Abstract:
In the process of wrapping a strip-like flexible repair substrate around a cylindrical article such as a pipe, an edge of the repair substrate is aligned with at least one visible indicia along the length of the previously wrapped repair substrate to easily control the amount of overlap, or pitch of the helix, between adjacent substrate layers created by successive wraps of the substrate about the article. Each of these indicia allow the substrate to overlap the previously wrapped substrate by a consistent amount, the amount desired being dependent upon the application and amount of strength required for the repair.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/132,612, filed May 5, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a process of wrapping a strip-like flexible repair substrate around a cylindrical structure. An edge of the repair substrate aligns with a visible indicia along the length of the previously wrapped repair substrate to control the amount of overlap, or helix pitch, between adjacently wrapped substrate layers. The indicia allows a consistent overlap, the amount of overlap desired being dependent upon the application and amount of strength required for the repair. 
     BACKGROUND OF THE INVENTION 
     Pipe systems provide basic utilities to the public, such as water, gas, petroleum, and sewage. These basic utilities and petroleum pipeline operators are often heavily relied upon by the public. As such, the pipe systems are usually in a state of full operation, i.e. optimal flow rate. There is usually a very limited amount of time that the pipes and pipe systems operate at a reduced flow rate, while not seriously affecting utility service. 
     Pipelines and other cylindrical structures, whether above ground or below, occasionally suffer damage. Over time, these cylindrical structures can be damaged from rust, corrosion or other degradation. Further, the damage can occur during repair or installation, for example from tool impact or falling debris. 
     At a damaged area of the pipe, there is a smaller cross-sectional thickness of the pipe. The thickness of the pipe is inversely proportional to the hoop stress of the pipe, i.e. the circumferential stress in the pipe due to the operational fluid pressures in the pipe. Accordingly, there is a larger hoop stress in the damaged area as compared to the rest of the pipe. 
     The hoop stress in the pipe is proportional to the strain in the pipe. Therefore, the larger hoop stress in the damaged area results in a proportionally larger strain. The larger strain in the damaged area of the pipe causes further damage. Consequently, the flow through the pipe, and resulting pressure therefrom, is usually reduced or stopped to prevent further breakage or leaking from the structure until the pipe is repaired or replaced. This flow reduction is undesirable because the utility service is correspondingly reduced. 
     It is usually more cost effective to permanently repair the leaking pipe rather than replace it. When the damaged pipe is replaced, the downtime of the system, the labor costs, the material costs, as well as the costs associated with the loss of utility services are usually large. 
     An expedient method of repair involves, at least in part, applying a structural reinforcement by way of wrapping the structure with a flexible repair substrate. Such flexible substrates are commonly tapes (defined principally by films) woven fabrics, and non-woven fabrics. Non-woven fabrics are characterized by the non-parallel, random organization of the component fibers, for example, paper. The flexible substrates are often used in conjunction with various adhesives, resins, putties, and fill materials. 
     The flexible repair substrate has a characteristic tensile strength of its own. The substrate preferably is tensioned or pulled when surrounding the pipe undergoing fluid pressures. In the finished repair, the several turns of the substrate about the pipe are in tension, thus applying to the pipe a compressive force pattern which acts in the pipe counter to hoop stresses created by pressure of the fluid in the pipe. When the pipe is strained by internal fluid pressure, the repair substrate in the repair also strains proportionally to share hoop stress with the pipe. This method of repair keeps the strain and stress in the damaged area of the pipe within acceptable limits, when full operational fluid pressures are applied within the pipe. If one layer of substrate cannot withstand the tension created by the shared hoop stress, additional layers of substrate are overlapped for added strength. As more layers of substrate are wrapped, there is a corresponding larger amount of hoop stress absorbed by the substrate and taken away from the pipe. 
     Further, the amount of substrate overlapping on the previously wrapped substrate corresponds directly to the amount of strength added to the pipe by the repair. For a smaller operational pipe pressure, a smaller amount of overlap is preferred. If there is too much overlap for the design pressures, the repair is too costly. For a higher design hoop stress, a larger substrate overlap is preferred. If there is not enough overlap, the substrate repair does not have enough strength to withstand the design pressures and the pipe will strain and become further damaged. 
     The layered structure results in a partial overlap between adjacent layers. The partial overlap of the adjacent layers renders the substrate being angled relative to the central axis of the. structure, or having a spiral-shape or helix-shape wrapping material about the structure. With a low helix pitch, there is a greater the amount of overlapping substrate. Conversely, with a greater helix pitch, there is a lesser amount of substrate that overlaps. 
     The most common structures that are repaired by way of wrapping with a flexible substrate are cylindrical structures, such as utility poles, architectural and industrial support columns, and pipes. However, other shaped structures, with both regular and irregular cross-section can also often be advantageously repaired by way of wrapping the structure with a flexible reinforcing substrate. 
     SUMMARY OF THE INVENTION 
     In order for the amount of overlapping of a flexible repair substrate to be at a consistent, economical, and structurally adequate level, the helix pitch of the substrate is controlled during application. The method of controlling the helix pitch involves aligning an edge of an overlapping flexible reinforcing substrate with visible indicia along the length of the previously wrapped substrate. Providing a guide to allow easy, accurate application of a reinforcing wrap is particularly helpful to minimize errors when the wrap is not easily removable once applied, because of strong adherence of successive wraps of the substrate to each other, for example. 
     When using the flexible reinforcing substrate with indicia along the substrate for controlling helix pitch or overlap as provided herein, the user begins by affixing, either permanently or removably, a transverse edge of the substrate to the damaged article. Then, the user wraps the substrate around the damaged article. As the substrate begins to overlap, the user aligns the edge of the substrate of the overlapping layer with the desired indicium provided for the desired helix pitch. Thereafter, the user merely maintains the alignment of the edge of the substrate with that indicium as the substrate is wrapped around the damaged article. When the desired coverage of the damaged article has been achieved, the user simply cuts off any excess substrate and affixes the trailing end of the substrate to the damaged article, either permanently or removably, as desired in a particular application. 
     When there is a constant amount of overlapping substrate, there is a constant amount of tensile strength provided by the substrate along the length of the completed repair. The amount of tensile strength (or overlapping substrate) that is needed to adequately repair the pipe is determined by the operational design pipe pressure. Each indicator on the substrate corresponds to a different level of tensile strength. As long as the design pipe pressure is known, the user knows which of several visible indicia to follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be appreciated as the same become better understood by reference to the following Detailed Description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 schematically illustrates a side view of a cylindrical structure wrapped with a substrate having visible indicia; 
     FIG. 2 schematically illustrates a substrate having multiple visible indicia along its length; and 
     FIG. 3 schematically illustrates an alternative embodiment of a substrate having a band along its length as a visible indicator. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a side view of a cylindrical structure  1  wrapped with a flexible reinforcing strip substrate  10  having a visible indicator  5 . The visible indicator  5  is parallel to and spaced at a constant distance from a longitudinal edge  11  of the substrate throughout the length of the substrate. 
     The visible indicator  5  is shown schematically as a discontinuous or dashed line in FIG. 1, but is not limited as such. For instance the visible indicator  5  may also be a solid continuous line along the length of substrate. In an alternative embodiment, a continuous fiber in a woven substrate is a discontinuous indicator because the fiber is woven into a fabric, such that the fiber is partially obscured by fibers running perpendicular to the trace fiber. 
     In this embodiment, the strip of substrate  10  is wrapped in a helical shape about the cylindrical structure  1  over a previously wrapped portion of the same substrate. The substrate has a transverse edge  12  and a longitudinal edge  11 . The transverse edge  12  is placed on the pipe as wrapping of the substrate is begun. The longitudinal edge of the overlapping substrate  10  is aligned with the visible indicia  5  of the previously wrapped substrate so that the amount that the new turn of substrate  10  overlaps the previously wrapped substrate remains substantially constant throughout the length of repair along structure  1 . 
     The substrate  10  has an upper section  15  and a lower section  16  separated by the visible indicator  5 . The lower section  16  has a constant width throughout the length of the substrate. Only the lower section  16  is overlapped by an additional wrapped layer of substrate  10 . As a result, the amount of overlapping is easily maintained throughout the repair. Further, the upper section  15  along the entire length of the substrate remains exposed, as shown in FIG.  1 . 
     In an embodiment shown in FIG. 2, there are a several visible indicia  5 ,  6 ,  7  provided along the entire length of the flexible reinforcing substrate at different distances from the longitudinal edge  11   a  of the substrate. Providing indicia at different distances from the edge  11   a  will allow the same substrate to be provided for use in repairs requiring different levels of overlap (i.e. different strengths are required of the substrate due to the different applications or pipe pressures). The indicia  5 ,  6 ,  7  are spaced from the edge  11   a  to provide for two or more helix pitches or levels of overlap as desired. In one usage, the longitudinal edge  11   a  aligns on top of the visible indicator  5 ,  6 ,  7 . In another usage, the longitudinal edge  11   a  aligns with a bottom edge of the visible indicator  5 ,  6 ,  7 . In yet another usage, the longitudinal edge  11   a  is positioned in between visible indicators  5  and  6 . 
     In between the longitudinal edge  11   a  and visible indicator  5  is a first upper section  17 . Section  17  remains exposed throughout the length of the repair when visible indicator  5  is used as the wrap pitch guide. In between the longitudinal edge  11   a  and visible indicator  6  is a second upper section  18 . Upper sections  17  and  18  remains exposed throughout the length of the repair when visible indicator  6  is used as the wrap pitch guide. In between the longitudinal edge  11   a  and visible indicator  7  is a third upper section  19 , and in between the longitudinal edge  11   b  and visible indicator  7  is section  20 . When visible indicator  7  is used as the wrap guide, either upper section  19  or upper section  20  remains exposed throughout the length of the repair, depending upon which of the longitudinal edges of the substrate is to be the exposed outer edge of the substrate as wrapped. 
     To further increase the versatility of the product, indicia  5 ,  7  are spaced relative to each longitudinal edge  11   a ,  11   b  of the substrate, so that indicia  5 ,  7  are provided for both right and left-handed applications of the substrate. Indicia provided along each longitudinal edge also allows a first substrate to be wrapped in a clockwise direction about the cylindrical structure, while following the indicator  5 . Simultaneously, a second substrate that follows indicator  7  can be wrapped counterclockwise on top of the first substrate when there are design pressures that call for at least two substrates overlapping and wrapping the pipe. 
     In a first embodiment, the visible indicia are designated by a color that contrasts with the substrate. The contrasting color can use ink, paint, or another applied pigment. In a flexible reinforcing substrate that is a woven material, contrasting fibers or filaments can be provided in the warp (wrapping) direction. For non-woven substrates, the indicia can use imbedded or attached trace fibers, or imprinted marks. In the embodiment shown in FIG. 2, each visible indicator  5 ,  6 ,  7  preferably has a different color trace fiber associated therewith throughout the length of the substrate in order to indicate different helix pitches. The color contrast to enable the user to readily discern the indicia from the substrate is from variations in the gray-scale, such as black and white. Alternatively, the contrasting colors can be from variations in the primary colors such as red, blue, yellow, or combinations thereof. The contrasting colors can be provided in solid lines along the length of the substrate. Alternatively, the contrasting colors can be provided in dashed lines or periodically throughout the length of the substrate. 
     In a second embodiment, the visible indicators  5 ,  6 ,  7  can be groups of trace fibers with different discernible thicknesses. The thicknesses are established by the size of each trace fiber, or alternatively, a number of trace fibers are grouped together to give the appearance of a thicker width. The thicker fibers are provided in a solid line along the length of the substrate. Alternatively, the thicker fibers are provided in a dashed line or periodically throughout the length of the substrate. 
     Alternatively or additionally to the embodiments of the indicators discussed above, the indicators  5 ,  6 ,  7  can have different textures that are followed by feeling the indicators. The textured fibers extend above the surface of the substrate. These indicators are desired for use in instances where there is limited lighting. The textured fibers are provided in a solid line along the length of the substrate. Alternatively, the textured fibers are provided in a dashed line or periodically throughout the length of the substrate. 
     In the embodiment shown in FIG. 3, a visible indicator  8  is a thick band along the length of the substrate. The thick band is a width of material that contrasts with the substrate. In a first embodiment, the contrast is a color of the band that contrasts with the substrate. In a second embodiment, the contrast is texture of the band. In a third embodiment, the contrast is a combination of color and texture. The band width provides the indicia of the desired overlap. 
     Substrates used to wrap cylindrical structures are preferably fiberglass and other composite fabrics impregnated or coated with resins that cure to a hard, structurally strong state within a short period of time. One example of this is a fiberglass substrate, pre-impregnated with a polyisocyanate resin which cures into a hard polyurea upon contact with water or atmospheric moisture. 
     A fiberglass substrate is formed by weaving fibers or filaments of desired characteristics. Fibers or filaments of different materials can be incorporated into the substrate. Commonly used fibers and filaments include glass, carbon, steel, kevlar, and plastic. 
     By substituting contrasting fibers at operative positions in the warp (wrapping) direction of the substrate, an indicia is provided to allow the user to easily apply the substrate in the desired helix pitch or amount of overlap. 
     In the case of non-woven fabrics as the substrate material, colored or contrasting fibers or imprinting processes are used to provide the indicia. For those types of substrates, the fibers are either imbedded within the substrate, or affixed to the surface of the substrate by any suitable means. 
     While various embodiments of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concept herein. For example, the visible indicia can be provided on any size substrate that wraps about cylindrical structures, and is not limited to smaller substrates such as those having widths of 4 inches to 7 inches. Further, the applications for the methods of the present invention are not limited to utility pipelines. For example, the methods of the present invention can similarly be used to wrap columns, such as those columns used to structurally support bridges. The columns may be in need of repair or may need retrofitting. In either case, the wrapping of the substrate about the column provides for additional structural support of the column. It is, therefore, to be understood that within the scope of the appended claims, this invention may be practiced otherwise than as specifically described.