U.S. patent number 3,868,847 [Application Number 05/311,800] was granted by the patent office on 1975-03-04 for system and apparatus for inspecting elongated welds.
Invention is credited to Walter A. Gunkel.
United States Patent |
3,868,847 |
Gunkel |
March 4, 1975 |
SYSTEM AND APPARATUS FOR INSPECTING ELONGATED WELDS
Abstract
An ultrasonic inspection system is disclosed for inspecting an
elongated weld, such as the long seam weld on pipe. Longitudinal
wave ultrasonic transducers are provided for inspecting along the
thickest portion of the weld and along the plate adjacent to the
weld, and shear wave ultrasonic transducers are provided for
inspecting the boundary zones between the weld metal and plate
being welded. Electronic pulsing and signal processing apparatus is
provided for providing drive to a data recorder on which separate
graphical representations of the condition of the weld, of the
condition of the plate adjacent the weld, and of the boundary zones
of the weld are simultaneously provided. The transducers are
mounted on an inspection head which is in turn mounted on a
carriage which may be inserted into racked pipe for inspecting the
long seam weld. The inspection head includes guide means, such as
rollers, for guiding the head along the long seam weld of the pipe.
The inspection head is resiliently urged against the inside wall of
the pipe and counterweights are provided for balancing the
inspection head in the position required for inspection so that the
seam may be inspected when the pipe is at any rotational
orientation.
Inventors: |
Gunkel; Walter A. (San Antonio,
TX) |
Family
ID: |
23208537 |
Appl.
No.: |
05/311,800 |
Filed: |
December 4, 1972 |
Current U.S.
Class: |
73/622; 73/609;
73/614; 73/625 |
Current CPC
Class: |
G01N
29/22 (20130101) |
Current International
Class: |
G01N
29/22 (20060101); G01n 029/04 () |
Field of
Search: |
;73/67.5,67.6,67.7,67.8,67.9,67.5R,67.8R,67.8S |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Queisser; Richard C.
Assistant Examiner: Kreitman; Stephen A.
Attorney, Agent or Firm: Hyer; W. F. Eickenroht; Marvin
B.
Claims
The invention having been described, what is claimed is:
1. Ultrasonic apparatus for inspecting an elongated butt weld
comprising, in combination: an inspection head adapted to be moved
along and adjacent to the weld; a longitudinal wave ultrasonic
transducer mounted on said inspection head and adapted to be
positioned on said weld to move along its length for inspection
through a substantial part of the heart of the weld; a plurality of
shear wave ultrasonic transducers mounted on said inspection head
to be positioned on each side of the weld to provide for inspection
of the boundary zone of the weld, and means on the inspection head
to restrain movement thereof to be longitudinally along the
elongated weld without any substantial movement laterally of the
weld.
2. The apparatus of claim 1 further including a pair of third
ultrasonic transducers mounted on said inspection head for
inspecting plate adjacent to and on each side of said weld.
3. The apparatus of claim 2 wherein said third transducers are
longitudinal wave ultrasonic transducers.
4. The apparatus of claim 1 wherein said shear wave transducers are
provided for inspecting each boundary zone of the weld and being
mounted on said inspection head to be on one side of the weld, one
of each pairs of transducers providing an ultrasonic impulse and
the other of each pair of transducers receiving ultrasonic echo
signals from said weld.
5. The apparatus of claim 4 including means for mounting each of
said shear wave transducers so that the lateral distance of each
transducers from weld being inspected may be adjusted, whereby the
transmitting transducer of each pair may direct an ultrasonic pulse
substantially into only one of the boundary zones of the weld, and
the receiving transducer of each pair receives ultrasonic echoes
from its respective only one boundary zone of the weld.
6. The apparatus of claim 4 wherein such a pair of shear wave
transducers is mounted on opposite sides of said inspection head to
be on opposite sides of said weld for inspecting the boundary zones
on either side of the weld, and wherein the receiving transducers
of a first pair of transducers on one side of said head is opposed
to and in line with the transmitting transducer of a second pair of
such transducers on the other side of said head, and the
transmtting transducer of said first pair of transducers is opposed
to and in line with the receiving transducers of said second pair
of transducers.
7. The apparatus of claim 4 wherein said transmitting shear wave
transducer includes a crystal mounted therein to provide an
ultrasonic pulse at an angle with respect to the plate surface
adjacent a weld to be inspected such that the pulse propagates
through said plate on a path at about a 40.degree.-50.degree. angle
with respect to surface of the plate, and said receiving shear wave
transducer includes a crystal mounted therein for primarily
detecting and responding to ultrasonic signals travelling through
said plate on such a path.
8. The apparatus of claim 7 wherein said crystal is mounted so that
said path is about 45.degree..
9. An ultrasonic inspection system for inspecting an elongated butt
weld comprising, in combination: electronic drive means for
providing periodic ultrasonic drive pulses, a first ultrasonic
transducer connected to said drive means and responding to such
drive pulses for inspecting a substantial portion of the thickness
of such a bead; first time base measurement means connected to said
first transducer for responding to echo ultrasonic pulses received
by said transducer to provide a first distinctive output signal
responsive to the condition of said weld; a plurality of second
ultrasonic transducers connected to said drive means and responding
to such drive pulses for inspecting the boundary zones of such a
weld; and electronic signal detecting means connected to said
second ultrasonic transducer for providing a second distinctive
output signal in response to an abnormal condition at at least one
of said boundary zones, means mounting said transducers to be moved
longitudinally along the weld without any substantial movement
laterally of the weld, and a plurality of third ultrasonic
transducers connected to said drive means and responding to such
drive pulse for inspecting plate adjacent to and on each side of
the weld, and second time base measurement means connected to each
of said third transducers for responding to ultrasonic echo signals
therefrom to provide a third distinctive output signal responsive
to the condition of said plate.
10. The apparatus of claim 9 further including a chart recorder
having a first channel responsive to said first distinctive output
signal to provide a first distinctive trace, a second channel
responsive to said second distinctive output signal to provide a
second distinctive trace, and a third channel responsive to said
third distinctive output signal to provide a third distinctive
trace whereby simultaneous inspection of said first, second and
third traces can provide distinctive and composite indications of
the condition of the heart of the weld, the condition of the
boundary zones of the weld, and the condition of the plate adjacent
the weld.
11. The system of claim 9 wherein the weld to be inspected is the
long seam weld of racked pipe, and further including a carrier
adapted to be inserted in and moved along the length of such pipe,
and an inspection head resiliently mounted on aid carrier to move
about and along said weld, and wherein said first, second, and
third ultrasonic transducers are mounted on said inspection
head.
12. Ultrasonic apparatus for inspecting longitudinal butt welds in
a pipe comprising, in combination: a carrier adapted to be moved
along the length of such a pipe; an inspection head resiliently
mounted on said carrier and adapted to be moved along the weld to
be inspected; means for guiding said head on the weld in a manner
to cause the transducer to move longitudinally along the weld
without any substantial movement laterally of the weld; means for
urging said head against the inside wall of a pipe being inspected;
a first ultrasonic transducer mounted on said inspection head and
adapted to be positioned over said weld to move along its length
for inspection through a substantial part of the weld bead; a
plurality of second ultrasonic transducers mounted on said
inspection head to be positioned and to provide for inspection of a
root of the weld; and a pair of third ultrasonic transducers
mounted on said inspection head for inspecting plate adjacent to
and on each side of said weld.
Description
This invention relates to a system and apparatus for ultrasonic
inspection of the condition of an elongated weld, such as the long
seam weld on pipe. In one of its aspects it relates to pipe
inspection apparatus for inspecting the long seam weld of a pipe,
particularly when racked.
Adequate inspection of pipe requires that the long seam weld be
inspected. In large pipe it is desirable to do this while the pipe
is racked in order to avoid pipe handling which requires expensive
equipment, is time consuming, and frequently damages the pipe.
However, when racked, the individual pipe lengths will generally be
at different rotational orientations and the prior art does not
provide practical inspection apparatus which will inspect along the
long seam weld requiring some orientation and handling of the pipe.
Also, even when pipe is laid out on the ground in an unracked
condition, prior art inspection devices that inspect along the
outside of the long seam weld generally require some rotating of
the pipe for orientation of the weld. Furthermore, it is desirable
that the inspection apparatus used be lightweight and portable and
that it be capable of operation by as small a crew as possible.
Also, in the past, ultrasonic inspection of the welds has generally
been provided by scattering or speading ultrasonic pulses generally
through the weld and noting the arrival of echo pulses in a
defective weld as opposed to a good weld. In some prior systems
longitudinal wave inspection is provided for, and in others shear
or transverse wave inspection is provided for. In one such system,
ultrasonic shear wave pulses are sent through the plate adjacent
the weld and on each side of the weld, at a propagation angle in
the plate of about 80.degree. so that a spead beam of pulses is
provided into the weld. The same ultrasonic signals are used to
inspect the boundary zones of the weld, the heart of the weld and
throughout its thickness, and the plate adjacent the weld. See
Krautkramer, Ultrasonic Testing of Materials, Springer-Verday, New
York, 1969. However, such a system provides relatively poor
selectivity, sensitivity and signal to noise ratio, particularly as
the beam is spead out to cover more area, and may miss defects in
the heart of the weld. Also, the type of readout provided by such a
system requires interpretation by an operator of considerable skill
in pipe inspection in order to determine the type and severity of a
defect located, and its exact location.
It is thus an object of this invention to provide apparatus for
inspecting the long seam weld of pipe at any orientation of the
weld being inspected.
Another object of this invention is to provide such apparatus which
is lightweight and portable and particularly adaptable to
inspecting the long seam weld of racked pipe, thereby eliminating
pipe handling, providing independence of yard activity, etc.
Another object of this invention is to provide such apparatus which
may be placed in the pipe and about the weld being inspected, so
that the apparatus can propel itself along the weld and accomplish
its inspection function automatically.
Another object of this invention is to provide such apparatus for
use in an ultrasonic inspection system which permits simultaneous
longitudinal and transverse inspection of the weld with the same
apparatus and with synchronism between the two types of weld
inspection provided for, to provide better and overlapping
inspections of the weld and weld areas.
Another object of this invention is to provide such apparatus that
is particularly adaptable for use in ultrasonic inspection of an
elongated weld, such as along the inside or outside of the long
seam weld of pipe or the girth weld.
Another object of this invention is to provide an ultrasonic
inspection system, and apparatus therefore, for inspecting
elongated welds with better selectivity, sensitivity, signal to
noise ratio, and reliability then provided by prior such
systems.
Another object of this invention is to provide such a system and
apparatus in which root or cap cracks and other defects in the
boundary zone of the weld, defects in the plate adjacent to the
weld, and defects in the heart of the weld can be reliably detected
and readily distinguished from each other by techniques specially
designed individually to provide maximum effectiveness in these
areas of the weld structure and to do so by persons of lesser skill
in the pipe inspection art than heretofore required.
Another object of this invention is to provide such a system and
apparatus which is sensitive to and provides an indication of the
porosity in the weld, the various defects of the weld, such as burn
through, and of the presence of cracks, slag inclusion, voids and
poor fusion of the weld, and offset plate.
Another object of this invention is to provide a relatively easily
read and understandable composite, permanent record on a single
recording medium of the condition of the weld, the condition of the
boundary zone of the weld, and the condition of the plate adjacent
the weld.
These and other objects of this invention, which will be apparent
upon consideration of the appended claims and drawings, and the
detailed description to follow, are accomplished in accordance with
the preferred embodiments of this invention disclosed by providing
a carriage that can propel itself along the inside of a pipe being
inspected and support a rotatable shaft along the axis of the pipe.
An inspection head may be rotatably and resiliently mounted on an
arm extending from the shaft so that it may be rotated to any
position about the circumference of the pipe corresponding to the
orientation of the weld, and resiliently urged against the inside
weld of the pipe about the weld. Guide means are provided on the
inspection head for guiding the inspection head along the weld as
the carriage moves throughout the pipe. A counterweight may also be
provided to substantially balance the inspection head at its
position on the circumference of the pipe, and the inspection head
may be mounted on and balance about the arm extending from the
shaft by an universal coupling so that it can float and ride along
the weld and adjust to irregularities in the weld or the inner wall
of the pipe. A second counterweight may also be provided to help
balance the inspection head on the arm supporting it.
The inspection head includes at least one inspection transducer,
which is preferably an ultrasonic transducer, which may be mounted
in the inspection head with a floating relationship so that it also
adapts to the irregularities in the surface of the weld or pipe
wall. Means may also be provided for maintaining a fluid coupling
and bearing surface between the transducer and the weld or pipe
wall.
The apparatus described may be used in a system for inspecting
elongated welds which includes, on the inspection head, a first
ultrasonic transducer which rides along the weld to specifically
inspect into the heart of the weld (and through its thickness); a
plurality of second transducers arranged along the inspection head
and specifically orientated to have substantially their maximum
signal sensitivity in response to defects, such as cracks in the
boundary zones of the weld (said boundary zones of the weld being
defined as the zone of the junctions of the weld with the plate
being welded); and third ultrasonic transducers for specifically
inspecting plate adjacent the weld. This arrangement can provide
for simultaneous longitudinal wave and transverse or shear wave
inspection of the weld with overlapping coverage, so that the first
and third transducers are longitudinal wave transducers and the
second transducers are shear wave transducers. Suitable pulsing and
signal processing electronics is provided for pulsing the
transmitting elements of the respective transducers and processing
echo signals received by the transducers. Output signals from the
electronics may be utilized to drive a chart recorder which will
simultaneously display a first indication of the thickness (or of
the presence of a defect) of the heart of the weld; a second
indication of the presence or lack or presence of a crack in one or
more of the weld boundary zones; and a third indication of the
thickness (or presence of a defect) in the plate adjacent the
weld.
Since each of the transducers mentioned can be specifically
oriented and adjusted for its specific inspection application a
spread beam is not required and better selectivity, sensitivity,
signal to noise ratio and reliability can be provided over prior
ultrasonic weld inspection systems. For example, better sensitivity
can be provided in steel with an ultrasonic beam travelling through
it with a propagation angle of about 45.degree. with respect to the
plate surface, and the shear transducers for inspecting each
boundary zone can be adjusted to provide such a beam which is
focused on the particular boundary zone to be inspected for maximum
response to a crack or other defect in the respective zone. Also,
by use of the separate transducers for inspecting different parts
of the weld (and the adjacent plate) distinctive readouts of the
condition of each part of the weld and adjacent plate being
inspected can be provided which yields useful defect discrimination
information and can be easily read and understood by persons of
lesser skill in pipe inspection than the readouts of prior
systems.
The inspection head can be mounted on a carriage for movement
through the interior of a pipe (including racked pipe) to inspect
the long seam weld of the pipe, or moved along the long seam weld
on the outside of the pipe. Also, the features of this invention
may be employed in other inspection apparatus for inspecting
elongated welds between two plates, girth welds between pipe, and
the like.
In the drawings, wherein like reference numerals are used
throughout to designate like parts and wherein preferred
embodiments of this invention are illustrated;
FIG. 1 is a perspective view of the preferred form of inspection
apparatus of this invention, prior to insertion into a pipe being
inspected;
FIG. 2 is an end view of the inspection apparatus of FIG. 1, shown
inside a pipe being inspected;
FIG. 2A is an enlarged view at 2A in FIG. 2 showing details of a
typical double submerged arc weld between two plates;
FIG. 3 is a top view of the inspection head of the FIG. 1 apparatus
shown in a pipe, and with the pipe partially cut away;
FIG. 4 is an enlarged end view of the inspection head of the FIG. 1
apparatus shown in the pipe;
FIG. 5 is a side view in elevation of the inspection head of the
FIG. 1 apparatus;
FIG. 6 is a longitudinal sectional view of the inspection head of
FIG. 1;
FIG. 7 is a sectional view taken at 7--7 in FIG. 6;
FIG. 8A is a perspective view of an alternate form of the mounting
of inspection head of the rotating shaft permitting retraction of
the inspection head when inserted into a pipe;
FIG. 8B is an end view in elevation of another form of guide means
for adjusting the position of the guide rollers;
FIG. 8C is a top view of the guide means of FIG. 8B;
FIG. 9 is a top view of the preferred form of inspection head of
the apparatus of FIG. 1 showing the details of the arrangement of
the transducers in the inspection system of this invention;
FIG. 10 is a sectional view taken at 10--10 in FIG. 6 with a
partial cut away;
FIG. 11 is a cross sectional representation of the relationship of
the transducers of the FIG. 8 inspection head, and a weld and
adjacent plate being inspected;
FIG. 12 is an overall schematic of the preferred arrangement of the
transducers, pulsing and signal processing electronics, and a chart
recorder of the system of this invention;
FIG. 13 is a more detailed schematic of a time base measuring
circuit utilized in the FIG. 12 circuit;
FIG. 14 is a more detailed schematic of the electronics of FIG.
12;
FIG. 15 is a wave form chart applicable to the signal outputs of
the FIG. 14 electronics;
FIG. 16 is a wave form chart illustrating the operation of the
pulser electronics;
FIG. 17 is a wave form chart showing the relationship of the main
bang transmitted signals and the echo signals at the transducers;
and
FIG. 18 is a pictorial representation of a typical chart recorder
readout obtained by use of the present invention.
Referring to the drawings, in FIG. 1 the preferred form of pipe
inspection apparatus of this invention, such as used for inspecting
racked pipe, is illustrated by the numeral 10 as including a
tubular sleeve 11 in which a rotatable shaft 12 is mounted. Sleeve
11 and shaft 12 may be supported along the axis of a pipe being
inspected, such as a pipe P having a long seam weld W as shown in
FIG. 2, by six legs 13, three located at each end of sleeve 11 and
mounted 120.degree. apart. Each of legs 13 include wheel 13a and
may be made of telescoping threaded members (the threads not being
shown in FIGS. 1 and 2) which can be adjusted in length by screwing
one of the members into the other, so that the carriage can be
mounted in pipes of different diameter with shaft 12 substantially
along the axis of the pipe. As shown, a sprocket 14 is provided on
one of wheels 13a and it may be connected by a belt to a drive
motor M (two motors may be used, if desired) which may be battery
powered. Of course, other arrangements of the carriage may be
provided for supporting rotary shaft 12. Apparatus 10 can be made
of aluminum so that it is lightweight and portable and can be
easily handled by a two man crew.
As shown in FIGS. 1 and 2 an inspection head 15 is supported for
rotation by shaft 12. A hub 16 is mounted on shaft 12 and supports
a pair of spaced apart, parallel support members 17 and 18
extending perpendicular to the axis of rotation of shaft 12, and an
arm 16A extending radially away from members 17 and 18. Inspection
head 15 is mounted on one end of an arm 19 as hereinafter explained
in detail, which is pivotally mounted by a pin 20 on and between
members 17 and 18. Inspection head 15 is preferably balanced about
its mounting on arm 19 and a counterweight 21 is mounted on the
other end of arm 19 to counterbalance the weight of inspection head
15 on arm 19, and this end of arm 19 is connected by a spring 22 to
a spacer block 23 (FIG. 6) mounted between arms 17 and 18.
Inspection head 15 is thus resiliently mounted on shaft 12 and
spring 22 provides a force urging inspection head 15 against the
inner wall of pipe P so that as carriage 10 moves along the pipe
inspection head 15 will move along and against the wall. Another
counterweight 16B (which may be adjusted up and down arm 16A by a
set screw) is provided on the end of arm 16A so that arm 16A and
members 17 and 18, and their attachments can be balanced on shaft
12 at any rotational orientation.
However, the tension of spring 22 should be such that as inspection
head moves along the inner wall of pipe P, it can move away from
the wall when irregularities in the surface are encountered,
otherwise it may bind against the wall or inspection transducers
may be damaged.
The preferred form of inspection head 15 illustrated includes two
flat aluminum plates 24 and 25 mounted on end blocks 26 and 27
which are sloped to confrom to the curved inner wall of pipe P.
Small, thin nylon strips 24A and 25A may be mounted on the outer
edges of plates 24 and 25 to serve as runners and space the plates
from the surface of the pipe. The ends of plates 24 and 25 at the
center of inspection head 15 are spaced apart to form an elongated
slot 28 into which a portion of weld W will extend when the
inspection head is placed over the weld, slot 28 being wide enough
so that it clears the weld by a small amount as shown in FIG. 4, so
that the edges of plates 24 and 25 adjacent weld W generally will
not rub against the weld. Also mounted on end plates 26 and 27 and
extending from each of inspection head 15, are water pipes 29 and
two roller support plates 30. Water pipes 29 are connected as
hereafter explained to a source of water for lubricating the
surface of pipe P ahead of inspection head 15 in either direction,
and to provide an acoustic fluid coupling and bearing surface for
each of the transducers of head 15.
In order to aid placing inspection head 15 in and taking it from a
pipe, a retracting mechanism such as shown in FIG. 8A may be
provided which lowers the head. In this case, plates 17 and 18 are
replaced by an arm including telescoping members 17A and 17B and a,
for example, set screw 18A in a slot in member 17A which permits
the position of member 17B inside of 17A to be adjusted and set. If
desired, a lever mechanism (not shown) may be provided for moving
member 17B in member 17A from a retracted position for head 15, to
a raised position for head 15 for inspection.
Two rollers 31 are mounted on each of support plates 30 so that
when head 15 is in position about weld W, and the weld is along
slots 28, one such roller is along an edge or side of weld W (see
FIG. 4) at each end of head 15, to function as guide means for
guiding inspection head along weld W and maintaining the proper
orientation of the inspection head transducers to the weld. Of
course, other forms of guide means may be provided, for example,
nylon or teflon bearing pads could be mounted on plates 24 and 25
on each side of slot 28 to rub against weld W. However, the roller
arrangement described is preferred since it provides smoother
operation and less force is required to move head 15 along the
weld.
In order to permit adjustment of the guide rollers for different
sizes of weld beads, the arrangement better shown in FIGS. 8B and
8C is preferred, the latter FIG. showing only one side of the guide
means in detail since it is symmetrical. In this arrangement plate
30 is mounted through slotted openings 30A to permit the vertical
position of rollers 31 to be adjusted. Also, rollers 31 are mounted
through a slotted opening 31A in the top of plate 30 to permit
adjustment of rollers 31 towards and away from weld W. A threaded
set screw 31B may be provided for adjusting the position of a plate
31C to which roller 31 is secured, so that plate 31C moves with
respect to plate 30 in the direction noted by the arrow in FIG. 8B.
When the position of the rollers 31 is set along the weld bead, a
set screw 31B may be pinned by a pin passing through it to avoid
displacement. When the rollers 31 are properly set, all of head 15
(including pads 24A and 25A) except the transducers will ride off
of the pipes wall with a small clearance unless an out of round
portion is encountered. Of course, this arrangement of guide means
described, as well as the arrangement of the transducers, on a
suitable inspection head could also be used to inspect a girth
weld.
The details of the counting of inspection head 15 on arm 19 is
shown in FIGS. 4, 5, 6, and 7. Arm 19 includes a plate 19A
extending at right angle to arm 19 and mounted on the end opposite
the end that counterweight 21 is mounted on. A universal coupling
32 including a swivel connector 32A (see FIG. 7) is mounted on
plate 19A and inspection head 15 is mounted on coupling 32 to
permit universal movement of inspectin head 15. As shown in FIG. 6
inspection head 15 includes two plastic water manifold blocks 33
and 34 mounted on the lower side of plates 24 and 25 and a bolt 36
which passes through and is secured to a center block 35 (see FIG.
3 also) mounted on plates 24 and 25 at a right angle to slot 28.
Bolt 36 also passes through swivel 32A to provide the mounting of
head 15 on universal coupling 32.
Fluid manifolds 33 and 34 are connected to a source of water 33A
and by suitable piping 33B (illustrated partially in FIGS. 6 and
10) to a number of water jets 34A (see FIG. 9), and water pipes 29
serve to provide additional fluid coupling for each of the
transducers of inspection head and a bearing surface on which the
transducers may float because of their resilient mounting, to be
described.
Referring now to FIG. 2A, an enlarged view of weld W is shown with
the root and bead areas shown. Also, as illustrated by the shaded
areas Z.sub.ID and Z.sub.OD, the boundary zones of the weld are
defined as the zone adjacent the I.D. and O.D. boundaries between
the weld and adjacent plate. The heart of the weld is labled as H.
An important feature of this invention is that specific inspection
of each of the I.D. and O.D. boundary zones Z.sub.ID and Z.sub.OD
is provided by shear wave inspection simultaneously with inspection
of the heart H of the weld and the plate adjacent the weld by
longitudinal wave inspection. As used in the present application,
longitudinal shear wave inspection refers to the generation and
detection of echo signals from ultrasonic waves directed from the
transducers down into and through the thickness of the weld or
adjacent plates, and travel in the direction of propagation. Also,
as used herein, transverse or shear wave inspection refers to the
generation and detection of echo signals from ultrasonic waves
travelling transverse to the direction of propagation and which lag
behind the longitudinal wave. Since it is difficult to either
longitudinally or transversely inspect all of a weld and its
adjacent plate, the combinations of these type of ultrasonic
inspection provides the required complete and overlapping
inspection.
Inspection head 15 straddles weld W so that it projects into groove
28 and as head 15 moves along the weld it may be inspected by the
plurality of transducers mounted on head 15. In the embodiment
illustrated in FIGS. 3 and 9 a first longitudinal wave transducers
40 is mounted in groove 28 so that it moves along and adjacent to
the heart H of weld W as shown in FIG. 11. The face of transducer
40 towards weld W is curved to substantially correspond with the
curvature of the weld, and a single housing may include both the
transmit and receive cyrstals as represented by the letters T and R
in FIGS. 9 and 11. Also, inspection head 15 includes a plurality of
shear wave transducers 41A, 41B and 42A and 42B mounted on plate
24, and 43A, 43B and 44A and 44B mounted on plate 25. These
transducers are mounted in pairs of transducers with a receiving
and transmitting transducer in each pair, and each pair of the
shear wave transducers inspects one of the O.D. or I.D. boundary
zones Z.sub.ID or Z.sub.OD of weld W. In the example illustrated,
transducer pair 41A and 41B (with transducer 41A being a receive
transducer and transducer 41B being a transmit transducer) are
mounted on plate 24 so that transducer 41B sends a shear wave pulse
into the plate adjacent weld W which propagates through the plate
at an angle of about 45.degree. to pass through the boundary zone
Z.sub.OD on plate 24 side of weld W, and transducer 41A receives,
upon occurence of a defect, an echo signal that returns from this
boundary zone at about a 45.degree. angle. Transducer pair 42A and
42B (with transducer 42A being a receiving transducer and 44B being
a transmitting transducer) are mounted on plate 24 so that
transducer 42B sends a shear wave pulse into the plate adjacent
weld W on an angle of about 45.degree. to pass through the boundary
zone Z.sub.ID on plate 24 side of weld W, and transducer 42A
receives an echo signal that returns from this boundary zone at
about a 45.degree. angle. Transducer pairs 43A and 43B, and 44A and
44B are arranged on plate 25 in the same manner (except that it is
preferred that the transmitting transducers 43A and 44A be opposite
receiving transducers 41A and 42A) to inspect boundary zones
Z.sub.OD and Z.sub.ID on the plate 25 side of weld W with a shear
wave pulse of about a 45.degree. propagation angle through the
plate adjacent weld W.
The relation of the shear wave transducers described is illustrated
in an exaggerated scale in FIG. 11 with only the transmitting
transducers shown since the corresponding receiving transducers
would be in line with its respective transmitting transducer. The
desired propagation angle of about 45.degree. is provided by the
angles at which each of the transducer crystals X are mounted in
the transducer, and the type of acoustical coupling used in the
transducer. By this arrangement the shear wave transducers are
mounted so that their respective beams are focused or aligned to
encounter one of the boundary zones of the weld, and the use of
spread beam for inspecting these roots is avoided. One way of
setting or focusing the shear wave transducers is to provide a test
standard (the same size as welds to be inspected) with a known
defect at the center of each boundary zone (generally a crack
between the weld and adjacent plate) and to adjust the position of
each of the shear wave transducers (as to be described) on plates
24 and 25 until the echo received for each respective crack by the
respective shear wave transducer is peaked.
In an embodiment of this invention actually constructed and tested,
the transmitting crystals X in transducers 41B, 42B, 43A, and 44A
are mounted on a plexiglass coupling block B (see FIG. 11) so that
shear wave ultrasonic signals from the crystals will strike the
plate of pipe P at an angle of about 36.degree. and propagate
through the plate at about a 45.degree. angle. An actual test,
satisfactory sensitivity with steel pipe was provided when the
shear wave propagation angle was from about 40.degree. to
50.degree. with peak at about 44.degree.. Of course, these figures
will vary slightly depending on the type of steel used in pipe P,
temperature, and the frequency of the inspection waves. When the
shear wave transmitting transducers are pulsed, a relatively fast
longitudinal or surface wave pulse having maximum sensitivity along
the wall of the pipe adjacent the tranducer (i.e., 0.degree. entry
angle) will be provided followed by slower shear wave pulses at the
desired about 45.degree. propagation.
In order to insure that the respective shear wave pulses pass
through the weld root to be inspected, it is preferred that each of
the shear wave transducers be mounted so that their lateral
distance from the weld can be adjusted. As shown in FIG. 9, slots
24B can be provided in plate 24, and slots 25B ca be provided in
plate 25 so that the shear wave transducers 41A, 41B, 42A and 42B
can be mounted in moved back and forth in slots 24B, and
transducers 43A, 43B, 44A, and 44B can be mounted in and slid back
and forth in slots 25B. For this purpose, each of the transducers
can be mounted on flat plastic or aluminum plates 41C (shown in
dotted lines in FIG. 9) which are in turn mounted by screws that
pass through elongated slots 41D on each side of slots 24B and 25B.
As shown in FIG. 9, the I.D. boundary zone transducers 42A, 42B,
44A and 44B would be mounted at one lateral distance from weld W,
and the O.D. transducers 41A, 41B, 43A and 43B at another lateral
distance from weld W. As noted, these positions can be set by
placing inspection head over a weld substantially the same size as
the welds to be inspected having known defects at the roots and
adjusting for maximum signal strength. By this arrangement one
inspection head 15 can be used to accommodate a wide range of wall
thicknesses and weld bead widths.
Also, in order to inspect the plate of pipe P adjacent weld W, a
longitudinal wave transducer 45 is mounted on plate 24 adjacent
groove 28 on one side, and a second longitudinal wave transducer 46
is mounted on plate 25 adjacent to and on the other side of groove
28. Each of transducers 45 and 46 preferably includes a receiving
and transmitting transducer in a single housing and provides for
longitudinal wave inspection of the plate on either side of and
adjacent to weld W for cracks or deviations from a normal weld
thickness.
The details of mounting the transducers described in head 15 may
take many forms. However, whether head 15 or the specific
transducers described takes the form of the example given or
different forms, it is preferred that they be mounted in their
respective mounting, such as in plates 24 and 25, with a sufficient
clearance C between the transducers and adjacent plate 24 or 25 to
permit canting of the transducer in response to irregularities in
the surface being inspected, and that each transducer be
resiliently mounting such as by a spring S (illustrated
schematically in FIG. 10) to permit the transducer to ride against
the surface it inspects (with a suitable fluid coupling injected
between the surface and the face of the transducer) against the
bias of the spring and to yield and cant when a surface
irregularity is encountered. Also, if the fluid bearing is provided
with sufficient force, the transducer can ride on a layer of fluid
off the surface being inspected.
For example, FIG. 10 illustrates the preferrred form of mounting of
transducer 40. Transducer 40 is mounted on a cylindrical housing
40A open at one end and closed on the other end and its face F is
urged out of the open end of the housing under the force of spring
S between the closed end of housing 40A and the shell of transducer
40. As shown, a small clearance C is provided between the shell of
transducer 40 and the edge of 40B at the open end of housing 40A,
and a shoulder 40C is provided on transducer 40 which abuts against
edge 40B to provide a stop preventing transducer 40 from coming out
of housing 40A. Housing 40A may be mounted in a circular opening in
a plate 45L mounted on end plate 26, and the size of the circular
opening in plate 45L may be adjustable to permit housing 40A to
slide back and forth for setting the position of transducer 40 on
weld W, and to permit transducer 40 to ride on a cushion of
coupling fluid of substantially constant thickness (generally
water) along the surface of weld W.
Referring now to FIGS. 12-18, the system of this invention and a
preferred form of electronic pulsing and signal processing and
readout electronic utilized with this system are shown. In FIG. 12,
the ultrasonic inspection transducers are arranged about an
imaginary weld W substantially as they are arranged on inspection
head 15. A dual avalanche pulser 47 is provided having two output
signals E.sub.1 and E.sub.2 and the transmitting transducers of
each of the shear transducers 41B, 42B, 43A, and 44A are connected
to output E.sub.1. The transmitting crystals of the longitudinal
wave transducers 40, 45 and 46 are connected to output E.sub.2 of
pulser 47. Pulser 47 also provides sync pulses E.sub.SL and
E.sub.SS as hereinafter described. The receiving crystals of
longitudinal wave transducers 45 and 46 are each respectively
connected to time base measurement circuits 48A and 48B (to be
described) and the outputs of circuits 48A and 48B are combined in
a summing circuit 49 to provide an output signal E.sub.3 which is
proportional to the smallest (or largest) of the signals from
circuits 48A and 48B to represent the thinnest of the plates on
each side of weld W inspected by transducers 45 and 46, or a defect
in one of the plates. Since this plate is generally uniform, signal
E.sub.3 will generally be a substantially constat value until a
defect such as a thin wall or lamination in the plate shows up in
one of the plates adjacent weld W. The output E.sub.3 of circuit 49
is connected to an output of one channel of a chart recorder 50
having a chart 50a to provide a trace 51 in responce to the value
of signal E.sub.3, and indicating the condition of the plate on
either side of and adjacent weld W.
The receiving crystal of longitudinal wave transducer 40 is also
connected to a time base measurement circuit 52 and its output
signal E.sub.4 proportional to the thickness of the weld or to a
defect in the weld, is connected to the input of another separate
channel of recorder 50 to provide another distinctive trace 53
indicating the condition of weld W through its heart.
FIG. 13 illustrates a preferred form of time base measurement
circuit for circuits 48A, 48B and 52 (the latter being shown in
FIG. 13). The details of a similar circuit are set out in a
co-pending patent application of Jerry Jackson, Ser. No. 117,663,
Feb. 22, 1971, entitled "Time Base Measurement Circuit," and
assigned to the applicant of this application (now U.S. Pat. No.
3,783,679). ). Circuit 52 includes a pre-amp 54 connected between
the receiver crystal of transducer 40 and a differential comparator
circuit 55 which functions to provide an output when an echo signal
of sufficient magnitude is detected and crosses zero. By this
method, as explained in the referenced patent application, the echo
arrival time is dependent on a phase condition of the echo signal
instead of an amplitude condition, except that the amplitude of the
echo signals must exceed the threshold level of circuit 55. The
output of circuit 55 is conducted to start-stop circuit 56 which
may be a Schmidt trigger that changes state to signal the receipt
of the echo signal by transducer 40. The start-stop circuit 56 is
initially turned on by receipt of a pulse from a block time
generator 57 which may be a monostable multivibrator that responds
to the sync pulse E.sub.s to provide a delayed start pulse for
triggering circuit 56. The period of delay is set to be equal to
the transit time of the main bang and echo pulses through the
transducer coupling medium so that the time period between
switching states of circuit 56 is proportional to only the travel
time of the transmitted and echo pulses in the object being
inspected. The change in output of circuit 56 may be used to drive
a digital to analog converter 58 to provide an analog output signal
E.sub.4 proportional to the time duration between the arrival of
the start and stop signals to circuit 58, and thus the time of
arrival of the echo signal after the pulsing of the transducer.
Referring again to FIG. 12, the receiving transducers 41A, 42A, 43B
and 44B of the shear wave transducers are connected through
amplifier and detection circuits 59 (which provide an output when a
certain input signal level is exceeded which is generally set just
above the grain noise of pipe P) and switches 60 to a circuit 61
which provides an output signal E.sub.S in response to the receipt
of an echo signal at one of the shear wave receiving transducers.
Unlike the longitudinal wave transducers, the shear wave receiving
transducers generally do not receive an echo signal of sufficient
level back from the specific weld boundary zone being inspected to
cause the detector 59 to provide an output unless a crack or other
defect is present in the boundary zone. Also, blanking signals are
provided to circuit 61, has hereinafter described to cut it off
except during the time that a true echo is likely to be received,
if present. Thus, the output E.sub.S of circuit 61, which drives a
third separate channel of recorder 50 to provide a trace 62, is
generally zero and trace 62 may be a straight line at a zero level
until a defect is detected in one of the weld boundary zones.
As noted, the shear wave readout provides an indicatin with pulse
duration proportional to the size of the defect (other than zero or
no trace) only when one of the shear wave receiving transducers
receives an echo signal back from one of the boundary zones that
the about 45.degree. focused beam is inspecting. This invention
further includes two features which help insure that these rceiving
transducers will respond to only the correct echo signal (if
present). First by the mounting arrangement of the shear wave
transducers shown in FIG. 9 where the receiving transducers 41A,
42A are directly opposite receiving transducers 43B and 44B, the
transmitted pulses from the transducers are less likely to be
coupled into the receiving transducer on the opposite side. Second,
as shown in FIGS. 14 and 15, inhibit or blanking pulses are
provided by pulser 47 which inhibits the operation of the shear
wave detector circuit 61 during a time period corresponding to the
generation of the pulses for driving the longitudinal wave and
shear wave transmitting transducers,and for a short period
thereafter, but prior to the expected arrival time of a true echo
pulse at one of receiving transducers 41A, 42A, 43B and 44B. Pulser
47 includes a clock 70 which may be an unijunction relaxation
oscillator for providing periodic pulses (line A in FIG. 15) for
example, at a repetition rate of 250 u sec. The output of clock 70
is conducted to a flip-flop 71 which provides two square wave
outputs B and C 180.degree. out ot phase with each other in
response to pulses A. The two outputs B and C of flip-flop 71 are
conducted to emitter followers 72A and 72B and then to unijunction
pulse drivers 73A and 73B to respectively provide one of alternate
spike pulses D and F at 250 u sec. intervals, or 500 u sec.
intervals for each of pulses D and F, to permit alternating,
non-interfering shear wave and longitudinal wave inspection in
synchronism and during the same inspection time. Pulse drivers 73A
and 73B may be, for example, unijunction transistors responding to
the leading edge of the output pulses of the emitter followers 72A
and 72B to provide short duration spike pulses. Pulses D are
conducted to a shear wave avalanche pulser 74A which, for example,
may include an SCR connected through its power electrodes to shunt
the transducer crystal voltage, to provide main bang pulses E.sub.1
at 500 u sec. intervals for transmitting transducers 41B, 42B, and
43A and 44A. Pulses F are conducted to a longitudinal wave
avalanche pulser 74B similar to pulser 74A to provide main bang
pulses E.sub.2 for the longitudinal wave transmitting crystals of
transducers 40, 45 and 46, at 500 u sec. intervals between the
intervals of pulses E.sub.1. Each of the drive signals E.sub.1 to
the shear wave transducers may be conducted through tuning coils
L.sub.1 and the drive signals to the longitudinal wave transducers
may be provided through tuning coils L.sub.2, which may be tuned to
peak the drive signals. The sync pulse output E.sub.SS of pulser
74A is also conducted to a shear blank circuit 75 which may be a
variable width monostable multivibrator providing, for example, a
short duration (i.e. about 25 u sec.) pulse G which is conducted to
a blocking gate circuit 76, and the sync pulse E.sub.SL output of
pulser 74B is conducted to a longitudinal wave blank circuit 77
which may also be a variable width monostable multivibrator
providing, for example, a relatively long duration pulse H' (i.e.,
about 250 u sec.) which is combined with pulse G (see FIG. 14) and
conducted to gate 76. Gate 76 is thus closed during the time period
of pulses G and H' which would be during the time interval from a
pulse E.sub.2 to pulse E.sub.1 plus the short delay of pulse G.
Gate 76 is connected in series with the shear wave signals so that
during this period in which the gate is closed, which would be
prior to arrival of the true echo signal at the shear wave
receiving transducers, should one or more of the shear wave
receiving transducers provide an output, this output would not pass
through gate 76.
As shown in FIG. 14, shear wave detection circuit 61 includes a
delay circuit 78 which delays the shear wave signals by a short
amount (i.e., 4 u sec.) to insure that complete blocking of
undesired signals occurs and that when the true shear echo signal
arrives, gate 76 will be opened, and an amplifier 79 conducting the
shear wave echo signal to gate 76. The output of gate 76 may be
conducted to an amplifier 80 for driving one channel of recorder 50
to provide trace 62. Since the shear signals are not analog, but
their absence or presence is being detected, trace 62 could be a
mark channel in which a Schmidt trigger driver (not shown) is
provided to cause a mark to be made on a chart when the output of
gate 76 is present in response to an echo signal. When a mark
appears, switches 60 can be individually opened and closed by the
operator to determine which of the shear wave receiving transducers
received the echo, to locate the boundary zone in which a defect
may be present.
FIGS. 16 and 17 illustrate the time relationship of the main bang
signals (the ultrasonic pulse emitted by the transmitting crystals
in response to the pulsers 74A and 74B) from the various
transmitting transducers and the echo signals received. Also, in
FIG. 15, the generation of the main bang signals is illustrated.
Since the higher the amplitude and the longer the duration of the
main bang signal, the more well defined the echo signal will be,
the avalanche pulsing scheme of FIG. 14 is designed to provide
relatively large amplitude and long duration main bang signals. As
shown in FIG. 16 (the curve of this figure applies to all of the
transducer transmitting crystals), between main bang signals, the
voltage level at the crystals is at a high level, for example 200
volts. When the SCR of pulsers 74A or 74B conducts to shunt the
drive voltage, this voltage mementarily goes to zero and the
crystal rings at its fundamental frequency (for example, 1.6 Hz for
the shear wave transducers and 800 Hz for the longitudinal wave
transducers). The period of ring determines the inspection period
and the crystal voltages slowly return to the 200 level through
their respective voltage paths. This sequence is repeated each 500
u sec. for each of the transmitting crystals. By using a common
drive oscillator for both the longitudinal wave and shear wave
pulsers, synchronism is provided between the two types of
inspection provided for (i.e., longitudinal and shear or
transverse) and these two types of inspection can thus be carried
on simultaneously (at alternate intervals) with the same inspection
equipment.
FIG. 17 illustrates the alternate longitudinal wave and shear wave
inspection, and with the notations thereon is self-explanatory. The
longitudinal wave curve also illustrates the difference in arrival
time of an echo due to a thin wall or a defect (the latter being in
effect a thin wall) at, for example, one of the plate transducers,
as opposed to normal wall. The shear wave curve illustrates receipt
of a defect echo and the shear wave curve under normal conditions
would not show the presence of an echo. Because the shear wave
signals are considerably slower than the longitudinal wave signals,
the arrival time of the shear wave echo is shown as 60 u sec.
whereas the arrival time of the normal thickness longitudinal wave
may be in the order of 12-15 u sec. after main bang. The arrival
time of the echo representing thin plate wall would be something
less than 12-15 sec.
FIG. 18 shows the type of chart readout that can be provided with
the arrangement of transducers described (the example being taken
from actual traces). The movement of the chart paper 50A can be
synchronized with the movement of head 15 along weld W so that when
a defect is encountered, its approximate location can be
determined. For example, the carriage 10 may be moved at a rate of
one foot per second and chart 50A can be moved at a rate of one
inch per second. Since this movement is slow compared to the
repetition rate of the ultrasonic inspection signals, a
considerable amount of redundant inspection is provided for any
area inspected so that the likelihood of missing a defect is small.
Trace 51, representing the condition of the plate adjacent weld W,
is shown as a straight line until an area 90 is reached at which
time lamination 91 (FIG. 11) may be encountered, or a change in
wall thickness adjacent the weld is encountered. A wall thickness
change will generally be noted as a very gradual change whereas a
lamination may be like a sharper change (the actual curve looking
something like a square wave). Of course, in the case of lamination
or other defect, a relative wall thickness measurement is provided
with the echo time proportional to the depth of the defect.
As noted, trace 51 will always represent the least wall thickness
of the plate on either side of weld W, although in the event of
loss of echo signal by one of the receiving crystals of transducers
45 and 46, indicating poor coupling or a small defect that does not
permit an echo signal, the pin causing trace 51 will be driven
against its limit. Trace 53 is an analog representation of the
thickness of the weld bead, or indicating a defect, and the level
53 represents normal thickness, the level 53A represents a
deviation from the normal thickness, and the level 53B a defect,
indicated by measuring the wall thickness from the inside wall,
pipe P to the defect, such as defect 92 in FIG. 11. If something
prevents good acoustical coupling so that an echo does not return,
or if a small defect is present which does not give an echo and
prevents the usual echo coming from the bead, a level 53C may be
provided where the recorder pin making trace 53 moves against the
stop. If, upon checking for reoccurance of the signal, coupling
appears not to be the problem, a defect can be assumed. For
example, in FIG. 18 level 53B correlates in time with a mark on
trace 62 (the slight lag in time being due to the fact that the
transducer 40 sees the defect first) so that a defect such as a
slag inclusion can be presumed. The same is true with mark 53D
shown to correlate with a small mark on trace 62 and lamination 91
in the plate, indicating that the lamination extended right up to
the weld.
Since the shear wave echos are only present when a defect is in or
about the boundary zones of weld W (it being understood that even
the sharply focused shear wave will inspect a small zone about the
point where it is focused), a mark signal on trace 62 is generally
not present, except as noted when a defect such as a crack 93 in
FIG. 11 is present. Such a defect may result in mark 62A the width
of which is proportional to the size of the defect. (This defect
was not recorded by the other inspection transducers so that no
time correlation is shown with traces 51 and 53.) Also, a meter or
light (not shown) can be provided in each of the shear wave echo
receiving channels to further aid in detecting which boundary zone
provided an echo defect signal.
Thus, as can be readily appreciated by reference to FIG. 18, chart
50A, which can be calibrated in feet, can provide a simultaneous
pictorial reprsentation of the condition of the bead of weld W, its
roots, at the adjacent plate, and information concerning their
location and size. Also, the speed of movement of chart 50A is
relatively slow compared to the ultrasonic inspection pulse
frequency so that overlapping is provided between inspected areas
to insure that any point of the weld is adequately inspected.
However, the overall speed of the system is such, with the
arrangement of carriage 10 described, only a few minutes is
required for inspecting the long seam weld on a standard 40 foot
length of pipe.
Also, while a single event trace is disclosed herein for the shear
wave outputs, and this is preferred because it permits easier
interpretation of the chart by relatively unskilled persons, it
would be possible with added recorder cost and complexity to
provide a separate analog trace for each shear wave receiver
output. This may be desirable where a person who is highly skilled
in pipe inspection is interpreting the results. Also, the
sensitivity of the system can be adjusted to suit the type of
person interpreting the results. For example, if he is less
skilled, then low sensitivity, so that only defects are recorded
may be desired, but if he is of higher skill, he may wish to see
smaller irregularities in the weld pattern which are not
defects.
In order to insure that carriage 10 stops automatically when it
reaches the end of a pipe being inspected, and does not fall out of
the pipe, a feeler arm 100 may be pivotally mounted on the front
head 15 to extend forward of the head, as shown in FIG. 1. Arm 100
may be biased towards the pipe wall by a spring (not shown) and a
normally closed micro switch 101 may be mounted on its end so that
when it is against the pipe it is open, and when the switch 101 is
clear of the pipe wall, it will be closed. An electric brake
mechanism may be mounted on one of the wheels 13a and operated by
switch 101 so that when switch 101 is closed, the brake is
activated. Also, if desired, more than one wheel 13a can be driven
(by one or more motors) to aid in traction, particularly since the
inside of the pipe will probably be wet.
Also, a suitable housing 103 may be provided on one end of the
carriage 10 for the mounting of the drive and receiving electronics
(except the recorder electronics) to reduce the number and length
of lead lines to carriage 10.
From the foregoing, it will be seen that this invention is one well
adapted to attain all of the ends and objects hereinabove set
forth, together with other advantages which are obvious and which
are inherent to the apparatus.
It will be understood that certain features and subcombinations are
of utility and may be employed without reference to other features
and subcombinations. This is contemplated by and is within the
scope of the claims.
As many possible embodiments may be made of the invention without
departing from the scope thereof, it is to be understood that all
matter herein set forth or shown in the accompanying drawings is to
be interpreted as illustrative and not in a limiting sense.
* * * * *