Fabric reinforced pipe

Reinforcement of buried or inaccessible existing pipes is achieved by applying a reinforcement layer which includes a fabric portion. A pipe system structure is achieved which permits an internal or external surface of an existing pipe wall to be reinforced without removing a section of the pipe and without requiring the pipe to be out of service of a long period of time. The reinforcement layer overlays a portion of the internal or the external surface of the pipe. An adhesive material is then applied to the surface of the pipe or to the reinforcement layer for bonding the reinforcement layer to the surface of the pipe to develop a composite system between the existing pipe and the reinforcement layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates a method and apparatus for reinforcing pipe 
walls to increase their strength and ductility without removing a section 
of the pipe from its original position. 
2. Related Art 
In general, pipes either below or above ground need to be repaired after a 
number of years of operation due to deterioration. Existing pipes formed 
from steel and/or concrete have numerous problems. For example, steel 
pipes are prone to losing their structural integrity over time due to 
corrosion and concrete pipes are subject to deterioration due to 
permeability of the exposed concrete by water. 
Previously, repairing pipes involved excavating the pipe from the ground, 
removing the section to be repaired and burying a new section. This 
process was expensive and time consuming, and also required that the pipe 
be out of service for a period of time. Subsequently, methods for 
repairing cracks and breaks in pipes have been developed whereby the pipes 
need not be excavated in order to be repaired. These methods include the 
use of inserts to act as new pipe walls. 
One such method of repairing an underground pipe involves inserting a 
sufficiently long tubular flexible liner bag into the pipe by means of a 
pressurized fluid, such as air or water. The tubular liner bag is made of 
a flexible resin-absorbent material impregnated with a thermosetting 
resin, and the outer surface is covered with a water impermeable plastic 
film. 
In particular, the tubular flexible liner bag is closed at one end and open 
at the other. The tubular flexible liner bag is first flattened, and then, 
the closed end of the tubular liner bag is tied to a control rope. The 
open end of the tubular liner bag is made to gape wide and is hooked 
(anchored) at the end of the defective or old pipe in such a manner that 
the wide-opened end of the liner completely and fixedly covers and closes 
the pipe end. A portion of the liner is pushed into the pipe. The 
pressurized fluid is applied to the portion of the tubular liner such that 
the fluid urges the tubular liner to enter the pipe. Since one end of the 
tubular liner is hooked at the end of the pipe, it remains there while the 
rest of the flexible liner bag is turned inside out as it proceeds deeper 
in the pipe. When the entire length of the tubular liner bag is everted 
(i.e., turned inside out) into the pipe, the control rope holds the closed 
end of the tubular liner bag to thereby control the length of the tubular 
liner in the pipe. The everted tubular liner is pressed against the inner 
wall of the pipe by the pressurized fluid. The tubular liner is hardened 
as the thermosetting resin impregnated in the tubular liner bag is cured. 
This process enables a pipe to be repaired without excavation or 
disassembly. However, if the process is applied to an underground pipe 
into which ground water penetrates, the problem arises that the 
thermosetting resin impregnated in the tubular pipe liner bag may be 
diluted or wash out of the material before it cures. Thus, neither 
adequate strength of the liner nor an adequate bond between the insert 
liner and the pipe may be maintained. Also, during the insertion process, 
material may accumulate on the outside of the resin impregnated liner bag, 
thereby reducing available bonding surface and consequently strength and 
sealing capabilities of the repair. In addition, void areas where resin is 
not present can occur in the liner bag, thereby causing areas of weakness 
and areas where the liner fails to properly bond to the pipe. 
Accordingly, there remains a need for an efficient and cost-effective way 
to adequately reinforce pipes so as to increase their resistance to 
structural failure due to deterioration. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a pipe system structure including 
a pipe wall having an internal and an external surface, a reinforcement 
layer overlaying at least a portion of the internal or external surface, 
the reinforcement layer having at least one fabric layer impregnated with 
resin and an adhesive material applied to the surface of the pipe wall or 
the reinforcement layer for bonding the reinforcement layer to the surface 
of the pipe wall to develop a composite system between existing pipe and 
the reinforcement layer. 
In one form of the invention, the fabric layer is in substantially one 
section and is in a partially cured state. In one embodiment, the fabric 
layer is rolled up to be easily carried through an existing passageway, 
such as a manhole, and is then applied to the internal surface of the 
pipe. An internal device such as a clamp or a balloon is then used to hold 
the section of the fabric in place while bonding occurs. In another 
embodiment, the fabric layer is rolled up but is applied to the external 
surface of the pipe. 
In another form of the invention, the fabric layer is pre-formed in a 
plurality of sections and is prepared outside of the pipe. The plurality 
of sections of the fabric layer are then easily carried through the 
existing passageway to the inside of the pipe and applied to the internal 
surface of the pipe. Alternatively, the plurality of sections are applied 
to the external surface of the pipe. 
In yet another form of the invention, the adhesive material includes a tack 
coat, such as contact cement, for holding the reinforcement layer to the 
pipe wall on contact. Alternatively, the adhesive material includes a wet 
primer coat and a tack coat. 
The present invention enables the interior of the pipe to be reinforced by 
using an existing passageway, such as a manhole, to access the interior of 
the pipe. The reinforcement material is delivered to the interior of the 
pipe through these existing passageways. In a preferred form of the 
invention, the surface of the pipe is cleaned of debris and then dried 
before the bonding of the reinforcement layer to the pipe surface.

Like reference symbols are employed in the various drawings and in the 
description of the preferred embodiment to represent the same or similar 
items. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention has wide application to the reinforcement of existing 
pipes or other conduits located either above or below ground. The 
following detailed description describes use of the invention to reinforce 
a pipe of circular cross-section buried underground. However, it will be 
understood by those skilled in the art that the invention is not limited 
to such pipes, but also may be applied to pipes of any size and any 
cross-sectional shape. FIGS. 1-8 illustrate a typical order of steps for 
reinforcing pipes in accordance with the invention. FIG. 1 shows a 
sectional view of an underground pipe 10 to be reinforced. Pipe 10 in this 
example is concrete. However, the pipe could equally be made from wood, 
metal or other materials. 
Initially, if necessary, pipe 10 is shut down to permit workers to enter 
and work in the pipe. Existing openings, such as manholes 14 provide 
workers with access via access openings 16 to the interior of pipe 10. 
Typically, such manholes 14 are arranged along the length of pipe 10 in 
approximately one mile intervals. 
In one embodiment of a pipe reinforcing system, the equipment used for 
implementing the process is set up aboveground, near the entrance to pipe 
10, as shown in FIG. 2. An air conditioning/air circulation truck 22 
situated near access 16 entrance of manhole 14 provides the necessary air 
ventilation and air circulation for the workers inside pipe 10. A tent 24 
may also be assembled at the entrance of manhole 14 to house and protect 
both the reinforcing material to be used in the method and the equipment 
26 for preparing the reinforcing material. A layout table 28 is used to 
layer the reinforcing material, take samples for testing, and to allow the 
reinforcing material to slightly pre-cure for ease of application. A 
carrying machine, such as a wagon 29, can also be used to facilitate 
movement of the reinforcing material through manhole 14 and into pipe 10. 
Existing pipe 10 may need to be reinforced by applying reinforcing material 
to either the interior or the exterior surface of pipe 10. In a first 
embodiment, as shown in FIGS. 1-6, the reinforcing material is applied to 
an interior surface 12 of pipe 10. It is preferred that the interior 
surface 12 of pipe 10 be thoroughly cleaned to remove any debris attached 
to pipe surface 12 prior to application of the reinforcing material, as 
shown in FIG. 3. Since bonding of a resin matrix and the reinforcement 
material to surface 12 of pipe 10 is preferred, pipe surface 12 should be 
sufficiently clean so that the resin matrix adheres well to the pipe wall. 
In one embodiment, this cleaning process is performed by a machine 
including a hose 34 which creates a water blast force (e.g., 10,000 psi) 
to loosen the debris and a scrub brush 32 to thoroughly clean pipe wall 
12. Pipe wall 12 is then dried using either an air drying or a chemical 
drying process. For example, compressed air or sodium can be used to clean 
off the excess water from the pipe surface. Sandbags also can be used to 
separate the area to be reinforced to keep it clean and dry. 
After the interior surface 12 of pipe 10 has been cleaned, it is often 
desirable (though not necessary) to repair the cracks in the pipe wall. 
For example, an epoxy injection material may be used to repair small 
circumferential hoop direction cracks. In addition, a portion of the pipe 
wall to be reinforced can be coated with a wet primer before application 
of the reinforcing material to the surface. If the surface is porous or 
has cracks, it may be desirable to allow the wet primer to penetrate the 
surface before applying the resin impregnated fabric layers to the pipe 
wall. In one embodiment, a water insensitive, high bond strength epoxy, 
such as TYFO.RTM. WP Epoxy, is applied to the pipe surface. This epoxy 
fills voids in the pipe surface and functions as a prime coat to which the 
composite reinforcement layer bonds. Subsequently, a tack coat, such as a 
contact cement, is applied to the primer coat. The tack coat layer 
provides stronger adhesion and is therefore particularly useful when 
bonding overhead. 
The reinforcing material is then applied to interior surface 12 of pipe 10. 
The composite reinforcement material is preferably formed by applying 
fabric layers impregnated with resin to the pipe wall. Examples of the 
fabric layers that may be used to reinforce the pipe are disclosed in U.S. 
Pat. No. 5,649,398, U.S. Pat. No. 5,218,810 and co-pending patent 
application Ser. No. 08/496,743 filed Jun. 29, 1995, each of which is 
incorporated by reference herein. In general, the fabric is highly 
resistant to both aggressive chemicals and waste water. 
Where a single layer of fabric is used, it will often be desirable to use 
weft cloth containing both horizontal and vertical fibers. Where multiple 
layers of fabric are used, it will often be desirable to alternate the 
orientation of the fibers to provide maximum strength along multiple axes. 
In one embodiment, the multilayer reinforcement material has an inner 
layer of longitudinal axial fibers and an outer layer of circumferential 
hoop fibers. For example, when two high strength composite reinforcement 
layers are applied to the pipe wall, the first reinforcement layer 
includes two fabric layers of carbon fibers in a longitudinal direction 
and the second high strength composite reinforcement layer includes three 
layers of carbon fibers in the hoop direction. In another embodiment, 
uncured high strength composite reinforcement layers are spirally wound 
around the inside surface of the pipe. In this manner, the method of the 
invention not only improves the integrity of the pipe, but also 
significantly reinforces the pipe against externally applied forces. 
Actual application of reinforcing fabric can be accomplished in more than 
one way. In a first embodiment, the fabric is unwound from a roll and 
dipped in resin for impregnation prior to application to the pipe surface. 
For example, as shown in FIG. 2, the fabric is fed through machine 26 to 
saturate the reinforcing material with the resin. The fabric is rolled as 
it is fed through the machine 26 so that the fabric can be easily applied 
to the pipe wall with a roller. Once a sufficient length of fabric has 
been impregnated within the resin, the impregnated fabric layer is cut 
from the roll and is applied to the face of the wall. In one embodiment, 
the resin impregnated fabric layer is allowed to partially cure outside of 
the pipe prior to entering the pipe, to allow for ease of application once 
inside the pipe. In another embodiment, the resin impregnated fabric layer 
expands to cover the desired section of the pipe. An internal device, such 
as a clamp or a balloon, may be used to assist in holding the reinforcing 
material until curing has taken place. Thus, the fabric layer is allowed 
to cure once in place on the pipe surface to form the composite 
reinforcement layer. The impregnation and application process is repeated 
until the selected portion of the pipe surface has been covered. 
Alternatively, it is desirable (though not necessary) that the composite 
reinforcement layers be pre-formed in sections. It is also preferable that 
these preformed sections be small enough to fit through the existing 
passageway, e.g., manhole, to facilitate the reinforcement process. In 
this way, the reinforcing material can be easily delivered to the pipe, 
transported to the section of the pipe to be reinforced, and applied to 
the pipe wall. If pre-formed sections are used, seams are spliced together 
using lap splice pieces comprised of sections of fabric impregnated with 
resin. For the lap splice pieces, as well as other areas where layers of 
fabric overlay, the layers should have a small overlap for corrosion 
protection and to provide maximum transverse strength. 
It is preferred that the fabric layers of a composite reinforcement layer 
be placed on the pipe surface so that substantially the entire pipe 
surface is covered. However, in certain applications, it may be desirable 
to only cover those portions of a pipe surface that are most likely to 
fail. Typically, a pipe to which reinforcing material has been applied 
according to the invention will be ready to be subjected to water pressure 
after approximately 10 hours. 
There are several different methods of applying the reinforcing material to 
the interior surface 12 of pipe 10, some of which are more desirable than 
others, depending on the diameter of pipe 12. When the interior diameter 
pipe of the pipe is too small to permit workers to stand inside, the 
process for the wrapping the reinforcing material can include a working 
seat 42 to permit the worker to apply the reinforcement material as shown 
in FIG. 4. In this exemplary embodiment, the diameter of pipe 10 is shown 
as 66". Thus, working seat 42 facilitates the ease with which a worker is 
able to manually apply the reinforcing material with a roller 44 inside 
narrow pipe 10. 
In contrast, when the interior diameter of pipe 10 exceeds that in which a 
worker could stand and apply the reinforcing material, a scaffolding 52 
can be constructed as shown in FIG. 5. In this exemplary embodiment, the 
diameter of pipe 10 is shown in the range of 121"-144". In both of these 
embodiments, the reinforcing material can be transported to the desired 
location using a carrier such as wagon 64. In addition, although FIGS. 4 
and 5 illustrate the process of applying reinforcing material by using a 
roller to roll the material onto the interior surface 12 of pipe 10, it 
will be appreciated that the present invention can be implemented using 
other application techniques. 
In a second embodiment of the reinforcing material application method of 
the invention, pipe 10 can be reinforced by applying the reinforcing 
material to an exterior surface 62 of pipe 10, as shown in FIG. 6. Such a 
reinforcing process involves excavating a section of pipe 10 to be 
reinforced to expose exterior surface 62. A system of high strength and 
high pressure airbags 64 are placed around the exterior of pipe 10 to 
support the section of the pipe to be reinforced during the reinforcing 
process. For example, as shown in FIG. 6, airbags 64 are provided between 
the ground and the bottom portion of pipe 10. 
Exterior surface 62 of pipe 10 is then cleaned and dried to promote better 
bonding of the reinforcing material to the exterior surface. This cleaning 
process is similar to that used to clean interior surface 12 of pipe 10. 
Subsequently, the reinforcing material is applied to pipe 10. The 
reinforcing material used is the same as that applied to interior surface 
12 of pipe 10. A scaffolding 72 can be assembled along the exterior of 
pipe 10 and within the excavation to facilitate the cleaning process and 
the application of the reinforcing material to pipe 10, as shown in FIG. 
7. 
An advantage to reinforcing existing pipe 10 by applying the reinforcing 
material to external surface 62 is that the reinforcing process can be 
conducted while maintaining pipe 10 in service. 
In all of the embodiments, curing of the resins is carried out in 
accordance with well known procedures which will vary depending on the 
resin matrix used. Various conventional catalysts, curing agents and 
additives which are typically employed with such resin systems may be 
used. It is desirable to use preformed sections of fabric in a cured or a 
partially cured state to further minimize time spent inside the pipe. Once 
the resin is cured, the combination of the fabric layers, the fabric 
members and the cured resin form an integral high strength composite which 
is permanently bonded to the pipe surface. Advantageously, the 
resin-impregnated fabric members in the above described surface are almost 
invisible and thus the foregoing method is useful when aesthetic 
considerations are important. 
It is desirable (though not necessary) that the composite reinforcement 
layers further include an exterior layer of a pre-stressed form, such as 
stretch wrap, when wrapping the exterior surface of the pipe. Once the 
reinforcement layer has been wrapped around the surface of the pipe, 
stretch wrap or other similar thin wrapping layer is wrapped over the 
reinforcement layer to assist in holding it in place for better bonding. 
The stretch wrap may be removed after final curing or, alternatively, it 
may be held in place. Any of the commonly used stretch wrap materials may 
be used to provide the containment layer. Stretch wrap is a polymer film 
which is widely used and readily available from any number of commercial 
sources. For example, stretch wrap is available from Mobil Oil Corporation 
under the trade names MOBILWRAP or MOBIL MASTERWRAP. The wrap is also sold 
by Borden Chemical Co. under the trade name BORDEN HANDWRAP. 
When wrapping inside the pipe, the use of an additional wrap material over 
the reinforcement layer is particularly preferable in situations where the 
pipe is subjected to turbulence. For example, the use of a plastic wrap is 
particularly preferred where fast flowing and/or turbulent water may be 
flowing through the pipe. 
If desired, the exposed surface of the composite reinforcement layer may be 
coated with a desired surface protectant, e.g., paint, urethane, acrylic, 
etc. In applications where it is preferable that the composite 
reinforcement layer be resistant to corrosion, a commercially available 
corrosive protectant coating may be used. 
It will be appreciated by those skilled in the art that the suitable 
materials for the wet primer, the tack coat, and resins for impregnating 
the fabric material, and the finish materials in accordance with the 
present invention include polyester, epoxy, vinylester, acrylic, modified 
acrylic, urethane, phenolic, polymide, bismaleimide, polyurea, or 
combinations thereof with epoxy being a preferred resin. Other materials 
may be utilized provided that they have the same degree of strength and 
toughness provided by the previously listed resins. In most applications, 
thermoset resins are preferred. However, enhancements to the process will 
allow the use of thermoplastic resin systems. Although the polymer 
materials may be mixed in the pipe, it is preferable that the materials be 
mixed outside the pipe to minimize the time spent inside the pipe. 
In all of the embodiments of the present invention, the reinforcing 
composite material may be adhered to the structural member, such as the 
pipe wall, through the adhesive properties of the polymer matrix itself, 
an additional adhesive, fiber fasteners, or other anchoring means. 
All of the embodiments described above may be modified if desired for 
retrofit and repair of already damaged structures. Pipe systems normally 
require strengthening in the longitudinal direction as well as in the hoop 
direction. Therefore, the damaged structures are examined to determine the 
actual fracture pattern present, and the cloth type, weave, fiber 
direction, and bias angle of cut are modified to provide maximum strength. 
In this way, an optimum weave design can be chosen to repair the pipe in 
both directions. 
A wide variety of composite materials may be used. While fabric impregnated 
with epoxy resin to reinforce a concrete pipe has been illustrated, those 
skilled in the art will appreciate that the present invention may be used 
with a wide variety of fibers and polymer matrices to reinforce a 
similarly wide variety of structures. 
The fabric for example, may be comprised of glass, graphite, polyaramid, 
boron, Kevlar, silica, quartz, ceramic, polyethylene, aramid, or other 
fibers. A wide variety of types of weaves and fiber orientations may be 
used in the fabric. Preferably, the fiber and polymer matrix are 
waterproof. 
Various other modifications and alterations in the structure and method of 
operation of this invention will be apparent to those skilled in the art 
without departing from the scope and spirit of this invention. Although 
the invention has been described in connection with specific preferred 
embodiments, it should be understood that the invention as claimed should 
not be unduly limited to such specific embodiments.