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Ultrasonic TestingUltrasonic TestingPart 1Part 1


Ultrasonic Testing

NDT Training & Certification


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 – 3:30 pm• Day End : 5:00 pm• Course Objective: To train and prepare

participants to obtain required skill and knowledge in Ultrasonic Testing and to meet the examination schemes requirements.


NDTMost common NDT methods:

Penetrant Testing (PT)

Magnetic Particle Testing (MT)

Eddy Current Testing (ET)

Radiographic Testing (RT)

Ultrasonic Testing (UT)

Mainly used for surface testing

Mainly used for Internal Testing


NDT

• Which 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


Basic Principles of Ultrasonic Testing

Sound is transmitted in the material to be tested

The sound reflected back to the probe is displayed on

the Flaw Detector


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 Testing

Principles of Sound


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)


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


Velocity

4 times

What is the velocity difference in steel compared with in water?

If 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?

Air

Remember the formula

= v / f


DRUM BEAT

Low Frequency Sound

40 Hz

Glass

High Frequency

5 K Hz

ULTRASONIC TESTING

Very High Frequency

5 M Hz


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



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


Sound waves are the vibration of particles in solids, liquids or gases.

Particles vibrate about a mean position.

One cycle

Displacement

The distance taken to complete one cycle

wavelength

wavelength

Wavelength

Wavelength is the distance required to complete a cycle.


f

V

Velocity

Frequency

Wavelength


Frequency & Wavelength

1 M Hz 5 M Hz 10 M Hz 25 M Hz

Which probe has the smallest wavelength?

SMALLESTLONGEST

Which probe has the longest wavelength?

= v / f

F F


Wavelength is a function of frequency and velocity.

5MHz compression wave probe in steel

mm18.1000,000,5

000,900,5

Therefore:

f

V V

for

or V f


• Which of the following compressional probe has the highest sensitivity?

• 1 MHz

• 2 MHz

• 5 MHz

• 10 MHz

10 MHz


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 (half the wavelength)


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 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


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


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

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

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 ?


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


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

• 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?


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?


Testing close to side walls

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