cursillo b¦sico 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
Piezoelectric Effect
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+
The effect inverses with polarity change
Piezoelectric Effect
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An alternating voltage generates crystal oscillations at thefrequency f
U(f)
Sound wavewith
frequency f
Piezoelectric Effect
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A short voltage pulse generates an oscillation at the crystalsresonant
frequency f0
Short pulse
( < 1 s )
Piezoelectric Effect
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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
Flaw location and echo display
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0 2 4 6 8 10
work piece
probe
back wallecho
flaw
flawecho
Flaw location and echo display
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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
Flaw location and echo display
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0 2 4 6 8 10
flaw echosequence
work piece
probe
flaw
Flaw location and echo display
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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
a2Tandem technique (middle)
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10 155 10 155T R
a2Tandem technique (middle)
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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 %
Defect evaluation by comparison
- 1
Defect evaluation by comparison
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0 2 4 6 8 10
IP BER
instrument gain: 34 dB
Defect evaluation by comparison
- 2
Defect evaluation by comparison
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0 2 4 6 8 10
IP BERE
+ 8 dB
instrument gain: 42 dB
Defect evaluation by comparison
- 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
top related