Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to testing of metal
structures, and more particularly to methods and apparatus for
detectingand locating faults such as "hard spots" in metal
pipelines.
A hard spot in a metal pipeline wall is a
structure defect which is formed in the pipe during its manu-
facture. For-example, it may be formed by accidental cooling
of a spot on the metal during fabrication of the pipe, e.g.
by cold water splashing onto a hot pipe. In any event, hard
10 spots are a point of weakness in the pipeline structure, and
will deteriorate with age. They are a particular problem in
pipelines conducting natural gas, since they tend to be
attacked by the hydrogen in the gas. Gas-conducting pipelines
frequently operate at elevated pressures, e.g. 1000 psi, and
so faults such as hard spots need to be located, and eliminated,
after the pipeline has been installed above or below ground.
It is known common practice to use a pig for
` detecting faults in pipelines from the inside of the pipe.
The pig is conveyed along the inside of the pipel-ine, e.g. by
20 the gas flow itself. The pig bears a magnetic coil detector,
an odometer and recorder. It measures the magnetic properties
of the pipeline, by inducing a magnetic field in the
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portion of the pipeline being surveyed, and it detects devia-
tions from normal readings of magnetic flux caused by faults
such as hard spots. It records the locations of such faults
and reports them Then it is necessary to unearth and expose
the pipe at the location indicated by the pig, and eliminate
the fault.
As a result of the use of the travelling pig
detector, the operator gets to know the location of a fault
such as a hard spot, to within about a one-foot length of the
pipe. The pig detector is not normally able to pin-point the
fault more exactly than that. Moreover~ it will not indicate
the circumferential location of the fault. It is now neces-
sary to use another detector to pin-point the fault within the
area indicated by the pig.
One form of such detector which is commercially
available is a portable Rockwell hardness tester, which probes
the pipe surface to determine hardness. For this to be used,
the pipe surface must first be stripped of its protective
coating (normally asphalt) and scoured. Such operations,
followed by probing into the metal to determine its hardness,
require the closing down of pressurized flows in the pipeline.
Another form of detector for surveying restricted
surface areas of the pipe, following the use of the pig with
its magnetic induction system, is a gaussmeter, which measures
magnetic properties of the metal. In fact, the gaussmeter
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determines the residual magnetism left in the pipe wall, as a
result of the previous passage of the pig which applied a
magnetic field to the pipe wall. The harder steel of a hard
spot in the pipe gives a greater degree of residual magnetism
than the surrounding steel. Measurements with a gaussmeter
as normally conducted are however imprecise and unsatisfactory.
The gaussmeter is not sufficiently sensitive to operate through
the corrosion-protective asphalt coating of the pipeline, so
that the coating must be removed from the area to be tested.
This entails abrading and scouring of the pipe surface which is
liable to upset the residual magnetic field left in the pipe by
the pig. The magnetic readings given by the gaussmeter are
highly sensitive to variation in the separation between the
magnetic probe on the gaussmeter and the metallic pipe surface.
It is an object of the present invention to provide a
novel apparatus for detecting faults in metal pipes.
According to the present invention, there is
provided a pipe surface testing apparatus comprising at least
two side rail structures adapted to extend axially along the
limited extent of the exterior of a pipe under test;
first and second end pieces fixedly receiving therein
opposed ends of said rail structures, each said end piece
having a lowermost surface adapted to be received against the
outer surface of the pipe under test;
detector mounting means mounted on said rail
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structures and movable therealong, said detector mounting
means extending circumferentially with respect to the pipe to
span the gap between said rail structures;
the lowermost surface of the detector mounting means
presented towards the pipe surface having a plurality of zones
each with a surface location adapted to be spaced an equal
radial distance from the pipe surface when said end pieces are
received against the outer surface of the pipe under test;
a detector assembly, including a sensing means,
movably mounted on said detector mounting means for movement in
a direction transverse to the direction of extent to the rail
structures, and having a mounting position in each zone of the
lowermost surface thereof in which the detector assembly may be
mounted so that the sensing means registers with the surface
location of said zone to be disposed the same radial distance
from the pipe surface in each of the mounting positions;
releasable securing means for releasably securing the
apparatus to the pipe, with the lowermost surfaces of said
end pieces received against the outer surface of the pipe.
By means of the apparatus of the present invention, a
limited section of the pipe surface may be scanned for
imperfections such as hard spots, conveniently and accurately.
The detector assembly, which may include a gaussmeter or other
known form of detector can be moved axially of the pipe surface
by moving the detector mounting means along the rail structures.
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It can be moved circumferentially of the pipe by moving it
along the detector mounting means. A next adjacent section of
the pipe surface can be scanned by releasing the releasable
securing means and moving the entire apparatus to another pipe
surface section. The sensing means of the detector is at all
times positioned the same radial distance from the pipe surface.
The accuracy and sensitivity of the measurements is enhanced,
to the extent that removal of external coatings form the pipe
prior to using the apparatus becomes much less important.
The size of the apparatus is suitably from about 1-4
feet in length, with a rail separation of 4-12 inches. Such an
apparatus can readily scan the pipe section indicated by the
pig as containiny a fault, and speedily pinpoint the precise
location of the previously indicated fault.
In the preferred embodiment of the invention, the
lowermost surface of the detector mounting means, instead of
being curved on a radius corresponding to that of the pipe
surface, has a series of stepped formations, the edges of
- which extend radially to define an edge of the zone. A part
of the surface of each zone lies on a circle concentric with
the cylindrical pipe surface. Then the detector assembly can
be mounted in each zone with an edge thereof against the step
formation, and the sensing means registering with that part of
the surface on the concentric circle, so that the sensing
means is always positioned the same radial distance from the
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pipe surface. Such a structure provides for more positive
positioning of the detector mounting means and consequently
more accurate determination and recording of the precise
location of a surface fault in the pipe. ~oreover, it is
simpler and more economical to manufacture a detector mounting
with an accurately finished stepped lower surface than an
accurately finished curved lower surface.
The lowermost surface of the end piece which is
received against the pipe surface normally constitutes the
lower structural surface of the piece itself. Preferably
however, there are included in the end pieces a plurality of
adjustable levelling screws permitting the apparatus to be
adjusted against the pipe surface to ensure t~at the detector
mounting means for the side rail structures is disposed with
its mounting zones at an equal distance above the pipe exterior
surface. The releasable securing means, which are suitably
flexible buckled straps encircling the pipe, are then tightened
to hold the apparatus firmly against the pipe surface, levelled
or otherwise correctly adjusted by the preset position of the
levelling screws.
Also in a preferred embodiment, one of the side rail
structures comprises a lead screw upon which the detector
mounting means is threadably mounted. The lead screw can be
driven by hand or powered means to rotate it and cause axial
movement of the detector mounting means down the pipe. The
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detector mounting means is suitably slidable along the other
rail structure.
A specific preferred embodiment of the present
invention is illustrated in the accompanying drawings, in which:
FIGURE 1 is a perspective view of an apparatus
according to a specific preferred embodiment of the present
invention, mounted in position on the exterior of a cylindrical
pipe; and
FIGURE 2 is a fragmentary sectional view along the
line 2-2 of Fig. 1.
Fig. 1 shows a portion of a generally cylindrical
pipe 10 with an apparatus according to the invention releasably
fastened thereto. The apparatus comprises first and second
straight, parallel side rail structures 11, 12. The first side
rail structure 11 comprises an elongated bar having a
longitudinal slot 13 therein, presenting an upper smooth
surface. The second s-~de rail structure 12 comprises a side
bar 14 completing the framework of the apparatus, and a lead
screw 15 extending alongside the side bar 14 axially of the
- 20 pipe 10. The ends of the side rail structures 11, 12 are
fixedly received in end pieces 16, 18. Each end piece as an
inner generally rectangular plate 20, 22, respectively
completing a rectangular framework with the rail structure 11
and side bar 14 of rail structure 12, and an outer, smaller
plate 24, 26 respectively, arranged in an upright position on
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the surface of pipe 10 and parallel to one another. Each end
piece 16, 18 is also provided with a respective lower spacer
bar 28, 29 extending across the centre lower part of the space
between the inner and outer plates thereof, and a pair of upper
spacer bars 30, 31 and 32, 33 respectively near the upper
corners of the outer plates 24, 26 and extending between the
inner and outer plates. The lowermost surface of each end
piece 16, 18 is formed by the bottom surface 34 of the inner
plates 20, 22, which as illustrated has three straight portions
angularly disposed with respect to one another. The centre
portion and side portions of this lowermost surface are
received in contact against the cylindrical outer surface of
the pipe 10. Each inner plate 20, 22 is provided with a pair
of adjustable levelling screws 35, 36 and 37, 38 respectively,
threadably received in end formations of the inner plates 20,
22 and protruding downwardly therethrough, so that the
apparatus as a whole can be adjusted as to height on the pipe
surface.
The end pieces 16, 18 are releasably held against
the pipe surface by means of respective flexible straps 39, 40
having buckles 41, 42. The straps 39, 40, pass through the
space between inner plates 20, 22 and outer plates 24, 26 over
the ends of outer spacer bars 30, 31 and 32, 33 respectively,
and under the central spacer bars 28, 29 respectively so that
they releasably tighten the apparatus onto the pipe surface.
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By first adjusting the levelling screws to the desired position
and then tightening the straps 39, 40, the apparatus is held
rigidly in position in the desired location, to permit
measurements to be made using it, on the pipe surface.
A detector mounting means 50 in the form of an
elongated metal block is mounted for movement along the rail
structures 12, 14. ~he end formation 51 of the block 50
passes through and slides along slot 13 in side rail structure
11. At the other endl the block 50 is provided with a screw
threaded housing 52 which is threadably received on the lead
screw 15. The block 50 thus spans the gap between the rail
structures 11, 12. It is provided with a slot 53 which
extends through the block 50 and in the circumferential
direction with respect to the pipe 10. A detector assembly 54
is mounted in the slot 53, this detector assembly comprising
a rod 55, a lower block 56 in the form of a cube, an
elongated sensing means 57 protruding downwardly through the
rod 55 of block 56, to present a sensor 58 extending a short
way below the bottom surface of the block 56. Downwardly
extending protrusions 59 are provided at each of the four
corners of the lowermost surface of the block 56, protruding
downwardly beyond the end of the sensing means 57, to
protect the sensor 58 located therebetween from damaging
contact with the surface of the pipe 10~ The detector assembly
54 also inciudes a washer 62, an upper knob 64 on the top of
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the rod 57 and a coil spring 66 bearing against the washer 62
and the knob 64. Thus by turning the knob 64, the detector
assembly can be clamped in position in slot 54, and released
for position adjustment therealong.
The undersurface of the block 50 is formed in a
series of zones 68 each defined by a stepped side formation 70
at its outer edge, and a flat top surface 72, extending in a
tangential direction with respect to the pipe 10. As shown in
Fig. 2, the centre location of each top surface 72 of the zones
68 is the same distance from the surface of the pipe 10, and
lies on a circle 74 concentric with the pipe surface. When
the block 56 is mounted in each zone, with its side abutting
against step 70, the sensor 58 registers with the centre
location of the zone. The arrangement of steps 70 thus
provides for positive location of the block 56 and sensing
means 60 in each zone, with the sensing means 60 spaced the
same distance from the pipe surface in each zone. Suitably,
the sensing means is spaced about 1/4" from the pipe surface.
A motor 76 e.g. an electric motor is mounted on the
- outside end of end piece 16, spaced therefrom to allow passage
of strap 39. The end of the lead screw 15 is journalled in
- end plate 20 of end piece 16, and is received in driving
engagement with motor 76, so that the lead screw may be
rotated therewith. At its other end, beyond end plate 22 of
end piece 18, the lead screw is received in a rotation counter
such as a Helipot (trade mark~, to sense and record the
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position of the threaded housing 52 of the detector mounting
means 50 therealong. This information is electrically fed from
the Helipot to a suitable recorder, e.g. an X-Y plotter, along
with other information received from the sensor, to give a
plot of readings for assistance in identifying the precise
location of an anomaly on the surface of the pipe 10.
The operation of the apparatus of the~invention will
be apparent from the foregoing de~ription and drawings. By
movement of the detector assembly 54 in slot 53, the area
within the rail structures 11, 12 and end frames 20, 22 can be
surveyed by sensor 58, and accurate readings of its
characteristics can be obtained. Then the releasable straps
39, 40 can be loosened and the apparatus moved to another
location on the pipe surface to repeat the operation. Once a
conventional moving detector such as a pig has recorded the
presence of a fault within a certain short length of the pipe
the apparatus according to the invention can be readily used
to pin-point the fault. The readings obtained using the
apparatus of the invention are accurate and reliable, since the
sensing means is positively positioned at precise locations,
and ensured to be mounted the same distance from the pipe
surface at each test location. The need to scour, abrade and
clean the exterior pipe surface is substantially reduced. The
apparatus is small and readily portable, and at the same time
simple but efficient to use.
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112~7
Whilst a specific preferred embodiment of the
invention has been described and illustrated in detail, it
will of course be understood that this is illustrative and by
way of example only and should not be construed as limiting.
Variations thereof will be apparent without departing from
the scope of the invention. The scope of the invention is
limited only by the appended claims.
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