Patent Publication Number: US-2007113971-A1

Title: Longitudinally reinforced cured in place liner and reinforced coating

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to cured in place liners for trenchless rehabilitation of existing conduits and pipelines, and more particularly to a cured in place liner longitudinally reinforced with a resin impermeable coated scrim on the outer surface of a liner with an inner impermeable layer, the liner suitable for trenchless rehabilitation of existing conduits.  
      It is generally well known that existing conduits and 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 pipelines. Alternatively, the leakage may be outward from the conducting portion of the pipeline into the surrounding environment. In either case of infiltration or exfultration, it is desirable to avoid this type of leakage.  
      The leakage in the existing conduit may be due to improper installation of the original pipeline, or deterioration of the pipe itself due to normal aging, or the effects of conveying corrosive or abrasive material. Cracks at, or near pipe joints may be due to environment conditions such as earthquakes, or the movement of large vehicles on the overhead surface, 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 possible creation of dangerous public health hazards. If the leakage continues it can lead to structural failure of the existing conduit due to loss of soil and side support of the conduit.  
      Because of ever increasing labor and machinery costs, it is increasingly more difficult and less economical to repair underground pipes or portions that may be leaking by digging up the existing pipe and replacing the pipe with a new one. As a result, various methods have been devised for the in place repair or rehabilitation of existing pipelines. These new methods avoid the expense and hazards associated with digging up and replacing the pipe or pipe sections, as well as the significant inconvenience to the public during construction. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process. The Insituform Process is described in detail in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, the contents of which are all incorporated herein by reference.  
      In the standard practice of the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material with an outer impermeable coating that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. In the most widely practiced embodiment of that process, the liner is installed utilizing an inversion process, as described in the &#39;211 and &#39;958 Insituform patents. In the inversion process, radial pressure applied to the interior of an inverted liner presses it against and into engagement with the inner surface of the pipeline as the liner unfolds along the length of the pipeline. The Insituform® Process is also practiced by pulling a resin impregnated liner into the conduit by a rope or cable and using a separate fluid impermeable inflation bladder or tube that is inverted within the liner to cause the liner to cure against the inner wall of the existing pipeline. Such resin impregnated liners are generally referred to as “cured-in-place-pipes” or “CIPP liners” and the installation is referred to a CIPP installation.  
      Conventional cured in place flexible tubular liners for both the inversion and pull-in-and-inflate CIPP installations have an outer smooth layer of relatively flexible, substantially impermeable polymer coating in its initial state. The outer coating allows a resin to be impregnated into the inner layer of resin impregnable material, such as felt. When inverted, this impermeable layer ends up on the inside of the liner with the resin impregnated layer against the wall of the existing pipeline. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing an inversion fluid, such as water or air to force the liner radially outwardly to engage and conform to the interior surface of the existing pipeline. Cure of the resin is initiated by introduction of hot curing fluid, such as water into the inverted liner through a recirculation hose attached to the end of the inverting liner. The resin impregnated into the impregnable material then cures to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the existing pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.  
      When tubular cured in place liners are installed by the pull-in-and-inflate method, the liner is impregnated with resin in the same manner as in the inversion process and pulled into and positioned within the existing pipeline in a collapsed state. In a typical installation, a down tube, inflation pipe or conduit having an elbow at the lower end is positioned within an existing manhole or access point and an inverting bladder is passed through the down tube, opened up and cuffed back over the mouth of the horizontal portion of the elbow and inserted into the collapsed liner. The collapsed liner within the existing conduit is then positioned over and secured to the cuffed back end of the inflation bladder. An inverting fluid, such as water, is then fed into the down tube and the water pressure causes the inflation bladder to push out of the horizontal portion of the elbow and cause the collapsed liner to expand against the interior surface of the existing conduit. The inversion of the inflation bladder continues until the bladder reaches and extends into the downstream manhole or second access point. At this time, the liner pressed against the interior surface of the existing conduit is allow to cure. Cure is initiated by introduction of hot curing water introduced into the inflation bladder in much the same manner as the recirculation line tied to the end of the inverting bladder to cause the resin in the impregnated layer to cure.  
      After the resin in the liner cures, the inflation bladder may be removed or left in place in the cured liner. Both the pull-in and inflate method as well as the inversion method typically require man-access to restricted manhole space on several occasions during the process. For example, man-access is required to secure the inverting liner or bladder to the end of the elbow and insert it into the collapsed liner.  
      Regardless of how the liner is to be installed a curable thermosetting resin is impregnated into the resin absorbent layers of a liner by a process referred to as “wet-out.” The wet-out process generally involves injecting resin into resin absorbent layers through an end or an opening formed in the outer impermeable film, drawing a vacuum and passing the impregnated liner through nip rollers as is well known in the lining art. A wide variety of resins may be used, such as polyester, vinyl esters, epoxy resins and the like, which may be modified as desired. It is preferable to utilize a resin which is relatively stable at room temperature, but which cures readily when heated with air, steam or hot water, or subjected to appropriate radiation, such as ultra-violet light.  
      One such procedure for wetting out a liner by vacuum impregnation is described in Insituform U.S. Pat. No. 4,366,012. When the liner has inner and outer impermeable layers, the tubular liner may be supplied flat and slits formed on opposite sides of the flattened liner and resin injected and on both sides as described in the &#39;063 Patent. Another apparatus for wetting out at the time of installation while drawing a vacuum at the trailing end of the liner is shown in U.S. Pat. No. 4,182,262. The contents of each of these patents are incorporated herein by reference.  
      Recent efforts have been made to modify the pull-in and inflate method to utilize air to evert a bladder into the pulled-in liner from a proximal access point. When the inverting bladder reaches the distal access point, steam is introduced into the proximal access point to initiate cure of the resin impregnated layer. This process offers the advantage of faster cure due to the increased energy carried by the steam as the curing fluid. However, the process still requires inversion of a bladder into the pulled-in impregnated liner. Efforts to avoid this step of inverting the bladder into the pulled-in liner include performing the inversion step above ground. For example, in U.S. Pat. No. 6,270,289, the process includes inverting a calibration hose into a flat-lying lining hose above ground prior to pulling the hose assembly into the existing conduit. This process avoids the inversion below grade, but is severely limited into the length of lining that can be laid out above ground prior to pulling-in.  
      A further suggestion to avoid this inversion is to manufacture a liner having an inner coating and an outer coating so that a curing fluid can be introduced directly into a pulled-in liner. The disadvantages here involves the difficulty faced when trying to impregnate the resin impregnable material disposed between the inner and outer impermeable coatings. The outer coating remains essential for handling the impregnated liner and to allow the liner to be pulled into the existing conduit and the inner coating is desired to all for curing with the steam.  
      A typical 8 inch diameter 6 mm thick liner weighs about 7.5 ounces per foot prior to wet out. About 3 pounds of resin per foot are impregnated, resulting in almost a seven fold increase in weight to about 3.5 pounds per foot. In this case, a 200 foot length of liner subject to a load of 350 pounds stretches about 3 percent in length. At 5000 pounds of load the 8 inch liner will stretch as much as 35 to 40 percent. Thus, a typical 300 foot liner between manholes may stretch as much as 30 feet. The increase in weight of the liner for larger diameter liners makes the load required for pull-in even more staggering. Thus, there are significant limitations on the lengths of liner that can be pulled in. The same is true to a greater extent for larger diameter liners. According to ASTM 1783-96, the acceptable longitudinal elongation of the fabric tube is not more than 5% of the overall length measured after the impermeable bladder has been installed in the fabric tube or exceed the recommended pulling force.  
      One solution to this stretching problem involves addition of a layer of reinforcing fibers into or between impregnable layers of the liner. For example, in U.S. Pat. No. 5,868,169 a web or mesh of reinforcing fibers is stitched or flame bonded to one of the resin absorbent layers of the liner. The webs disclosed are in a graphical or grid pattern, include longitudinal fiber held together by radial fibers, cross-hatched or a cross-hatched web with randomly oriented fibers.  
      While these suggestions to increase longitudinal strength are available, there are difficulties in handling webs and attaching them to one of the resin absorbent layers as a heavy web tends to hinder impregnation and reduce the circumferential stretch need for CIPP installation. Accordingly, it is desirable to provide a longitudinally reinforced liner that can be easily manufactured and avoid the difficulties faced in the prior art.  
     SUMMARY OF THE INVENTION  
      Generally speaking, in accordance with the invention, a resin impregnated cured in place liner having a longitudinally reinforced outer impermeable layer for trenchiess rehabilitation of existing pipelines is provided. The liner may be continuously formed from a length of a resin absorbent material having an impermeable layer bonded to one surface formed into a tubular member and sealed with the impermeable layer on the inside of the tubular member. The tubular member may be wrapped with additional layers of resin absorbent material in tubular form and impregnated with a thermosetting resin. An outer layer of resin impermeable coated scrim having greater strength in the warp direction is applied to the outer surface of the impregnated liner. This coated scrim layer may be applied to the outer surface of the liner by inverting a liner of impermeable coated scrim material onto the inner tubular member as the tubular member is fed into a tubular stuffing device, or by wrapping and sealing continuously with an impermeable coated scrim layer.  
      The coated scrim layer provides increased longitudinal reinforcement. This increase in longitudinal strength allows for pulling-in of long lengths of liner, and substantially reduces stretch of the resin impregnated liner during pull-in. The impermeable coating applied to the scrim is a polyolefin or other material that will withstand temperatures during steam cure of the liner. The coated scrim as the outer impermeable layer increases and evens out the stress across the entire circumference of the coated scrim layer and provides better performance in reducing longitudinal stretch as the warp scrim yarns and coating act more like a composition than the separate scrim and film layers.  
      Accordingly, it is an object of the invention to provide an improved longitudinally reinforced cured-in-place liner having an inner impermeable coating.  
      Another object of the invention is to provide an improved method for manufacturing a longitudinally reinforced liner having an inner impermeable coating.  
      Another object of the invention is to add a coated scrim during the manufacture of a CIPP liner that will limit longitudinal stretch without reducing circumference stretch.  
      A further object of the invention is to provide an improved method of manufacture of a longitudinally reinforced cured in place liner by disposing a coated scrim layer on the outer layer of resin absorbent material.  
      Yet another object of the invention is provide an improved method of continuously manufacturing a longitudinally reinforced resin impregnated cured in place liner having an inner impermeable layer and a coated scrim layer.  
      Still another object of the invention is to provide a method of applying a longitudinal reinforcement to a CIPP liner after the impregnable layer is wet-out with resin.  
      Yet a further object of the invention is to provide a method of manufacturing a cured in place liner having inner impermeable layer and coated scrim layer for pull-in and inflate trenchless pipeline installation.  
      Still other objects and advantages of the invention will in part be obvious and will 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, the apparatuses embodying features of construction, combinations and arrangement of parts that are adapted to effect such steps, and the products that possess the characteristics, features, properties, and the relation of components, 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 drawing(s), in which:  
       FIG. 1  is a perspective view of a length of a typical resin impregnable cured in place liner suitable for use in lining an existing pipeline of the type generally in use today and well known in the art;  
       FIG. 2  is a cross-section view of a cured in place liner having longitudinal reinforcement and inner and outer impermeable layers constructed and arranged in accordance with the invention;  
       FIG. 3  is a schematic view of the apparatus used for preparing the inner portion of the liner having an outer felt layer with an inner high temperature polymeric layer used in connection with preparation of the cured in place liner of  FIG. 2 ;  
       FIG. 4  is a cross-sectional view showing the structure of the inner portion of the liner produced by the apparatus of  FIG. 3  before being impregnated in accordance with the invention;  
       FIG. 5  is a schematic in elevation showing resin impregnation and mating with longitudinal reinforcing coated scrim and wrapping of the tubular member of  FIG. 4  for preparing an impregnated CIPP liner in accordance with the invention;  
       FIG. 6  is a cross-sectional view of the edge sealer in the sealing and wrapping apparatus of  FIG. 3  taken along line  6 - 6 ;  
       FIG. 7  is a cross-section of the liner prepared by the apparatus of  FIG. 5 ;  
       FIG. 8  is a schematic in elevation showing wrapping of the tubular member exiting a resin impregnation apparatus with an outer coating by passing the wet out liner through a liner stuffer having a tubular wrapping of longitudinal reinforcing coated scrim stored thereon;  
       FIG. 9  is a cross-section of a liner wrapped by the apparatus of  FIG. 8 ; and  
       FIG. 10  is a graph comparing the elongation of a standard CIPP liner with integral inner layers, that same standard CIPP liner with 12″ scrim under the outer layer, and a CIPP liner formed with a longitudinally reinforced with an outer reinforced scrim layer prepared in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      A resin impregnated cured in place liner prepared in accordance with the invention has a longitudinal reinforcing coated scrim layer as the outer impermeable layer. When prepared with an integral internal impermeable layer, it can be installed by the pull-in-and-inflate method and be inflated and cured with a heated fluid without the use of an inflation bladder. A liner with inner impermeable longitudinal reinforcing coated scrim layer may be prepared in continuous lengths. It may be impregnated as it is assembled in view of the increased effort necessary to impregnate a flattened liner having a resin absorbent material between an inner and an outer coating using conventional vacuum impregnation technology.  
       FIG. 1  illustrates a flexible cured in place liner  11  of the type generally in use today and well known in the art. Liner  11  is formed from at least one layer of a flexible resin impregnable material, such as a felt layer  12  having an outer impermeable polymer film layer  13 . Felt layer  12  and outer polymer layer  13  are stitched along a seam line  14  to form a tubular liner. A compatible thermoplastic film in a form of a tape or extruded material  16  is placed on or extruded over seam line  14  in order to ensure the impermeability of liner  11 . In the embodiment illustrated in  FIG. 1  and used throughout this description, liner  11  includes an inner tube of a second felt layer  17  also stitched along a seam line  18  positioned at a point in the circumference other than the location of seam line  14  in outer felt layer  12 . Outer felt layer  12  with polymer layer  13  is then formed around inner tubular layer  17 . After impregnation liner  11  in a continuous length is stored in a refrigeration unit to suppress premature cure of the resin. Liner  11  is then cut to a desired length after being pulled into the existing pipeline, or is cut prior to being inverted into the existing pipeline.  
      Liner  11  of the type illustrated in  FIG. 1  is impermeable to water and air. This will allow use in an air or water inversion as described above. However, in a pull in and inflate installation in accordance with the invention, the outer coating on the liner need only be sufficiently impermeable to allow for easy handling wet-out and retention of resin and to prevent damage to the liner as it is pulled into the existing pipeline.  
      For larger liner diameters, several layers of felt or resin impregnable material may be used. Felt layers  12  and  17  may be natural or synthetic flexible resin absorbable material, such as polyester, acrylic polypropylene, or inorganic fibers such as glass and carbon. Alternatively, the resin absorbent material may be a foam. Impermeable film  13  on outer impregnable layer  12  may be a polyolefin, such as polyethylene or polypropylene, a vinyl polymer, such as polyvinyl chloride, or a polyurethane as is well known in the art. Any form of sewing, adhesive bonding or flame bonding, or any other convenient means can be used to join the material into tubes. In the initial step in all trenchless rehabilitation installations, the existing pipeline is prepared by cleaning and videotaping.  
      Referring now to  FIG. 2 , a longitudinally reinforced cured in place liner  21  prepared in accordance with the invention is shown in cross-section. Liner  21  is constructed in similar fashion to convention liner  11 , but includes an inner impermeable layer  22  that has a thin felt or resin impregnable layer  23  bonded thereto. Inner felt layer  23  and impermeable layer  22  have been sewn along a seam line  24  by a row of stitches  26  and sealed with a tape  27  applied over stitches  26 . An outer felt layer  28  is wrapped about inner thin felt layer  23  and formed into a tube by stitches  29 . Finally, a longitudinal resin impermeable reinforcing coated scrim layer  35  is formed into a tube with an edge seal  32  and continuously inverted over outer felt layer  28  so that an edge seal  32  is encapsulated under longitudinal reinforcing coated scrim layer as will be described in more detail below.  
      The reinforcing coated scrim can be formed of any high-strength low-elongation fibers, such as glass, polyester, polyethylene, fibulated polypropylene, nylon, carbon, Aramid and even steel. The scrim may be woven or non-woven, but preferably is woven. It can be formed of any continuous, flexible, high strength and low elongation fabrics or films, since they will not affect the impregnation process and circumferential expansion of the finished liner. The ease of fabrication allows for the continuous assembly of the longitudinally reinforced liner from plain felt supplies in a continuous manner by the apparatus disclosed.  
      The impermeable coating may be a polyolefin, such as polyethylene or polypropylene, a vinyl polymer, such as polyvinylchloride, or a polyurethane as is well known in the art for use in CIPP liners. Of course, if steam is to be used for cure, the material is polypropylene or other polymeric material that withstands the temperatures generated during the steam cure.  
      In a preferred embodiment, the longitudinal reinforcing coated scrim is formed of woven polypropylene having increased longitudinal strength. The properties of an uncoated polypropylene scrim available from Belton Industries as Style  244  are as follows:  
                                                       Typical   Minimum   English       Physical Property   Test Method   Value   Value   Units                                        Composition   POLYPROPYLENE       Construction   24 × 6       Color   NATURAL                                 Mass Per Unit Area   ASTM D-3776   2.6   2.2   OZYD2       Tensile Strength-   ASTM D-4632   180   100   LB       Warp       Tensile Strength-Fill   ASTM D-4632   70   40   LB       Elongation-Warp   ASTM D-4632   20.0   10.0   PERCENT       Elongation-Fill   ASTM D-4632   17.5   10.0   PERCENT       Bursting Strength   ASTM D-3786   260   185   PSI                  
 
 The scrim having greater strength in the warp direction is coated with a polymeric material to render it impermeable. When polypropylene is used with the preferred Belton material, the coating is between about 5 to 15 mils in thickness, preferably about 7 to 10 mils. 
 
      The liner prepared in accordance with the process described in connection with  FIG. 3  is then readily impregnated in an open top resin tower and enveloped with the coated reinforcing scrim as described in connection with the apparatus shown in  FIG. 5 . The smooth outer surface renders the liner ready for pull-in-and-inflate installation.  
      By manufacturing a liner in this manner, it is not necessary to evert the liner during installation or evert an inflation bladder after the liner has been pulled into the existing conduit. Longitudinal reinforcing coated scrim layer  35  allows pulling-in of longer length while avoiding stretch and inherent thinning of the liner wall.  
      Felt layers  23  and  28  may be impregnated in the usual manner using vacuum. Alternatively, felt layers  23  and  28  are first impregnated with resin and then longitudinal reinforcing coated scrim layer  35  is applied. First impregnating the felt avoids the difficulty faced when attempting to impregnate a finished liner having an inner impermeable layer and an outer impermeable longitudinal reinforcing coated scrim layer. Liner  21  is manufactured from endless rolls of flat coated felt and plain felt and continuously impregnated prior to mating with longitudinal reinforcing coated scrim layer  35 . This may be accomplished by the method using the apparatuses illustrated in  FIGS. 3 and 5  resulting in a liner  21  and  74  as illustrated in  FIGS. 2 and 7 .  
      While felt layers  23  and  28  are formed into tubes by stitching and/or taping, any of the conventionally known methods for forming felt or other resin impregnable material into liners is suitable. For example, tubes can be formed by use of various glues or adhesives as well as flame bonding. Tape may be applied to inner felt layer  23  and inner impermeable layer  22  by applying an adhesive strip or extruding a layer of polymeric material in order to seal the butted edges of the felt material and the holes formed in layer  22  during a sewing operation.  
      Referring now to  FIG. 3 , a method for continuously forming a length of a tube or resin impregnable material with a sealed inner impermeable layer is shown. A roll of coated felt  36  having a continuous length of felt  37  with an impermeable layer  38  is fed over a directional roller  39  in flat form with coated side facing roller  39  to a tube forming device  41 .  
      Tube forming device  41  includes a tubular support frame  42  having a proximal end  42   a  and a distal end  42   b  and a film deformer  40 . A seaming device  43  that may be a sewing and taping machine, gluing machine or flame bonding apparatus is mounted above support frame  42 . Felt  37  with impermeable layer  38  facing roller  39  is fed in the direction of an arrow A to the proximal end of tube forming device  41  where it is deflected by deflector  40  and wrapped around support frame  42  and seamed into a tube  44  along a seam line  46  with felt  37  on the inside and impermeable layer  38  on the outside. Tube  44  then passes a taping device  47  where a tape  48  is placed over seam line  46  to form an impermeable coated taped tube member  45 .  
      Taped tube member  45  then continues to travel along tubular support frame  42  to an inverter ring  49  at the distal end of support frame  42 . Taped tube  45  is then inverted into tubular support frame  42  so that impermeable layer  38  is now on the inside of tube  45  as it is withdrawn from the proximal end of tubular support frame  42  along a line defined by an arrow B. At this point inverted tube  45  has the structure illustrated in cross-section in  FIG. 4  with impermeable layer  38  on the inside and felt layer  37  on the outside. Tube  45  is then stored for further use or may be passed directly to a resin impregnation step and reinforcement as shown in  FIG. 5  prior to final wrapping.  
       FIG. 5  illustrates in schematic impregnation of a supply  51  of taped tubular material  45 . Here, tube  45  is pulled in a direction indicated by arrow C by a pair of rubber covered pulling rollers  52  and  53  into an open top resin tower  54 . Resin tower  54  is filled to a predetermined level with a curable thermoset resin  57  to form an impregnated or wet-out tube  55 . Tube  45  passes over roller  53  and down the full height of tower  54  to a bottom roller  59  that turns tube  45  in an upward direction to a pair of calibration rollers  61  and  62 . Tower  54  is between about six to fourteen feet in height, but can be any height sufficient to provide a pressure head sufficient to wet out and impregnate the outer impregnable layer of tube  45  to form an impregnated tube  45  to form an impregnated tube  55 . The height necessary to provide sufficient head to impregnate the impregnable material is dependent on the viscosity of the resin, the thickness of the impregnable material and the speed through the tower.  
      At this time, impregnated tube  55  exiting tower  54  in the direction of an arrow D is ready for adding a longitudinal reinforcing coated scrim layer  67 .  
      Film wrapping and sealing station  63  shown in  FIG. 5  includes a former pipe  64  having an inlet end  64   a  and an outlet end  64   b  and an edge sealer  65  positioned above the mid-section of former pipe  64 . Roll  66  of longitudinal reinforcing coated scrim layer material  67  that is to be wrapped about impregnated tube  55  as it is fed in a direction indicated by an arrow D into former pipe  64 . Longitudinal reinforcing coated scrim layer material  67  is fed from roll  66  about a series of direction rollers  68   a  -  e  and pulled by a pair of drive rollers  69   a  and  69   b  as film  67  is fed over rollers  70   a  -  d  to former pipe  64 . A deflector  71  guides film  67  onto former pipe  64  prior to being fed into edge sealer  65  to form film  67  into a tube  72  with an edge seal  73  extending outwardly therefrom. Tube  72  of longitudinal reinforcing coated scrim material  67  moving along former pipe  64  is pulled in a direction indicated by an arrow E to inlet end  64   a  of former pipe  64  whereupon tube  72  is continuously inverted into the interior of former pipe  64  and onto impregnated tube  55 . Tube  72  of longitudinal reinforcing coated scrim material  67  is averted onto impregnated tube  55  to form a wrapped liner  74  having outer wrapping of longitudinal reinforcing coated scrim tube  72  with an edge seal  73  as shown in cross-section in  FIG. 7 . Wrapped liner  74  is pulled by a pair of final pulling rollers  79  and  81  and fed along a dashed arrow F to a refrigerated truck for shipment to an installation site.  
      In another embodiment in accordance with the invention, a layer of an impermeable reinforcing scrim material may be used as inner impermeable layer  38 . In this case, a liner of substantially increased longitudinal reinforcement is provided.  
      Referring to  FIG. 6 , a cross-sectional view through sealer  65  and former pipe  64  along line  6 - 6  in  FIG. 6  is shown. Sealer  65  forms edge seal  73  in film tube  72  as film tube  72  passes over the outside of former pipe  64 . Once tube  72  is inverted, edge seal  73  is now inside wrapped wet-out liner  74  as it is pulled from outlet end  64   b  of former pipe  64 . Outer longitudinal reinforcing coated scrim tube  72  may be applied prior to or after wet-out. In the case where this is prior to wet out, tube  45  prepared as shown in  FIG. 3  is fed directly to liner forming assembly in  FIG. 5  and provides liner  74  shown in cross-section in  FIG. 7 .  
       FIG. 8  illustrates an alternative apparatus for wrapping an outer impermeable longitudinal reinforcing coated scrim tubular layer  85  about impregnated tube  55  is shown generally as  82 . Here tube  55  may be impregnated in the same manner as described in connection with tower  54  as shown in  FIG. 5 , or into an open resin tank with compression rollers. Tube  55  is then fed in a direction of arrow D′ into a stuffer pipe  83  having an inlet end  83   a  and an outlet end  83   b . Reference numerals as used in  FIG. 5  are applied to identical elements here.  
      A length of a flexible impermeable longitudinal reinforcing coated scrim tube  85  is loaded onto the outside surface of stuffer pipe  83  having an inlet end  83   a  and an outlet end  83   b . Impregnated tube  55  leaving resin tank  54  is fed into inlet end  83   a  of and inverted about inlet end  83   a  into the inside of stuffer pipe  83  to envelope impregnated tube  55  as it leaves outlet end  83   b . This forms a completed liner  86  having inner impermeable layer  38  and outer impermeable longitudinal reinforcing coated scrim  85 . Liner  86  with outer coated scrim layer  85  is removed from outlet end  83   b  of stuffer pipe  83  by a pair of drive rollers  87  and  88 , or other pulling device such as tractors, in a direction of an arrow F. When an extruded impermeable tube is used in this embodiment, there is no seam in outer impermeable coated scrim layer  85 . The sole limitation of preparing liner  86  in this manner is the length of impermeable longitudinal reinforcing coated scrim liner  85  that can be placed on stuffer pipe  83 . About 500 to 750 feet of an impermeable liner can be compressed onto a stuffer liner of about 20 feet in length. Longer lengths can be stored on longer stuffer liners.  
       FIG. 9  is cross-section of finished CIPP liner  86  as it exits stuffer pipe  83 . Liner  86  includes inner tubular member of resin absorbent material  37  having an impermeable inner coating  38  sealed with a tape  48  as described in connection with  FIG. 3 . After exiting stuffer pipe  83 , liner  86  includes outer tubular longitudinal reinforcing coated scrim layer  85 . In view of the fact that tubular layer  85  is a previously extruded tube, outer layer  85  does not have any seams as liner  21  in  FIG. 2  or liner  74  in  FIG. 7 .  
      Once at the installation site, reinforced and wrapped impregnated liner  74  or  86  having inner impermeable layer  38  and outer impermeable longitudinal reinforcing coated scrim layer  67  or  85  is ready for installation by the pull-in-and-inflate method. This method is fully described in U.S. Pat. No. 4,009,063, the contents of which are incorporated herein by reference. In the case of installation by the pull-in-and-inflate method, a separate inversion bladder is not necessary to inflate the liner due to the presence of inner impermeable layer  38 . By proper selection of materials for inner impermeable layer  38 , such as polypropylene, curing can be done with steam introduced into the liner  74  once in position in the existing conduit.  
      As can be readily seen, there is provided a convenient method of increasing the longitudinal strength of a flexible cured in place liner having inner and outer impermeable layers. By placing an impermeable reinforced layer of a coated scrim having greater strength in the warp direction around the liner, a flexible cured in place liner of increased potential longitudinal strength is obtained. This allows for pulling in long lengths of liners or liners of substantially larger than the 8 inches typically utilized for main lines and conventional sanitary sewers without experiencing unwanted stretch of the liner.  
       FIG. 10  is a graph illustrating the elongation of three CIPP liners. Liner A is a typical 8 inch diameter CIPP liner that is 6 mm in thickness. Liner B is an 8 inch diameter CIPP liner that is longitudinally reinforced with a 12″ wide scrim having greater strength on the warp direction on one lay flat surface between the impregnated layer and outer impermeable layer. Liner C is an 8″ CIPP liner reinforced with an outer layer of coated scrim in accordance with the invention. This graph shows that the elongation of Liner C with reinforced wrap is substantially reduced compared with the Liner A. As the pulling force increases, the elongation of the liner increases. For example, Liner A stretches almost 9 percent in length when a pulling force of 1000 lbs. is used. At the same pulling force, reinforced Liner C prepared in accordance with the invention stretches less than about 3 percent in length. This is a 66% decrease in the elongation of Liner C with reinforced wrap when compared to Liner A at a pulling force of 1000 lbs.  
       FIG. 10  also shows that the elongation of Liner C is reduced compared with Liner B. As the pulling force increases, the elongation of the liner increases. For example, Liner B stretches over 5 percent in length where a pulling force of 1000 lbs. is used. At the same pulling force, Liner C prepared in accordance with the invention stretches less than about 2.5 percent in length. This is a 50% decrease in elongation of Liner C with reinforced wrap when compared to Liner B at a pulling force of 1000 lbs.  
      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 in carrying out the above process, in the described product, and in the construction(s) 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 drawing(s) 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 therebetween.