cursillo b¦sico de ultrasonido

8/4/2019 CURSILLO BSICO DE ULTRASONIDO

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Principios Basicos dePruebas conUltrasonido

Teoria y Practica


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PORQUE EL USO DE LOS ULTRASONIDOS ?

Los slidos son buenos conductores de las ondas sonoras.

Las ondas no solamente son reflejadas por las interfaces

pero tambin por las fallas internas. El efecto de interaccin de las ondas con el material es msfuerte entre menor sea la longitud de onda, esto significaentre mayor sea la frecuencia.

Con frecuencias ms bajas la interaccin de las ondas conlas fallas ser muy pequeo.

Ms econmico y sin ningn riesgo.


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Espectro de sonido

Rango deFrecuencia Hz Descripcion Ejemplo

0 - 20 Infrasonido Earth quake

20 - 20.000SonidoAudible Speech, music

> 20.000 UltrasonidoBat, Quartzcrystal


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TAREAS PRINCIPALES.

1. Deteccin de reflectores.

2. Localizacin de reflectores.

3. Evaluacin de reflectores.

4. Diagnostico de reflectores.Tipo orientacin etc.


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Reflector:Todo lo que aparece en la pantalla.

Discontinuidad:Irregularidad que se supone que esuna falla. Solamente despus de localizarla yevaluarla se determina si es una falla o no.


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2. FISICA DE LOS ULTRASONIDOS


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Ejemplos de oscilacion

Bola en unresorte

pendulo Rotacion deLa tierra


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La bola empieza a oscilar tan pronto es empujada.

Pulse


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Oscilacion


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Movimiento de la bola sobre el tiempo.


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Time

One fulloscillation

T

Frequency

De la duracin de unaoscilacin t, la frecuencia

F (el nmero deoscilaciones por segundo)es calculado:

Tf


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gas liquido solido

Estructura Atomica.

low density weak bonding

forces

medium density medium bonding

forces

high density strong bonding

forces

crystallographicstructure


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Understanding wave propagation:

Spring = elastic bonding

force

Ball =

atom


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T

Distance travelled

From this we derive:

or Wave equation

During one oscillation T the wavefront propagates by the distance

:

Tc

fc


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Direction ofoscillation

Direction of propagationLongitudinal wave

Sound propagation


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Direction of propagationTransverse wave

Direction of oscillation

Sound propagation


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Wave propagation

Air

WaterSteel, long

Steel, trans

330 m/s

1480 m/s

3250 m/s

5920 m/s

Longitudinal waves propagate in all kind of materials.Transverse waves only propagate in solid bodies.

Due to the different type of oscillation, transversewavestravel at lower speeds.

Sound velocity mainly depends on the density and E-modulus of the material.


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Reflection and Transmission

As soon as a sound wave comes to a change in material characteristics,e.g. the surface of a workpiece, or an internal inclusion, wavepropagation will change too:


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Behaviour at an interface

Medium 1 Medium 2

Interface

Incoming wave Transmitted wave

Reflected wave


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Amplitude of sound transmissions:

Strong reflection Doubletransmission

No reflection Singletransmission

Strong reflectionwith invertedphase

No transmission

Water - Steel Copper - Steel Steel - Air


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3. PRINCIPIO PIEZOELECTRICO


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Piezoelectric Effect

Piezoelectrical

Crystal (Quartz)

Battery

+


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+

The crystal gets thicker, due to a distortion of the crystallattice



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+

The effect inverses with polarity change



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An alternating voltage generates crystal oscillations at thefrequency f

U(f)

Sound wavewith

frequency f



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A short voltage pulse generates an oscillation at the crystalsresonant

frequency f0

Short pulse

( < 1 s )



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Reception of ultrasonic waves

A sound wave hitting a piezoelectric crystal, inducescrystal vibration which then causes electrical voltages

at the crystal surfaces.

Electricalenergy

Piezoelectricalcrystal Ultrasonic wave


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4. METODOS DE ENSAYO.


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s

Flaw distanceS=CT/2

PULSO - ECO


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4.1. DETECTOR DE FALLAS PORULTRASONIDOS


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start signal(pulse)

finish signal(echo)

transmitter

transit time

measurement

probe

work piece

sound transit

path

Stop-

watch

time measurement


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0 2 4 6 8 10

CRT / A-scan display


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0 2 4 6 8 10

work piece

probe

sound wave starts at crystal

light point

transmittertransmission

pulse

Priciple, transmission pulse


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0 2 4 6 8 10

work piece

probe

sound wave

transmitter

Sound wave in the workpiece


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0 2 4 6 8 10

work piece

probe

transmitter

Sound pulse at the back wall

t t


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0 2 4 6 8 10

work pieceprobe

transmitter

oun pu se at t e coup ngsurface


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0 2 4 6 8 10

work piece

probe

back wallecho

transmitter

Echo display and 2nd run


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2 4 6 8 10

protecting face

crystalprobe

electricalzero

(initial pulse)

mechanicalzero

(surface)

Probe delay


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0 2 4 6 8 10

work piece

probeback wall

echo

flaw

flawecho

Flaw location and echo display


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0 2 4 6 8 10

work piece

probe

back wallecho

flaw

flawecho



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0 2 4 6 8 10

work piece

probe

back wallecho

flaw

flawecho



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4.3. RESOLUCIN CERCANA.

3


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near field

far field

acoustical axis (central beam)

N = near field length

= angle of divergence

Sound field


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0 2 4 6 8 10

dead zone

Dead zone


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0 2 4 6 8 10

flaw echocoveredby initialpulse

work piece

probe

back wallecho

flawFlaw location and echo display


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0 2 4 6 8 10

back wallecho:

without

with flaw

work piece

probe

flaw



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0 2 4 6 8 10

flaw echosequence

work piece

probe

flaw



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electicalzero

(initial pulse)

mechanicalzero

(surface)sound wave

work piece

delay(wedge)

probe 0 2 4 6 8 10

Probe delay


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4.3. EL PALPADOR


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Ultrasonic Probes

socket

crystal

Damping

Delay / protecting face

Electrical matching

Cable

Angle beam probeTR-probeStraight-Beam Probe


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socket

matching-element

damping-block

crystalprotecting face

(probe delay)

housing

workpiece Sound pulse

Straight beam probe


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direction ofosscillation

direction of propagation

wave length

Longitudinal wave


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Bad flaw orientation


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10 20 30 40

Perfect flaw orientation


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crystal

perspex wedge(probe delay)

damping blocks

socket

housing

workpiece Sound pulse

Angle beam probe


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direction ofosscillation

direction of propagation

wave length

Transverse wave

Relection and refraction


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L

LL

L

L

medium 1

medium 2

reflectedwave

refracted

wave

incidentwave

Relection and refraction

T

T

Angle beam probe with both


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0 2 4 6 8 10

10 20 30 40

L

T

possible flawlocations

Angle beam probe with bothwave types


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T

L

L

T

L

perspex

steel

reflectedwave

refracted

waves

incidentwave

= 1 = 27.5T = 33.3L = 90

Longitudinal surface wave


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T

L

T

perspex

steel

reflectedwave

refracted

transverse wave

incidentwave

= 36.4T = 45

45 transverse wave in steel


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L

T O

surfacewaveperspex

steel

reflectedwave

incidentwave

= 2 = 57T = 90

Transverse surface wave


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L

total reflection

perspex

steel

reflectedwave

incidentwave

> 57

Total reflection


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27,5

57

33,3

90perspex

steel

L

T

Ranges for incident waves


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10 20 30 40

crack

Angle reflection


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Angle reflection


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10 20 30 40

Vertical, near surface flaw


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10 155 10 155T R

a1

Tandem technique (top)


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10 155 10 155T R

a2Tandem technique (middle)


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10 155 10 155T R

a3

Tandem technique (bottom)


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10 155 10 155T R



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10 155 10 155T R



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10 20 30 40

Improper flaw orientation

Flaw detectability with improper


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sound beamflat defect

15105

reflected soundwaves

Flaw detectability with improperflaw orientation


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receiversocket

transmittersocket

damping blocks

crystal

delay

acoustical

barrier

TR-probe / dual crystal probe


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0 2 4 6 8 10

IP

BE

work piece

TR-probe

Probe delay with

TR-probes


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0 2 4 6 8 10

IP

BE

flaw

cross talkecho

flaw

echo

TR-probe

Cross talk at

high gain


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0 2 4 6 8 10

s

s

Wall thickness measurement

Corrosion


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surface =sound entry

backwall flaw

1 2

water delay

0 2 4 6 8 10 0 2 4 6 8 10

IE IEIP IP

BE BEF

1 2

Immersion testing


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Straight beam inspection techniques:

Direct contact,

single element probe

Direct contact,

dual element probe Fixed delay

Immersion testingThrough transmission


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Through transmission testing

0 2 4 6 8 10

Through transmission signal

1

2

1

2

T

T

R

R

Flaw


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5. LOCALIZACIN DE

DISCONTINUIDADES


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5.1. CALIBRACIN DEL INSTRUMENTO


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0 2 4 6 8 10

0 100 mm50

steel, L

div.

Range calibration

C lib i bl k 1 i h l


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5 10 15

70

45

60

Calibration block 1 with angle

beam probes

1 h f i l i


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5 10 15

0 2 4 6 8 10

100 mm

1st echo from circular section

Echo sequence from 100 mm


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5 10 15

0 2 4 6 8 10

100 mm 200 mm 300 mm

qradius

25 di f lib ti bl k


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s = 25 mms = 100 mms = 175 mmetc.

12

3

this wave will beabsorbed !

25 mm radius of calibration block

2

50 di f lib ti bl k


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s = 50 mms = 125 mms = 200 mmetc.

12

3

50 mm radius of calibration block

2


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5 10 15

0 2 4 6 8 10

0 100 mmsteel

100 mm range calibration on K2

Flaw loaction


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51015

work piece reflector

s

0 2 4 6 8 10

s = kR

s = sound path

k = scale factorR = screenreading

Flaw loaction

Flaw location with angle beamb


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flaw location

a

s d

Sound entry point projection

point

a = ssin d = scos

= probe angles = sound path

a = surface distance

d = depth

"flaw triangle"

gprobes

Flaw location with angle beam


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51015

work piece reflector

aa'

s d

x

index point -front edge of probe

a = surface distance

a' = reduced surface distance

x = x-value = distance:

gprobes

Fl l ti ith l b


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51015

apparent flaw location

a

sd = apparent depth

T

Flaw location with an angle beam

probe on a plate

Flaw location with an angle beam


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51015

apparent flaw location

real flaw location

a

sd

d'

d' = apparent depthd = real depth

T = work piece thickness

T

a = s sind = s cosd = 2T - d

gprobe on a plate


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6. EVALUACIN DE DISCONTINUIDADES


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1. DISCONTINUIDADES GRANDES.

Large defects parallel to the


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scanning surface


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Scanning the edge of the defect

Flaw echo drops to 50%of its maximum value


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Plate testing

delaminationplate

0 2 4 6 8 10

IP

F

BE

IP = Initial pulse

F = Flaw

BE = Backwall echo


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"half value" positions

delaminationprobe positionwith echo amplitudereduced to 50 %

Determination of the defect area


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2. EVALUACIN DE PEQUEASDISCONTINUIDADES

Small Defect evaluation


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F


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2.1. MTODO DGS

Flaw sizes and echo amplitudes


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0 2 4 6 8 100 2 4 6 8 10 0 2 4 6 8 10

IP BER IP BER IP BER

p

Flaw distances and


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0 2 4 6 8 10

0 2 4 6 8 10

0 2 4 6 8 10

IP BER

IP BER

IP BER

echo amplitudes

La altura de los ecos son proporcionales asu areao la altura de los ecos son proporcionales al

cuadrado de su dimetro

La altura de los ecos se reduceinversamente al cuadrado de su distancia.

Distance amplitude curves on the


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0 500100 200 300 400

B 4 S

BE

F

CRT screen

ERS: EQUIVALENT REFLECTOR SIZE


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2.2. EL MTODO DE BLOQUE DE REFERENCIA


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2.2.1. COMPARACIN DE AMPLITUDES DE ECO

Defect evaluation by comparison


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0 2 4 6 8 10

IP BEF

F

instrument gain: G = 34 dB

80 %


- 1



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0 2 4 6 8 10

IP BER

instrument gain: 34 dB


- 2



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0 2 4 6 8 10

IP BERE

+ 8 dB

instrument gain: 42 dB


- 3

Resultado: El eco de la discontinuidadEs 8 dB mayor que el eco de referenciaPorque la ganancia se incrementa en 8 dB


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2.2.2. CURVAS DAC/TCG


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0 2 4 6 8 10

10 20 30 40 10 20 30 40 10 20 30 40 10 20 30 40

1

1

2

2

3

3

4

4

Echo

Position

Distance amplitude curve (DAC)

EREH: Excess Recording echo height


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10 20 30 10 30 40 10 20 30 40 10 20 30 40

Distance amplitude curve (DAC)

VENTAJAS DEL MTODO DAC1. No es necesario estar comparando continuamente.

2. No se necesita estar transportando bloques pesados3. Estas curvas se graban en la memoria.


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0 2 4 6 8 100 2 4 6 8 10

time corrected gainDAC

DAC and TCG

cursillo b¦sico de ultrasonido

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