AU698461B2 - Pipe rehabilitation - Google Patents

Description

PIPE REHABILITATION

TECHNICAL FIELD

The present invention relates to rehabilitating existing pipelines of various lengths and diameters and, in particular, to a method for performing such rehabilitation.

BACKGROUND ART

Underground pipe systems deteriorate over time as a result of degradation of materials and outside influences such as tree roots, compression from above, expansion

and contraction and numerous other factors. In order to avoid the expense of excavating

the pipes and replacing them a number of "in situ" rehabilitation techniques have been developed. Most of these systems involve lining internally the old pipe using a plastic

liner which is fed into the old pipe via existing manholes or other existing access points. The liner is normally expanded into the required position against the internal wall ofthe existing pipe and cured to provide a rehabilitated pipe. Known techniques typically use polyvinylchloride (PVC) liners which are hot-

cured. The liner is fed into the existing pipe in a heated and softened form and then is

further heated and expanded using pressurised steam to force the liner against the internal wall ofthe existing pipe. The steam is then replaced by pressurised air and the liner allowed to cool and cure while still being held firmly against the internal pipe wall. Such systems have a number of disadvantages. They require expensive, specialised plant and equipment. For example, special semi-trailers, capable of carrying

large industrial generators and compressors. The capital equipment may cost in the

order of hundreds of thousands of dollars and is required by each crew to rehabilitate each pipeline. Each pipeline may take ofthe order of 6-12 hours to complete. In view ofthe high capital equipment costs, duplication of capabilities is very costly, making

response to market demands difficult.

Hot cure systems are also susceptible to shrinkage both longitudinally and

diametrically. This can produce a number of problems including doubts as to the structural integrity ofthe pipeline. Longitudinal shrinkage may result in infiltration and

blockages, particularly in respect of connections to branch lines. For example, where the

liner shrinks after the connections for the branch line have been cut, the cut out portion

ofthe liner may move further along the pipe wall resulting in infiltration through the

liner. Further, movement ofthe liner with shrinkage may result in the liner moving

across and blocking the branch connection.

It is also difficult to stop infiltration, or flow from a branch line during the

rehabilitation process. This can result in the heated liner coming into con tact with a

head of water. The water causes what is known as a "cold spot" in the hot cure method.

This cold spot can inhibit the curing process which in turn leads to a failure ofthe line.

Often hot cure PVC liners do not expand beyond the diameter ofthe host pipe.

This can result in an indentation not forming where the branch line connects to the

mainline. This makes location of laterals and branches very difficult and time

consuming. Further, hot cure PVC lines normally require their branch line connections

to be cut using an expensive remotely operated internal lateral cutter. Hot cure PVC

liners also normally require two access points to the host pipe.

Cold cure techniques are also known, most notably, a system using an inverted

liner saturated with resin. The liner is turned inside out or inverted and then forced into position in the pipeline by pressurised water normally produced by a static head of water

in a vertical inversion tube or pressure vessel being fed into an open end ofthe liner.

Though ambient or cold cure resins can be used with this system, thermo activated

polyester resin systems are preferred.

DISCLOSURE OF THE INVENTION

The present invention seeks to overcome or at least ameliorate the above problems

associated with the prior art by providing a cold cure method of lining existing pipelines

in-situ.

According to the present invention there is provided a method for rehabilitating

existing pipelines in-situ comprising the following steps:

a) forming a tubular liner of a generally absorbent material;

b) feeding at least one expandable bladder into said liner;

c) impregnating said liner with a cold curable resin;

d) coating an external surface of said liner and/or the internal surface ofthe

pipeline to be rehabilitated with a water resistant adhesive coating;

e) feeding said liner into the pipeline to be rehabilitated together with its

associated bladder;

f) inflating said bladder with a gaseous fluid to force the liner against the

internal wall of said pipeline; and g) maintaining said inflation until the resin impregnated liner has cured.

Preferably, the method includes the further steps of removing the bladder from the

cured liner. In a preferred form, the liner is formed of a felt-like material. For preference, the bladder is coated with a release agent prior to insertion into the liner tube.

Preferably, the gaseous fluid is compressed air.

The resin curing time may be adjusted by adjusting the ratios of base resin and

catalysts used. Further, where extended curing time is required, the resin may be cooled below ambient temperature during the set up process. BRIEF DESCRIPΗON OF THE DRAWINGS

A preferred embodiment ofthe present invention will now be described, by way of

example only, with reference to the accompanying drawings in which:

Figure 1 shows a pictorial representation ofthe liner prior to insertion into the host pipe;

Figure 2 shows a sectional representation ofthe liner and bladder prior to insertion

into the host pipe;

Figure 3 shows a sectional part cutaway representation ofthe liner inserted into the pipeline.

Figure 4 shows a pictorial representation ofthe lining method where there is only a

single access point and a boundary trap at one end.

MODES FOR CARRYING OUT THE INVENTION

Before discussing the process or method used in lining existing pipelines, an initial description ofthe materials used will be provided. The liner 5 is typically a felt-like

material with a flexible coating 6 applied to the outside ofthe felt. Typically, the felt is

formed from interlocked polyester with a thin membrane of polyurethane forming the flexible coating. It is tubed, stitched or vulcanised to form the shape ofthe pipeline. One or more extruded tubes 7 are coated with a release agent and inserted inside the felt tube or liner 5 to form an inflatable bladder. The extruded tubes 7 are typically formed

of PVC or other suitable plastics material although any form of flexible tubing capable

of forming an inflatable bladder containing compressed air may be used. The inflatable

bladder 7 may be inserted in the liner 5 before or after the felt is stitched or vulcanised.

The steps of a preferred method of lining an existing pipeline 8 will now be

discussed with reference to the accompanying drawings. Firstly, the pipeline 8 to be

lined is surveyed to access the length of pipeline to be lined and the location of any

relevant junctions. These junction distances are then marked on the liner 5 and a thin

flexible additional piece of tubing 9 is attached to the liner 5, as best shown in Figure 1.

This additional tubing 9 is optional, but desirable, in that it prevents excess resin

impregnating the liner 5 from bulging into the junctions and also assists in the cutting of

the junctions once the liner 5 is cured.

The liner 5 is next placed in a straight line on the ground and air plugs 10, 11

inserted into each end ofthe inflatable bladder 7. A short piece of tubing 12 is placed

over the end of bladder 7 adjacent the air plug 10, 11 and the air plug 10, 11 is inflated to

retain the bladder end 13 between the air plug 10, 11 and the short piece of tubing 12.

Air is supplied to the air plugs by air line 3 and to the bladder 7 by air line 4. The end of

the bladder 13 is spaced from the end ofthe liner 14 to prevent the end ofthe liner being

retained. The liner 5 is then inflated through one or both ofthe air plugs 10, 11. The

liner 5 is inflated sufficiently to form the desired shape ofthe pipeline 8 to be relined.

Once this is done both air plugs 10, 11 are pulled in opposite directions so as to stretch

the bladder 7 within the felt liner 5. This process eliminates any ridges. The air plugs

10, 11 are then deflated and removed. The bladder 7 is also deflated. A cold cure resin is then mixed and introduced between the bladder 7 and the felt

liner 5 such that the resin impregnates into the liner material. The liner 5 can then be

winched into position within the pipe 8 to be rehabilitated. As it is being winched into

position through an access hole 15, a water resistant adhesive coating 16 is applied to

outer flexible coating 6 ofthe liner 5. This water resistant coating 16 helps prevent

infiltration in the rehabilitated pipe 8.

Once the liner 5 is winched into the correct position within the pipe 8, a blank air

or mechanical plug 17 is inserted in one end ofthe liner inside the bladder end and a

flow through air plug 18 is inserted in the other end ofthe bladder in the same manner.

The bladder 7 is then inflated using compressed air. Once inflated, the bladder 7 may be

stretched to remove any ridges. A number of deflated bladders 7 may be used inside the

liner 5 as a form of security. Should the outer bladder fail through bursting or fails to

hold pressure for any reason, then the air plugs 17, 18 are easily removed and inserted

into a spare bladder.

The resin is then allowed to cure for the required time. During the curing process,

the liner 5 is held against the inner wall 19 of the pipeline 8 by the pressurised bladder 7.

The liner 5 is also attached to the inner wall 19 by means ofthe water resistant adhesive

16 previously applied. Following completion ofthe curing process, the plugs 17, 18 are

removed and the internal bladder 7 removed after deflation. Preferably, the bladder 7 is

attached to a cable which rotates the bladder tubing 7 while withdrawing it from the

liner.

Once this stage is completed, the junctions can be cut internally by use of a remote

control lateral cutter working in conjunction with a closed circuit TV (CCTV) camera. Alternatively, an electric drain cleaner can be used externally to cut the junctions from

relative access points.

Where there is only one access point to the pipeline 8 to be relined, the liner 5 is

pushed into position with hand rods or other suitable means. The remote ends ofthe

bladder 7 are sealed to prevent escape of inflation air and a flow through plug 18 is

inserted into the accessible end ofthe bladder 7. The process is then performed in a

similar manner to that described above.

In the case, where the only other access to the pipeline is a boundary trap, the

method according to a further aspect ofthe present invention includes introducing a

CCTV camera through the boundary trap to monitor and ensure correct positioning of

the liner in the pipeline. This is shown in Figure 4. The liner 5 has one end 20 sealed.

This end 20 is pushed toward the boundary trap 21 using hand rods (not shown) or the

like until the CCTV camera 22 shows that the liner 5 is correctly positioned within the

pipeline 8. The liner 5 can then be inflated using the internal bladder 7 in the usual

manner through the accessible end via flowthrough plug 18.

It will be understood that the present invention overcomes or at least ameliorates

the problems of shrinkage by use of an adhesive between the liner and the pipeline as

well as a cold cure technique. Further the cold cure technique enables long lengths of

pipe to be rehabilitated without the use of expensive, sophisticated equipment. It will be appreciated that further embodiments and exemplifications ofthe

invention are possible without departing from the spirit or scope ofthe invention

described and the invention is not limited to the particular embodiments described.

Claims (9)

CLAIMS:

1. A method for rehabilitating existing pipelines in-situ comprising the following

steps:

a) forming a tubular liner of a generally absorbent material;

b) feeding at least one expandable bladder into said liner;

c) impregnating said liner with a cold curable resin;

d) coating an external surface of said liner and/or the internal surface ofthe

pipeline to be rehabilitated with a water resistant adhesive coating;

e) feeding said liner into the pipeline to be rehabilitated together with its

associated bladder;

f) inflating said bladder with a gaseous fluid to force the liner against the

internal wall of said pipeline; and

g) maintaining said inflation until the resin impregnated liner has cured.

2. A method according to claim 1 including the further step of removing the bladder

from the cured liner.

3. A method according to claim 1 or claim 2 wherein the liner is formed of a felt-like

material.

4. A method according to claim 3 wherein the felt-like material is formed from

interlocked polyester with a thin membrane of polyurethane forming a flexible outer

covering.

5. A method according to claim 1 wherein the bladder is coated with a release agent

prior to insertion into the liner tube.

6. A method according to claim 1 wherein the gaseous fluid is compressed air.

7. A method according to claim 1 including the step of cooling the resin impregnated

liner below ambient temperature prior to step (e) to lengthen the curing time ofthe resin.

8. A method according to claim 1 including the step of reinforcing the regions ofthe

liner which, in use, coincide with junction points along the pipeline.

9. A method according to claim 1 wherein the pipeline to be rehabilitated has access

at one end for feeding in of said liner and the only other access to the pipeline being a

boundary trap, the method including the step of introducing a TV camera through the

boundary trap to monitor and ensure correct positioning ofthe liner in the pipeline.