the marker on the screen

0 10 20 30 40 50 60

60 mm

Thickness / depth measurement

A

A

B

B

C

C

The THINNER the material the less

distance the sound travel

The closer the reflector to the

surface, the signal will be more to the left of the screen

The thickness is read from the screen

684630

Ultrasonic Inspection

0 10 20 30 40 50

initial pulse defect echo

CRT Display

sound path

Angle Probe

defect

Surface distance

The Sound Beam

Dead Zone Near Zone or Fresnel Zone Far Zone or Fraunhofer Zone

The Sound Beam

NZ FZ

Distance

Intensity varies

Exponential Decay

Main Beam

Main Lobe

Side Lobes

Near Zone

Main Beam

The 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 energy

The side lobes has multi minute main beams

Two identical defects may give different amplitudes of signals

Sound Beam

Near Zone Thickness

measurement Detection of

defects Sizing of large

defects only

Far Zone Thickness

measurement Defect detection Sizing of all

defectsNear zone length as small as possible balanced against acceptable minimum detectable defect size

Near Zone

V

fD

f

V

D

4Near Zone

4Near Zone

2

2

Near Zone What is the near zone length of a 5MHz

compression probe with a crystal diameter of 10mm in steel?

mm

V

fD

1.21

000,920,54

000,000,510

4Near Zone

2

2

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

V

fDD

4

4Near Zone

22

1 M Hz 5 M Hz

1 M Hz

5 M Hz

Which of the above probes has the longest Near Zone ?

Beam Spread In the far zone sound pulses spread out

as they move away from the crystal

Df

KV

D

KSine or

2

/2

Beam Spread

Df

KV

D

KSine or

2

Edge,K=1.2220dB,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?

o

Df

KVSine

35.7 1278.0

105000

592008.1

2

1 M Hz 5 M Hz

1 M Hz

5 M Hz

Which of the above probes has the Largest Beam Spread ?

Beam Spread

The bigger the diameter the smaller the beam spread

The higher the frequency the smaller the beam spread

Df

KV

D

KSine or

2

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

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 RESOLUTIONLong 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

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

Inclined incidence(not at 0o)REFRACTIONInclined incidence(not at 0o)REFRACTION

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

Snell’s Law

C

Perspex

Steel

C

20

48.3

2 Materialin

1 Material

Vel

inVel

RSine

ISine

5960

2730

48.3

20

Sine

Sine

4580.04580.0

Snell’s Law

C

Perspex

Steel

C

15

34.4

2 Materialin

1 Material

Vel

inVel

RSine

ISine

5960

2730

R

15

Sine

Sine

2730

596015SinSinR

565.0SinR

4.34R

Snell’s Law

C

Perspex

Steel

C

20

S

48.3

24

1st Critical Angle

C

27.4

S

33

C Compression wave refracted at 90 degrees

2nd Critical Angle

C

S (Surface Wave)90

C

Shear wave refracted at 90 degrees

57

Shear wave becomes a surface wave

1st Critical Angle Calculation

C

Perspex

SteelC

5960

2730

90

I

Sine

Sine

5960

2730SinI

458.0SinI

26.27I

S

190 Sin

27.2

C

Perspex

Steel

C

3240

2730

90

I

Sine

Sine

3240

2730SinI

8425.0SinI

4.57I

S190 Sin

57.4

2nd Critical Angle Calculation

Sound at an Interface Sound will be either transmitted

across or reflected back

Reflected

Transmitted

Interface

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

Formula

VZ

• Measured in kg / m2 x sec

• Steel46.7 x 106 • Water 1.48 x

106

• Air 0.0041 x 106

• Perspex 3.2 x 106

= Density , V = Velocity

% Sound Reflected at an Interface

reflectedZZ

ZZ%100

2

21

21

% 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

reflected%10048.17.46

48.17.462

reflected%10018.48

22.452

reflected%88.0910093856.0 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.

Steel

AirSteel

Air

Steel

Steel Aluminum

Steel

Large Acoustic Impedance Ratio

Large Acoustic Impedance Ratio

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

1

010..20H

HLogdB

2 signals at 20% and 40% FSH.

What is the difference between them in dB’s?

2..2020

4020 1010.. LogLogdB

3010.020dB

dBdB 6

1

010..20H

HLogdB

2 signals at 10% and 100% FSH.

What is the difference between them in dB’s?

10..2010

10020 1010.. LogLogdB

120dB

dBdB 20

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

SIZING METHODS 0O PROBE

There are four main sizing techniques used with 0o probes:

• 6 dB drop

• Maximum Amplitude

• Equalisation

• DGS

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

BWEDefect

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 defectPlan View

6 dB Drop

Plan View

Now the whole beam is on the defect

Defect

Back wall echo is now may be reduced or disappeared

6 dB DropBWEDefe

ct

Plan View

The probe is moved back until the echo is reduced by half of it’s original heightAt this point the probe centre beam is directly on the edge of the defectThe probe is then removed and the centre is marked, and repeat to size the whole defect

Maximum Amplitude Technique

For sizing multifaceted defect – eg. crackNot very accurate Small probe movement

Maximum Amplitude

The whole probe beam is on the defect

At this point, multipoint of the defect reflect the sound to the probeThe echo (signal) show as a few peaks

Multifaceted defect : crack

Maximum Amplitude

Multifaceted defect : crack

The probe is moved out of the defect, the signal disappearedIf the edge of the beam strike the edge of the defect, a very small echo appears

If the probe is moved into the defect, the signals height increase

At this point the MAIN BEAM is directly at the edge of the defect

One of the peak maximised

Maximum Amplitude

The probe is to be moved to the other end of the defect

The signals will flactuate as the beam hits the different faces of the defectsThe probe is moved back into the defect and to observe a peak of the signal maximises

Mark the point under the centre of the probe which indicates the edge of the defectThe length of the defect is measured

Length

Remember: The peak which maximised does not have to be the tallest or the first

one

Equalization Technique

At this point the whole beam is on the back wall

BWE

At this point the whole beam is on the defect

The BWE is at it maximum

The Defect echo is at it maximum

Defect

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

The equalization technique can ONLY be used if the defect is halfway the thickness

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

Using Ultrasound for Testing:PULSE ECHO

Using Ultrasound for Testing:PULSE ECHO

Using Ultrasound for Testing:PULSE ECHO

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

Tx Rx

Presence of defect indicated by reduction in transmission signal

No indication of defect location

Transmission with Reflection

RT

Also known as:

Tandem Technique or

Pitch and Catch Technique

Transmission with Reflection

T R

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

Immersion Testing

Water path distance

Water path distance

Front surface Back surface

Defect

Using Ultrasound for Testing

PULSE ECHO

450

450

40

40

ULTRASONIC EXAMINATION OF

WELDS

DOUBLE SIDED “T” JOINT

BACK GOUGE

ULTRASONIC EXAMINATION OF

WELDS

00

00

100 (appro

x.)

COVERAGE OF FUSION

FACES

COVERAGE OF WELD VOLUME

450

45 0

450

45 0

COVERAGE OF FUSION

FACES

COVERAGE OF WELD VOLUME

ULTRASONIC EXAMINATION OF

WELDS

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:

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

CRACK SLAG

ORBITAL SCAN

ROTATIONAL SCAN

TYPICAL ECHO DYNAMIC PATTERNS

Calibration Blocks and Their Usage

I.I.W (International Institute of Welding) Block / V1 / A2 Block

100mm

300mm

91mm 85mm

200mm

50mm Dia Perspex

5mm

10mm

15mm

35mm1.5mm Dia

15mm

100mm

23mm 25mm

USESCompressional

Shear

A4 / V2 / DIN 54/122 / KIDNEY BLOCK

R50R2512.5mm or 20mm

PLAN VIEW1.5 OR 5mm dia. hole

USES

i. Calibration

This block can be purchased having a thickness of either 12.5mm or 20mm.b) Shear Probes

a) Compressional Probes

i. 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.

ii. Index Point

Aiming at 25mm or 50mm radius, maximise signal and mark index.

iii. Probe Angle

By maximising echo from either 1.5mm or 5mm diameter hole and reading off engraved

on side of test block.