Not expect to find deep - seated discontinuities Must be ...

Not expect to find deep-

seated discontinuities

Must be applied in at least

two directions, approx. 90

deg. apart

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Copyright (KC Wong) 62

70 kHz1-5

MHz

(Bats Range) (Steel)

Intrasonic 16 Hz20

kHz200 kHz

15 MHz

(Below Audio) (Sonic Audible) (Ultrasonic Test Range)

Acoustics

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Introductions

The ultrasonic method is applicable to almost all

materials.

The ultrasonic method uses the transmission of

mechanical energy in wave form at frequencies above the

audible range.

Reflections of this energy by discontinuities in metals are

detected in a manner somewhat similar to the detection

of reflected light waves in transparent media.� � � � � � � � � � � � � � � �

1

2

3

4

5

Initial wave

Back Wall

HalfWay

Echo Received

Echo Return

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Velocity of sound in common materials m/sec

Material Compressional Shear

Aluminum 6320 3080

Steel 5920 3250

Copper 4700 2260

Brass 3830 2050

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Compressional or Longitudinal Wave

Shear or Transverse Wave

Surface Wave

Lamb Wave


May also called longitudinal Wave

Molecules vibrate backwards and forwards in same direction

Greatest penetration power


Lowest attenuation

Best for thickness measurement, detection of laminations

Can be propagated in solids, liquids and gases


May also called Transverse Wave

Molecules vibrate perpendicular to the direction of wave propagation

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Velocity is approximately ½ of longitudinal wave

Higher sensitivity, Higher attenuation

Can be propagated in solids, but generally not propagate in liquids and gases


Ultrasound is generated by transducer through “Piezo-Electric Effect”

Means changes mechanical energy into electrical energy or vice versa


In the pulse-echo technique, a transducer transmits a pulse of high frequency sound into and through the material and the reflected sound is received from a discontinuity, the opposite surface or other surfaces of the part.

The reflected sound is received as an echo, which together with the original pulse, is displayed on the screen of a cathode ray tube (CRT). � � � � � � � � � � � � � � � �

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Ultrasonic Flaw Detector

Transducers / probes

Couplant

Calibration standard block

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An electronic instrument with either a CRT or digital display

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Capable of

determining the location, size and type of many discontinuities

Determining dimensional measurements, such as material thickness

Available in a wide variety of sizes and styles



Probe Type

Straight Probe or Normal

Probes

Angle or Shear Probes

Surface Wave Probes

Twin Crystal Probes

Single Crystal Probes

Only one crystal for both transmission and receiving ultrasound wave

Initial pulse induces dead zone

Any signal from a reflector at a short distance than the initial pulse will be concealed in the initial pulse


Has two crystals mounted on perspexshoes angled inwards slightly to focus at a set distance in the test material


One for transmission and other for receiving of sound wave

Can reduce the dead zone

Good surface resolution and near-surface detection

May be called 0 Degree Probe or Normal Probe

Generate longitudinal or compression wave


Best for thickness measurements, depth of discontinuity below material surface (Laminations)


May be called Shear Probe

Generate shear or transverse waves of any angle into specimens

Usually 45 , 60 , 70



Used extensively for weld evaluation

Without the need for removal of the rough weld reinforcement

Generate surface wave


Used to exclude air from between the probe face and the specimen

Common couplants include

Oil,

Grease,

Water

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Before testing is begun, the detector should be calibrated against reference block to ensure the accuracy

The calibration block should contain a pre-set machine “Flaw”

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Aspects to be calibrated

Probe index

Angle of refraction

Time base

Sensitivity

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The most versatile calibration block are

IIW block 1 (A2 or V1)

IIW block 2 (A4 or V2) (Best for field applications)

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Not expect to find deep - seated discontinuities Must be ...

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