Note: Descriptions are shown in the official language in which they were submitted.
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LINER PIPE FOR REPAIR OF A HOST PIPE
Background of the Invention
This invention relates to liner pipes for use in
the repair of pipes, and preferably for trenchless
reconstruction of underground pipes such as sewer lines.
Deterioration of underground pipes due to aging is
a major problem. Aging of underground pipes results in
corrosion, loose joints, cracks, holes and missing sections
in pipes. Excavation and replacement of deteriorated
underground pipes such as sewer lines is extremely costly,
time consuming and disruptive to traffic, utilities and
other activities in the area surrounding the excavation
site.
Prior art liner pipes have been developed for
"trenchless" reconstruction of underground pipes, completely
eliminating the need for excavation in most cases. Liner
pipes are typically inserted into a damaged section of pipe
from above ground at an end of the pipe to be repaired. The
damaged pipe into which the liner pipe is inserted is
typically referred to as the "host" pipe. After insertion,
the liner pipe is molded to conform to the inner size and
shape of the host pipe, thus effectively providing it with a
new lining.
During manufacturing of a typical prior art liner
pipe, the cross-sectional size and shape of the liner pipe
is substantially reduced by deformation. This typically
involves folding the liner pipe along its longitudinal axis,
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giving it a U-shaped cross-section and a substantially
reduced cross-sectional area and size. This reduced cross-
sectional shape and size allows the liner pipe to be
smoothly inserted into the host pipe.
After insertion into the host pipe, the liner pipe
is unfolded to increase its cross-sectional size and shape
and conform it to the inner cross-sectional shape and size
of the host pipe.
Typically, the prior art liner pipe is rigid when
inserted and the entire liner pipe must be softened by
heating before it can be unfolded. In one prior art method,
heat is applied by passing pressurized steam through the
liner pipe, thus heating the pipe from the inside only. As
a result, more heat is applied to the inner surface of the
liner pipe than the outer surface, and the inner surface
becomes softer than the outer surface. This uneven heating
causes uneven expansion of the liner pipe, and can result in
gaps being left between the outside of the liner pipe and
the inner surface of the host pipe.
one prior art system has been developed which
simultaneously heats both the inside and outside of the
liner pipe. This produces even heating, resulting in even
expansion and a tight fit of the liner pipe inside the host
pipe.
This prior art system utilizes a thin, flexible
plastic sleeve which is first inserted into the host pipe.
A conventional, prior art folded liner pipe is inserted into
the sleeve so that the sleeve completely surrounds the liner
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pipe. Pressurized steam is passed through the sleeve,
evenly heating both the inside and outside of the liner
plpe .
The even heating of the liner pipe achieved by
this system results in even expansion and a high quality
installation, with the liner pipe fitting tightly inside the
host pipe.
However, the sleeve cannot be recovered and reused
after installation of the liner pipe. The sleeve remains
inside the host pipe between the host pipe and the installed
liner pipe. The use of a new sleeve for each installation
increases the material cost of the repair process. Further,
the extra step of inserting the sleeve into the host pipe
substantially increases the labour and the time required for
the installation.
The prior art liner pipes and methods have
disadvantages, some of which are discussed above, which
relate to ease and expense of installation.
Summary of the Invention
Accordingly, it is an object of the present
invention to at least partially overcome the disadvantages
of the prior art. Therefore, it is an object of this
invention to provide an improved type of liner pipe and a
method for its installation.
Accordingly, in one of its broad aspects, the
present invention resides in providing a liner pipe for
repair of a host pipe; the liner pipe having a hollow
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inside; a length defining a longitudinal axis; and a cross-
sectional shape and size in a plane transverse to the
longitudinal axis; the cross-sectional shape and size of the
liner pipe being such that the liner pipe can be fed through
the host pipe; the liner pipe comprising an inner layer and
an outer layer; the outer layer being comprised of flexible
thermoplastic material; and the inner layer being comprised
of rigid thermoplastic material which, when heated, becomes
sufficiently pliable to allow the cross-sectional shape and
size of the liner pipe to conform to an inner cross-
sectional shape and size of the host pipe.
Also, in another of its broad aspects, the present
invention resides in providing a method for using a liner
pipe to repair a host pipe having a section to be repaired,
said method comprising: feeding a liner pipe into a
position in the host pipe so that the liner pipe covers
substantially the entire section to be repaired; wherein the
liner pipe has a hollow inside, a length defining a
longitudinal axis, a cross-sectional shape and size in a
plane transverse to the longitudinal axis which allows the
liner pipe to be fed through the host pipe, an outer layer
comprising flexible thermoplastic material, and an inner
layer comprising rigid thermoplastic material; heating the
inner layer of the liner pipe to an extent whereby the inner
layer of the liner pipe is softened; conforming the cross-
sectional shape and size of the liner pipe to an inner
cross-sectional shape and size of the host pipe while the
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inner layer is softened; and cooling the liner pipe so that
the inner layer becomes rigid.
Brief Description of the Drawings
Further aspects and advantages of the present
invention will become apparent from the following
description, taken together with the accompanying drawings,
in which:
Figure 1 is a front perspective view of a fully
folded liner pipe according to the present invention
received in a host pipe according to a preferred method of
the present invention;
Figure 2 is a front perspective view of the liner
pipe and host pipe of Figure 1, wherein the liner pipe has
been partially unfolded; and
Figure 3 illustrates the liner pipe and host pipe
of Figures 1 and 2, wherein the liner pipe is fully
unfolded.
Description of the Preferred Embodiments
Preferred embodiments of the present invention are
now described with reference to Figures 1 to 3.
The liner pipe and method for its installation
according to the present invention are most advantageous in
the repair of underground pipes. However, they can be used
with equal success to repair pipes above ground.
Most preferably, the liner pipe and method of its
installation according to the present invention are used in
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the repair of underground sewer pipes for sanitary sewers or
storm sewers. However, the liner pipe and method of the
present invention may also be used in the repair of pipes
for transfer of a wide variety of gas and liquid materials,
such as water, oil and gas pipelines.
Figures 1 to 3 schematically illustrate three
successive stages in a preferred method of repairing a host
pipe having a section to be repaired according to the
present invention.
Figure 1 illustrates a liner pipe 10 of the
present invention, prior to softening, inserted into a host
pipe 12. Liner pipe 10 has a hollow inside 14 and a length
L which is shown as being the distance between a first end
16 of liner pipe 10 and a second end 18 of liner pipe 10.
The liner pipe 10 has a longitudinal axis A which
is defined by and parallel to the length L of liner pipe
10. In any plane transverse to the longitudinal axis A, for
example the plane in which the first end 16 of liner pipe 10
lies, the cross-sectional shape and size of the liner pipe
10 allows the liner pipe 10 to be fed through the host pipe
12.
In Figure 1, the cross-sectional size of liner
pipe 10 is defined as the outer cross-sectional area of
liner pipe 10 enclosed by outer surface 20 of liner pipe
10. The cross-sectional shape of liner pipe 10 is defined
as the shape of the outer cross-sectional area enclosed by
outer surface 20 of liner pipe 10. Figure 1 illustrates a
preferred U-shaped cross-sectional shape of liner pipe 10,
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wherein the liner pipe 10 is "folded" along its longitudinal
axis A.
In contrast, host pipe 12 has an inner cross-
sectional size which is defined as the cross-sectional area
enclosed by the inner surface 22 of host pipe 12 in a plane
perpendicular to longitudinal axis A. The inner cross-
sectional shape of host pipe 12 is shown in Figure 1 as
being circular.
Prior to softening, the liner pipe 10 has an outer
cross-sectional area less than the inner cross-sectional
area of the host pipe 12.
As shown in Figure 1, the cross-sectional size of
host pipe 12 is substantially larger than that of liner pipe
10. Preferably, the cross-sectional size of liner pipe is
not greater than about 60 percent of the cross-sectional
size of host pipe 12. This ensures that liner pipe 10 may
be easily inserted into host pipe 12. Further, the cross-
sectional shape of liner pipe 10 shown in Figure 1 is such
that the liner pipe 10 may be easily inserted into host pipe
12. Easy insertion of liner pipe 10 into host pipe 12 is
preferable so that neither liner pipe 10 nor host pipe 12
are damaged during the installation of liner pipe 10.
The liner pipe 10 according to the present
invention has a wall 23 comprised of two layers, an inner
layer 24 and an outer layer 26. Inner layer 24 is comprised
of a rigid thermoplastic material, whereas outer layer 26 is
comprised of a flexible thermoplastic material.
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The layers 24 and 26 of liner pipe 10 can be made
from a wide range of thermoplastic materials, with PVC,
polyethylene, polypropylene, polystyrene and blends thereof
being preferred.
For a liner pipe 10 used in the repair of sewer
pipes, the layers 24 and 26 are preferably made from
polyethylene or PVC. Most preferred is PVC, which is also
widely used in the manufacture of sewer pipes. As typical
ambient temperatures encountered in sewer lines typically
range from about -20C to about 40C, it is preferred that
inner layer 24 is rigid and outer layer 26 is flexible
throughout this temperature range.
The thickness of wall 23 of liner pipe 10 is
preferably about the same thickness as that of prior art
liner pipes. Preferably, inner layer 24 and outer layer 26
have substantially the same thickness.
When heated, the rigid thermoplastic material
comprising inner layer 24 becomes sufficiently pliable to
allow the cross-sectional shape and size of the liner pipe
10 to conform to the inner cross-sectional shape and size of
host pipe 12.
Figure 1 schematically illustrates a first step in
a method for using liner pipe 10 to repair host pipe 12
according to the present invention. Figure 1 illustrates
host pipe 12 having a section to be repaired 28 comprising a
hole 30 completely through the wall 32 of host pipe 12.
Although hole 30 represents a common type of defect in host
pipes, liner pipe 10 and the method for its installation
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according to the present invention can be used in the repair
of host pipes having numerous other defects, such as cracks,
leaking joints and missing sections.
In the first step of the method shown in Figure 1,
liner pipe 10 is fed into a position in host pipe 12 so that
the liner pipe 10 covers substantially the entire section to
be repaired, i.e. the ends 16 and 18 of liner pipe 10 extend
in the host pipe 12 on either side of the section to be
repaired 28.
After the liner pipe 10 is inserted into host pipe
12 as schematically illustrated in Figure 1, the inner layer
24 of liner pipe 10 is heated to an extent whereby inner
layer 24 is softened. Preferably, liner pipe 10 is heated
from the inside 14 only.
Preferably, inner layer 24 is heated by steam
heat, and most preferably by passing pressurized steam
through the hollow inside 14 of liner pipe 10. However, it
is to be understood that other methods of heating may be
equally suitable. For example, hot water, electricity and
exothermic chemical reactions can be used to heat and soften
inner layer 24.
The softening temperature of the thermoplastic and
the time required to soften inner layer 24 can be altered by
changing the composition of the thermoplastic material. For
example, additives such as heat conducting materials may be
added to the thermoplastic to increase heat conductivity and
the heating rate of the thermoplastic material. Further, a
lower softening temperature may be desired to increase the
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softening rate of the inner layer 24 or to adapt the liner
pipe 10 to use with a cooler heating medium.
After the inner layer 24 of liner pipe 10 is
softened, the cross-sectional shape and size of the liner
pipe 10 are conformed to the inner cross-sectional shape and
size of the host pipe 12. Conforming the cross-sectional
shape and size of the liner pipe 10 may be accomplished by
any other suitable method.
The preferred method of conforming inner layer 24
is to pressurize the hollow inside 14 of liner pipe 10 with
pressurized steam. The pressurized steam exerts pressure on
the inner surface 34 of liner pipe 10, thereby pushing the
wall 23 of the liner pipe 10 outward in the direction of the
inner surface 22 of host pipe 12.
Compressed air can also be used for pressurizing
the hollow inside 14 of liner pipe 10. However, pressurized
steam is most preferred because it functions to
simultaneously heat and pressurize the inside 14 of liner
pipe 10.
Liner pipe 10 is preferably forced to conform to
the cross-sectional shape and size of the host pipe 12 by
pressurizing the inside 14 of liner pipe 10 while the inner
layer 24 is in a softened state. However, it is to be
understood that it is not necessary to pressurize liner pipe
10. Liner pipe 10 may be conformed to the shape and size of
the host pipe 12 by other suitable means. For example, a
cylindrical object may be forced through the hollow inside
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14 of the softened inner layer 24 to conform the liner pipe
10 to the inner shape and size of the host pipe 12.
Figure 2 schematically illustrates an intermediate
stage in the preferred method. In this stage of the
process, liner pipe 10 has been partially "unfolded" so that
its cross-sectional size has expanded from that shown in
Figure 1. As shown in Figure 2, the cross-sectional shape
of liner pipe 10 is no longer U-shaped, but rather is
approximately "kidney-shaped" approaching the circular
cross-sectional shape of the host pipe 12.
Although the cross-sectional size of liner pipe 10
expands, preferably this expansion results only from the
"unfolding" of liner pipe 10, rather than stretching of
layers 24 and 26.
When softened, the inner layer 24 preferably has a
flexibility similar to that of the outer layer 26, resulting
in even expansion of the cross-sectional shape and size of
liner pipe 10. This results in a high quality installation
with a tight fit of the liner pipe 10 inside host pipe 12.
Figure 3 schematically illustrates a final stage
in the method for using liner pipe 10 to repair host pipe 12
having a section to be repaired 28. At this stage, the
cross-sectional shape and size of the liner pipe 10 has been
substantially completely conformed to the inner cross-
sectional shape and size of the host pipe 12. As shown in
Figure 3, the cross-sectional shape of liner pipe 10 is
substantially circular, the same as the inner cross-
sectional shape of host pipe 12. Further, the cross-
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sectional size of liner pipe 10 is substantially identicalto the inner cross-sectional size of host pipe 12. The
outer periphery of the liner pipe 10, defined as the
distance around outer surface 20, is substantially equal to
the inner periphery of the host pipe 12, defined as the
distance around inner surface 22. Therefore, liner pipe 10
is tightly received inside host pipe 12, with outer surface
20 of liner pipe 10 firmly engaging the inner surface 22 of
host pipe 12.
As shown in Figure 3, liner pipe 10 has completely
closed the hole 30 in liner pipe 12.
After the cross-sectional shape and size of liner
pipe 10 have been substantially completely conformed to the
inner cross-sectional shape and size of host pipe 12, the
liner pipe 10 is cooled so that the inner layer 24 of liner
pipe 10 becomes rigid. In the most preferred embodiment,
the liner pipe 10 is cooled by passing compressed air
through the hollow inside 14 of liner pipe 10. However,
cooling may also be conducted by other suitable means, such
as by liquid coolants or by allowing the liner pipe to cool
merely through the action of surrounding air circulating
through the inside 14 of liner pipe 10.
The inner layer 24 of liner pipe 10 preferably has
a very smooth inner surface 34 which serves as an inhibitor
for any future buildup of foreign material that could reduce
flow capacity.
Although the invention has been described in
connection with certain preferred embodiments, it is not
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intended to be limited thereto, rather, it is intended that
the invention cover all alternate embodiments as may be
within the scope of the following claims.
