Execution of upstream services during exploration, development and production in the oil and gas industry

ppt

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Ultrasonic TestingUltrasonic Testing
Part 3Part 3

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Sound Generation
•Hammers (Wheel tapers)
•Magnetostrictive
•Lasers
•Piezo-electric
magnetostrictive

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Piezo-Electric Effect
•When exposed to an alternating current a
crystal expands and contracts
•Converting electrical energy into mechanical
- + + - - +

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Piezo-Electric Materials
QUARTZ
•Resistant to wear
•Insoluble in water
•Resists ageing
•Inefficient converter of
energy
•Needs a relatively high
voltage
Very rarely used nowadays
LITHIUM SULPHATE
•Efficient receiver
•Low electrical
impedance
•Operates on low
voltage
•Water soluble
•Low mechanical
strength
•Useable only up to 30ºC
Used mainly in medical

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Polarized Crystals
•Powders heated to
high temperatures
•Pressed into shape
•Cooled in very
strong electrical
fields
Examples
•Barium titanate (Ba Ti O
3)
•Lead metaniobate
(Pb Nb O
6)
•Lead zirconate titanate
(Pb Ti O
3
or Pb Zr O
3
)
Most of the probes for conventional usage use
PZT : Lead Zirconate Titanate

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Probes

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Probes
•The most important part of the
probe is the crystal
•The crystal are cut to a
particular way and thickness to
give the intended properties
•Most of the conventional crystal
are X – cut to produce
Compression wave
Z
X
X
X
Y

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Probes
•The frequency of the probe depends on
the THICKNESS of the crystal
•Formula for frequency:
Ff = V / 2t
Where Ff = the Fundamental frequency
V = the velocity in the crystal
t = the thickness of the crystal
Fundamental frequency is the frequency of the material ( crystal )
where at that frequency the material will vibrate.

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Probes
•The Thinner the crystal the Higher the frequency
•Which of the followings has the Thinnest crystal ?
1 MHz Compression probe
5 MHz Compression probe
10 MHz Shear probe
25 MHz Shear probe
25 MHz Shear
Probe

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Probe Design
•Compression Probe
–Normal probe
–0°
Damping
Transducer
Electrical
connectors
Housing

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Probe Design
•Shear Probe
–Angle probe
Damping
Transducer
Perspex wedge
Backing
medium
Probe
Shoe

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Probe Design
Twin Crystal
Advantages
•Can be focused
•Measure thin plate
•Near surface
resolution
Disadvantages
•Difficult to use on
curved surfaces
•Sizing small defects
•Signal amplitude /
focal spot length
TransmitterReceiver
Focusing
lens
Separator /
Insulator

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Sound Intensity
Comparing the intensity of 2 signals
1
0
1
0
P
P
I
I

Electrical power proportional to the
square of the voltage produced
2
1
2
0
1
0
)(
)(
V
V
P
P

2
1
2
0
1
0
)(
)(
V
V
I
I
Hence

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Sound Intensity
2
1
2
0
1
0
)(
)(
V
V
I
I
 Will lead to large ratios
2
1
2
0
10..
1
0
10..
)(
)(
V
V
Log
I
I
Log Therefore
dB
V
V
Log
I
I
Log
1
0
10..
1
0
10..
20
BELS
V
V
Log
I
I
Log
1
0
10..
1
0
10..
2

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1
0
10..
20
H
H
LogdB
2 signals at 20% and 40% FSH.
What is the difference between them in dB’s?
2..20
20
40
20
1010.. LogLogdB 
3010.020dB
dBdB6

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1
0
10..
20
H
H
LogdB
2 signals at 10% and 100% FSH.
What is the difference between them in dB’s?
10..20
10
100
20
1010.. LogLogdB 
120dB
dBdB20

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Amplitude ratios in decibels
•2 : 1=6bB
•4 : 1=12dB
•5 : 1=14dB
•10 : 1=20dB
•100 : 1=40dB

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Automated Inspections
•Pulse Echo
•Through Transmission
•Transmission with Reflection
•Contact scanning
•Gap scanning
•Immersion testing

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Gap Scanning
•Probe held a fixed
distance above the
surface (1 or 2mm)
•Couplant is fed into
the gap

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Immersion Testing
•Component is placed in a water filled tank
•Item is scanned with a probe at a fixed
distance above the surface

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Immersion Testing
Water
path
distance
Water path distance
Front surface Back surface
Defect