Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Back~roullcl of the rnvelltio
Field of the I_vention
The present invention relates to automatic and
accurate me-thod ancl apparatus capable of detecting rlaws
mainly in circumferential weld zones of pipe lines.
Description o-f the Prior Art
X-ray penetration testing has conventionally been
applied for non-destructive inspective of weld zones. In
conjunction with the improved performance of ultrasonic flaw
detection appar~tus, the application of ultrasonic flaw
detection methods and techniques have recently been required
for improved detection accuracy, shortened detection time,
safe operation and decreased detection costs. In particular,
in the non-destructive inspection of circumferential weld
zones for high-pressure pipe lines, such weld zones have
been inspected by the combined use of X-ray penetration
testing and ultrasonic flaw detection techniques. Ultrasonic
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flaw detection has been performed mainly manually. However,
manual ultrasonic flaw detection requires considerable skill
and experience for the discrimination of the jamming echoes
due to the weld bead, from the flaw echoes and also requires
considerable technical skills. Under certain operational
conditions, weld flaw detection has to be performed under
severe conditions at sites such as common workshops where
other operations are also being performed. Such conditions
present intolerable burdens to the welding operations and
inspectors.
In order to overcome sucn problems, it is desirable
to automate welding flaw detection methods and techniques
and also the associated necessary data processing, such as
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recording and evaluation and the like of the detected
results.
SU~lMARY OF THE INVENTION
It is an object oE the invention in accordance
with such requirements to provide automatic ultrasonic
flaw detection methods and apparatus employing a calcu-
lator having an operational function to systematize the
data processing of automatic ultrasonic Elaw detection.
The inventior. consists of a method for automat-
ically detecting flaws in circumferentially extending pipewelding zones, comprising the steps of: moving a welding
flaw detector in at least two different directions in
tracking relationship to a weld zone; subdividing the
width of said weld zone into a plurality of areas; trans-
mitting pulsed energy to said weld zone; generating output
signals from a plurality of gate circuits each respect-
ively responsive to the echo signals produced by said
pulsed energy from a specified one of said areas; generat-
ing position signals representative of the position of
said flaw detector from a reference point; and displaying
said output signals and said position signals in assoc-
iated relationship to indicate any welding flaws and their
respective positions in each one of said plurality of
areas of the weld zone.
The invention also consists of apparatus for
automatically detecting flaws in circumferentially extend-
ing pipe welding zones, comprising: a welding flaw de-
tector movable in at least two different directions in
tracking relationship to a welding zone; means for trans-
mitting pulsed energy to said welding zone; means for
;~ generating output signals from a plurality of gate
~ circuits each respectively responsive to the echoes
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produced by said pulsed ene~gy from a respective one of alike plurality of areas subdividing tlle width of said
welding zone; means for generating position signals repre-
sentative of the position of said flaw detector from a
reference point; and means for displaying said output
signals and said position signals in associated relation-
ship to indicate any welding flaws and the respective
position thereof in each one of said plurality of areas in
the weld zone.
BRIEF DESCRIPTION OF T~E DRAWINGS
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Fig. 1 is a side view of a self-propelled carrier
flaw detection apparatus according to an embodiment of the
invention;
Fig. 2 is a partially cut-away plan view of the
self-propelled carrier of Fig. 1 on an enlarged scale;
Fig. 3 is a longitudinal sectional view taken
along line III - III in Fig. 2;
Figs. 4A, 4B and 4C are illustrations showing
respective scanning patterns of probes of a self-propelled
carrier;
Fig. 5 is a block diagram showing data processing
apparatus; and
Figs. 6A, 6B (with Figs. 4A-C) show respective
e~amples of printed records of deteoted flaws as obtained
from such apparatus.
DETAILED DBSCRIPTION OF THE PREFERRED E~BODIMENT
The embodiment comprises the ~ollowing components. A
; weld-following mechanism enables the flaw de~ection apparatus to
track the weld ~ones with weld detection probe holders.
Motors provide circum-Ferential movement and scanning o~ the probe
holders and the probes carried thereby. A detector
enables determination o-~ the position oF the
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probes. A self-propelled carrier on which the probes are
mounted detects Elaws by axial scannin~ movements of the
probes while the probes are moved along the circum~er-
ential weld zone at a predetermined speed (the maximum
speed being about 3 m/min.). Display apparatus electri-
cally displays the position of the probes and the height
of the echoes. A data processing unit automatically
prints the detection results.
The apparatus is characterized, in particular, by
the incorporation of a data processiny unit comprising a
calculator having reading and calculating functions for
the high speed processing of the automatic ultrasonic flaw
detector.
As shown in Fig. 1, self-propelled carrier 1 is
constructed so that probe holders 4 are mounted at the
center portion of trestle 2, which is driven by motor 3
for circumferential movement of the trestle. Self-
propelled carrier 1 is secured to the outer periphery of
pipe 5, which is to be inspected, by a pair of semi-
circular holder bands 7, each of which is secured totrestle 2 at one end thereof, and includes a plurality of
spaced rollers 6 for maintaining the trestle at a fixed
distance from the outer periphery of pipe 6. Holder bands
7 are attached to one another by clamping units 8 attached
at the opposing ends of each of the holder bands.
As shown in Figs. 2 and 3, the travelling
mechanism of the carrier comprises connecting four driven
magnetic rollers 9, respectively mounted at both the front
and rear ends of carrier 2, to respective driving shafts
10 driven by gears 9a, 9b which are, in turn, respectively
connected to a transmission shaft 11 driven by reduction
gears 12, connected to a-shaft of motor 3.
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The mechanism is thus constructed so that one motor 3 can
drive concurrently fo~r magnetic rollers 9. It should be
understood that such a mechanism is illustrated only as an
exemplary embodiment and other suitable mechanisms can be
employed, if desired.
Probe holder 4 travels on rails 16 attached to
the inner walls of outer right and left frames 15 by
multiple sets of roller mechanisms, each set including two
rollers 14 mounted vertically with respect to one
10 another. Probe holder 4 is suspended to be movable verti-
cally and in a plane perpendicular thereto with respect to
weld zone 17. Probe holder 4 is suspended by connecting
outer frame 15 to supporting shaft 18, attached rotatably
to carrier 2 through a recess defined at the central
portion thereof as illustrated in Figures 2 and 3.
Thereby, probe holder 4 is mounted on carrier 2 so as to
be pivotable horizontally about supporting shaft 1~ and to
be horizontally movable, at the same time, in a direction
perpendicular to weld zone 17.
A rotating shaft, constructed in two independ-
~ ently operable sections 20, 20' is threaded through a
;; tapped hole in block B for mounting probes T, T' and each
of the shaft sections 20, 20' is driven respectively by
scanning motors 19, 19' secured to holder 4 so that either
one, or both, probes T, T' can be independently or con-
currently moved, as desired, by actuating either motor 19
or 19'. The displacement of both probes T, T' is measured
by rotary encoder 21 which measures the axial scan
position and the circumferential scan position of both
30 probes T, T' in a manner known to those skilled in the
art. Probes T, T' are movable because it is necessary to
adjust the distance between end faces of the probes as the
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width of the weld bead is not constant due to the
different radius o~ pipe to be inspectecl.
In the flaw detection of weld zones, it is
essential to know the distance between the center of the
weld bead and the point of incidence of the ultrasonic
wave from the probes T and T'. It is necessary that a
mechanism for following the weld bead be used in the auto-
matic flaw detection apparatus. Such following mechanisms
include optical and electrical types. As such mechanisms
are too complex and large to be used in situ at the sites
where the pipe lines are being inspected, the apparatus
adopts a system wherein four magnets 22 are attached to
outer frame 15 o~ probe holder 4 to be magnetically
attracted to the pipe on both sides of weld zone 17,
thereby enabling probes T and T' to follow the weld zone.
Such a following or tracking mechanism is simple. Probes
T, T' can be isolated from any vibration due to the close
contact of magnets 22 with the outer surface of the pipe
by means well known to those skilled in the art. There-
; 20 fore, probes T, T' are always in contact with, or closelyadjacent to, the surface of the pipe and the tracking of
the probes with respect to the bead is kept within an
accuracy of 2mm, which is sufficient such that no problem
is encountered in the practical use of the system.
Probes T, T' each incorporate vibrator Ta for
obliquely detecting flaws, and vibrator Tb for perpendic-
ularly detecting the reflected waves from the bottom of
the material (see Fig. 5). To avoid cluttering the draw-
ing, only the electrical connectors to vibrator Tb are
shown. The electrical connections to vibrator Ta are
the same as those shown for vibrator Tb. Probes T, T'
each function to maintain the flaw detecting sensitivity
at a constant level by receiving the reflecting waves from
the bottom of the material, i.e., the pipe to be
inspected, namely from the radially confronting inner sur-
face of the pipe, to calibrate the re~lected waves in
accordance with the change in the contacting conditions o-f
the probe with the material due to the unevenness of the
surface thereof. Specifically, the characteristics of the
obliquely or perpendicularly incident ultrasonic energy
into the material depends on the contacting conditions of
the probe with the surface of the material to be
inspected. The change in such contacting conditions
causes fluctuation in the flaw detecting sensitivity,
thereby leading to failures in the evaluation of welding
defects. Therefore, it is necessary to calibrate the flaw
detecting sensitivity to maintain it at a constant level.
Taking such a requirement into account, the detector employs
vibrators Tb in each of probes T, T' which can calibrate
- 20 the sensitivity automatically within a range of 20dB.
Such calibration is performed automatically by switching
between vibrators Ta and Tb in each of probes T and T'.
Figs. 4A, 4B and 4C show the scanning patterns
for only one of probes T, T', as both probes scan in the
same manner. Fig. 4A shows lateral or axial scanning,
~ Fig. 4B shows longitudinal or circumferential scanning and
;~ Fig. 4C shows a scanning pattern representing the combined
scanning patterns of Figs. 4A and 4B (referred to herein-
after as rectangularly lateral scanning). Lateral or
axial scanning performs sufficient flaw detection within a
skip from 0.5 to 1.0 at a distance from the probe to the
center of the bead ranging from 20 to 95mm for pipes having
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a thickness t ranging from 8 to 15mm. The pitch for rect-
angularly lateral scanning can also be adjusted to a
minimum of lmm.
As shown in Fig. 5, the data processing unit for
obtaining the results Erom the automatic ultrasonic ~law
detector comprises position display 23 which indicates the
X and Y coordinates of the position of probes T, T',
namely scanning laterally in the axial direction (Y) and
longitudinally, circumferentially (X) around the pipe with
respect to weld zone 17. Multichannel gate circuitry 24,
may for example as illustrated include the channel gates
providing outputs in 10~ units of the echo amplitude from
each subdivision of the weld zone, defined by subdividing
the width of the weld zone into a plurality of sub-
divisions. Cathode ray tube 25 displays the echo ampli-
tudes from the ten channel gates in multi-channel gate
circuitry 24 in synchronization with the signals indicat-
ing the respective position of the probes. Printer 26
prints the echo amplitudes of any welding defects that are
~0 present, as determined by the ten channel gate output,
` together with the position of the probes.
In the operation of the automatic flaw detecting
apparatus using the aforedescribed detector, self-
propelled carrier 1 is mounted on pipe 5 over weld zone
17, which is to be inspected. After setting the correct
distance from the welded bead to the probes T, T', carrier
1 is conveyed circumferentially in the direction X along-
side the welded bead. Probes T, T' are laterally moved in
the axial direction Y relative to weld zone 17 to carry
30 out the flaw detection. The positions of the probes are
displayed by position display 23 and at the same time, the
echo amplitudes are displayed on cathode ray tube 25.
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The display of the probe signals frorn either probe T or ~r~
can be selectively displayed by a switch (not shown) in
accordance with teachings well known to those skille~ in
the art. The presence of echo 27 indicates a defect with-
in any of the channel gates of multi-channel gate circuitry
24. The displayed echoes are always in synchronization
with the lateral and longitudinal movement of the probes~
The amplitudes o-f such eclloes are digitized in 10~ units
and printer 26 prints out the echo amplitudes having levels
higher than a predetermined threshold value.
Exemplary printed records of welding defects
detected by the present detector are shown in Figures 6A
and 6B, wherein Fig. 6A shows lateral scanning relative to
the axial direction and Fig. 6B shows an example of rect-
angularly lateral scanning at a scanning distance of lmm.
Fig. 6A shows the results of the flaw detection when the
probe was positioned at a point 7~.5mm from a reference
point on the circumference of the pipe, which was scanned
. laterally relative to the axial direction over ten sub-
divisions of the weld zone width. If an echo representing
a defect is present within the ten channel gates, the echo
amplitude will be digitized in 10% units so that numeral l
represents 10%, numeral 2 represents 20% of the echo
height, and so forth. The asterisks represent echo ampli-
; tudes greater than 100%. In Fig. 6A, the higher values
recorded within the portion enclosed by a solid line,
namely from the third gate to the sixth gate, indicates
that a number of defects are found within the third to the
sixth zones of the ten subdivisions in the weld zone.
Similarly, the rectangularly lateral scanning pattern,Fig. 6B, indicates that a number of defects are present
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within the portion enclose~ by the solid line, namely,
from the second to the fifth zones, at distances 17 to 18
mm from a reference point.
In sur~ary, a weld zone is scanned by probes
movable laterally with respect to the axial direction of
the longitudinal movement along the weld zone of a self-
propelled carrier on which the probes are mounted. The
echo amplitudes of welding defects present within each
gate output, associated with a subdivision oE the weld
zone, is synchronized with the position coordinates of the
probes on a printer so that approximate conditions of the
welding defects are indicated during the flaw detection
operation and the distribution of the welding defects can
be observed at a glance to concurrently determine the
severity of the defects to be classified. In addition,
the self-propelled carrier on which the detector is
mounted has a structure enabling detection oE welding
defects in a constantly stable manner, so that the
accuracy of the flaw detection apparatus and method is
very high. Furthermore, it is possible to graphically
depict the depth of welding defects, echo amplitudes, the
length and severity of the welding defects incorporating a
mlni-computor in a cordance with the foregoing de~cription.
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