Abstract:
Fusion of facing portions of the turnback portion of an installed everted resin impregnated cured in place liner installed in an existing conduit is avoided by adhering a high temperature turnback release film to a portion of the trailing end of the everting liner. After cure and removal of the downstream end of the liner, the high temperature release film is peeled away from the cured liner. This avoids the need to remove the fused portion of the turnback by cutting or excavation of a section of the liner. Fusion generally occurs due to the exotherm from the crosslinking of the thermosetting resin impregnated into the flexible lining.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method for installation of a cured in place liner into an existing conduit by everting the liner, and more particularly to a method for preventing the portion of the liner which turns back during eversion from bonding to the inner wall of the liner as it is cured, and to the liner assembly including a turnback release protection film. 
     It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage. The leakage may be inward from the environment into the interior or conducting portion of the pipe. Alternatively, the leakage may be outward from the conducting portion of the pipe into the surrounding environment. In either case, it is desirable to avoid this leakage. 
     The leakage may be due to improper installation of the original pipe, or deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive material. Cracks at or near pipe joints may be due to environmental conditions such as earthquakes or the movement of large vehicles or similar natural or man made vibrations, or other such causes. Regardless of the cause, such leakages are undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and in a possible creation of a dangerous public health hazard. 
     Because of ever increasing labor and machinery costs, it is increasingly more difficult and less economical to dig up and replace underground pipes or portions that may be leaking. As a result, various methods had been devised for the in place repair or rehabilitation of the existing pipelines. This avoids the expense and hazard associated with digging up and replacing the pipes or pipe sections. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process and is described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, the contents of all of which are incorporated herein by reference. 
     In the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. The impregnated liner may be pulled into the conduit by a rope or cable and a fluid impermeable inflation bladder or tube is then everted within the liner. Generally, the liner is installed utilizing an everting process, as described in the later two identified Insituform patents. 
     The flexible tubular liners has a smooth layer of relatively flexible, substantially impermeable polymer coating the outside of the liner in its initial state. This impermeable layer ends up on the inside of the liner after the liner is everted during installation. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing a fluid such as water which forces the liner radially outwardly to engage and conform to the interior surface of the existing pipeline. The resin which has been impregnated to the impregnable material is then cured to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and that repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment. 
     Generally, in the Insituform® Process, the resin impregnated liner is flat and is typically stored in layers. It is transported to a manhole adjacent to the pipeline to be lined. The leading end of the liner is sealingly clamped to the distal end of an eversion tube in order to create a fluid seal. Pressurized fluid, such as water then forces the liner to evert into the pipeline. Various means have been provided for controlling the rate in which the liner everts as it is fed into the pipeline. Typical means within the Insituform Process for controlling the feed rate of the liner is by retaining the trailing end of the resin impregnated liner as it is everted into the pipeline using a cable or hold-back rope. By restraining the trailing uneverted end of the liner, the liner does not evert too quickly, thereby ensuring that the pressure against the line is maintained throughout the everting liner. 
     When the liner is everted under a head of water, the liner stretches to an undeterminable length due to many different variables. This includes, but it is not limited to the inherent properties of the flexible lining material, the pressure of the everting fluid, the slope of the existing pipeline, the effects of different individuals installing the lining and the environment and condition of the existing pipeline. This requires that the installer provide a liner at least the length of the pipeline to be lined that almost always results in some portion of liner that turns-back at completion of installation. 
     This is the portion of the tube held by the hold-back rope remaining inside of the new cured in place lining and is identified as the “turnback” portion. When turnback occurs during eversion and hot water is circulated through the everted liner to initiate the cure, the turnback portion of the lining comes into contact with the surface wall of the liner as it is being cured. In other words, during the cure cycle of the cured in place pipe installation, the impermeable polymer coating of the turnback portion comes into direct contact with the impermeable coating of the liner against the host pipe wall. The heat from the exotherm of the resin causes the impermeable layers to melt, since the temperature exceeds the melting point of the coating thereby causing the two surfaces to fuse together. After cooling the cured liner, the fused portion of the turnback portion and the lining become one. 
     When the cure is completed, the end of the everted resin impregnated liner extends into the downstream manhole, the remaining turnback portion of lining inside of the new cured in place liner is usually removed. The difficulty is that the remaining turnback portion of the lining tube is now fused to the lining wall. This requires a substantial amount of resources, in time and dollars to remove the remainder of the tube from inside the cured liner. This is a costly operation, especially in large diameter pipe which can be as large as 8 feet in diameter or greater. Even more critical here is that when the diameter is too small for man entry, the turnback portion now fused to the liner wall must be cut from the manhole. When access is not possible in extreme situations, the entire section of pipe must be dug up and replaced resulting in extremely prohibitive costs. 
     It is also difficult to resolve this problem where the turnback occurs at a bend near the end of a host pipe. Similarly, at a bend the impermeable layer comes into contact with each other and there is the possibility that the two surfaces will fuse together. Again, this can be very difficult to remove, especially if it is not possible for human entry. 
     Accordingly, it is highly desirable to eliminate occurrence of fusion of the thermoplastic impermeable layers of a flexible cured in place liner during the cure after eversion of the liner. 
     SUMMARY OF THE INVENTION 
     Generally speaking, in accordance with the invention, a method for eliminating the fusion of the thermoplastic impermeable surfaces of a cured in place liner during installation by eversion is provided. Fusion of the turnback portion to the lining surface is avoided by temporarily bonding a high temperature release barrier between the two facing surfaces. The film is a high melt temperature film which is applied to the trailing end of the liner by a self-tack adhesive formulated to bond to the impermeable layer and that is water insoluble. After the installed liner is cured, the end of the everted liner is removed and the remaining high temperature film removed by peeling from the upstream end of the film. 
     The turnback protection film is applied to the trailing end of the liner in a length equal to from about 1 to up to 5% or more of the total length of the liner. A compatible spray adhesive is applied to about one-third of the release film length at the side of the trailing end of the liner and folded over to encompass the liner completely to form a turnback liner assembly. The turnback liner assembly is then everted into the existing pipeline in the usual manner using an everting fluid. After cure of the resin, the end of the liner extending to the down stream manhole is cut and the turnback protection film remaining within the lined conduit is peeled from the lining and removed. 
     Accordingly, it is an object of the invention to provide an improved method for eversion of a cured in place liner in an existing conduit. 
     It is another object of the invention to provide an improved method for preventing turnback fusion between the thermoplastic layer of the turnback portion and the lining after eversion of a cured in place liner in an existing conduit. 
     It is a further object of the invention to provide an improved liner assembly having a high temperature turnback protection film releasably secured about the trailing end of the liner for preventing turnback fusion after eversion of a cured in place liner. 
     Still other objects and advantages of the invention will in part be obvious and in part be apparent from the specification. 
     The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the article possessing the features, properties, and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a perspective view from the trailing end of a typical resin impregnable cure in placer liner suitable for use in accordance with the invention; 
     FIG. 2 is a cross-sectional elevational schematic view showing a cured-in-place liner at the start of eversion into an underground conduit using a hold-back rope to control the feed rate of the everting liner; 
     FIG. 3 is a view of the installation of FIG. 1 at the end of eversion; 
     FIG. 4 is a expanded cross-sectional view of the distal end of the eversion showing the turnback portion of the liner of FIGS. 1,  2  and  3  showing turnback fusion occurring; 
     FIG. 4A is identical to FIG. 4 after removal of the distal end of cured liner extending in the downstream manhole; 
     FIG. 5 is an exploded view of a turnback release film being adhered to the trailing end of a cured in place liner in accordance with the invention; 
     FIG. 6 illustrates how the turnback protection film of FIG. 4 is adhered to the liner in accordance with the invention; 
     FIG. 7 is a perspective view of a turnback release film liner assembly constructed and arranged in accordance with the invention;. 
     FIG. 8 is a cross-section of liner assembly of FIG. 7 taken along line  8 — 8 ; 
     FIG. 9 is a cross-sectional view similar to FIG. 4 showing the leading end of the everted liner using the assembly of FIGS. 7 and 8; and 
     FIG. 10 is a cross-sectional view of the eversion liner of FIG. 9 with the everting face removed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, when an existing pipeline or conduit  11  is not sound, it is desirable to use one of the accepted rehabilitation methods, such as a cured in place flexible liner  12  of the type disclosed in U.S. Pat. Nos. 4,009,063 and 4,064,211. In the eversion process described in the &#39;211 Patent radial pressure applied to the interior of liner  12  to presses it out into engagement with the inner surface of pipeline  11 . 
     Cured in place liner  12  shown in FIGS. 1 and 5 is formed from at least one layer of a flexible resin impregnable material such as a felt layer  13  having an outer impermeable polymer film layer  14 . Felt layer  13  and film layer  14  are stitched along a seam line  16  to form a tubular liner. A compatible thermoplastic film in a form of a tape or extruded material  17  is placed or extruded over seam line  16  in order to ensure impermeability of liner  12  to be everted. In the embodiment illustrated in FIG.  5  and used throughout this description, liner  12  includes an inner second felt layer  18  also seamed along a stitch line  19  which is positioned at a point other than the location of seam line  16  in outer felt layer  13 . For larger diameter liners, several layers of felt material may be used. Felt layers  13  and  18  may be natural or synthetic flexible resin absorbable material, such as polyester or acrylic fibers. Impermeable film  14  may be polyolefin, such as polyethylene or polypropylene, or a polyurethane as is well known in the art. 
     Prior to installation pursuant to the method illustrated in FIGS. 2 and 3, a curable thermosetting resin is impregnated into felt layers  13  and  18  pursuant to a process generally known as “wet-out”. The wet-out process generally involves injecting resin into the liner, drawing a vacuum and passing the impregnated liner through nip rollers and is well known in the lining art. One such procedure is described in Insituform U.S. Pat. No. 4,366,012, the contents of which are incorporated herein by reference. 
     Once liner  12  has been wet-out, it is generally stored in a folded layered condition  21  in preparation for eversion into pipeline  11  from an upstream. Liner  12  has a leading end  22  and a trailing end  23 . The eversion may be accomplished by feeding leading end  22  through a down tube  24  with leading end  22  turned over and secured to the outlet end of down tube  24 . A hold-back rope  26  is secured to trailing end  23  so that once the full length of liner  12  has passed through down-tube  24  the speed of liner  12  can be controlled by control of hold-back rope  26  by means of any type of release device, such as a winch  27 . 
     Referring to FIG. 2, leading end  22  is secured to down-tube  24 . An everting fluid, such as water  28  is fed into down-tube  24  by a first water pump  29 . As in FIG. 2, water pressure in liner  12  causes it to evert into pipeline  11  exhausting the supply of liner  12 . When conduit  11  is fully lined with liner  12  hold-back rope  26  is secured. Referring now to FIG. 3, a boiler  30  provides a supply of hot water  31  to be circulated through liner  12  through a hot water pump  32 . This causes the resin in liner  12  to crosslink, thereby forming a substantially rigid liner within existing conduit  11 . 
     As shown in FIG. 3, everting face  42  of liner  12  extends into manhole B and is cured in that manner. Trailing end  23  of liner  12  forms a turnback portion  41  which remains within newly lined pipeline  11  and liner  12 . This is shown in more detail in FIG.  4 . 
     In FIG. 4, turnback portion  41  is shown resting at the base of everted liner  12  in conduit  11  with everting face portion  42  extending into manhole B. After the resin has cured, liner portion  42  extending to manhole B is removed as shown in FIG.  4 A. At this point, turnback portion  41  remains in everted liner  12  with two sections of polymer coating  14  having fused together at a turnback fusion point  43 . Fusion occurs at turnback fusion point  43  because of the exotherm created during the crosslinking reaction of resin within felt layers  13  and  18 . This exotherm can cause temperatures of between about 250° F. to 400° F. or greater depending on various factors mentioned above. Thus, when impermeable layer  14  is a polyolefin, temperatures in excess of about 200° F. can cause fusion. When layer  14  is polyurethane the melting range is from about 330 to 365° F. so that fusion may occur less frequently than with polyolefin. 
     Fused turnback portion  43  which remains within everted liner  12  must be physically removed by hand after everting face portion  42  in manhole B is removed. In order to avoid formation of turnback fusion portion  43 , a turnback release liner assembly  51  illustrated in FIG. 7 in accordance with the invention is applied to liner  12  prior to eversion. 
     Assembly  51  is assembled by adhering an adhesive  55  to at least about one-third, preferably one-half the desired length C of turnback release film  52  as shown in FIG.  5 . In FIG. 6, liner  12  is then positioned onto release film  52  and a first end  56  of release film  52  is folded over liner  12  in arrow direction D and then opposed end  57  is folded in arrow direction E to form assembly  51  as shown perspective in FIG.  7  and in cross-section in FIG.  8 . 
     FIG. 7 turnback release assembly  51  includes a liner identical to liner  12  and having a high temperature turnback release film  52  partially adhered to trailing end  23  of liner  12 . With turnback release film  52  in place, fusion at turnback fusion point  43  is avoided as illustrated in FIG.  9 . Installed liner assembly  51  has been installed in the identical fashion as described with respect to FIGS. 2-4, except that now turnback release film  52  at trailing end  23  contacts itself at a turnback point  53 . In view of the high temperature characteristics of release film  52  fusion of outer impermeable polymer layer  14  as occurred in the showing in FIGS. 4 and 5 is avoided. 
     FIG. 8 illustrates turnback release assembly  51  in cross-section through lines  8 — 8  of FIG.  7 . As can be seen, the construction of liner portion  12  is identical to that shown and described with respect to FIG. 4 except for the positioning of the turnback release film  52  at trailing end  23 . 
     After eversion of assembly  51 , an everting face  54  of assembly  51  extends into manhole B and is removed in the same fashion described with respect to FIG. 4A. A turnback section  56  can be removed by simply pulling on turnback section  56 , since fusion between the facing surfaces of release film  52  does not occur. 
     Turnback release film  52  is an ultra high temperature film which is interposed between the two facing surfaces of polymer layer  14  at turnback portion. The materials selected for film  52  should have a melting point in the range of at least about 400° F. and be adhesively bondable to impermeable coating  14 . Preferably film  52  is a high-temperature fluorocarbon film having a maximum use temperature of about 650° F. (343° C.). Many such fluorocarbon films are commercially available. 
     The adhesive is preferably a fast tack spray adhesive formulated to bond polyurethane, polyethylene, polypropylene or any other polymer suitable for use as impermeable layer  14  to itself and be water insoluble. Suitable adhesives for use with polyolefins are typically formulated of synthetic resin and styrene butadiene copolymer mixtures in an alaphatic and keytone solvent. Such adhesives are available commercially. 
     The length of the turnback release film applied to the trailing end of a liner may vary widely. Typically, between about 1 to 5% of the length of the tube being installed can be used, and preferably between 1.5 to 3.5% of the length. In special applications, the length may be longer. Adhesive is placed on at least about one-third of the length of the release film for smaller size diameters such as 24 inches and less. In this manner, when the liner assembly is installed and everting end removed the upstream most end portion of the release film will not be bonded and will allow for ready removal of the bonded portion once the end of the installed liner has been cut in the B manhole. This is done by pulling release film  52  in the direction of arrow F in FIG.  10 . 
     In FIGS. 5 and 6, adhesive  55  is shown being applied to about one-half the length C of turnback film  52 . For installation in larger diameter pipelines, such as diameters larger than 24 inches, adhesive may be applied to the full surface of the release film. This is due to the fact that once such larger diameters are cut, it is possible for the worker in the manhole performing the cut to reach into the lined conduit and peel off the release film adhered to the cured liner. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made and carrying out the above method and in the construction set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.