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The quantitative assessment of touch point corrosion wall loss at contact supports
David Alleyne
7MENDT, Bahrain
14 September 2015
1
2Guided Ultrasonics Ltd. - 29/09/2015
Presentation Outline
Biography
Basics of Guided Wave Testing (GWT)
Generations of Guided Wave Testing Technologies
From screening to quantitative measurements
Examples of Touch point corrosion
Developing application specific techniques
3Guided Ultrasonics Ltd. - 29/09/2015
Biography Summary of GUL
Guided Ultrasonics Limited: Primary function development, design and manufacture of GWT equipment (Wavemaker® systems).
Guided Ultrasonics Ltd. was set up in 1998 to commercialize guided
wave inspection systems.
World experts in Guided wave testing of plates and pipe from Imperial
College of Science, Technology and Medicine (London, UK). Patent
holder for GWT methods in pipes, plates.
Over 200 man years experience in the guided wave field within GUL,
including outstanding academic contributions supported by field and
application specific knowledge and experience.
Driver for the development of GWT standards, qualification and
certification.
Motivation
Supports are areas of increased risk and are inaccessible to direct assessment.
© Guided Ultrasonics Ltd. 2014
Requirement for both fast screening due to the huge number and quantitative evaluation.
Basics of GW Testing
The pipe walls form a guide for ultrasonic waves,
which directs them down the length of the pipe
Propagation of ultrasonic waves (kHz range) guided by pipe wall along the pipe, excited by a transducer array.
Transducer
Structure
Region of structure inspected
Transducer
Structure
Region of structure inspected
Conventional
Guided waves
© Guided Ultrasonics Ltd. 2014
6
1st Generation – Lamb waves
Longitudinal mode (LRUT) 1986 – 1996 Researcher, Academic staff (GW
technology patented while at Imperial College)
Dispersion curves - Disperse software developed
Finite element modelling methods developed
Single mode and single direction
Laboratory expertise on plates, bars and pipe
Data processing methods, 2D-FFT
Transduction and electronics developed
Guided Ultrasonics Ltd. - 29/09/2015
7
2nd & 3rd Generation – Guided Waves
Torsional & Flexural modes
1999 – Present
Pipe testing system
Battery powered portable GWT system
Generalised PZT based transduction
Development of training schemes
Development of GWT (site expertise)
Guided Ultrasonics Ltd. - 29/09/2015
8
On-board calibration channel and self checking
HD rings and modules for different corrosion types
Axial and circumferential configuration and GWT strategies
Wide frequency range for optimum selection
Improved SNR and O/P power boost
Guided Ultrasonics Ltd. - 29/09/2015
4th Generation Application Specific
9
GWT Result
Guided Ultrasonics Ltd. - 29/09/2015
10Guided Ultrasonics Ltd. - 29/09/2015
From screening to quantitative measurements
In order to make quantitative measurements it is necessary to calibrate the guided wave response.
Several methods of calibration have been historically been used in GWT Assumed weld reflection Measured weld parameters Absolute calibration
In addition to this it is necessary to be able to convert from reflection coefficient to change in cross-sectional area.
11
Guided Waves Calibration
DAC curves are used to estimate the CSC of other indications
-18dB
-20.0 -10.0 0.0 10.0 20.012
9
6
3
12
Clo
ck
-20.0 -10.0 0.0 10.0 20.00.0
0.5
1.0
1.5
2.0
Distance (m)
Am
p (
Lin
ear)
W3
S2
S1
F1
U1
W4
S3
B1
S4
U2
Distance (m)
Am
plit
ude
(a
rb.)
Standard reflection amplitude of a weld can corresponds to approximately 10 – 25% CSC
Weld DAC 20 – 25%
Call DAC
Guided Ultrasonics Ltd. - 29/09/2015
12
Guided Waves Calibration
One method: Measure dimensions
Wavemaker® software calculates weld reflection
In general very good approximation
Guided Ultrasonics Ltd. - 29/09/2015
13
Guided Waves Calibration
Still errors in calibration if
Weld defective in a way that reflection amplitude influenced
Variation in the measured dimensions even in a single weld
Also not satifactory if
There are no welds in the test range
The weld dimensions cannot be measured
Guided Ultrasonics Ltd. - 29/09/2015
New calibration method
14
Guided Waves Calibration
-18dB
-20.0 -10.0 0.0 10.0 20.012
9
6
3
12
Clo
ck
-20.0 -10.0 0.0 10.0 20.00.0
0.5
1.0
1.5
2.0
Distance (m)
Am
p (
Lin
ear)
W3
S2
S1
F1
U1
W4
S3
B1
S4
U2
Distance (m)
Am
plit
ude
(a
rb.)
Guided Ultrasonics Ltd. - 29/09/2015
Advantages
Direct measurement of reflection coefficients
Works also with other features (not just welds), even if defective
Accurate weld DAC then allows accurate prediction of cross-sectional area change of anyother signal
Difficulties
Not always possible to generate reverberation signals– Due to high attenuation
– Lack of suitable test location
15
Guided Waves Calibration
Guided Ultrasonics Ltd. - 29/09/2015
16
Contact corrosion types at touch points The cross-sectional change of the corrosion (shape and depth) is
important for detectability and quantification
Guided Ultrasonics Ltd. - 29/09/2015
17
GWT work instructions
GWT Procedures and work instructions using knowledge of specific application and corrosion type that is the major threat
– Equipment and certification requirements
– SNR and access restrictions
– Accuracy and range
– Limitations
– Confidence
Calibration is critical
Guided Ultrasonics Ltd. - 29/09/2015
18
Example 1
Guided Ultrasonics Ltd. - 29/09/2015
-16dB
-20 0 20 40 6012
9
6
3
12
Clo
ck
-20 0 20 40 600.0
0.2
0.4
0.6
0.8
1.0
1.2
Distance (ft)
Am
p (
Lin
ear)
F
weld
ed p
late
Weld
Weld
Cat 1
Corr
osi
on
Support
Weld
Cat 3
Support-F1
Call DAC 4%
Touch point corrosion
patch with pitting
19
Example 3
Guided Ultrasonics Ltd. - 29/09/2015
-18dB
-10.0 0.0 10.0 20.012
9
6
3
12
Clo
ck
-10.0 0.0 10.0 20.00.0
0.5
1.0
1.5
Distance (ft)
Am
p (
Lin
ear)
-F1
+F1
+F2
20
Example 4
Guided Ultrasonics Ltd. - 29/09/2015
Touch point corrosion
patch. GWT used for
detection and
classification of the
corrosion.
-18dB
-8.0 -6.0 -4.0 -2.0 0.012
9
6
3
12
Clo
ck
-8.0 -6.0 -4.0 -2.0 0.00.0
0.5
1.0
1.5
2.0
Distance (m)
Am
p (
Lin
ear)
Conta
ct support-F1
6 o’clock
position
Developments
Monitoring
using repeated measurement from same location
Alternative transduction
Guided wave tomography
21Guided Ultrasonics Ltd. - 29/09/2015
22
GWT can monitor supports
Guided Ultrasonics Ltd. - 29/09/2015
5.0 10.0 15.0 20.0
1
0.5
0.25
0.1
0.05
0.025
G3-5
1#1583 (
34dB
)
5.0 10.0 15.0 20.0
1
0.5
0.25
0.1
0.05
0.025
Distance (m)
G3-9
6#5453 (
34dB
)
weld
conta
ct s
upport
weld
weld
+F1
conta
ct s
upport
weld
Call DAC 1%
Call DAC 1%
CollectionOct 2007
CollectionDec 2011
Corrosion growth at support area over 4 year period
GWT transduction options
23Guided Ultrasonics Ltd. - 29/09/2015
+
+ +
+ +
Pulse echo
Pitch catch
Direct transmission
Aim
Produce map of depths of corrosion
Critical parameter is maximum depth
GW tomography
Concept of tomography
GW tomography
26Guided Ultrasonics Ltd. - 29/09/2015
GW tomography
Transducer arrays placed either side of defect
27Guided Ultrasonics Ltd. - 29/09/2015
0.0 0.2 0.4 0.6
0.000000
0.000005
0.000010
0.000015
0.000020
Time (ms)
Am
p (
mV
)
Pulse Echo Traces (25 kHz 3 cycle Hanning Toneburst)
0.0 0.2 0.4 0.6
0.000000
0.000005
0.000010
0.000015
0.000020
Time (ms)
Am
p (
mV
)
Pulse Echo Traces (25 kHz 3 cycle Hanning Toneburst)
GW tomography
Results from defect free case Results from defect case
Development of this as an inspection technique is in the processing of this type of data to produce defect maps
Two Main Tomography Techniques:
Time of Flight Tomography (TFT)
Diffraction Tomography (DT)
Ray Approximation d >> λ
d ~ λ
GW tomography
As reduced size and cost of computing power has enabled site implementation of GWT, tomographic techniques have required similar improvements to become practical.
29
GWT enables rapid screening of many supports
Improved calibration allows better
estimation/measurement of wall loss at supports
Requires detailed procedures and training
Continuing research for quantitative measurements
of touch point corrosion using GW tomograghy.
Conclusions
Guided Ultrasonics Ltd. - 29/09/2015
30
Questions
Guided Ultrasonics Ltd. - 29/09/2015
Thank you