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Name Copyright © 2004 WI Ltd Ultrasonic Testing Ultrasonic Testing Part 2 Part 2
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Page 1: TWI - UT- 2

NameCopyright © 2004 WI Ltd

Ultrasonic TestingUltrasonic TestingPart 2Part 2

Page 2: TWI - UT- 2

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Ultrasonic Testing techniques

• Pulse Echo

• Through Transmission

• Transmission with Reflection

Page 3: TWI - UT- 2

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Pulse Echo Technique

• Single probe sends and receives sound

• Gives an indication of defect depth and dimensions

• Not fail safe

Page 4: TWI - UT- 2

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Defect Position

No indication from defect A (wrong orientation)

AB

B

Page 5: TWI - UT- 2

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Through Transmission Technique

Transmitting and Transmitting and receiving probes receiving probes on opposite sides on opposite sides of the specimenof the specimen

Tx Rx

Presence of defect Presence of defect indicated by indicated by reduction in reduction in transmission signaltransmission signal

No indication of No indication of defect locationdefect location

Fail safe method

Page 6: TWI - UT- 2

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Page 7: TWI - UT- 2

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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

Page 8: TWI - UT- 2

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Transmission with ReflectionRT

Also known as:Also known as:

Tandem TechniqueTandem Technique or or

Pitch and Catch TechniquePitch and Catch Technique

Page 9: TWI - UT- 2

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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

Page 10: TWI - UT- 2

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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

Page 11: TWI - UT- 2

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Ideal Pulse Length

5 cycles for weld testing

Page 12: TWI - UT- 2

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The Sound Beam

• Dead Zone

• Near Zone or Fresnel Zone

• Far Zone or Fraunhofer Zone

Page 13: TWI - UT- 2

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The Sound Beam

NZ FZ

Distance

Intensity varies

Exponential Decay

Main Beam

Page 14: TWI - UT- 2

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Main Lobe

Side Lobes

Near Zone

Main Beam

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

The side lobes has multi minute main beams

Two identical defects may give different amplitudes of signals

Page 15: TWI - UT- 2

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Sound BeamNear 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

Page 16: TWI - UT- 2

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Near Zone

V

fD

f

V

D

4Near Zone

4Near Zone

2

2

Page 17: TWI - UT- 2

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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

Page 18: TWI - UT- 2

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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

Should large diameter crystal probes have a high or low frequency?

V

fDD

4

4Near Zone

22

Page 19: TWI - UT- 2

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1 M Hz 5 M Hz

1 M Hz

5 M Hz

Which of the above probes has the longest Near Zone ?

Page 20: TWI - UT- 2

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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

Should large diameter crystal probes have a high or low frequency?

V

fDD

4

4Near Zone

22

Page 21: TWI - UT- 2

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Beam Spread• In the far zone sound pulses spread out

as they move away from the crystal

Df

KV

D

KSine or

2

/2

Page 22: TWI - UT- 2

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Beam Spread

Df

KV

D

KSine or

2

Edge,K=1.2220dB,K=1.08

6dB,K=0.56

Beam axis or Main Beam

Page 23: TWI - UT- 2

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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?

Page 24: TWI - UT- 2

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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

Page 25: TWI - UT- 2

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1 M Hz 5 M Hz

1 M Hz

5 M Hz

Which of the above probes has the Largest Beam Spread ?

Page 26: TWI - UT- 2

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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?

Page 27: TWI - UT- 2

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Testing close to side walls

Page 28: TWI - UT- 2

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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

Page 29: TWI - UT- 2

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The Phenomenon of Sound

REFLECTIONREFRACTION

DIFFRACTION

Page 30: TWI - UT- 2

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The Phenomenon of Sound

REFLECTIONREFRACTION

DIFFRACTION

Page 31: TWI - UT- 2

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Law of Reflection

• Angle of Incidence = Angle of Reflection

60o 60o

Page 32: TWI - UT- 2

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Inclined incidence(not at 90o )

Incident

Transmitted

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

Page 33: TWI - UT- 2

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REFRACTION• Only occurs when:The incident angle is other than 0°

Water

Steel

Steel

Steel

Water

Steel

30°

Refracted

Page 34: TWI - UT- 2

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REFRACTION• Only occurs when:The incident angle is other than 0°

Steel

Steel

Water

Steel

30°

Refracted

The Two Materials has different VELOCITIES

No Refraction

30°

30°

65°

Page 35: TWI - UT- 2

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Snell’s Law

I

R

Material 1

Material 2

2 Materialin

1 Material

Vel

inVel

RSine

ISine

Incident

Refracted

Normal

Page 36: TWI - UT- 2

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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

Page 37: TWI - UT- 2

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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

Page 38: TWI - UT- 2

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Snell’s LawC

Perspex

Steel

C

20

S

48.3

24

Page 39: TWI - UT- 2

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Snell’s Law

Perspex

Steel

S

CC

CC

S

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

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

When a waveform changes into another waveform: MODE CHANGE

Page 40: TWI - UT- 2

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Snell’s Law

Perspex

Steel

C

CS

C

SC

S

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

Up to a point where the Compression Wave is at 90° from the Normal

90° This happens at the

FIRST CRITICAL ANGLE

Page 41: TWI - UT- 2

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1st Critical Angle

C

27.4

S

33

C Compression wave refracted at 90 degrees

Page 42: TWI - UT- 2

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2nd Critical Angle

C

S (Surface Wave)

90

C

Shear wave refracted at 90 degrees

57

Shear wave becomes a surface wave

Page 43: TWI - UT- 2

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1st Critical Angle Calculation

C

Perspex

SteelC

5960

2730

90

I

Sine

Sine

5960

2730SinI

458.0SinI

26.27I

S

190 Sin

27.2

Page 44: TWI - UT- 2

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2nd Critical Angle Calculation

C

Perspex

Steel

C

3240

2730

90

I

Sine

Sine

3240

2730SinI

8425.0SinI

4.57I

S190 Sin

57.4

Page 45: TWI - UT- 2

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1st.

2nd.

33°

90°

Before the 1st. Critical Angle: There are both Compression and Shear wave in the second material

S C

At the FIRST CRITICAL ANGLE Compression wave refracted at 90°

Shear wave at 33 degrees in the material

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

C

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

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

Page 46: TWI - UT- 2

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Page 47: TWI - UT- 2

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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.

C

S

C S

One Defect Two Echoes

Page 48: TWI - UT- 2

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Snell’s Law• Calculate the 1st critical angle for a

perspex/copper interface

• V Comp perspex : 2730m/sec

• V Comp copper : 4700m/sec

5.355808.04700

2730SinI