Abstract:
A composite tubular assembly formed by a core or tube which is reinforced by a multitape product which is wrapped in alternate non-bonded helical wraps on the core or tube. Each tape is first formed by impregnating a fibrous strip with a resin and then such tapes are fed from spools to the core of the tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Serial No. 60,132,207 filed May 3, 1999. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the invention is flexible pipe for conducting petroleum or other fluids subsea or on land and the method of forming same. 
     2. Description of the Related Art 
     Conventional bonded flexible pipe is described in American Petroleum Institute document API Specification  17 J. These types of pipe are typically used for both “sweet” and “sour” service production, including export and injection services. Fluids transported include oil, gas, water and injection chemicals and gas. A typical construction is made up of a plurality of tubular layers, starting with an interlocking metal carcass and followed by a liner tube of plastic to retain the fluid within the pipe. Hoop strength armor reinforcement in the hoop direction is provided by helical metal wires which may be in several layers and wound in opposite helical directions. Additional layers may also be used, with a final jacket extrusion to complete the assembly, with a tough wear resistant material. 
     U.S. Pat. Nos. 5,261,462 and 5,435,867, both issued to Donald H. Wolfe, et al., are examples of tubular composite pipe in the prior art. Those patents relate to tubular structures having a plastic tube for the fluid conductor, which has an outer layer formed form alternating spirally wound strips of composite and elastomer. It is believed that the prior art composite pipes, such as disclosed in the above patents, have been limited to relatively short commercial lengths, by reason of the method by which such tubular structures have been made. 
     Typically, composite flexible pipes are made by filament winding, which involves turning the pipe while feeding and moving resin impregnated fibers from bobbins back and forth along the length of the pipe. Such technique limits the length of the reinforced flexible pipe which can be manufactured because of the number of bobbins required for the large number of fibers that are used in each pass. As a practical matter, it was not known how to make relatively long lengths of composite pipe sufficient for subsea use because of such problem. 
     In single bobbin machines, unloading and reloading time is a function of the time taken to thread each end of the fibers, the number of bobbins, and the time required to replace each bobbin. Also, due to the material payload requirements, a single bobbin-type machine will require each end to travel some distance from its bobbin over rollers, sheaves, eyelets, etc., through the machine to the closing point on the pipe, thus creating a time-consuming task. Because of the hundreds, and even thousands of bobbins, extremely large machines would be required to make a composite reinforced pipe in long lengths by such prior art techniques, consequently, the industry has not had available composite flexible pipes in long lengths suitable for subsea production and well operations. Multiple fiber tows are also not practical for long pipe lengths because of the fiber loading times required. 
     SUMMARY OF THE INVENTION 
     With the present invention, discrete tapes are first formed from the fibers and resin or the like, so that the tapes are wound on spools which reduces the number of bobbins required as compared to the number of bobbins required for single fiber filaments, whereby it is possible to manufacture long lengths of composite flexible pipe. The tapes are initially formed and then are fed from tape spools rather than the fiber bobbins in the prior art. Also, each tape is composed of a plurality of superimposed thin tape strips formed of predominantly, unidirectional fibers, which are impregnated with an epoxy or other suitable bonding resin which cures with heat, cold, ultraviolet (UV) or other curing methods. The multi-layer tapes are wrapped with a polyethylene or similar plastic or thin metallic strip or covered by thermoplastic extrusion to confine them as a unit together, with bonding adhesive between the tape strips being prevented from escaping from the wrap. Each tape thus made is fed from a tape spool to the tubular core as the tubular core is rotated, or as the spools are rotated relative to the core, which produces helical wraps of each of the tapes on the tubular core in the same or opposite helical directions for reinforcement of the core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a typical fiber arrangement for the tape of this invention; 
     FIG. 2 is a view of the fibers of FIG. 1 embedded in a resin such as an epoxy resin; 
     FIG. 3 is a cross sectional view of the final tape which has a plurality of fiber tapes laminated together with a thermoplastic or elastomeric material to form a composite tape as a unit; 
     FIG. 4 is a schematic illustration of a method of this invention showing the method and apparatus for making the resin impregnated fiber tapes of this invention; and 
     FIG. 5 is an isometric view of a pipe made in accordance with this invention, showing the arrangement of the tapes helically wound on the fluid conducting core or tube. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to FIG. 1, a preassembled fiber tape strip is shown which is formed of a plurality of fibers  11  which extend parallel to each other in the warp direction which is the main direction of the tape. Those fibers are made of fiber glass, Kevlar, carbon or similar materials. Fibers  12  are disposed perpendicular to the fibers  11  and extend underneath them and typically are joined together with a stitch in the manufacturing and assembly process. Such fibers  12  are in the weft direction across the tape strip. Preferably, the majority strength of the tape strip is provided in the direction of the fibers  11 , and in some instances each strip of tape may be formed solely of warp fibers  11 . Also, strips of thin metal of steel, aluminum, or other metal, some being perforated, may be used between or outside of the fiber strips in each laminate  15 . 
     The fiber matrix formed of the fibers  11  and  12  may be separately formed and thereafter impregnated with a resin such as an epoxy resin, or the fiber matrix may be made on the same machine that impregnates such fibers with the resin. 
     FIG. 2 is an illustration of the tape strip T of this invention, one form of which is made by impregnating the fibers  11  and  12  with an epoxy resin or the like to form a single laminate  15 . The laminates need to be as thin as possible to reduce strain in them when they are bent onto a pipe surface. Typically, the thickness of each laminate layer is from about 0.010″ to about 0.030″. This is somewhat of a trade-off between (a) very thin tape which provides for very efficient but long production process, and (b) a thicker tape which is less efficient (more strain) but requires less production time. 
     Each laminate  15  which is formed by this invention is a separate tape T. A plurality of such tapes T are superimposed on each other as shown in FIG. 3 and, as will be explained, are bonded together by an adhesive which may initially be an uncured epoxy or resin between the tapes T which is later cured during or after the tapes A are wrapped on the core C. Once the adhesive between the tapes cures, the overall laminate product A assumes the radius to which it was bent. This happens because the tapes  15  slide over each other, and then when the adhesive cures, they cannot slide. 
     In FIG. 3, the finished tape A is shown in cross-section schematically with the warp fibers  11  exposed at the ends, and the epoxy impregnating and bonding the multiple tapes into the final tape T. The weft fibers are not shown in FIG. 3 because they extend across FIG. 3 just behind the cut line for FIG.  3 . 
     An external protective jacket  20  of nylon, polyethylene, or similar flexible thermoplastic or elastomeric material surrounds the superimposed tapes T and encloses the adhesive between such tapes T so that none of the uncured adhesive escapes from the jacket  20  during curing. 
     A typical arrangement for forming the final tape A shown in FIG. 3 is illustrated by the equipment schematically shown in FIG.  4 . 
     By way of example, the laminates  15  or tapes T are arranged in a superimposed relationship and are fed through squeeze rollers  25 . Prior to reaching the squeeze rollers  25 , the tapes T are spaced apart so that adhesive in the form of a resin or the like is applied between the tapes T with any suitable type of applicator  27  or spray which supplies adhesive or resin from an injector  28  and header  29  suitably connected to the applicator  27 . 
     Guide rollers  35  serve to maintain the tapes T in a superimposed alignment with each other. 
     Finally, a rotatable spool  37  which has a wrapping strip  39  of polyethylene, nylon or similar flexible thermoplastic or elastomeric material thereon is positioned for feeding a helical wrap of the strip  39  to form a protective jacket  20  by rotating the spool head  37 . Such protective jacket  20  is thus formed by the tape  39  being wrapped about the tapes T to form the final multitape product A shown in cross-section in FIG.  3 . Instead of the helical wraps  39 , a “cigarette” wrap may be formed by a longitudinal strip that extends lengthwise of the tape T, and which is folded to partially or fully extend around or substantially around the tape T. The helical wrap  39  preferably may then be wrapped outside of the cigarette wrap to complete product A. 
     Referring now to FIG. 5, a simple pipe construction is illustrated for showing the use of the tape A for reinforcing an inner core or tube C which is formed of a flexible fluid conducting material such as flexible polyethylene or metal which is thick enough to have some rigidity but thin enough to still be flexible without significant deformation or collapse. An anti-abrasive layer B of relatively thin polyethylene or the like is preferably disposed between the helical wraps of the tapes A to provide for anti-abrasion between two layers of the helical wraps. Although the wraps of the tapes A are shown as opposite helical wraps, the invention is not limited thereto. For example, the construction may have two or more wraps with a left hand lay, and two or more with a right hand lay, and then two or more with a left hand lay. 
     It is noted that the tapes A are in a non-bonding relationship to the core or tube C and to each other so that when the core or tube C flexes during use, the tapes A may slide to a limited extent relative to the core or tube C and to each other to permit the flexing of the entire assembly. Additionally, it is noted that there are small gaps or helical spaces  40  between each of the tapes A to provide for limited relative movement of the tapes A with respect to the core or tube C and to each other for flexibility when the core or tube C is flexed. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the details of the illustrated apparatus and construction and method of operation may be made without departing from the spirit of the invention.