Development of Ultrasound Phased Array System for Weld Inspections at Elevated Temperatures

102 Pages·2014·4.07 MB·English

Development of Ultrasound Phased Array System for
Weld Inspections at Elevated Temperatures
by
Mohammad Hassan Marvasti
A thesis submitted in conformity with the requirements
for the degree of Doctor of Philosophy (PhD)
Department of Mechanical and Industrial Engineering
University of Toronto
© Copyright by Mohammad Hassan Marvasti 2014
Development of Ultrasound Phased Array System for Weld
Inspections at Elevated Temperatures
Mohammad Hassan Marvasti
Doctor of Philosophy (PhD)
Mechanical and Industrial Engineering
University of Toronto
2014
Abstract
Interruption of plant operation can be avoided if non destructive testing inspections are
performed on-line at operating temperatures, which may be up to several hundred degrees
Celsius in a petrochemical or electric power generating plant. However, there are operational
temperature limits of the phased array transducers and associated plastic wedges used for
ultrasonic inspections. In addition, there is a major gap in terms of professionally-approved high-
temperature inspection techniques. In this project, the design and operation of an ultrasonic
phased array system are described for inspections of engineering components such as pipe welds
at elevated temperatures of up to 350oC. Wedges are built from plastics resistant to high
temperature degradation, and equipped with a cooling jacket around the array. A model of the
ultrasonic beam skew pattern due to thermal gradients inside a wedge is developed. The model is
used in a separate algorithm to calculate transmission and reception time delays on individual
array elements for generation of plane waves or focused beams in a hot test piece, while
compensating for thermal gradient effects inside the wedge.
The algorithm is also used to investigate the magnitude of thermal gradient effect on the
calculated time delays of the phased array elements. The algorithm results for inspections of test
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pieces at 150oC demonstrate that application of conventional element time delays can lead to
serious phase errors. This results in major distortion of the desired beam profile, and very poor
imaging resolution. However, experimental trials indicate that plane waves and focused beams
can be generated in a hot test piece using the new focal law algorithm with appropriate timing
delays applied to all active array elements.

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Acknowledgments

I would like to express my sincere gratitude to my supervisor, Professor Anthony Sinclair, for his
guidance and support without which this research work thesis would not have been possible to be
completed.
I am grateful to National Science and Engineering Research Council of Canada (NSERC), and
Eclipse Scientific for sponsoring my research and more importantly, for giving me a
distinguished opportunity to work on a rewarding academic/industrial collaborative research
project.
I wish to thank my colleagues Jonathan Lesage, Hossein Amini, Babak Shakibi and Jill Bond at
Ultrasonic Nondestructive Evaluation Laboratory at the University of Toronto for their help and
assistance in this project.
I would also like to express my gratitude to Robert Ginzel, Edward Ginzel, Jeff van Heumen and
the team at Eclipse Scientific for their kind helps in this project. Working with them was an
invaluable experience for me.
Finally, I am particularly thankful to my wonderful wife, my parents and my family for their
support and encouragement throughout the course of my thesis.
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Table of Contents
Abstract……………………………………………………………………………………………ii
Acknowledgments .......................................................................................................................... iv
Table of Contents ............................................................................................................................ v
List of Tables ................................................................................................................................ vii
List of Figures .............................................................................................................................. viii
1 Introduction .............................................................................................................................. 1
2 Background Theory and Literature Review.......................................................................... 4
2.1 Ultrasonic Non-Destructive Testing ................................................................................... 4
2.2 Fundamentals of Ultrasonic Wave Propagation in Solid Media ......................................... 4
2.2.1 Wave Propagation Modes ....................................................................................... 4
2.2.2 Speed of Propagation .............................................................................................. 5
2.2.3 Reflection, Refraction and Mode Conversion ........................................................ 6
2.2.4 Ultrasonic NDE System .......................................................................................... 6
2.2.5 Display Modes ........................................................................................................ 7
2.3 Principles of Phased Array Ultrasound ............................................................................... 9
2.3.1 Beam Steering and Focusing Using Phased Arrays .............................................. 10
2.3.2 Phased Array ultrasonic Inspection System .......................................................... 11
2.3.3 Phased Array Scanning Configuration .................................................................. 13
2.3.4 Phased Array Display Modes ................................................................................ 15
2.4 Weld Inspections with Phased Arrays .............................................................................. 16
2.5 Phased Array Inspection at Elevated Temperatures ......................................................... 17
3 High Temperature Wedges ................................................................................................... 20
4 Temperature Distribution Model ......................................................................................... 23
5 Velocity Measurements at Elevated Temperatures ............................................................ 26
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6 Focal Law Algorithm – Planar Waves ................................................................................. 31
6.1 Room Temperature Inspection .......................................................................................... 31
6.2 Elevated Temperature Inspection ..................................................................................... 35
7 Experimental Validation – Planar Waves............................................................................ 44
7.1 Concept for Experimental Validation ............................................................................... 44
7.2 Experimental Details ......................................................................................................... 46
7.3 Experimental Results and Analysis - Room Temperature ................................................ 47
7.3.1 Systematic Errors .................................................................................................. 49
7.3.2 Random Errors ...................................................................................................... 51
7.4 Experimental Results and Analysis - Elevated Temperature ............................................ 53
8 Focal Law Algorithm – Focused Beam ................................................................................ 64
8.1 Algorithm Details .............................................................................................................. 65
8.2 Magnitude of Thermal Gradient Effect ............................................................................. 68
8.3 Experimental Evaluation ................................................................................................... 73
9 Summary, Conclusions and Future Work ........................................................................... 82
References ..................................................................................................................................... 84

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List of Tables

Table 7-1 Inputs to the focal law calculating algorithm at room temperature: the levels of
uncertainty in the measured values of inputs are listed and the magnitude of their resulting effect
on the bias error on the first element of the aperture is presented. ............................................... 50
Table 7-2 Magnitude of the experimental results associated with generation of a 45o shear plane
wave at 150oC as depicted in Figure 7.5. The results of 15 repeated time delay measurements of
echo signals of the first and central elements of the active aperture are presented for two cases:
active aperture = elements 1-16; and active aperture = elements 49-64. ..................................... 59
Table 7-3 Experimental results associated with generation of a 60o shear plane wave at 150oC as
depicted in Figure 6. The results of 15 repeated time delay measurements of echo signals of
selected elements of the active aperture are listed in separate columns. ...................................... 62

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List of Figures

Figure 2.1 Ultrasonic wave propagation modes: (a) Longitudinal (Compression) mode and (b)
Shear (Transverse) mode [5]. .......................................................................................................... 5
Figure 2.2 Refraction and mode conversion of a longitudinal wave at the boundary of two media
[6]. ................................................................................................................................................... 6
Figure 2.3 Major components of a typical ultrasonic inspection set up in pulse/echo configuration
mode where one transducer is used for both transmission and reception of the ultrasonic waves
[8]. ................................................................................................................................................... 7
Figure 2.4 Representation of A-scan display: (a) transducer position, (b) signal display [9]. ....... 8
Figure 2.5 Representation of B-scan: (a) test configuration, (b) scan display [9]. ......................... 8
Figure 2.6 Representation of C-scan display: (a) transducer movement pattern (b) C-scan display
[9]. ................................................................................................................................................... 9
Figure 2.7 Phased array probe cross-sectional view [13]. ............................................................ 10
Figure 2.8 Beam steering with phased arrays, (a) unfocused beam (plane wave) and (b) focused
beam [14]. ..................................................................................................................................... 11
Figure 2.9 Typical components of a phased array inspection system. .......................................... 12
Figure 2.10 Electronic (linear) scan performed by focused beam normal to array elements [17].14
Figure 2.11 Sectorial scanning with phased arrays: the sound beam sweeps through a series of
angles [17]. .................................................................................................................................... 14
Figure 2.12 S-scan of 3 side drilled holes in a steel block through phased array sectorial scanning
[18]. ............................................................................................................................................... 15
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Figure 2.13 Scan plan of a phased array ultrasonic inspection of a weld in a steel block, as
generated by a ray-tracing algorithm. The scan plan covers a range of inspection angles (46o-72o)
inside the steel piece. The blue lines represent the direction normal to the plane wave fronts
generated by the active phased array elements. ............................................................................ 17
Figure 3.1 PEI high temperature wedge schematic with sloped front and dampening material at
the top of the wedge: ray 1 (solid line) and ray 2 (dashed line) illustrate reflection pattern of steep
and shallow beam incidence at the wedge bottom. As a result of wedge elongation and angled
front, the internally reflected beams reflect to the top of the wedge where they are absorbed by
the dampener. ................................................................................................................................ 22
Figure 3.2 High temperature phased array inspection system including: Eclipse WA10-HT55S-
IH-B PBI wedge prototype based on the geometry of the Olympus linear phased array model
5L16-A10 with 16 elements and center frequency of 5MHz, water cooling jacket, coolant tubing
system and mounting arms. ........................................................................................................... 22
Figure 4.1 PEI wedge temperature distribution modeling result, the color palate represents the
temperature distribution inside the wedge between 25oC and 150oC. Surface temperature
measurements located on the dashed lines were used to validate the model results. ................... 25
Figure 4.2 Comparison of COMSOL and experimental results for the temperature distribution on
the surface of the PEI wedge mounted on a 150oC steel pipe. Solid lines on the graph and the
error bars represent average temperature values of 5 experiments and standard deviations of the
measurements: the red circles represent COMSOL model results at the specified locations on the
wedge surface. ............................................................................................................................... 25
Figure 5.1 Phase velocity measurement from two successive backwall echoes. The phase of
each pulse is determined relative to left side of the pulse acquisition window. ........................... 27
Figure 5.2 Experimental set up for measuring phase velocity at high temperatures. The sample
and the delay line were wrapped in high temperature insulation to lessen the temperature gradient
inside the plastic block. The mean block temperature was estimated from thermocouples placed
on top and bottom of the plastic block. ......................................................................................... 28
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Figure 5.3 Phase velocity data of PEI (a) and PBI (b) plastic blocks at selected elevated
temperatures. Solid lines and the error bars represent the mean and standard deviation of 5
repeated experimental measurements. .......................................................................................... 29
Figure 5.4 Phase velocity of PEI (a) and PBI (b) as a function of temperature at 5 MHz
frequency. The empirical relations shown on the graphs indicate the functional change of phase
velocity results with temperature T expressed in degrees Centigrade. ......................................... 30
Figure 6.1 Wave propagation pattern for a shear plane wave at angle Фs in a steel block at a
uniform temperature of 25oC. The ray traces are applicable for a wave transmitted from the array
into the test piece, or equivalently for a wave travelling from the test piece back to the array. In
the latter case, the waves associated with sample points along an arbitrary plane wave front
propagate in a direction perpendicular to the wave front and reach the piece-wedge interface at
locations labeled as interface points. Then they refract into the wedge based on Snell’s law and
propagate through the wedge to the array-wedge interface at points labeled as array-line points.
....................................................................................................................................................... 33
Figure 6.2 Wave propagation pattern for a shear plane wave at angle Фs in a steel block at a
uniform temperature of 150oC. The ray traces are applicable for a wave transmitted from the
array into the test piece, or equivalently for a wave traveling from the test piece back to the array.
In the latter case, the waves associated with sample points along an arbitrary plane wave front
propagate in a direction perpendicular to the wave front and reach the piece-wedge interface at
locations labeled as interface points. Then they refract into the wedge based on Snell’s law and
propagate through the wedge to the array-wedge interface at points labeled as array-line points.
The waves propagate along arced paths (red lines) in the wedge due to thermal gradient induced
velocity variation. ......................................................................................................................... 37
Figure 6.3 Calculated relative element time delays for the generation of a 60o shear plane wave
for Eclipse WA12-HT55S-IH-G PEI wedge and the Olympus linear phased array model 5L64-
A12 one a) the first 16 elements of the array (elements 1-16) were used and b) the last 16
elements of the array (elements 49-64) were used. The blue and red data points represent the
results for room (25oC) and elevated temperature (150oC) inspection condition respectively and
the delays are expressed relative to the first element of the used active aperture......................... 39
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