NONDESTRUCTIVE EVALUATION OF DOUBLE BEVEL
T-JOINT BY TANDEM ARRAY ULTRASONIC
TRANSDUCER
H. Shirahata1, C. Miki2 and R.Yamaguchi2
1
Department of Civil Engineering, Musashi Institute of Technology
1-28-1 Tamazutsumi Setagayaku, Tokyo 158-8557 Japan
2
Department of Civil Engineering, Tokyo Institute of Technology
2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 Japan
ABSTRACT. The double bevel T-joint is one of the most fundamental joints of steel bridges.
Double bevel T-joint can be seen at beam-column connection of bridge pier, In the Japanese
specifications, the welding should be full penetration. However, weld defect of incomplete penetration could be left in the joint due to the lack of quality control in welding. Fatigue cracks can
be propagated from the weld defects. The authors developed a tandem array transducer. The
tandem array transducer consists of 10 elements aligned in the same direction. Tandem scanning
can be simulated by the transducer. Image reconstruction of incomplete penetration by synthetic
aperture focusing technique was carried out. The test results showed sufficient detect ability of
incomplete penetration by the tandem array transducer. Height of incomplete of penetration
could be estimated.
INTRODUCTION
T-joint is one of the most fundamental joints of steel bridge structure. T-joint is
applied to column-beam connections and to main girder and lateral girder connections.
There are two types of T-joints. One is full penetration weld and the other is butt
weld. Pull penetration is applied to joints where fatigue should be considered. Butt
weld is applied to joints where fatigue doesn't have to be considered.
Partial penetration isn't allowed by the Japanese specifications. In partial penetration, root face remains in the welded joint. It is difficult to control the quality
of root face such as length, gap and roughness of the surface. For a T-joint of full
penetration, it happens that root face remains due to incomplete penetration. In such
case, fatigue cracks can be initiated and propagated from the incomplete penetration.
Incomplete penetration must be eliminated. Reliable inspection technique is needed.
The objective of this study is to detect and estimate the height of an incomplete
penetration in a T-joint. Ultrasonic tests were carried out. Considering a column-beam
connection of box section, radiographic test isn't applicable. Incomplete penetration is
a planar defect. Tandem technique is effective to detect planar defects [1-3]. A tandem
array transducer was developed. For the display of weld defect, synthetic aperture
focusing technique (SAFT) [4] was applied to reconstruct the image of incomplete
penetration.
CP657, Review of Quantitative Nondestructive Evaluation Vol. 22, ed. by D. O. Thompson and D. E. Chimenti
© 2003 American Institute of Physics 0-7354-0117-9/03/S20.00
1164
254mm
4————————————————^
chl 2 3 4 5 6 7 8 9 chip
_—
..
"
i LI I i
70deg
10 elements aligned
each channel
incident angle 70 degrees
frequency
5MHz
FIGURE 1. Tandem array transducer.
•<
50
° ^
(mm)
500
*
r"
60deg
A
t* S
i
———— ,
\ \ ^
^
t
X
- "" ^V
600
>f
partial pen<
parameters:^,/!
25
(mm)
full penetration
t:thickness of plate
/irheight of root face
FIGURE 2. Specimen.
EXPERIMENT
Tandem Array Transducer
A tandem array transducer was developed. Figure 1 shows the transducer. The
transducer consists of ten aligned elements of angle beam. Frequency of each element
is 5MHz and incident angle of each element is 70 degrees. Incomplete penetration is
a planar defect. Incident waves are reflected specularly at the defect. It is sometimes
difficult to receive spcularly reflected waves by one probe technique. Tandem technique
has shown effectiveness for detection of planar defects. There are ten patterns for
transmitting and receiving. Totally, 100 patterns of wave forms can be obtained by
the transducer without moving back and forth.
Specimen
Figure 2 shows a specimen. Two plates were welded at the center of the specimen. The parameters of the specimens were thickness of the plate t and the height
of incomplete penetration h. Two types of specimens were made. Parameters of the
specimens are shown in Figure 2. Both types of the specimens have almost the same
thickness as the plates used in column-beam connections.
1165
obtain 10x10 patterns
of wave forms in 2 sec
switcher/multiplexer
joint
specimen
FIGURE 3. Experimental setup.
x 25 (mm)
10 1 9
8|7
>
6h
4
2
3
it
x closest distance between the front of
transducer and column
obtained 100 wave forms
FIGURE 4. Experiment.
Setup
Figure 3 shows an experimental setup. The system consists of a personal computer, ultrasonic flaw detector, switcher/multiplexer, and transducer. The flaw detector generates pulse signals. The switching device switches the signal to each of the
channels for transmitting and receiving. The computer calibrates the flaw detector
and acquires wave data by digital I/O interface. 100 wave forms can be obtained
within two seconds.
In the experiment, the transducer was put at the closest position from the weld
toe, as shown in Figure 4. Transducer position x is defined as the distance between
the front of the transducer and the column plate. 100 wave forms were obtained at
the closest position from the weld toe.
DETECTABILITY OF INCOMPLETE PENETRATION BY THE TANDEM ARRAY TRANSDUCER
Figure 5 shows some of the wave forms. The horizontal axis is distance from
the transmitter. The vertical axis is related to echo height. Ten wave forms of one
transmitter and different receiver channels are shown in each of Figures 5(a) and (b).
The thickness of the plate t was 25mm. Figures 5 (a) and (b) are wave forms when
the transmitter was channel 1 and 2, respectively. When the transmitter was channel
1, a higher echo can be found when the receiver was channel 4.
1166
(a)
T^rn?
(b)
45
|5
25
2
±
4 |3 | 2 | 1 £
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x= 1 5nm transnitter ch2
receiver
±±L
rfe-»/U
. i|. i IkJL
3L
100 200 300 400 500
distance of propagation (mm)
TOO 200 300 400 500
distance of propagation (mm)
10
FIGURE 5. Wave forms, the thickness of the plate t:25mm, height of incomplete penetration
n, (a) transmitter channel 1, (b) transmitter channel 2.
(a)
transducer position;
x =15mm
:
transmitter chl "
receiver ch4 :
jo
•g
(b)
100
200
300
distance of propagation (mm)
FIGURE 6. Defect echo and the path, thickness of plate t:25mm, height of incomplete penetration
/i:8.5mm.
(a
24
mreT8l7l6l5l4l?TZ]T
40|
x=24irm
|
|
•
Iran
transnitter chl
receiver
rec
transnitter ch2
receiver
——— lo
>
HHMAMhMhJMM*4MkMMMUte
5
__
_________10
100 200 300 400 500
distance of propagation (mm)
10
100 200 300 400 500
distance of propagation (mm)
FIGURE 7. Wave forms, the thickness of the plate t:40mm, height of incomplete penetration
follmm, (a) transmitter channel 1, (b) transmitter channel 2.
1167
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:
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43
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CD
(b)
transducer position:
x=24mm
:
transmitter ch2
receiver ch7 .
13)
j-
x=24mrc
9 f 8 17 I 6 I5I4I312T11
200
300
400
distance of propagation (mm)
FIGURE 8. Defect echo and the path, thickness of the plate t:40mm, height of incomplete penetration to: 11 mm.
receiver transmitter
receiver transmitter
n n
receiver
r\
transmitter
r\
reflector
*. reflector
transmitter receiver
transmitter receiver
n n
' r\
transmitter receiver
r\___r\
^reflector
3* reflector
FIGURE 9. Six paths to be considered for image reconstruction.
The wave form of combination of channel 1 and 4 is shown in Figure 6 (a). An
echo can be seen around 180mm from the transmitter. The wave path is shown in
Figure 6(b). The incident wave was reflected at the defect specularly and reflected at
the bottom and received by channel 4.
Figure 7 shows wave forms obtained from a specimen of which thickness t was
40mm. Figures 7 (a) and (b) are wave forms when the transmitter was channel 1 and
2, respectively. In case of combination of transmitter channel 2 and receiver channel
7, an echo could be found. The wave path is shown in Figure 8.
Figures 5 and 7 show that defect echoes could be seen clearly. Specularly reflected
waves at an incomplete penetration could be received at least one of the channels of
the tandem array transducer. Those defect echoes could be obtained in two seconds
without moving the transducer.
IMAGE RECONSTRUCTION
For the display of weld defects, synthetic aperture focusing technique was applied. Comparing with one probe method, the wave path of defect echo becomes more
complicated. Six paths of wave propagation were considered as shown in Figure 9.
Figure 10 shows the reconstructed image. The thickness of the plate of the
specimen t was 25mm and the height of incomplete penetration ft was 8.5mm An
image could be seen around the position of incomplete penetration.
It is possible to pick up some specific wave forms and reconstruct an image by the
reconstruction program in the computer. Figure 11 (a) shows an image reconstructed
by three wave forms. Figure ll(b) is an illustration of the image. Figure ll(c) shows
1168
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25
"&&$!• JSH $$~M?M
column
ch2
eh I
25
reconstruction area
FIGURE 10. Reconstructed image, thickness of the plate £:25mm, height of incomplete penetration
/i:8.5mm.
(a)
_C2
transmitter chl:
•receiver
distance of propagation (mm)
W)
'53 :'
& f
£9 :
I transmitter chl:
1 receiver ch4i
-
Xx - -
--- i4 "
TOO
200
300
distance of propagation (mm)
•a
lower tip echo
transmitter ch2
receiver ch2
l L .
TOO
200
300
distance of propagation (mm)
FIGURE 11. (a) Reconstructed image by three wave forms, thickness of the plate i:25mm, height
of incomplete penetration /i:8.5mm (b)illustration of the image (c) geometry of the joints (d) wave
forms.
1169
;
^i mm
d*2
chj
^ ^ (itint)
Jk
1
145
j k
40
if
11
145
^f
>
k
:
FIGURE 12. Reconstructed image, thickness of the plate £:40mm, height of incomplete penetration
actual size of the incomplete of penetration. Figure ll(d) are wave forms picked up.
Those wave forms were combination of "transmitter channel 1 and receiver channel
1", "transmitter channel 1 and receiver channel 4", and "transmitter channel 2 and
receiver channel 2". Echo of "combination 1 and 1" could be an upper tip echo from
the incomplete penetration. Echo of "combination 1 and 4" could be a specularly
reflected echo at the incomplete penetration. Echo of "combination 2 and 2" could be
a lower tip echo from the incomplete penetration. The height of incomplete penetration
estimated from the image was 9 rnm. The actual height is 8.5 mm. Prom those three
wave forms, the incomplete penetration was detected and the height of the incomplete
penetration was estimated accurately.
Figure 12 shows another example. The thickness of the plate of the specimen t
was 40 mm and the height of the incomplete penetration h was 11 mm. As well as
Figure 10, Figure 12 is an image reconstructed by all the 100 wave forms. Figure 13(a)
shows an image reconstructed by three wave forms. Each of the wave forms is shown
in Figure 13(d). Echo of "combination 1 and 1" could be an upper tip echo from the
incomplete penetration. Echo of "combination 2 and 7" could be a specularly reflected
echo at the incomplete penetration. Echo of "combination 2 and 2" could be a lower
tip echo from the incomplete penetration. The height of incomplete penetration was
estimated accurately.
It takes less than one minute to reconstruct an image. The system makes quick
and accurate inspection of T-joint possible. As the procedure of inspection, the authors
recommend to (l)obtain 100 wave forms, (2)reconstruct an image, (3)check wave form
on by one, and (4)pick up some of the specific wave forms and estimate the height.
1170
(a)
200
distance of propagation (mm)
400
distance of propagation (mm)
TOO
200
300
distance of propagation (mm)
FIGURE 13. (a) Reconstructed image by three wave forms, thickness of the plate £:40mm, height
of incomplete penetration /i:llmm (b)illustration of the image (c) geometry of the joints (d) wave
forms.
SUMMARY
The authors developed a new tandem array instrumentation and image reconstruction program by synthetic aperture focusing technique. The results show that
the instrumentation can be successfully applied for inspection of T-joint. Weld defects
could be detected. Height of incomplete penetration was estimated accurately.
REFERENCES
1. Bowker, K.J.,Coffey, J.M.,Hanstock, D.J,, Owen ,RC. and Wrigley, J.M.: CEGB
inspection of plates 1 and 2 in UKAEA defect detection trials, British Journal of
NOT, Vol.25,No.5,pp.249-255,1983.
2. Barbian, O.A.,Engl, G.,Grohs, B.,Rathgeb, W. and Wiistenberg, H.: A second
view of the German results obtained in the defect detection trials, UKAEA, British
Journal of NOT, Vol.26,No.2,pp.92-96,1984.
3. Barbian, OA.,Grohs, B. and Kappes, W.: Evaluation of time-of-flight data with
the ALOK-method, British Journal of NDT, VoL26,No.4,pp.214-217,1984.
4. Miiller, W.,Schmitz, V. and Schafer, G.: Reconstruction by the synthetic aperture focusing technique(SAFT), Nuclear Engineering and Design, Vol.94,pp.393404,1986.
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