Patent Publication Number: US-11384889-B2

Title: Pipe liner and method of making and installing the same

Description:
FIELD 
     The present invention generally relates to a cured-in-place pipe liner and, more specifically, to cured-in-place pipe liner comprising strengthening fibers. 
     BACKGROUND 
     Over time or because of a particular event or condition (e.g., seismic activity, exposure to excessive or uneven loads or moments, poor compaction, crown corrosion, corrosive soil, etc.), the structural integrity or capacity of force mains, other pipes, and like structures may diminish. For example, such items may crack, corrode, deteriorate, and the like. Damage to a pipe is particularly problematic when the pipe is used to carry a high pressure fluid because the pressurized fluid can impart significant forces, particularly in the hoop direction, on the pipe. Different methods of repairing or otherwise strengthening damaged pipes and other items are known. For example, reinforced fabric liners can be attached to one or more portions of a pipe interior. In cured-in-place pipe (CIPP) lining applications, liners are impregnated with a curable resin or epoxy, positioned along the interior surface of a host pipe, and allowed to cure, thereby forming a watertight barrier between the host pipe and the pipe interior. Various techniques for positioning a CIPP liner inside a host pipe (e.g., eversion, pull-in and inflate, etc.) and curing the liner (e.g., steam curing, ultraviolet light curing, etc.) are known. In addition, CIPP liners have been formed from various materials that have been constructed in many different ways. For example, it is known to form pressure-bearing liners from mats and fabrics that are laden with strengthening fibers such as glass fibers, etc. 
     SUMMARY 
     In one aspect, an eversion liner for lining a pipe comprises an outer impermeable portion having an interior. The outer impermeable portion comprises a fluid-impermeable material. The fluid impermeable material is formed into a longitudinally extending tube. The liner comprises inner and outer strength portions. The outer strength portion is located in the interior of the outer impermeable portion. Each of the inner and outer strength portions has an interior. Each of the inner and outer portions is arranged to form a respective longitudinally extending tube and comprises strengthening fibers. At least one of the inner and outer strength portions comprises a unitary sheet of strength material. The sheet of strength material has a width and opposite first and second longitudinal edge margins spaced apart along the width. The sheet of strength material comprises chopped strands of fiber oriented generally parallel to one another and distributed along the sheet of strength material. The first and second longitudinal edge margins of the sheet of strength material are positioned in overlapping engagement. The at least one of the inner and outer strength portions comprises joining structure connecting the first and second longitudinal edge margins of the sheet of strength material together in overlapped relation to form a longitudinal overlap portion extending parallel to a length of the at least one of the inner and outer strength portions. A middle portion has an interior. The middle portion comprises felt. The felt is formed into a longitudinally extending tube. The middle portion is located in the interior of the outer strength portion. The inner strength portion is located in the interior of the middle portion. 
     In another aspect, a method of manufacturing a liner for lining a pipe comprises forming a first strength tube comprising strengthening fibers. At least one felt tube is formed around the first strength tube. A second strength tube comprising strengthening fibers is formed around the at least one felt tube. An impermeable tube is formed around the second strength tube. At least one of the steps of forming the first strength tube and forming the second strength tube comprises: arranging a unitary sheet of strength material so that a width of the sheet extends in a hoop direction of the respective one of the first strength tube and the second strength tube. The sheet of strength material comprises chopped strands of fiber oriented generally parallel to one another and distributed along the sheet of strength material. First and second longitudinal edge margins of the sheet are joined together in overlapped relation to form a longitudinal overlap portion extending parallel to a length of the respective one of the first strength tube and the second strength tube. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary perspective of a liner; 
         FIG. 2  is a schematic cross section of the liner; and 
         FIG. 3  is a schematic fragmentary top plan view of a sheet of material for forming a strength layer of the liner. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , one embodiment of a liner for being cured in place inside a host pipe (not shown) is generally indicated at reference number  10 . The illustrated liner  10  is configured to be installed by eversion. It is understood that aspects of the disclosure could be adapted for use with liners that are installed by other methods without departing from the scope of the invention. The liner  10  has a first end and a second end spaced apart along a length L of the liner. As will be explained in further detail below, the liner  10  comprises an outer portion  12 , an outer strength portion  14  nested in the outer portion, a middle portion  16  nested in the outer strength portion, and an inner strength portion  18  nested in the middle portion. Each of the outer portion  12 , the outer strength portion  14 , the middle portion  16 , and the inner strength portions  18  comprises one or more flexible tubes in the illustrated embodiment. The tubes are nested in a concentric arrangement to form the liner  10 . Prior to installation, the inner strength portion  18  defines the interior of the liner  10 , but after the liner is everted into a host pipe, the outer portion  12  defines the liquid flow passage of the installed liner. Throughout this disclosure the terms “inner” and “outer” (as well as other similar terminology) are used in reference to the arrangement of the liner  10  prior to eversion and as shown in the drawings. As will be described in further detail below, the illustrated liner  10  is configured so that the discrete portions  12 ,  14 ,  18 ,  16  are connected to one another so that liner can be reliably everted into a host pipe as a single unit. Furthermore, as discussed below, the strengthening portions  14 ,  18  of the liner  10  are configured to provide the installed liner with standalone pressure-bearing capacity and, moreover, do so substantially without creating wrinkles in the installed liner. 
     Referring to  FIG. 2 , the outer portion  12  has a length that extends from the first end to the second end of the liner  10  and comprises a coated felt that is formed into a tube that extends along the length of the outer portion. The outer portion  12  comprises an inner layer of felt  12 A (e.g., non-woven threads that are needle-punched, matted, condensed, or otherwise pressed together) and a fluid-impermeable coating  12 B. The coating  12 B can be formed by a polymer that is applied to the felt  12 A in fluidic form and then cured to permanently bond to the felt. Alternatively, the coating  12 B can be formed from an impermeable polymer film that is permanently bonded to the felt  12 A using an adhesive, heat, etc., such that there is a bond between the coating and the felt that is substantially continuous along substantially the entire surface area of the felt. The felt  12 A comprises a resin-impregnable material such as polyester felt. The impermeable coating  12 B can comprise a polymer, for example a polyolefin, such as polyethylene or polypropylene; a vinyl polymer, such as polyvinylchloride; or a polyurethane. Exemplary methods of forming a coated felt outer portion  12  are described in U.S. Pat. Nos. 7,857,932, 7,261,788, and 7,238,251, each of which is hereby incorporated by reference in its entirety. 
     To form the outer portion  12  to a desired length, multiple sheets of coated felt are arranged end-to-end and joined together at adjoining end margins. The sheet of coated felt is folded into a tube such that side margins of the sheet engage one another, the felt layer  12 A defines the interior of the tube, and the impermeable coating  12 B defines the exterior of the tube. The side margins are joined together at a seam  19  (e.g., a butt seam, an overlap seam, etc.) by joining structure such as stitching, an adhesive bond, a flame bond, etc. In the illustrated embodiment, the seam  19  extends lengthwise of the outer portion  12 . A fluid-impermeable tape  20  is applied to the exterior surface of the outer portion  12  along the length of the seam  19 . The tape  20  can be heat-boned or chemically bonded to the exterior surface of the outer portion  12  in certain embodiments. The tape  20  seals the seam  19  so that the outer portion  12  provides a fluid-impermeable barrier. 
     The coating  12 B on the outer portion  12  is preferably airtight and the tape  20  provides a fluid seal of the seam  19  so that the liner can be everted and expanded into contact with the pipe by fluid pressure. Suitably, the coated felt that forms the outer portion  12  is configured to stretch circumferentially when the liner  10  is expanded radially from a first diameter to a larger second diameter. When the liner  10  expands radially during installation, the coated felt stretches circumferentially while the seam  19  remains intact and sealed by the tape  20 . After being everted into a host pipe, the coating  12 B defines a substantially smooth, watertight surface, which extends continuously along the interior of the installed liner  10 . 
     In the illustrated embodiment, each of the strength portions  14 ,  18  is formed from the same type of material and is assembled in the same general manner. It will be understood that, in other embodiments, the strength portions could have different configurations without departing from the scope of the invention. Each strength portion  14 ,  18  has a length extending from the first end to the second end of the liner  10  and comprises a multilayer composite material formed into a tube that extends along the length of the respective strength portion. The outer strength portion  14  extends longitudinally through the interior of the outer portion  12  and defines a longitudinal interior of its own. The middle portion  16  extends longitudinally through the interior of the outer strength portion  14 , and the inner strength portion  18  extends longitudinally through the interior of the middle portion. Although the illustrated liner  10  includes an outer strength portion  14  concentrically arranged between an outer portion  12  and a middle portion  16  and an inner strength portion  18  nested inside the middle portion, other embodiments can include other numbers and arrangements of strength portions. 
     Referring to  FIG. 3 , each strength portion  14 ,  18  is formed from a sheet  30  of a multilayer composite fabric.  FIG. 3  has been broken away to illustrate its constituent layers. It is understood that, in order to be of a desired total length, each strength portion  14 ,  18  could also be formed multiple sheets that are connected together in an end-to-end arrangement. Each sheet  30  has first and second end margins spaced apart along a length LS. In the assembled liner  10 , the length LS of the sheet  30  extends along a length L of the liner. Each sheet  30  also has first and second side margins spaced apart along a width W. In the assembled liner  10 , the width W of each sheet extends in the hoop direction (e.g., about the circumference) of the liner. To form each of the strength portions  14 ,  18 , the respective sheet is folded into a tube such that the side margins engage one another and are joined together at a respective seam  52 ,  54  ( FIG. 2 ) that is circumferentially offset from the other seam and from the seam  19  of the outer portion  12 . 
     The multilayer sheet  30  comprises a first impregnation layer  32  formed from resin-impregnable material, a second impregnation layer  34  formed from resin-impregnable material, and a strength layer  36  that includes strengthening fibers received between the impregnation layers. In the illustrated embodiment, the strength layer  36  is also configured to be impregnated with resin or other curable polymer. Other strength portions can comprise other multilayer materials (e.g., a multilayer material comprising a single impregnation layer and one or more strength layers; two or more strength layers and impregnation layers; etc.) or a single-layer material. 
     In the illustrated embodiment, each of the impregnation layers  32 ,  34  is formed from a resin-impregnable felt, e.g., a polyester felt, which extends continuously along the length LS and width W of the sheet  30 . In the illustrated embodiment, the non-woven fibers of the felt layers  32 ,  36  are needled to the strength layer  36  to secure the strength layer between the felt layers. Needling the felt layers  32 ,  34  to the strength layer  36  enables the composite fabric  30  to be handled as a unitary sheet of material when the liner  10  is assembled. The felt layers  32 ,  34  provide good resin-impregnation characteristics and also provide structure that is suitable for being handled by industrial sewing machines when forming the composite fabric  30  into the respective tube  14 ,  18 . An exemplary material for the felt layers  32 ,  34  is polyester felt. Such felts are used by Aegion Corporation of St. Louis, Mo., in various cured-in-place pipe lining products such as, for example, InsituMain® pipe liners. Other types of felts or other resin-impregnable materials can be used to form the impregnation layer(s) of the strength portions without departing from the scope of the invention. 
     Suitably, the strength layer  36  comprises strengthening fibers, such as glass fibers, carbon fibers, etc. The strength layer  36  extends continuously along the length LS and width W of the fabric sheet  30 . In the illustrated embodiment, the strength layer  36  is formed from first, second, and third sublayers  36   i ,  36   ii ,  36   iii , and each of the sublayers extends along the length LS and width W of the fabric sheet  30 . In the illustrated embodiment, the first sublayer  36   i  is a mat formed from randomly oriented chopped fibers  42  distributed throughout the strength layer  36 . The second sublayer  36   ii  is formed from continuous fibers  44  oriented generally parallel to the length LS and distributed throughout the strength layer  36 , and the third sublayer  36   iii  is formed from long oriented chop material containing long fibers  46  oriented generally parallel to one another and transverse to the continuous fibers and distributed throughout the strength layer. In the illustrated embodiment the sublayer of long oriented chopped fibers  46  is sandwiched between the sublayers of random oriented fibers  42  and continuous fibers  46 ; however, other arrangements of the sublayers are also possible without departing from the scope of the invention. The different types of fibers  42 ,  44 ,  46  are illustrated schematically in  FIGS. 2 and 3 . It will be understood that the strength layers can have other configurations in other embodiments. 
     The chopped fibers  42  are matted together in random orientations to form the sublayer  36   i  of the strength layer  36 . The random oriented chopped fibers  42  are loosely held together in a mat such that they can shift relative to one another and allow the sublayer  36   i  to stretch circumferentially as the liner  10  expands radially. The random oriented fibers  42  are configured to enhance the strength of the respective strength portion  14 ,  18  in a non-directional manner (e.g., the random oriented fibers strengthen the liner  10  in a hoop direction and also in other directions). Moreover, as described in further detail below, the mat of random oriented fibers  42  provides a backing structure to which the bundles of fibers  44 ,  46  are secured to form the strength layer  36 . Securing the bundles of fibers  44 ,  46  to the sublayer  36   i  of randomly oriented fibers  42  allows sheet material including the three sublayers  36   i ,  36   ii ,  36   iii  of strengthening fibers to be handled independently during manufacturing before it is needled or otherwise secured to one or both of the felt layers  32 ,  34 . 
     In the illustrated embodiment the continuous fibers  44  are arranged in bundles that extend continuously along the length LS of each sheet  30 . The bundles of continuous fibers  44  are spaced apart along the width W of the sheet  30 . When the sheet is formed into the respective one of the outer and inner strength portions  14 ,  18 , the bundles of continuous fibers  44  are spaced apart about the circumference of the respective strength portion. The bundles of continuous fibers  44  can move along the width W of the sheet  30  and about the circumference of the respective strength portion  14 ,  18  so that each strength portion can stretch circumferentially when the liner  10  expands radially. The illustrated continuous fibers  44  form a one-bundle-thick sublayer  36   ii  of fibers, but in other embodiments the bundles of continuous fibers can be stacked to form a sublayer of continuous fibers that is more than one bundle in thickness. The continuous fibers  44  provide longitudinal reinforcement of the sheet  30  and thus provide longitudinal reinforcement of the liner  10 . 
     The long fibers  46  in the sublayer  36   iii  of the illustrated strength layer  36  extend generally parallel to the width W of the sheet  30 . More specifically, the long fibers  46  are arranged in bundles extending generally parallel to the width of the sheet. The individual long fibers  46  thus extend generally parallel to the bundles of which they are a part. The bundles of long oriented chop fibers  46  are spaced apart from one another along the length LS of the sheet  30  to form the middle sublayer  36   iii  of the strength layer  36 . The illustrated long fibers  46  form a one-bundle-thick sublayer  36   iii  of fibers, but in other embodiments the bundles of chopped fibers can be stacked to form a sublayer that is more than one bundle in thickness. The illustrated bundles of long fibers  46  are oriented generally perpendicular to the bundles of continuous fibers  44 . In each of the assembled strength portions  14 ,  18 , the bundles of long fibers  46  are spaced apart along the length of the respective strength portion and extend in the hoop direction (about the circumference of the respective strength portion) to circumferentially reinforce the liner  10 . In the illustrated embodiment, each bundle of long fibers  46  extends about the entire circumference of the respective strength portion  14 ,  18 . Each long fiber  46  has a length that is long in comparison to random oriented fibers  42 , but is less than the width W of the sheet  30  and the circumference of the respective strength portion  14 ,  18 . The fibers  46  can all have the same length or have different lengths without departing from the scope of the invention. Although the chopped fibers  46  are arranged in bundles in the illustrated embodiment, circumferentially oriented chopped fibers can also be supported in the strength layer without being arranged in bundles in other embodiments. 
     Referring to  FIG. 2 , because the bundles in each sublayer  36   iii  are formed from long fibers  46  instead of continuous fibers, each of the strength portions  14 ,  18  can stretch circumferentially when the liner  10  expands radially. In each strength layer  36 , the long fibers  46  are held together loosely so that they can move relative to one another within each respective bundle in directions parallel to their lengths, along the circumference of the liner  10 . Since the long fibers  46  can move relative to one another along their lengths, the middle sublayer  36   iii  of the strength layer  36  of each strength portion  14 ,  18  can be stretched circumferentially when the liner  10  expands radially. Since the felt layers  32 ,  34  and inner and outer sublayers  36   i ,  36   ii  of the strength layer  36  are also formed from circumferentially stretchable material as explained above, each strength portion  14 ,  18  is configured to stretch circumferentially as the diameter of the liner  10  increases when it is expanded during eversion. 
     In the illustrated embodiment stitching  50  loosely secures the bundled long fibers  46  and bundled continuous fibers  44  to the mat of random oriented fibers  42  to form the strength layer  36 . But in other embodiments, other ways of loosely securing the strengthening fibers can be used without departing from the scope of the invention. The stitching  50  is sufficiently loose to permit the long fibers  46  within each circumferential bundle to move relative to one another along the circumference of the strength layer  36  but is sufficiently strong to hold the fibers  42 ,  44 ,  46  of the strength layer together during manufacturing. The stitching  50  is also configured to allow the random oriented fibers  42  to shift and the bundles of continuous fibers  44  to move circumferentially of the liner  10  during installation. Thus, the stitching  50  is configured to maintain the general arrangement of the strengthening fibers  42 ,  44 ,  46  during installation while permitting the strengthening fibers to move as required to facilitate circumferential stretching of the strength layer  36  when the liner  10  is radially expanded. 
     In each strength portion  14 ,  18 , the composite fabric sheet  30  is folded so that the side margins of the fabric sheet overlap one another at a respective seam  52 ,  54 . Each seam thus comprises an overlap portion that extends generally along the length L of the liner  10 . In the illustrated embodiment, overlap stitching  56 ,  58  secures the overlapping side margins of the respective sheet  30  together in each strength portion  14 ,  18 . In other embodiments, the overlapped side margins could be secured together by other types of joining structure, e.g., a heat bond, an adhesive bond, etc. 
     Each overlap portion  52 ,  54  has a width WO 1 , WO 2 . In certain embodiments each width WO 1 , WO 2  is in an inclusive range of from about 1.5 inches (3.8 cm) to about 2.5 inches (6.46 cm). Widths in this range can be suitable for using an industrial sewing machine to stitch the overlap portion  52 ,  54 . However, it will be understood that overlap portions of other widths can be used in other embodiments. The stitching  56 ,  58  allows the tube to expand circumferentially without breaking the respective seam  52 ,  54 . Because the impregnation layers  32 ,  34  and strength layer  36  are configured to stretch circumferentially, when each strength layer  14 ,  18  expands from a first diameter to a larger second diameter during installation, the width WO 1 , WO 2  of the respective longitudinal overlap portion  52 ,  54  does not decrease. Instead the width WO 1 , WO 2  of the respective longitudinal overlap portion  52 ,  54  either stays the same or increases, increasing proportionally with the increase in circumference of the respective strength portion  14 ,  18 . The stitching  56 ,  58  holds the longitudinal side margins of the sheet  30  together at each seam  52 ,  54  even after the diameter of the respective strength portion  14 ,  18  increases. 
     In one or more embodiments, each overlap portion  52 ,  54  is reinforced with a reinforcing strip  60 ,  62 . The reinforcing strips  60 ,  62  can comprise any suitable reinforcing material. In certain embodiments, each reinforcing strip  60 ,  62  comprises a two-layer material comprising a felt layer and a fibrous layer that is needle punched or otherwise secured to the felt layer. In one embodiment, the reinforcing strip  60 ,  62  is attached to the outer felt layer  34  of the respective strength portion  14 ,  18  at locations on opposite sides of the overlap seam  52 ,  54 , e.g., by flame bonds, adhesive bonds, stitching, etc. In certain embodiments, each reinforcing strip  60 ,  62  extends continuously along the length of the respective strength portion  14 ,  18 . Each reinforcing strip  60 ,  62  can be bonded to the outer felt layer  34  of the respective strength portion  14 ,  18  on opposite sides of the seam  52 ,  54  continuously along, or at spaced apart locations along, the length of the respective strength portion. 
     The middle portion  16  has a length extending from the first end to the second end of the liner  10  and comprises felt formed into a tube having an interior. As explained above, the middle portion  16  extends longitudinally through the interior of the outer strength layer  14 , and the inner strength layer  18  extends longitudinally through the interior of the middle portion. The middle portion  16  comprises one or more discrete felt layers  16 A,  16 B, each formed into a discrete felt tube. The felt tubes  16 A,  16 B are each configured to be impregnated with a curable polymer such as resin. In the illustrated embodiment, the middle portion  16  comprises two discrete felt tubes  16 A,  16 B that are arranged concentrically. It will be understood that the middle portion of other liners can have other numbers of felt tubes (for example zero or more felt tubes, e.g., a number of felt tubes in an inclusive range of from 1 to 5, etc.) 
     Each discrete felt layer  16 A,  16 B comprises a sheet of felt (or a plurality of sheets of felt arranged end-to-end) having first and second end margins spaced apart along a length that extends along the length of the middle portion  16  and first and second side margins spaced apart along a width that extends about a circumference of the middle portion. Each felt sheet  16 A,  16 B is folded into a tube such that the side margins of the sheet engage one another and are joined together at a respective seam  66 ,  68 . In the illustrated embodiment, the side margins are joined together at a stitched butt seam, but the side margins can be joined together in other ways without departing from the scope of the invention. Suitably, each seam  66 ,  68  is configured to withstand circumferential stretching of the middle portion  16  as the liner  10  expands radially during installation. In one or more embodiments, all of the seams  19 ,  52 ,  54 ,  66 ,  68  in the liner  10  are offset circumferentially from one another. 
     In the illustrated embodiment, the outer portion  12 , the outer strength portion  14 , each of the middle felt tubes  16 A,  16 B, and the inner strength portion  18  each comprises a respective tube of the liner  10 . The individual tubes  12 ,  14 ,  16 A,  16 B,  18  included in the liner  10  are bonded together at bonds  70 A- 70 D. In one or more embodiments, each of the bonds  70 A- 70 D extends continuously or intermittently along the length L of the liner  10 . The outer portion  12  of the liner is bonded to the outer felt layer  32  of the outer strength portion  14  at a bond  70 A; the inner felt layer  34  of the outer strength portion is bonded to the outer felt tube  16 A at a bond  70 B; the outer felt tube is bonded to the inner felt tube  16 B at a bond  70 C; and the inner felt tube is bonded to the outer felt layer  32  of the inner strength layer  18  at a bond  70 D. Because the opposing surfaces the tubes  12 ,  14 ,  16 A,  16 B,  18  are all formed of felt material, the bonds  70 A- 70 D can comprise flame bonds. In other words, in the illustrated embodiment, each discrete tube  12 ,  14 ,  16 A,  16 B,  18  is flame bonded to an adjacent tube to form a unitary liner  10 . It will be understood that other types of bonds (e.g., adhesive bonds, a mix of flame bonds and adhesive bonds, etc.) can also be used to secure together two or more tubes of a liner in other embodiments. 
     In an exemplary method of manufacturing the liner  10 , the manufacturer folds a composite fabric sheet  30  into an inner strength tube  18  so that the longitudinal side margins overlap one another at an overlap seam  54 . The manufacturer guides the inner strength tube  18  through a stitching machine to stitch the side margins together along the overlap seam  54 . The manufacturer then bonds the reinforcing strip  62  to the overlap portion  54  using an adhesive bond, a flame bond, etc. 
     After forming the inner strength tube  18 , the manufacturer wraps one or more sheets of felt  16 A,  16 B around it to form the middle portion  16 . In one embodiment, the manufacturer guides each sheet of felt through a stitching machine to stitch together the longitudinal side margins at the seams  66 ,  68 . Suitably, the manufacturer wraps each felt sheet so that the seams  66 ,  68  are circumferentially spaced from the seam  54  of the inner strength tube  18 . Each felt tube  16 A,  16 B is also flame bonded to the tube that is received in its interior. For example, in the illustrated embodiment, the manufacturer flame bonds the felt tube  16 B to the inner strength portion  18  at flame bond  70 D and flame bonds the felt tube  16 A to the other felt tube at flame bond  70 C. 
     After the desired number of felt tubes is/are formed and flame bonded to the inner strength portion  18 , the manufacturer wraps another composite fabric sheet  30  around the middle portion  16  to form the outer strength tube  14 . The manufacturer folds the sheet  30  around the middle portion  16  so that the longitudinal side margins of the sheet overlap one another at an overlap seam  52 . Suitably, the manufacturer wraps the composite fabric sheet  30  so that the overlap seam  52  is circumferentially spaced from the overlap seam  54  and each of the seams  66 ,  68 . The manufacturer guides the outer strength tube  14  through a stitching machine to stitch together the longitudinal side margins of the composite fabric sheet  30  along the overlap seam  52 . The manufacturer then bonds the reinforcing strip  60  to the overlap seam  52  using an adhesive bond, a flame bond, etc. The outer strength tube  14  is also flame bonded to the outer felt tube  16 A at a flame bond  70 B. 
     The manufacturer then wraps a sheet of coated felt around the outer strength tube  14  to form the outer tube  12 . Specifically, the manufacturer folds the coated felt around the outer strength tube  14  so that the longitudinal side margins engage one another and the coating  12 B defines the exterior of the tube. The manufacturer guides the coated felt tube  12  through a stitching machine to stitch together the side margins of the material at the seam  19 . The manufacturer then applies impermeable tape  20  along the seam  19  to seal the seam. 
     To install the liner  10  in a host pipe (not shown), the liner is initially impregnated with curable polymer such as resin. Various techniques for impregnating a liner with curable polymer are known or may become known, and any suitable technique can be used without departing from the scope of the invention. For example, a resin impregnation system is disclosed in U.S. Pat. No. 7,238,251, which is hereby incorporated by reference in its entirety. In one embodiment, the step of impregnating the liner  10  with resin is performed at a factory remote from the host pipe and the impregnated liner is transported to the site of the host pipe in a suitably climate controlled truck. In other embodiments, the crew could impregnate the liner  10  at the site of the host pipe without departing from the scope of the invention. Suitably, the step or impregnating the liner  10  with resin distributes resin throughout the felt layer  12 A of the outer tube  12 , each of the layers  32 ,  34 ,  36  of the outer strength tube  14 , each of the felt tubes  16 A,  16 B, and each of the layers  32 ,  34 ,  36  of the inner strength tube  18 , as well as through each of the reinforcing strips  60 ,  62 . 
     After the liner  10  is impregnated with resin, the crew installs the liner inside the host pipe by everting the liner. In the eversion process, the liner  10  is turned inside out, advancing down the host pipe as more of the liner is everted. The eversion process presses the inner strength portion  18  against the interior surface of the host pipe and causes the coating  12 B of the outer portion  12  to become the interior surface of the lined pipe. Thus, after eversion is complete, the impermeable coating  12 B provides a resin barrier that prevents the resin in the liner  10  from escaping into the interior of the pipe. During the eversion process, the flame bonds  70 A- 70 D maintain secure connections among the discrete tubes  12 ,  14 ,  16 A,  16 B,  18  such that liner retains its structure and can be everted as a single unit. Various techniques for everting the liner  10  are known or may become known, and any suitable technique can be used without departing from the scope of the invention. For example, systems for everting a liner are disclosed in U.S. Pat. Nos. 9,453,597, 8,066,499, 7,866,968, and 7,766,048, each of which is hereby incorporated by reference in its entirety. 
     Prior to eversion, the liner  10  and each of the tubes  12 ,  14 ,  16 A,  16 B,  18  has a respective initial diameter. The eversion process stretches the liner  10  and each tube  12 ,  14 ,  16 A,  16 B,  18  from its initial diameter to a larger second diameter. As explained above, the arrangement of strengthening fibers  42 ,  44 ,  46  within each of the strength portions  14 ,  18  allows the strength portion to stretch circumferentially without reducing the width WO 1 , WO 2  of the respective overlap portion  52 ,  54 . The stretching of the liner  10  helps prevent wrinkles from forming as the liner is positioned in contact with the interior surface of the host pipe  10 . Thus, after eversion is complete, the impermeable coating  12 B forms a smooth surface along which liquid may flow with minimal drag. The continuous fibers  44  resist elongation of the liner  10 . 
     Once the liner  10  is positioned in continuous contact with the interior surface of the host pipe, the resin in the liner cures to form a cured-in-place liner along the interior surface of the host pipe. In certain embodiments, the resin cures in ambient conditions. In other embodiments, the crew cures the resin by directing a suitable form of curing energy, such as heat, ultraviolet radiation, etc., toward the resin impregnated liner  10 . Various techniques for curing a resin-impregnated liner are known or may become known, and any suitable technique can be used without departing from the scope of the invention. For example, curing systems are disclosed in several of the U.S. patents incorporated by reference above, as well as in U.S. Pat. No. 7,360,559, each of which is hereby incorporated by reference in its entirety. 
     The cured resin strongly binds each of the tubes  12 ,  14 ,  16 A,  16 B,  18  together after the installed liner  10  is put into service. Furthermore, the strength layers  36  (in particular, the circumferentially oriented fibers  46 ) of the inner and outer strength tubes  14 ,  18  circumferentially reinforce the host pipe to withstand internal loads (e.g., internal fluid pressures, etc.) and/or external loads (e.g., seismic loads, etc.). As can be seen therefore, the liner  10  can be installed by eversion and provide a new, high strength pipe inside a host pipe that defines a substantially smooth, watertight flow passage. 
     Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 
     As various changes could be made in the above constructions and methods without departing from the 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.