CONTINUOUS ONSITE-MANUFACTURED PIPE

Abstract

Method and article of manufacture are disclosed for onsite-manufacturing of any length, any shape, size, and any thickness pipe. Sheets of fabrics saturated with resin may be wrapped around desired shape mandrels, cured, and removed to form such pipes onsite. Cured laminated sheets of resin-saturated fabrics may be wrapped around to also form onsite manufactured pipes. Disclosed pipes eliminate almost all weaknesses of plastic, metal and concrete pipes and noticeably reduce costs of transportation as well as manufacturing. One of the advantages of the disclosed pipes is that they have few joints, limiting the leakage and other problems associated with joints in ordinary pipes.

Description

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This application claims the benefit of the priority date of the U.S. Provisional Patent Applications No. 61/633,685, filed on Feb. 16, 2012, titled “Long Continuous Onsite-Manufactured Pipe”.

TECHNICAL FIELD

This application relates generally to construction. More specifically, this application relates to a method and apparatus for on-site manufacturing of pipes of any length and any size and shape.

BACKGROUND

For centuries pipes have been used to carry fluids, gases, etc. in water, wastewater, gas, oil, mining and other industries. All these pipes, especially for large projects, are manufactured in factories in pieces that are typically 16-24 feet long and are shipped by trailers or trains to the jobsite for installation. During the installation process, the short pieces are joined together to create a longer pipe. In buried pipes, a trench must be excavated to place the pipe below ground.

There are several shortcomings with such a system. (1) The shipping is very costly as often these pipes are bulky and hollow; in fact the trucks carry a lot of “empty” and unused space enclosed within the hollow pipes. When larger diameter pipes (4-ft and larger) are transported only a few pieces of pipe can be placed on a truck bed which adds tremendous expense to the project. (2) The pipe sections are very heavy and require heavy lifting equipment onsite to remove the pipe from the truck bed and position it in the trench. (3) The joints in all pipes are the major source of leakage; there are numerous organizations such as ASCE and EPA that provide statistics on the continuous waste of water, and leakage of pollutants such as sewer, gas, oil, etc., and waste of other resources because of leakage through the pipe joints while contaminating the surrounding areas. The joints are also a point where roots can penetrate sewer pipes, for example, causing clogging of such pipes. (4) When steel or concrete pipes are used, the steel in these pipes corrodes over time, causing failure of the pipes which in turn incur major repair or replacement costs. (5) In industries such as gas and oil, where steel pipes are frequently used, cathodic protection systems must be installed to protect these pipes against corrosion. These systems require continuous monitoring and replacement of components to ensure proper operation. These costs become significant over the life of the pipe. (6) The electrical current that passes through gas or oil pipes, for example, can become stray and accelerate corrosion of other nearby metallic structures. This, for example, is a concern of the electrical utilities where their steel poles corrode at a much faster rate due to these stray currents. Depending on the strength of the current, a pipe may adversely affect a utility pole that is hundred feet or more away from the pipe.

The construction of currently used pipes that are made of steel, concrete or plastics (e.g. PVC, fiberglass, etc.) requires major manufacturing equipments that must be housed in a factory and which are not portable. For example, the equipments needed to melt the steel or roll a steel sheet into a cylindrical pipe is very bulky and heavy. Likewise, mixing of concrete and casting it in a mold to produce a concrete pipe is very difficult and does not lend itself to onsite manufacturing. Even in the case of fiberglass or other plastic pipes, their manufacturing requires a great deal of heat and spinning equipment (since many of these pipes are cast in centrifugal rotating machines), which require large spaces and facilities and are generally not portable to job sites. Therefore, such pipes can never be constructed onsite on an “as-needed” basis.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings, when considered in connection with the following description, are presented for the purpose of facilitating an understanding of the subject matter sought to be protected.

FIG. 1 shows an example of repairing a deteriorated pipe using onsite manufactured pipe;

FIG. 2 shows an example method of manufacturing an FRP-and-Resin pipe; and

FIG. 3 shows an example cross-section of a disclosed pipe.

FIG. 4 shows relative stiffness of same pipe materials with different thickness Spacer layers.

FIG. 5 shows an example process of manufacturing a pipe.

DETAILED DESCRIPTION

While the present disclosure is described with reference to several illustrative embodiments described herein, it should be clear that the present disclosure should not be limited to such embodiments. Therefore, the description of the embodiments provided herein is illustrative of the present disclosure and should not limit the scope of the disclosure as claimed.

Briefly described, methods and articles of manufacture are disclosed for replacing, repairing, reinforcing existing pipes, and onsite-manufacturing of new pipes of various shapes and sizes and lengths, with minimum cost, effort, and time. These methods and articles of manufacture can replace an entire pipe or a part or a segment of a pipe or repair a pipe or a structural member from outside, inside, or both. FIG. 1 shows an example of repairing a deteriorated pipe 110 using onsite manufactured pipes 120 and 130. FIG. 1 depicts the possibility of using onsite manufactured pipe 120 inside the damaged pipe 110 or onsite manufactured pipe 130 on the outside of the damaged pipe 110, or both.

Pipe manufacturing and installation, and also pipe repair and replacement can be expensive, cumbersome, and time consuming. Pipes can get damaged due to a variety of factors, such as earthquakes, overloading, weight of traffic, wear and tear, corrosion, explosions, and the like. If damage does occur to a pipe, a cost-effective and speedy method of repair is clearly desirable. While pipe repair and replacement are emphasized in this disclosure, other structures, damaged or undamaged, can benefit from the disclosed methods and apparatus. The disclosed onsite manufactured pipes can even be used as concrete molding, such as for bridge columns, and can be left around the concrete structural elements for protection.

In various embodiments, the pipe is constructed from fiber-reinforced material, such as Fiber Reinforced Polymer (FRP) to give the pipe more resistance against various types of loading, such as blast loading. Those skilled in the art will appreciate that many types of reinforcement fibers may be used for manufacturing the disclosed pipes including polymer, fiberglass, metal, cotton, other natural fibers, and the like. The sheet materials used in manufacturing these pipes may include fabrics made with fibers such as glass, carbon, Kevlar, Nomex, aluminum, and the like, some saturated with a polymer such as polyester, vinyl ester, or epoxy for added strength, wear resistance, and resilience. The fibers within a reinforcement sheet may be aligned in one direction, in cross directions, randomly oriented, or in curved sections to provide various mechanical properties, such as tearing tendency and differential tensile strength along different directions, among others. Other multi-dimensionally woven materials, known as multi-axial fabrics, can also be used in the manufacture of these pipes. Such materials are currently obtainable from companies such as Fiber Materials, Inc., 5 Morin Street, Biddeford, Me.

In this disclosure, the word “fiber” is used for any sheet of material the strength of which, at least partially and at least in one direction, depends on fibers of some kind, whether the fibers are woven, stitched, or held together by other means such as glue.

The reinforcement layers that form the onsite manufactured pipes may be laminated in the field using epoxy, various glues, or similar adhesives to create a laminated composite that is stiffer than the sum of the individual reinforcement layers. Different reinforcement layers may use sheets with fibers oriented in different directions, such as orthogonal directions, with respect to other sheets to further reinforce the laminated composite. Other materials, as will be described below, such as foams, honeycomb sheets or multi-axial fabrics, may be included in the laminate layers to achieve different desirable mechanical, structural, and other characteristics. Those skilled in the art will recognize that many other types of reinforcement layers such as honeycomb, hollow structures, or laminated structures are possible without departing from the spirit of the present disclosures.

The interior layers of the fabric can provide abrasion and chemical resistance, for example when the pipe is carrying chemicals and slurry-type materials that could result in excessive wear on the surface of the pipe. These same interior layers can also be designed to resist internal pressure of the pipe.

Example materials for building pipes and their reinforcement layers and sheets are “FRP” and resin,” and in some embodiments spacer sheets, all of which are very light-weight and can be delivered to the job site or even stored on a mobile platform such as a trailer or a truck that can move along the trench where the pipe is being made or repaired.

The following is an example method of manufacturing a pipe, which is depicted in FIG. 2. Some of the disclosed steps may be totally eliminated or reordered, as a user may decide.

1) Provide a mold or a mandrel 250 that represents the desired size and shape of the pipe being manufactured. For example, an already available cylindrical corrugated metal pipe may be used as mandrel 250. This mandrel can also be designed to be “collapsible,” so once the pipe is constructed the mandrel is collapsed to a smaller size to allow effortless removal of the finished pipe and easy transportation of the mandrel. Those skilled in the art will realize that the cross-section of the mandrels and manufactured pipes need not be circular and can have any desired geometric shape, such as oval, square or polygon;

2) Apply a release agent to the mandrel 250 or wrap a plastic/nylon sheet 260 around the mandrel 250, or use any other means, to allow easy removal of the finished pipe 270 from the mandrel 250;

3) Saturate an FRP fabric with Resin;

4) Wrap any desired number of layers of saturated FRP fabric around the mandrel 250, over plastic/nylon sheet 260;

5) If desired, wrap any number of spacer layers such as honeycomb or multi-axial fabric type layers between any number of FRP layers. As briefly mentioned above, spacers are optional layers for achieving different desirable mechanical, structural, and other characteristics by utilizing, for example, hollow cells on a surface, and/or using wrinkled or corrugated material sheets, creating a largely hollow core layer, which may be filled with resin or other reinforcing material to increase its stiffness and strength. A spacer may be foam that is sprayed in the field or pre-formed into sheets similar to NexCore produced by Milliken (Spartanburg, S.C.). A spacer may even be an already manufactured laminated sheet of FRP layers. If the spacer sheet is not long enough to go around the mandrel 250 in one piece, one may use multiple sheets. If the spacer material is thick and/or stiff, the spacer may be scored to allow it to bend to fit around the curvature of the mandrel 250. The ends of the spacer sheet(s) can be trimmed at an angle for better butt-joints. For manufacturing a long pipe, in some embodiments a few inches of at least one FRP layer is left exposed at one or both ends of each pipe section to be used for joining the pipe sections together;

6) Allow the assembly to at least partially cure. Cure time may be reduced for example by exposure to air, heat, or UV light for some resins. The full curing of the pipe may continue for a while after removal from the mandrel until the pipe reaches its full strength;

7) Remove the manufactured pipe section 270 from the mandrel 250 by sliding it over the release agent or the plastic/nylon sheet 260; and

8) Butt-joint molded pipe sections 270 using the exposed FRP's and/or wrapping additional resin-saturated FPR bands around the butt-joints.

Those skilled in the art will recognize that, as an alternative method of manufacturing these pipes, some of the disclosed steps may also be used to manufacture flat or merely curved laminated sheets, and that such flat and curved laminated sheets can be later wrapped around and sealed to form a pipe onsite. This alternative makes it possible to manufacture laminated sheets away from the job-site and easily and economically transport them to the job-site, where they can be readily formed into pipes. For example, a square or rectangular laminated sheet may be wrapped around to bring two of its opposite sides together, forming a seam that is subsequently covered by one or more straps of resin-saturated fabric. In another exemplary embodiment the opposite ends may be glued together in an overlapping arrangement.

In yet another exemplary embodiment the fabric and spacer can be dry or partially saturated with resin and wrapped around the mandrel, then the entire assembly is sealed in an air-tight plastic bag and resin is introduced through vacuum suction to saturate the entire pipe assembly; this technique is commonly referred to as “vacuum molding” in the FRP industry.

In cases where the manufactured pipe is being inserted into a damaged host pipe to replace the function of a part of the damaged pipe, at least a part of the outside surface of the manufactured pipe such as its ends may be roughed, for example by sanding or by sand blasting or by spraying a mixture of sand and Resin, to enhance bonding of the pipe to the host pipe in the field.

The mandrel 250 can be mounted on wheels as a moving station that can travel alongside the trench. The above procedure allows the light-weight constituent materials of the pipe, namely FRP, resin and the optional spacer layer to be delivered to the crew while the pipe is constructed and placed. If desired, the raw materials can be placed on the same moving platform as the mandrel 250 or on a separate moving platform adjacent to the mandrel platform for higher productivity.

According to the described embodiments, it is possible to build pipes of unlimited lengths without any joints. However, periodically along the length of the pipe, joints may be necessary based on other considerations. Pipe joints of different kinds are well known in the industry.

Another advantage of the disclosed pipe is that it can be easily cut and spliced in the field. Splicing of the pipe will later require joints to connect the splice, where the above-mentioned joining systems can be used. Moreover, externally wrapped FRP bands can also provide a leak-proof and strong joint. Alternatively, a larger size pipe of similar construction disclosed here can be built and cut into 1-ft long slices; these slices can serve as coupling sleeves that would slip over the ends of adjoining pipes (about 6 inches on each pipe); the small annular space between the original pipe and the coupling sleeve can be sealed with a rubber gasket or a hydrophilic seal that would expand after exposure to water to create a compression seal between the coupling sleeve and the pipe. If the pipe diameter is large enough to allow man entry, the joint can be made internally with FRP, or clamps such as Weko Seal and/or other similar products that are readily available.

The disclosed pipes are flexible enough to accommodate small radii of curvature as most pipes do. However, if an abrupt change of angle is needed, it may require a special mandrel for constructing a pipe with a particular shape or angle. Alternatively, a joint may be introduced at such locations and an especially-made curved pipe can be used to complete the change of direction of the pipe.

The materials including resins used in the construction of the disclosed pipes may be selected from a family of environmentally safe products so that the finished pipe is safe for potable water. QuakeWrap, Inc. (Tucson, Ariz.), for example, provides such fibers and resins that meet the NSF-61 industry standards for potable water.

The disclosed pipes are extremely light and very strong. For example, these pipes weigh approximately 1 pound per square foot compared to a fiberglass pipe manufactured by Hobas Pipe USA (Houston, Tex.) that weighs over 16 pounds per square foot. While all components of the pipe (for example, FRP, resin, and spacer) work together to provide the stiffness and resistance to external loads (e.g. soil, traffic, impact, blast, etc.), the internal pressure rating of the pipe is primarily dependent on the interior FRP layer(s). A typical FRP layer is less than 0.05 inch thick; therefore, one may significantly increase the internal pressure rating of a pipe by adding one or more layers of FRP to the interior surface of the pipe, which will only cause a tiny increase in the pipe wall thickness and the weight of the pipe while increasing the pipe strength significantly.

FIG. 3 shows an example cross-section of a disclosed pipe 300. To better maintain its cross-sectional integrity and withstand different kinds of external loads such as the deadweight of a road and the live weight of cars and trucks passing over the road, the pipe wall needs to be thick. However, material strength of the pipe wall need not be uniform throughout the wall thickness 340 since the major portion of the wall stresses under an external load is generated within the outer layer 310 and inner layer 330 of the pipe wall. Placing a Spacer 320 between the outer layer 310 and inner layer 330 of the pipe wall closely resembles an I-beam web between the two I-beam flanges. The thicker the Spacer 320, the less stress is created within the outer layer 310 and inner layer 330 of the pipe wall. Additionally, the inner layer 330 resists the internal pressure of the pipe and the outer layer 310 provides protection against corrosion from soil or UV light, etc. In some embodiments the outer layer 310 and inner layer 330 of the pipe wall are designed to carry all or most of the stresses caused by the external loads, while the Spacer layer may experience some radial stress.

FIG. 4 shows an example table of relative stiffness of same pipe materials with varying thickness Spacer layers. FIG. 4A sets two layers of saturated fabric, without any Spacer, to be the baseline for stiffness comparison. In FIG. 4B, a layer of Spacer is added between the two layers of saturated fabric such that the combination is twice as thick as the two saturated layers of fabric. Even without taking into account the stiffness of the Spacer, the resulting stiffness is seven (7) times the stiffness of the two layers of saturated fabric alone. In FIG. 4C, the thickness of the Spacer layer is twice as the thickness of the Spacer layer in FIG. 4B; however, the resulting relative stiffness is thirty seven (37) times that of FIG. 4A. As seen from the same table, the increase in weight, as a result of adding Spacer layers, is almost negligible.

FIG. 5 shows an example process of manufacturing a pipe using resin saturated FRP layers. Process 500 proceeds to block 510 where a mold or a mandrel of desired length and cross-section is provided. Readily available products, such as pipes, whose outside dimensions fulfill the user's requirements, can be adopted to operate as a mandrel. The process proceeds to block 520. At block 520, a release agent is applied to or a plastic/nylon sheet is wrapped around the mandrel, or any other means, to allow easy removal of the finished pipe from the mandrel. The process proceeds to block 530. At block 530, wrap any desired number of resin-saturated FRP layers around the mandrel, over plastic/nylon sheet. At block 540, if desired, wrap any number of spacer layers such as honeycomb, foam or multi-axial fabric type layers between any number FRP layers. Spacers are optional layers for achieving different desirable mechanical, structural, and other characteristics. The process proceeds to block 550. At block 550, allow the assembly to at least partially cure. The process proceeds to block 560. At block 560, remove the manufactured pipe section from the mandrel by sliding it over the release agent or the plastic/nylon sheet or partially collapse the mandrel, if collapsible mandrel is used, to remove the manufactured pipe section. The process proceeds to block 570. At block 570, butt-joint molded pipe sections. The process proceeds to block 580, at which step the process ends.

The above manufacturing process lends itself well to automation. As another embodiment, a mobile platform can be constructed that will house the raw materials (e.g., resin, FRP, spacer), the mandrel, and the fabrication machinery. The equipment can include moving arms that will pick up the raw materials and apply them around the mandrel and cure the resin. Certain changes in the procedure simplify the process for the robot without adversely affecting the quality of the finished pipe. For example, it may be easier for a robot to apply a film of resin (like a paint spray), apply the dry FRP fabric and spray more Resin on top of the dry fabric to saturate it. Robots can significantly increase quality of the finished product and the production rate. At the same time the cost of a pipe manufactured with such robots can be much lower than a hand-made pipe. In some embodiments a combination of man and robots may be employed to manufacture the disclosed pipes. For example, a worker may provide and wrap the Spacer around the mandrel while a robot applies the Resin and the FRP layers.

Changes can be made to the claimed invention in light of the above Detailed Description. While the above description details certain embodiments of the invention and describes the best mode contemplated, no matter how detailed the above appears in text, the claimed invention can be practiced in many ways. Details of the system may vary considerably in its implementation details, while still being encompassed by the claimed invention disclosed herein.

Particular terminology used when describing certain features or aspects of the disclosure should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the disclosure with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the claimed invention to the specific embodiments disclosed in the specification, unless the above Detailed Description section explicitly defines such terms.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

The above specification, examples, and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. While the present disclosure has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.

Claims

1. A method of manufacturing a pipe of any length, the method comprising:

wrapping a first desired number of resin-saturated fabric layers around a mandrel;

placing at least one spacer layer over the first wrapped layers;

wrapping a second desired number of resin-saturated fabric layers over the at least one spacer layer;

curing, at least partially, the resin-saturated first or second wrapped layers, or both wrapped layers, to form a pipe segment;

removing the pipe segment from the mandrel; and

connecting two or more removed pipe segments to each other end to end.

2. The method of claim 1, further comprising wrapping a layer of bond-inhibiting material over the mandrel before wrapping the resin-saturated fabric layers around the mandrel.

3. The method of claim 1, further comprising partly removing the pipe segment from the mandrel such that a portion of a wrapped fabric remains on the mandrel to be joined with another pipe segment subsequently made on the mandrel.

4. The method of claim 1, wherein the resin is applied to the fabric before and/or after the fabric is wound.

5. The method of claim 1, wherein the Spacer layer is not made of fiber-based material.

6. The method of claim 1, wherein the fabric is a fiber-reinforced material.

7. The method of claim 1, wherein the fabric is a Fiber Reinforced Polymer.

8. The method of claim 1, wherein the method is at least partially performed by a robot.

9. A method of manufacturing a pipe section, the method comprising:

wrapping a first resin-saturated fabric layer around a mandrel;

wrapping a spacer sheet over the first resin-saturated fabric layer;

wrapping a second resin-saturated fabric layer over the spacer sheet;

curing, at least partially, the resin-saturated fabric to form a pipe section; and

removing, at least partially, the pipe section from the mandrel.

10. The method of claim 9, further comprising wrapping a layer of bond-inhibiting material over the mandrel before wrapping the resin-saturated fabric layers around the mandrel.

11. The method of claim 9, further comprising removing the at least partially cured pipe section from the mandrel such that a portion of the pipe section remains on the mandrel to be joined with another pipe section subsequently made on the mandrel.

12. The method of claim 9, wherein the Resin is applied to the fabric before and/or after the fabric is wound.

13. The method of claim 9, wherein the first and the second layers are designed to carry all or most of stresses caused by an external load on the pipe section and wherein the Spacer sheet may experience some radial stress.

14. The method of claim 9, wherein the fabric is a fiber-reinforced material, a Fiber Reinforced Polymer, or a multi-directional woven fabric.

15. The method of claim 9, wherein the Spacer sheet has properties different from the resin-saturated fabric layers.

16. The method of claim 9, wherein curing is done with light, heat, a liquid, or a combination thereof.

17. A method of manufacturing a pipe section, the method comprising:

spreading any desired number of resin-saturated fabric layers on top of each other on a preferred surface to form a first laminated composite sheet;

spreading any desired number of resin-saturated fabric layers on top of each other on the same or another preferred surface to form a second laminated composite sheet;

curing, at least partially, the first and the second laminated composite sheets;

wrapping-around the first laminated composite sheet to bring two edges of the first laminated composite sheet together;

butt-jointing or overlapping the two edges of the first laminated composite sheet and permanently attaching the two edges together;

placing a spacer layer over the first wrapped composite sheet;

wrapping-around the second laminated composite sheet over the spacer layer to bring two edges of the second laminated composite sheet together;

butt-jointing or overlapping the two edges of the second laminated composite sheet and permanently attaching the two edges together to complete the pipe section.

18. The method of claim 17, wherein the laminated composite sheets are manufactured offsite and the rest of the process is performed onsite.

19. The method of claim 17, wherein the preferred surface is a flat or a curved surface.

20. The method of claim 17, wherein the butt-joint is covered with one or more straps of resin-saturated fabric.