Note: Descriptions are shown in the official language in which they were submitted.
CA 02415067 2010-05-27
A PIG FOR DETECTING AN OBSTRUCTION IN A PIPELINE
Background of the Invention
The present invention relates to an obstacle monitoring pipeline pigs used in
checking the interior of a pipeline for obstacles which might impede the
movement
of subsequently used pipeline inspecting devices or which exceed industry
guidelines.
A number of caliper pigs are on the market that provide detection of
anomalies inside pipelines. They are usually expensive to produce and operate.
These existing pigs monitor all restrictions along a pipeline regardless of
the size of
the anomalies. They normally collect a significant amount of data that
requires
interpretation by a technician or computer programs. This type of caliper pigs
is
represented, for instance, by the disclosure of US Patent 4,953,412 and
5,088,336 (both Rosenberg et al.) and also by US Patent 3,755,908 (VerNooy).
US Patent 4,481,816 (Prentice) describes a caliper pig provided with a
monitoring arrangement comprising a substantially circular array of detecting
portions which deform upon contact with the interior surface of the pipeline
and
remain deformed to provide an indication that the minimum radial distance has
been
exceeded. Viewed from the standpoint of the present invention, the device
disclosed is of a relatively complex structure and allows only a single use of
the
detecting portions. Also, if a relatively large deformity is encountered prior
to
reaching a somewhat smaller deformity, the latter may be undetected.
US Patent 4,227,309 (Jones) describes a pipeline pig which includes a
flexible disc at a foremost part of the body. The disc is fixedly secured to
the body
of the pig and is provided with strain gauges which transmit deformations of
the
disc to electrical impulses to show which portion of the disc has been
deformed by
an abnormality within the pipeline. The use of the strain gauges renders the
overall
structure of the flexible disc complex thus increasing the cost of replacement
of a
damaged disc. Furthermore, the strain gauges are too sensible for the rough
working environment of a damaged pipeline and may therefore produce false
readings. The piezo electric strip was found working as a microphone; it
recorded
all vibrations and one could not differentiate between the vibrations and
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restrictions. Vibrations of the body and thus of the disc are often
encountered in
use of the pig. There is no backup system which would indicate, at least
roughly,
the location of an abnormality in case of failure of the electronic system.
The
location of the disc at the foremost end of the body is disadvantageous as
distorted
readings of the deformation of the disc by an abnormality occur at a straight
portion
of the pipeline and in bends of the pipeline. Also, the disc being fixedly
secured to
the body, it cannot maintain the same angular clock position as it inevitably
changes such position with the rotation of the pig about its longitudinal
axis. Such
rotation may occur when an abnormality is encountered by the guiding cups. The
device therefore is not capable of showing the clock position of an
abnormality
instantly recorded.
US Patent 4,299,033 (Kiley et al.) presents a calipering tool for oil wells or
the like applications. It operates with a plurality of feelers which are in a
constant
contact with the pipe of a well. The tool is of a complex structure. While it
may be
useful in calipering wells, it is not suitable for applications where only
major
deformities of the pipe are required to be discovered to avoid damage to a
subsequently used caliper pig. Also, the tool of this reference is raised and
lowered
by means of a suspension cable which cannot be used in pipeline calipers as
they
often have to travel long distances of tens of miles.
US Patent 4,443,948 (Reeves) describes a pig for monitoring the internal
surface profile of a pipeline. It is provided with a plurality of sensors
which are in
constant contact with the inner surface of the monitored pipeline. A complex
system is required to compare output signals from the sensors with an expected
value and reference signal generated when they differ by more than a
predetermined amount.
US Patent 4,457,073 (Payne) shows a pipeline pig with sensing means
capable of monitoring small changes in the internal configuration of a
pipeline. A
complex mechanism is used to monitor dragging effect to which an elastomeric
cap
is submitted upon encountering an obstacle. A major obstacle would most likely
destroy or at least damage the mechanism used to record the deformities, as
the
radial cup is in a constant contact with the interior of the monitored
pipeline.
US Patent 4,098,126 (Howard) is provided with a plurality of sensors
disposed about the circumference of a resilient holding cup. A spring system
forces
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the sensors against the inside of the pipeline. The device is suitable for
monitoring
relatively small deformities but would become damaged if a major or sharp
deformity is encountered. It is of relatively complex structure with a number
of flat
spring elements constantly pressing the sensors against the pipeline.
US Patent 4,091,678 (Potter) shows a device for detecting dents or out of
round conditions of a buried pipeline. The pig contains two concentric rings.
The
outer ring is sized to accurately fit the inspected pipeline. It carries on
its inner
surface electrical contacts adapted to co-operate with contacts provided on
the
outer surface of the inner ring to close an electric circuit when the outer
ring is
deformed radially inwardly. The device may be suitable for detecting minor
anomalies of the cross-section of the pipeline. Larger deformities would
destroy or
at least damage the system of coaxial rings.
My Canadian Patent Application No. 2,261,542, published August 18, 1999,
presents an improvement comprising a mechanism wherein the deformation of a
resilient disc-shaped member is transmitted by a linkage to an axially
moveable slide
which operates a switching mechanism. While this structure is believed to
present
an improvement over the above prior art in that it provides a simple
structure, it
requires an additional disc registering scratches caused by anomalies in the
pipeline.
Since both the disc-shaped member and the additional disc rotate in common
with
the body of the pig about the axis of the pipeline as the pig travels through
the line,
the accurate determination of the location of the anomaly circumferentially of
the
pipeline cannot be achieved.
Summary of the Invention
It is an object of the present invention to provide an obstacle monitoring or
caliper pig which would be of a simple structure permitting relatively low
manufacturing costs, monitoring only major obstacles of a predetermined
minimum
magnitude and providing a simple operation and indicating the location of the
obstacles with an improved accuracy.
The present invention is generally characterized by a combination, wherein
a detector, particularly for use in a caliper pig for detecting an obstruction
in a
pipeline, is provided. It comprises, a resiliently deformable body including a
securement portion adapted to be secured to a support, and a flexing portion
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spaced from the securement portion and adapted to flex relative to said
support
when subjected to a force in a predetermined direction;
said body comprising
a resiliently deformable first member having
a leading face and a trailing face and
a resiliently deformable second member having
a leading face and a trailing face;
the trailing face of said first member being turned toward the leading face of
said
second member;
the distance between the trailing face of said first member and the leading
face of
said second member being at a predetermined minimum when the body is in a
relaxed state;
signal generating means disposed in said flexing portion of the body and
remote
from said securement portion thereof,
said signal generating means comprising:
a first generating element secured to said first member; and
a second generating element secured to said second member in an
alignment with the first generating element when the body is in a
relaxed state;
said first and second generating elements being adapted to co-operate to emit
a
first signal when the elements are close to each other, and a second signal,
distinct
from said first signal, when the elements are remote from each other due to a
difference between the degree of flexing between the first and second
deformable
members.
Brief Description of the Drawings
The invention is described in greater detail with reference to the attached
simplified, diagrammatic, not-to-scale drawings, it being understood that
while
these are presently preferred embodiments, they may be modified to a
substantial
degree without departing from the gist of the present invention. In the
drawings:
Figure 1 is a simplified section view of the pig of the present invention;
Figure 2 is a simplified, diagrammatic view taken in the direction of arrows 2-
2
of Fig. 1;
Figure 3 is a view of mutual arrangement of a sensor spring relative to the
detector surface;
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Figure 4 is a view of an exemplary embodiment of the structure of a sensor
spring of the present invention;
Figure 5 is a section view of another embodiment of the present invention;
Figure 6 is a detail of the embodiment of Fig. 5 showing the sensor in an
operative position when encountering a relatively small irregularity of
the pipeline;
Figure 7 is a view similar to that of Fig. 6 showing the sensor at the initial
stage of encountering a larger irregularity; and
Figure 8 is a view similar to that of Fig. 6 at the stage following the
initial
contact of Fig. 13, with the sensor in an actuated state.
Detailed Description
The inventive pig comprises a pair of front and rear resilient guide rings 60,
61. The front ring 60 is secured to a tubular body 62 having an axis L of
elongation, by way of a front end cap 63 threadably engaging a threaded
portion
64 projecting from a plug 65 which is fixedly secured, by welding or
adhesively, to
the inside of the tubular body 62 at the front end thereof. The front end cap
63
holds the front ring 60 between an inner front flange 66 and an outer front
flange
67. The inner front flange 66 is fixedly secured to the front end of the
tubular body
62. Thus, the outer front flange 67, the front ring 60 and the cap 63 are all
fixedly
secured relative to the tubular body 62.
Similarly, the ring 61 is secured to the tubular body 62 by way of a rear end
cap 68 threadably engaging a threaded portion 69 projecting from a rear plug
70
which is fixedly secured, by welding or adhesively, to the inside of the
tubular body
62 at the rear end thereof. The rear end cap 68 holds the rear ring 61 between
an
inner rear flange 71 and an outer rear flange 72. The inner rear flange 71 is
fixedly
secured to the rear end of the tubular body 62. The outer rear flange 72, the
rear
ring 61 and the cap 68 are thus all fixedly secured relative to the tubular
body 62.
A tubular mandrel 73 is mounted for a free rotation on the body 62. The
mandrel 73 rotates on bushings 74, 75. The bushings also prevent axial
displacement of the mandrel 73 relative to the body 62. The mandrel 73 is also
freely rotatable relative to the inner front flange 66 and the inner rear
flange 71 and
their associated assemblies of the front and rear rings 60, 61.
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Welded to the lower exterior of the mandrel 73 is a tubular member 76 with
screwed sealed cap 77. The tubular member 76 has two functions: it houses a
recording system and at the same time provides ballast which maintains the
freely
rotatable mandrel 73 in a position shown in Fig. 1, regardless of the actual
instant
position of the discs 60, 61 and the tubular body 62 fixedly secured to them.
The
tubular member 76 is thus maintained at a downward, essentially 6 o'clock
position
when viewed axially relative to the mandrel 73. As a result, all portions of
the face
of a disk-shaped detector 78 are maintained at all times at a generally
constant
position with respect to a fictitious vertical reference plane coincident with
the axis
L.
The resilient disc-shaped detector 78 abuts against a plate or shoulder
portion 79 which is fixedly secured relative to the mandrel 73 by a weld 80 to
the
mandrel 73. The rear surface of the plate detect
or 78 abuts a circular plate 81 which, in turn, abuts an annular spacer member
82.
At the opposite end of the spacer member 82, a plate 83 sealingly encloses the
interior of an annular cylindric chamber 83a disposed between the radially
outer
surface of the spacer member 82 and an outer annular wall 83b. The entire
chamber 83a, the spacer member 82, the rear annular plate 81, the plate
detector
78 and the front annular plate 79 welded to the mandrel 73 are fixedly secured
to
each other and thus to the mandrel 73 by a series of bolts 84. The bolts 84
are
disposed at a uniform circumferential spacing about the above members and pass
through bolt passages 84a (Fig. 2).
The portion of the disc 78 radially outwardly of the plates 79, 81 is
generally
referred to as a flexing portion of the detector 78.
L-shaped springs 86 made of a commercially available spring steel of about
1/16" have each an axial arm 87 and a radial arm 88 adjoining each other at a
coiled central section 89 at an angle, in the embodiment shown, a right angle.
The
central section 89 has about 3 - 4 coils. The axial arm 88 is provided at its
free end
with a coiled support section 95. Both arms are resiliently flexible.
Each spring 86 is pivotable, at the central section 89, relative to the plate
81
about an associated pivot pin 94 passing through the central section 89 and
projecting to both sides thereof. Each pivot pin 94 is held in place by a
short,
tangential groove 96 (Fig. 3) machined in the face of the annular rear plate
81
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turned towards the disc detector 78. The opposed ends 94a, 94b of each pin are
pressed against the resilient surface of the detector 78 and are thus held in
place.
In other words, each spring can swing within a respective plane defined by the
L-
shape, i.e. a plane parallel with (in the embodiment shown, generally
coincident
with) the axis-L of the mandrel 73. The springs 86 are evenly
circumferentially
spaced with respect to the disc 78 as best seen in Fig. 2. It will be
appreciated that
the coincident arrangement with axis-L is not absolutely necessary even though
it
is preferred.
Each axial arm 87 is provided at its free end with a permanent magnet 90
held in place by the respective support section 95. Assigned to each magnet 90
is
a magnetic position switch 91. In the embodiment of Figs. 1 and 2, a magnetic
position switch commercially available under the trade name Hamlin has been
proposed. As is known, the magnetic position switch 91 is located in a non-
magnetic envelope fixedly secured to the surface of the annular spacer 82. The
non-magnetic envelope can be made from a number of suitable materials for
instance from stainless steel, aluminum or a thermoplastic material. In many
applications, the magnetic sensors are grouped depending on the accuracy of
indication of the pipeline anomaly required.
Figures 2 and 3 show that the radial arms 88 of springs 86 are evenly
spaced around the detector 78. The radial arms 88 are each located in an
associated groove 92 milled into the face of the disc 78. The grooves 92
terminate
short of the edge of the disc 78. The remaining portion from the radially
outer end
of grove 92 to the edge on disc 78 contains a radial hole 97 (Fig. 3). Free
end
portions 93 of the radial arms 88 of the springs 86 are each inserted into a
respective hole 97. The holes co-operate with the pivots 94 to keep the radial
arms
88 of springs 86 secured to and generally flush with the surface of the disk
78 at
all times.
Figure 2 further shows that, in the embodiment described, the grooves 92
or the free end portions 93 divide the entire circumference of the disc 78
into
twelve segments. They have each a predetermined arc and length of its chord.
In
the embodiment of Figure 2, the arc and thus the length of the chord is the
same
in each segment.
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While this arrangement is preferred in most applications, it can be modified
to two or more different arcs of the segments.
There are twelve switches disposed about the circumference at slightly
counter-clock wise offset locations in which the XII o'clock point is offset
counterclockwise by 151 so that the uppermost point of the circle is between
the
XII o'clock and I o'clock position.
If it is desired to find out only whether a particular obstacle is in the
upper
or lower part of the pipeline, then only two groups of the signal developing
switches are required of the usual twelve switches. In case of twelve switches
disposed about the periphery of plate 81 and offset as described, a group of
switches at the offset X, XI, XII, I, II and III o'clock positions would serve
in
determining an anomaly in the upper part of the pipeline, while switches in
the IV,
V, VI, VII, VIII and IX 'o clock position would transmit a signal
corresponding to the
anomaly in the lower part of the pipeline. If a more detailed indication is
required,
more groups, each having a fewer number of switches, would be grouped or each
switch would indicate anomaly at its position about the circumference of the
pipeline. Customers normally specify their requirements concerning the
accuracy
required.
In operation, the pig is propelled through an associated pipeline in a fashion
as already described. When an obstacle is encountered, a segment of the disc
78
becomes deflected in the direction D shown at the bottom of Fig. 1. Assuming
that
the detected obstruction is at the lower part of the pipeline, the radial arms
88
follow the local deflection of the disc raising the axial arms 87 of the lower
springs
86 at the offset 6 and 7 o'clock positions to bring the associated magnets 90
into
contact with the magnetic sensor switches 91. The sensing switches 91 then
transmit electric signal to a conventional electronic recording device located
within
the tubular member 76. This is effected by leads, not shown; passing through
passages 98 in the disks 81, 78 and 79.
The springs 86, holding each a magnet and the annular spacer 82 holding a
plurality of magnetic switches 91 can also be generally referred to as
transmission
devices comprised of a first transmission member and a second transmission
member. In the embodiment described the spring 86 functions as the first
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transmission member. The spacer 82 of the embodiment described is an example
of a second transmission member. It will be understood that the particular
embodiment described is not the only one readily conceivable and that the
functions
can be easily reversed. The designation of the transmission members as first
and
second is therefore to be understood as a general definition of the two and
does not
necessarily refer to which of the members carries the magnet 90 and which
carries
the switch 91. For the same reason, the term "first support portion" of the
embodiment shown is designated as the one carrying permanent magnet while the
"second support portion" of the second transmission member carries the switch,
it being understood that this function can readily be reversed. Therefore the
above
general terms must be interpreted in their general meaning and not to be
limited to
their meaning with respect to the embodiment disclosed.
The sensing switches, their leads (not shown) passing through one or more
passages 98 to the recording device in the tubular member 76 and the recording
device itself do not form a part of the present invention and are therefore
not
described in detail. They are comprised of commercially available components.
Fig.5 shows an improvement of the embodiment of Fig. 1. The improved
embodiment presents a substantially simpler and thus less expensive structure
and
an improved reliability in operation.
The front and rear carrying guide rings 60, 61, the mandrel 73 rotatable on
the elongated body or carrier 62, and the tubular member 76 secured to the
lower
portion of the mandrel 73, are identical in structure and function with the
embodiment of Fig. 1 and are therefore referred to with the same reference
numbers.
In Fig. 5, the resilient, disc-shaped detector body 178 has a different,
substantially simplified structure. The detector is provided with two
coaxially
arranged, resiliently flexible discs 179, 180, each having a resiliently
flexible outer
portion and, preferably, with an intermediate scratch indicating layer 181.
The disc
179 presents an embodiment of what is referred to as "a first member," the
disc
180 as "a second member" or vice-versa. In the embodiment shown the layer 181
is a thin sheet of plastic material cut into a disc-like configuration having
the same
diameter as the rear or trailing disc 180, as viewed from the standpoint of
direction
D in which the pig advances through the pipeline. The diameter of the trailing
disc
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180 is, preferably, but not necessarily, larger than that of the leading disc
179. The
layer 181 is sandwiched between the leading disc 179 and the trailing disc
180.
The assembly of discs 179, 180, 181 is fixedly secured to the mandrel 73
by a pair of opposed flanges 182, 183 presenting and embodiment of what can
generally be referred to as "a support of a securement portion." The flanges
are
welded or otherwise fixedly secured to the mandrel 73, generally as in the
previously described embodiment. The bolts 184, disposed at a uniform
circumferential spacing, secure the discs much in the same fashion as in the
previously described embodiment.
Thus, the assembly of discs 179, 180 and 181 is freely rotatable about the
axis L by virtue of its securement to the freely rotatable mandrel 73. Viewed
from
the standpoint of direction D, each disc 179, 180, has a leading face and a
trailing
face.
Embedded in the leading disc 179 near its trailing face 185 is a series of
equidistantly circumferentially spaced apart permanent magnets 186. Similarly,
there are embedded in the trailing disc 180 near its leading face 187,
equidistantly
circumferentially spaced apart magnetic switches or sensors 188 which are
aligned
each with one of the magnets 186. Each pair of the magnet 186 and sensor 188
presents an embodiment of an electronic signal generating means, wherein the
magnet and the sensor forms a first and a second electronic signal generating
element or vice-versa.
The switches or sensors 188 co-operate with the magnets 186 in a fashion
similar to that of the previously described embodiment of Fig. 1. That is to
say,
when a respective magnet 186 is at a close proximity to its associated sensor
188,
the sensor 188 is activated to emit a first signal communicated by the
respective
lead 189 to a conventional recording device located in the tubular member 76.
The
close proximity between the magnets and the sensors 188 exists when the two
discs 179, 180 are in a relaxed state shown in Fig. 5.
As shown in Figs. 6 - 8, when an obstruction is encountered, as the body 62
advances in the direction D, the close proximity of one or more of the sensors
188
with their associated magnets 186 is disturbed causing a change in the
electronic
signal.
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The sensors 188, the magnets 186 and the recording device located in the
tubular member 76 are all commercially available items. Their particular
design does
not form a part of the present invention and therefore is not described in
detail.
Turning now to Fig. 6, a situation is depicted where a relatively small
obstruction 190 has been encountered by the pig traveling in the direction D.
At a
position shown, the obstruction 190 protrudes into the inside of the pipeline
at a
radius (measured from the axis L) which is larger than the radius of the
leading disc
179 but smaller than that of the trailing disc 180. Therefore, the leading
disc 179
passes by the obstruction 190 maintaining its relaxed state. As a flexing part
of the
trailing disc 180 encounters the obstruction 190, it is subjected to an axial
force
directed opposite to the direction D. The opposite force is also referred to
as "a
force in a predetermined axial direction." The flexing part of the trailing
disc 180
flexes rearwards as shown in the drawing. This flexing causes disturbance of
the
relationship between the respective pair comprised of the magnet 186 and the
associate sensor 188. As a result, a second electronic signal, different from
the
first signal, is communicated to the recording device in tube 76. The position
of the
disturbed arrangement is also recorded since the ballast, formed by or secured
to
the tube 76 maintains a position of the tube 76, vertically aligned with the
axis L.
In Fig. 7 a larger abnormality 190 has been encountered which reaches into
the pipeline at a radius smaller than either of the two discs 179, 180. At the
outset, both discs flex rearwards as shown. The magnet or magnets 186 remain
at a close spacing from the associated sensor 188. However, as shown in Fig.
8,
as soon as the leading disc 179 passes the obstruction, it springs forwards to
a
relaxed state while the trailing disc 180 remains flexed thus disturbing the
close
arrangement between the magnet 186 and the associated sensor 188 again
resulting in a change of the electronic signal.
The presence and radial position of the abnormality 190 can be double
checked upon eventual examination of the scratches caused by the abnormality
190 on the leading surface of the scratch disc 181 which, preferably, is a
thin,
separate disk from plastic polyethylene.
In an exemplary embodiment suitable for a pipeline having a 20" ID, the
outside diameter of the large, (in the embodiment shown, trailing) disc 180
would
be about 191/2" and that of the small diameter, leading disc 179 would be
about
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19". The thickness of each disc is about 3/4". The discs 179, 180 are each
preferably integrally formed but an embodiment wherein they would be
subdivided
into a plurality of independently flexing segments with aligned pairs of
signal
generating devices may also be feasible under certain circumstances.
Those skilled in the art will readily appreciate that many equivalent
arrangements to those described may exist. For instance, the disposition of
the
magnets 186 and the sensors 188 can be reversed and does not even have to be
uniform but may alternate within one of the two discs with an appropriate
modification of the other disc. While it is preferred that the trailing disc
180 have
a diameter larger than that of the leading disc, the arrangement is optional.
The two
discs may also have generally the same diameter. In an extreme, not
recommended, the disc 179 could even have a larger diameter than of the
trailing
disc 180.
The flexing portion described is a disc. However, an equivalent arrangement
could be made in an embodiment where the disc would be replaced by a plate or
a strip where the checkup of a generally planar surface is required. Even in a
pipeline monitoring arrangement, a system of several independent strips, each
having a leading flexing portion and a trailing flexing portion, could be
used, while,
obviously, the disc-shaped arrangement is preferred for its simplicity.
It is also well know that other, equivalent systems producing electronic
signal
suitable for use in the mechanism of the present invention are commercially
available.
Accordingly, many different modifications of the overall arrangement of the
monitoring pig of the kind disclosed can be made which may depart from the
embodiments described without departing from the gist of the present
invention.
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