Abstract:
A flexible method that includes a tubular member defining a longitudinal passage adapted to contain a conveyed fluid, and a plurality of layers of flexible material helically wrapped around the tubular member.

Description:
BACKGROUND 
     This disclosure relates generally to a flexible pipe, and, more particularly, to a flexible pipe having overlapping layers. 
     It is well known to provide flexible pipes that consist of a inner tubular member over which is wrapped one or more layers of flexible material to improve the strength and performance characteristics of the pipe. However, many of these prior devices suffer from one or more problems. For example, gaps are often formed between the wrapped sections of one or more of the layers through which the inner tube member can extrude. A common method used to avoid this problem is to bond the layers-to the tube and to each other which prohibits independent movement of the layers in response to stresses on the pipe. Typically, these bonded pipes have a fairly short life when used in dynamic service because of the stresses between layers that tend to separate the pipe layers. 
     Therefore, what is needed is a flexible pipe formed by a plurality of wrapped layers which avoids the above problems. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are partial isometric views of a portion of a flexible pipe according to an embodiment. 
     FIGS. 3 and 4 are sectional views taken along the lines  3 — 3  and  4 — 4 , respectively, of FIG.  1 . 
     FIGS. 5 and 6 are partial isometric views of the complete pipe of the above embodiment. 
     FIG. 7 is a sectional views taken along the line  7 — 7  of FIG.  6 . 
     FIG. 8 is a view similar to that of FIG. 4, but depicting an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 depict a portion of a flexible pipe shown, in general, by the reference numeral  10 , according to an embodiment of the present invention. The pipe  10  includes an internal, pressure-containing, inner sheath, or barrier, in the form of a tube  12  having a layer  14  of a flexible material helically wound thereover in a helical manner. The layer  14  can be formed by a tensile element preferably in the form of a relatively wide steel strip having a rectangular cross section. 
     The layer  14  is wound at an angle that, for the purpose of example only, extends approximately 52° to the longitudinal axis of the tube  12 . The helical winding of the layer  14  forms a plurality of sections  14   a ,  14   b ,  14   c , and  14   d  axially spaced along the length of the tube  12 , and the winding is such that relatively small gaps  16  extend between adjacent sections. As a non-limitative example each gap can be 5-10% of the width of the layer. Although the entire length of the tube  12  is not shown in FIGS. 1 and 2, it is understood that the layer  14  is wound for its entire length thus forming additional sections. 
     As shown in FIG. 2, a layer  20  of a flexible material, which can be identical to that of the layer  14 , is wound over the layer  14  in a helical manner the same direction, and at substantially the same angle, as the layer  14 . (In this context the angles can not be identical since the layers  12  and  14  are laid on the tube  12  at slightly different diameters.) The helical winding of the layer  20  forms a plurality of sections  20   a ,  20   b ,  20   c , and  20   d  axially spaced along the length of the tube  12 , and the winding is such that relatively small gaps  22  are formed between adjacent sections. It is also understood that the layer  20  is wound for the entire length of the tube  12 . 
     The layer  20  is wound so that its sections  20   a ,  20   b ,  20   c  and  20   d  overlap the gaps  16  between the adjacent layers of the layer  14 . Thus, the gaps  22  of the layer  20  are overlapped by the sections  14   a ,  14   b ,  14   c  and  14   d  of the layer  14 . 
     As shown in FIG. 4 diametric opposite portions of the layer  14  are bent radially outwardly to form tabs  14   t  that extend in the gap  22  between two adjacent sections of the layer  20 . Similarly, diametric opposite portions of the layer  20  are bent radially inwardly to form tabs  20   t  that extend in the gap  16  between two adjacent sections of the layer  14 . The tabs  14   t  and  20   t  prevents any relative movement between the layers  14  and  20  which may otherwise occur, especially if the pipe  10  is subject to a great deal of flexure. This also allows each gap  16  to grow and shrink as the pipe  10  is bent. 
     As shown in FIG. 5, a layer  30  of a flexible material, which may be identical to that of the layer  14 , is wound over the layer  20  in a helical manner at the same angle as, but in an opposite direction of the winding of the layers  14  and  20 . The helical winding of the layer  30  forms a plurality of sections  30   a ,  30   b ,  30   c , and  30   d  axially spaced along the length of the tube  12 , and the winding is such that relatively small gaps  32  are formed between adjacent sections. It is also understood that the layer  30  is wound for the entire length of the tube  12 . 
     As shown in FIGS. 6 and 7, an optional layer  40  of a flexible material identical to that of the layer  14  can be wound over the layer  30  in a helical manner at the same angle, and in the same direction, as the layer  30  and therefore in an opposite direction to the layers  14  and  20 . The helical winding of the layer  40  forms a plurality of sections  40   a ,  40   b ,  40   c , and  40   d  axially spaced along the length of the tube  12 , and the winding is such that relatively small gaps  42  extend between adjacent sections. It is also understood that the layer  40  is wound for the entire length of the tube  12 . 
     The layer  40  can be wound so that its sections  40   a ,  40   b ,  40   c , and  40   d  overlap the gaps  32  between the adjacent layers of the layer  30 ; and the gaps  42  of the layer  40  are overlapped by the sections  30   a ,  30   b ,  30   c  and  30   d  of the layer  30 . 
     Although not shown in the drawing in the interest of clarity, it is understood that one or more tabs, identical to the tabs  14   t  of the previous embodiment can be provided on the layer  30  that extend radially outwardly into the gap  42  between adjacent sections of the layer  40 . Also, one or more tabs, identical to the tabs  20   t  of the previous embodiment can be provided on the layer  40  that extend radially inwardly into the gap  32  between two adjacent sections of the layer  30 . These tabs on the layers  30  and  40  function in the same manner as the tabs  14   t  and  20   t.    
     When fluid is introduced into the tube  12 , the internal fluid pressure forces the tube radially outwardly against the layers  14 ,  20 ,  30 , and  40 , causing tension to develop in the layers which creates a reaction load against the tube  12 . Due to the overlapping relationship of the layers  14 ,  20 ,  30 , and  40 , the entire outside surface of the tube  12  is supported, and there are no gaps between the layers through which the tube can extrude. Moreover, the layers  30  and  40  supply a twisting moment in the opposite direction from layers  14  and  20 , offsetting the moment applied by the layers  14  and  20  to the tube  12  as internal pressure is applied. Thus, the layers  30  and  40  tend to balance the longitudinal and circumferential components of load in the pipe  10 . As a result, both the diameter and the length of the pipe  10  change very little with changes in internal pressure. 
     In each of the above embodiments, an optional protective layer may be applied over the outer layers to provide environmental protection for the above tensile elements. 
     Variations and Equivalents 
     It is understood that the tabs  14   t  and  20   t  (and corresponding tabs on the layers  30  and  40 ) can be eliminated and the outer surface of the layer  14  can be welded, or otherwise bonded, to the inner surface of the layer at diametrically opposite portions thereof, to form two weldments, or joints,  50  and  52  (FIG.  8 ). The weldments  50  and  52  are preferably located adjacent the gap  16  formed between adjacent sections of the layer  14  and prevent any relative longitudinal movement between the layers  14  and  20 . Although not shown in the drawings, in the interest of clarity, it is understood that weldments can be provided between the layers  30  and  40  and/or between the layers  30  and  40  in a similar manner. 
     It is understood that the layer  40  can be eliminated and the size of the layer  30  can be approximately doubled when compared to the thickness of the layers  14  and  20 . Also, the layers  14  and  20  can be replaced by a single layer that is wound on the tube  12  with an overlap. This integrates the function of the simple layers  14  and  20  into a single layer with somewhat similar structure. Further, the layers  30  and  40  can be replaced by a single layer that is wound on the adjacent inner layer  20  with an overlap. Moreover, one or more of the layers  14 ,  20 ,  30  and  40  can be formed by a plurality of relatively narrow strips disposed in a side-by-side relation; by a high strength tape with oriented polymer chains; by tapes reinforced with fibres, composites of strength-adding polymers, or strips of other metals; or by tapes containing metal reinforcements, including steel, aluminium, or copper alloys. Still further, the number, size, and specific composition of the layers, sections, and gaps disclosed above can vary within the scope of the invention. Also, the layers can be wound at angles different from that disclosed above, and each layer can be wound at a different angle than the other layer or layers in the same pipe. Moreover, the steel strip forming the layers is not limited to being rectangular in cross-section, but can take other shapes. Further, coatings can be provided on any or all of the layers  14 ,  20 ,  30 , and  40 . 
     Since other modifications, changes, and substitutions are intended in the foregoing disclosure, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.