UT Principles

8/2/2019 UT Principles

1/26

9th Sep, 2001

BASIC ULTRASONIC PRINCIPLES

P.J SURYAVAMSHI

NDE-HZW


2/26

A. What is Ultrasound?

Sound generated above the human hearing range

(20 KHz) is called ultrasound.

Although ultrasound behaves in a similar manner

to audible sound, it has a much shorter wavelength.

This means it can be reflected off very small

surfaces such as defects inside material.

The frequency range normally employed in

ultrasonic testing is 100 KHz to 50 MHz.


3/26


B. Velocity of Ultrasound and Wavelength:

Ultrasonic vibrations travel in the form of a wave,

similar to the way light travels. However, unlike

light waves, which can travel in a vacuum,ultrasound requires an elastic medium.

= v/f Where: = Wavelength

v = material sound velocity

f = frequency


4/26



5/26


C. Wave Propagation and Particle Motion:

The most common methods of ultrasonic examinationutilize either longitudinal waves or Shear wave.

Longitudinal Wave : A wave in which the particle

motion is in the same direction as the propagation of

wave.Shear Wave : A wave motion in which the particle

motion is perpendicular to the direction of the

propagation.


6/26



7/26


D. Sound Field

The sound field of a transducer (probe) is divided

into two zones; the near field and the far field.

Near Field: The region directly in front of the

transducer where the echo amplitude goes through aseries of maxima and minima and ends at the last

maximum.

The near field is the natural focus of the transducer.

It is the function of the transducer frequency, element

diameter, and the sound velocity of the test material.


8/26


N

N = D2

/ 4N = Near field Distance

D = Crystal Diameter


9/26


Far Field: The far field is the area beyond nearfield where the sound field pressure gradually

drops to zero.In the far field the sound beam diverges.

N

Sin (/2) = 0.514 / D

/2 = Half Angle beam

Spread.


10/26

DESIGN CHARACTERISTICS OF TRANSDUCER

A. What is an Ultrasonic Transducer?

A transducer is any device that converts one formof energy to another. An ultrasonic transducer

converts electrical energy to mechanical energy,

in the form of sound, and vice versa.

The main components are the active element,

backing, and wear plate.


11/26

DESIGN CHARACTERISTICS OF

TRANSDUCER


12/26


TRANSDUCER

The Active Element:

The active element, which is piezo electric material,converts electrical energy such as an excitation pulse

from a flaw detector into ultrasonic energy.Backing:

The backing is usually a highly attenuative, highdensity material that is used to control the vibration

of the transducer by absorbing the energy radiating

from the back face of the active element.


13/26


TRANSDUCER

Wear Plate:The basic purpose of the transducer wear plate is to

protect the transducer element from the testingenvironment.

In the case of contact transducers, the wear platemust be a durable and corrosion resistant material

in order to withstand the wear caused by use on a

material such as steel.


14/26

TYPES OF TRANSDUCER

Dual Element Transducer:

Dual element transducer utilize separate transmittingand receiving elements, mounted on delay lines that

are usually cut at an angle.

This configuration improves near surface resolution.

Roof Angle

Delay lines


15/26

TYPES OF TRANSDUCER


16/26

TYPES OF TRANSDUCER

Angle Beam Transducer:Angle beam transducer use the principles of

refraction and mode conversion to produce

refracted shear or longitudinal waves in the test

material.Longitudinal Wave

Shear Wave

First Critical Angle = 28 0

Second Critical Angle = 57 0


17/26

TYPES OF TRANSDUCER


18/26

TYPES OF TRANSDUCER

Beam Path

Surface

Distance


19/26

TYPES OF TRANSDUCER


20/26

FOCUSED PROBE Focusing Configuration:

Focusing is accomplished by either the addition

of a lens or by curving the element.

By definition, the focal length of transducer is the

distance from the face of the transducer to thepoint in the sound field where the signal with the

maximum amplitude is located. Because the lastsignal maximum occurs at a distance equivalent

to the near field, focal distance will be always less

than near field length.


21/26

FOCUSED PROBE


22/26

FOCUSED PROBETypes of focusing:

a.Spherically Focused (Spot Focused)b.Cylindrically Focused (Line Focused)


23/26

RTD PROBES


24/26

RTD PROBES

Hazira RTD Probe 700TRL2-Aust.

2(8 X 14)

SA 100,FS - 21

Wave Mode:

700 Longitudinal

Frequency : 2 MHz

Powai RTD Probe 700TRL2-St

2( 18 - R150)SA 250,FS - 18

Wave Mode:

700 Longitudinal

Frequency : 2 MHz


25/26

RTD PROBES

Hazira RTD Probe

Material to be tested:Aust. Steel

Able to detectdiscontinuity in Aust.

Steel & Steel

Crystal Shape:

Rectangular

Line Focused

Powai RTD Probe

Material to be tested:Steel

Able to detectdiscontinuity in Steel

Crystal Shape:

Elliptical

Spot Focused


26/26

RTD PROBES

Hazira RTD Probe Focus Sound Path:

21 mm

Roof Angle: 100

Powai RTD Probe Focus Sound Path:

18 mm

Roof Angle: 250

UT Principles

Documents

Transcript of UT Principles