Note: Descriptions are shown in the official language in which they were submitted.
2d'~~ODC
FIELD OF T~iE INVENTION:
The present invention relates to a pipeline weighting device.
More particularly, the present invention relates to a device for
countering post-installation buoyant displacement forces that may
undesirably effect a pipeline emplacement, particularly in
subterranean emplacements.
BACKi~ROUND OF TI3E INVENTION:
Pipeline emplacements are often subject to various forces, such
as hydrodynamic and hydrostatic forces, for example, which can
manifest in the displacement of the pipeline from its originally
installed position. consequential pipeline rupture can have adverse
environmental and financial repercussions.
Responsible pipeline companies and contractors are committed to
installations whose designs provide for a high margin of design
tolerance over and above any purely structural requirement for
pipeline weighting. This abundance of caution is intended to offset
the catastrophic potential attached to taking unwarranted risks that
might lead to displacement and consequential pipeline damage,
including service interruption, and environmental damage.
To that end, the traditional, and still predominating practice
in the industry, entails weighting the pipeline with massive concrete
weights. Earlier designs include clamp-on-weights of various
descriptions, as well as the more typical large pre-cast concrete arch
structures that are arranged in bridging relation over top of the
pipeline. These latter mentioned designs are currently the most
widely-used. At the same time, they are expensive to fabricate,
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transport, entail labour intensive installation practices, and
generally require increased trench depth and width dimensions in order
that their installation can be properly accommodated. Current
thinking in the relevant art is that even though these weights are
very expensive, the protection they afford in terms of securely
anchoring a pipeline more than offsets their associated materials and
installation costs, once consideration is given to the repair and
clean-up costs that could ensue in the event of any breech, or
rupture, such as might otherwise be attributable to shifting of an
unweighi:ed, or improperly weighted pipeline emplacement.
Although such weights might be used in any number of situations,
they appear most commonly in in-ground installations. In subterranean
pipeline emplacements, the problem of pipeline leakage is, (from the
point of view of precisely locating the problem, rapidly containing
spillage and repairing any damage), most acute. Underground
emplacements are also susceptible to hydrostatic forces, which can
cause the pipeline to be displaced from the position it occupied when
originally installed, possibly leading to such a rupture or breech.
With this in mind, it will be readily appreciated that subterranean
emplacements are quantitatively demanding, if not qualitatively
exceptional from the point of view of pipeline weighting in such
emplacements.
dne proposed alternative for dealing with the problem of
maintaining the positioning of a pipeline within a subterranean
emplacement is disclosed in US patent 3,170,663 - Fite. This patent
discloses an anchoring device for a pipeline, which incorporates an
arcuate collar that is secured in straddling relation about the upper
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exterior surface of the pipeline. The collar is held in tensioned
relation against that surface by a laterally spaced apart pair of
anchoring rods having spiral flights thereon that extend beyond the
under surface of the pipeline are adapted to positively engage the
underlying soil substrate on either side thereof.
Another proposal entails the use, in muskeg environments, of
simple two-dimensional sheets of a fabric that are intended to be
deployed in a pipeline trench, overlaying the installed pipeline.
Backfill is then layered over the fabric in the hope that the
collected "unit weight" of the resulting overburden will be sufficient
to counter any buoyant forces that local ground water might exert on
the pipeline. Resort to this approach has been entertained only when
alternatives are simply not available, (ie in remote muskeg areas).
Moreover, there is a risk that ground water flows will displace some
of the "unit weight" of the "disturbed" backfill from above the
pipeline. This would be a particular problem in areas where ground
surface contours or the grading of the emplacement or a non-level
transit of the pipeline, might result in either or both surface and
ground water flows that could be channelled within the fabric, almost
in the manner of an artificial canal.
There remains a need in the art to reconcile the necessity of
anchoring pipelines for the purpose of avoiding or reducing the impact
of some of the problems set out above, with the apparently
antithetical desire for any reduction in the high costs heretofore
associated with the practices that the industry has been willing to
embrace.
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S~Y OF TIE INVENTION:
In accordance with one aspect of the present invention, there is
provided a conduit weighting device comprising containment means
adapted to supportingly receive therein a superposed charge of ballast
material having an associated unit weight. The superposed ballast
material is received in contained relation within an enclosure that
is circumscribed on all sides by upwardly extending walls of the
containment means. These walls are adapted to retainingly confine the
ballast charge between them. The containment means is adapted to be
positioned in saddling, superposed relation over a conduit of one
description or another, to thereby at least partly counter
displacement forces that might otherwise effect the positioning of the
conduit.
The confinement of the ballast in the manner provided for in
accordance with the above, is important to the reliability of the
present device. Were the ballast otherwise unconstrained in any
material way, then sloping or a wash-out of a loose ballast, might
seriously erode any margin of safety that had been contemplated in the
unit-weight design parameters associated with an emplacement.
Clearly, such a possibility would not be even remotely acceptable to
an industry which has historically gone to great lengths and expense
to ensure against risks of that type.
The present invention finds application, inter alia, in
connection with subterranean emplacements. In such environments
buoyant hydrostatic forces might tend to ~~float~~ a trench-installed
conduit, notwithstanding any countervailing influence of backfill
overburden. In addition, the current of any hydraulic flows
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associated with the local ground water, might also encourage the
conduit to be displaced from its intended location.
Preferably the walls are particularly adapted with a view to
providing substantial isolation of the ballast charge from external
hydraulic flows. This is particularly significant in situations were
any substantial proportion of the unit weight of the ballast comprises
other than coarse mineral materials. Finer materials otherwise might
be carried off under the influence of any significant hydraulic flows,
thereby diminishing the unit weight of the ballast, and opening the
door to the possibility that a ground water buoyant effect might
exceed the ability of the remaining ballast to resist the anticipated
conduit displacement forces.
Moreover, when unconsolidated material is relied upon to secure
a conduit emplacement, the unit weight which actually acts to secure
the conduit in place is limited primarily to the mass of the vertical
overburden and the mechanical shear characteristics thereof.
Accordingly, in situations of the type wherein a vertical overburden,
such as trench backfill for example, is relied upon to hold the
conduit in position, a certain minimum height of overburden,
(typically specified in the art as a ~~unit weight's parameter of any
particular overburden material), is required to deal with any
anticipated displacement forces. In accordance with the present
invention, however, the unit weight of an enclosed but otherwise
unconsolidated ballast material can be made to bear on the conduit in
resisting displacement thereof, without necessarily having the ballast
material arranged vertically above the conduit. The emplacement in
such situations, therefore need not necessarily be as deep when the
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present invention is employed.
While the present invention is not necessarily constrained in its
application to any particular type of conduit, it is nevertheless
especially valuable in connection with pipelines, and in particular
with. petroleum, petrochemical, or other chemical pipelines.
In accordance with an especially preferred form of the present
invention, at least the walls of the containment means are formed from
a flexible material. Related advantages ensue to an even greater
degree in embodiments of this aspect of the invention, wherein the
entirety of the containment means is formed from such a flexible
material.
More particularly, advantages related to this aspect of the
present invention include the fact that such embodiments are
relatively inexpensive to manufacture, yet can be produced from
suitably durable materials. Naturally, the selected material should
stand up well to subterranean conditions associated with in-ground
pipeline emplacements, and other environmental effects to which any
other particular application might lead them to be exposed. While any
number of appropriately environment-stable materials will undoubtedly
occur to the person skilled in the relevant art, examples of such
include heavy gauge polymer products such as, by way of example only,
polypropylene, polyester or nylon fabrics. Moreover, the resulting
devices tend to be both lightweight and compact. They can be mass-
produced, and stored without consuming undue amounts of storage space,
and the production lead time required for making them available in
commercial quantity is relatively short, thereby easing a logistical
constraint that heretofore has always been a concern in organizing
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pipeline laying and repair projects.
Not the least of the advantages of such a flexible device lay in
the fact that it can be made from a unitary fabric web adapted to be
formed into containment means, wherein portions of the web correspond
to respective wall portions adapted to be mutually secured in
enclosure defining relation. Upon erection the assembled web forms
the containment means whose plurality of walls in turn define an
enclosure for receiving ballast material in the manner already
elaborated upon herein.
Where stitching is utilized in the construction, a
predetermination of the anticipated loading to which the stitched
seams will be exposed should be undertaken. This is well within the
extant skill in the present and related arts, having regard,
generally, for the teachings herein contained.
Various pieces of hardware may be usefully employed in
combination with the present invention, to facilitate filling, and/of
handling of the device according to the present invention. Grommets,
for example, can be advantageously employed in a manner such as that
set forth in greater detail elsewhere herein.
Use of flexible materials in accordance with the practice of one
general aspect of the present invention allows for the weight of the
contained ballast, in a quantum predetermined by buoyancy offsetting
design criteria, to be borne other than by the top of the pipe. The
mass of material in the side portions of the containment means (as
might by analogy be referred to as "saddle bag" portions), need only
be exerted on the top of the pipeline in response to buoyant
displacement forces. In this sense, the present system is dynamically
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responsive to the amount of buoyancy the water exerts. In the absence
of buoyant displacement forces, the pipeline only need bear the unit
weight of the vertically immediate overburden. Moreover, and perhaps
even more importantly, the flexibility of the containment means allows
for installation to be less exacting a procedure than it might
otherwise have been when the prior art cast cement arches were
employed. With the old cement arches too high a placement could
result in the pipeline being suspended in an unweighted condition
beneath the casting. On the other hand pipeline damage could ensue
if all of the castings weight were crushingly borne on the pipe line
during installation.
The flexible character of the preferred embodiments of the
present invention, render the containment means operably responsive
to the application of extrinsic containment-means shaping forces, to
conform the containment means to a desired external shape in response
to how those forces are applied. With the present device situated in
a pipeline emplacement, the walls flexibly conform with the supporting
surfaces of the underlying or adjacent surfaces of the pipeline,
primarily according to the dictates of gravitational forces acting on
the ballast material contained within the device. Of even greater
significance, however, is the fact that the devices polymorphic
character can be selectively utilized to control the conformation of
the device during the filling and installation operations. In an
especially preferred form of this aspect of the present invention,
control and lifting straps are used to effect and maintain a
predetermined, general conformation during and following the
introduction of ballast, to facilitate installation of the device
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within the emplacement. Once the lifting and control straps are
relieved, with the device duly positioned within the emplacement, the
device relaxes and takes up the above mentioned straddling relation
over and around the adjacent pipeline surfaces. In accordance with
the teachings of the present specification, it will be appreciated
that these straps can be seen in retrospect, to have a functional
similarity to the lines used by puppeteers to control their
marionettes. The straps may be fixedly attached to the containment
means. In one alternative there might only be points of attachment
on the containment means, each adapted to enable a contractor to
removably secure some conformational control means (be it a strap or
otherwise), to the containment means for the above described purposes.
These, or for that matter any convenient functionally fungible device,
can be used to facilitate the quintessential purpose thereof, namely
controlled selective shaping and posturing of the containment means
through the application of forces at selected points thereon.
It will, of course, be appreciated that an internal frame
assembly could be used, for imparting a predetermined conformational
structure to the flexible containment means contemplated herein.
DETAILED DESCRIPTION OF THE INVENTION:
INTRODUCTION TO THE DRAWINGS:
Over the course of the description of the present invention
that follows below, reference will be made to the appended
drawings, in which:
Figure 1 is a transverse sectional view taken through a
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subterranean pipeline emplacement depicting the application of
a pre-cast pipeline weighting device, typical of those employed
in prior art pipeline emplacements;
Figure 2 is a comparable, transverse sectional view through
a subterranean pipeline emplacement depicting the application of
a device according to the present invention;
Figure 3 depicts a preferred form of a device according to
the present invention; and,
Figure 4 is a perspective view of a portion of the device
depicted in Figure 3.
Referring now to Figures 2, 3 and 4 of the drawings, there is
depicted a preferred em3~odiment of a conduit weighting device 1,
according to the present invention, wherein a containment means 2
contains ballast material 3, within two "at least one" enclosures 4.
Enclosures 4 are defined between respective, mutually interconnected
walls 5, which are adapted to conform in a straddling relation over
a pipeline 6, in a pipeline emplacement such as that illustrated in
Figure 2.
The depicted embodiment also includes attachment means 7, straps
8, and a folded-over and sewn lip 9.
More particularly, there is provided a containment means 2
comprising a pair of enclosures 4, each formed from respective ones
of a unitary web of flexible, environmentally-stable plastic material.
Portions of each of these webs correspond to respective wall portions
in containment means 2, and are adapted to be, respectively, mutually
secured in enclosure defining relation in the form of a plurality of
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interconnected walls 5. As illustrated, these respective wall
portions are mutually secured along seams such as those marked with
reference numeral 5a, to form the containment envelope that surrounds
the corresponding enclosure 4. In addition, a folded over lip 9 is
formed along the bottom of each of the envelopes.
The pair of enclosures 4 are mutually, hingably secured along
contacting portions 10 of mutually adjacent walls 5. Stitching is
used for this purpose. In addition, attachments means 7 in the form
of press-fit, rust-resistant grom.~nets, are employed to further secure
the two contacting walls 5. Moreover, straps 8 are sewn along
exterior surfaces of each of the enclosures 4, and extend between the
enclosures 4 in bridging, mutually securing relation. In this way
straps 8 reinforce the containment means 2 generally, and in
particular, straddle the top of conduit 6 in an emplacement, to
thereby help resist tensioned separation of the two enclosures 4.
This strap arrangement is perhaps best illustrated in Figure 4 of the
drawings.
Note also that lifting the conduit weighting device 1, (relative
to array 7b), by arrays 7a and 7c of attachment means grommets 7 on
the respective mutually spaced apart walls 5, opens the separation
between the respective bottoms of the two enclosures 4. Straps 8
reinforce walls 5, communicating the tension forces generated during
such a lifting operation. On the whole, such a lift facilitates
arrangement of device 1 in straddled relation over conduit 6, by
conforming device 1 to permit better separation between the enclosures
4, around the upper surface of conduit s.
Another advantage that can be accrued in accordance with the
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practice of aspects of the present invention are that the depth of the
trench in an emplacement need not be as deep as is required to
facilitate the use of prior art trench weights. Referring in that
connection to Figures ~. and 2 of the drawings, note that the prior art
structure illustrated in Figure 1 occupies a substantial amount of
headroom above the pipeline. This provides the necessary structural
strength needed to facilitate the handling and longevity of the
device. Unfortunately, the highest point of pipeline emplacements
must in many cases be buried to a specified below-surface depth. If
the highest point of the emplacement is the top of the prior art
weight, then the pipeline itself must be buried correspondingly
deeper. The device according to the present invention need not extend
above the pipeline, as will be appreciated by skilled persons in light
of the present disclosure. That being the case, the trench of the
emplacement need not be as deep, with collateral savings in
installation costs, and subsoil structure disruption. Moreover, this
embodiment of the present invention is far less likely to visit damage
to the pipeline during installation, than is the prior art device
illustrated in Figure 1.
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