Abstract:
A flexible supply line to connect media transporting underground supply lines includes a metal corrugated bellows, a connection member at each end of the metal bellows and a flexible wrap wrapped along the metal bellows and the connection members. The invention also includes a method for attaching the wrap to the metal bellows.

Description:
BACKGROUND OF THE INVENTION 
     Applicant claims priority under 35 U.S.C. §119 based upon PCT Patent Application PC/DE95/008743 filed Jul. 6, 1995, and German Patent Application P44 23 921.1 filed Jul. 7, 1994. 
     1. Field of the Invention 
     The present invention relates in general to flexible piping, and, more specifically to a flexible pipe used to connect rigid media conducting underground supply pipes comprising a metal corrugated bellows (or pipe) with connecting elements provided on both ends and a flexible wrap (or jacketing) extending along the entire length of the corrugated bellows and at least a part of one or both of the connecting elements. 
     2. Background Art 
     In mining areas, the surface of the earth often includes sink holes, fissures and compressions of the ground. Consequently, pipes that are layed in the ground are, over time, often displaced, pulled and buckled. Damage to the supply through these pipes often results if no elements are provided that can compensate for these movements. A particular potential for danger is inherent in gas pipe lines, wherein damage to the pipes may result in the leaking of gas, and, in turn, ignition of such a gas-air mixture. 
     Generally, supply pipes that are under low pressure and/or those that have nominal widths up to about DN 150 are often constructed of plastic material. Older supply pipes that have existed for years as well as newer pipes greater than DN 150 and/or those capable of withstanding higher pressures are constructed of steel or other metals. The steel/metal pipes are usually provided with plastic corrosion protection. 
     Gland extenders are disclosed in German patents DE OS 39 39 956, DE 28 53 726 and DE OS 37 02 693 as comprising an inner and an outer pipe wherein the pipes can move axially relative to each other. An elastomeric gasket or gland packing prevents the outflow of the gas from the pipe. A fundamental disadvantage of such an extender having the gaskets arises when the extender has undergone one or more displacements. Under such conditions, the extender is capable of developing leaks, permitting gas to flow out into the atmosphere, resulting in a dangerous condition. Further, dangerous conditions may result from the outflow of gas which follows along the pipe and, under certain circumstances, enters into buildings which are fed by the pipes. 
     Another disadvantage of the extender with gaskets is that the absorption of lateral or angular movements is generally non existent, or minimal at best. Thus, if lateral forces are imposed, leaks may develop in the pipes. 
     Generally, the above described extender comprises two flanges with the gasket therebetween, wherein the flanges are pressed against each other in order to provide the necessary compression for the gasket. If the extender must be insulated for purposes of corrosion protection, any parts that deviate from a cylindrical shape are difficult to insulate. To provide the proper insulation, it is also a disadvantage that the entire extension of the element is positioned only at a point at which the inner pipe leads into the outer pipe. A covering has to be produced that absorbs the entire displacement/movement at the point of entry. In sum, a cost effective and overall adequate solution is virtually impossible with this type of construction. 
     Corrugated pipes, corrugated hoses and compensators--bellows--for the purpose of equilibrating movements in steel pipes are also known. They are generally comprised of a stainless steel which is substantially flexible. As such, they require no addition of gaskets. These corrosion protected corrugated pipes are preferably used with underground pipes up to DIN 100. 
     German Patent DE 25 58 478 specifies a corrugated hose with a pipe stub connected at both ends which bears a covering composed of a shrink wrap hose for corrosion protection. The metallic corrugated hose on the inside is well suited for longitudinal, traverse and angular movements. The shrink wrap hoses are constructed by pre-extending them to larger diameters, then polymerizing them by radiation. These hoses are then shrunk back to the original narrower diameter (previous to the extension) upon application of heat. A covering that is comprised of shrink wrap hose is, however, only extendible to a limited extent. 
     The axial extendibility of PE shrink hoses which are suitable for corrugation for laying underground pipes do not, when overlayed, achieve the extendibility of the underlying stainless steel corrugated hoses. German Patent DE 97 46 08 specifies a wrapped metal hose with a PVC jacket, however the problems relating to axial extension are unfortunately the same. German Patent DE OS 37 02 676 specifies a corrugated hose having a braiding and a shrink wrap hose/coating, however, due to the braiding, axial extension is not possible. Moreover, while it is also known to apply viscous bitumen to metal corrugated hoses to form a coating, the ability for the hose to extend is limited after the bitumen mass has cooled. 
     Until now, the binding of a stainless steel bellows was wrapped with an overlap from winding to winding. G94 04 814.2 specifies the possibility of achieving axial extension by means of an elongated covering which comprises a corrosion protective wrapping that is separated from the corrugated surface. However, when axial extendibility is the most important characteristic for compensators, and previous jacketings have not achieved the axial extendibility of metal bellows, a jacketing that features greater extendibility is necessary. 
     SUMMARY OF THE INVENTION 
     An essential step for increasing the axial extension has been achieved by the introduction of corrosion protection wrap on a corrugated body. In this case, a multilayered corrosion protection wrap, composed of rubber and PE, is wound onto a corrugated hose in an overlapping manner. While the rubber layers of the wrap fuse with each other, they are able to allow the windings of the corrosion protection wrap to slide on top of one another without impairing the sealing ability thereof. The windings permit the longitudinal extension of the element to a greater extent than the extension of the PE material in the corrosion protection layer. 
     Accordingly, an object of the present invention is to provide a pipe line compensator composed of stainless steel bellows for application with underground supply lines for gaseous and liquid media which achieves a high level of axial extension as a primary solution, permits lateral movement, provides corrosion protection for the bellows and the connection parts, and is cost effective to produce. 
     Indeed, it is a particular advantage that the invention unites the extendibility of the helically wound wrap with the extendibility of a casing in a bellows form. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of the corrugated metal bellows with the wrap interjecting partially into the intermediate spaces of the corrugations; 
     FIG. 2 is a partial cross-sectional view of the stretched metal bellows with the corresponding enlarged intermediate spaces and the wrap positioned thereon; 
     FIG. 3 is a partial cross-sectional view of the overlapped, wound, three layer wrap, with an insert showing, in magnification, the PE carrier layer and the rubber layer; 
     FIG. 4 is a partial cross-sectional view of the wrap showing the two layer construction; and 
     FIG. 5 is a partial cross-sectional view of the metal bellows and the applied wrap. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail, a specific embodiment with the understanding that the present disclosure can be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. 
     The present invention comprises a flexible supply line having a helical winding/wrap that is composed of a three layer corrosion protection covering/wrap 22. The wrap interjects itself into the intermediate spaces, such as spaces 16, between corrugations 11 of corrugated pipe/bellows 10. Bellows 10 includes connection members 12, 14 attached at either end thereof and guide pipes 15, 17, which may be received in the respective connection elements 12, 14, to prevent inadvertent buckling of the bellows. The connection members are of sufficient length so as to prevent damage to the wrap thereon upon welding/fusing the connection members to the outside pipes/pipe networks. 
     The three layer wrap 22 comprises a PE carrier layer 24 and rubber layer 26. PE carrier layer 24 includes outer PE layer 32 and rubber layer 34. As can be seen in FIGS. 3 and 4, wrap 22 includes width 28 and, when wrapped upon the bellows, the windings overlap distance 30. While other materials are contemplated, the rubber layers and PE layers are of materials which are pliable and capable of fusing regardless of temperature. 
     The intrinsic stiffness of PE carrier layer 24 in wrap 22 impedes the formation of the complete profile of bellows 10 when protection wrap 22 is wrapped on. A method is employed that permits the band to interject itself partially into intermediate spaces, such as intermediate spaces 16. Narrow wraps lead to the wrap falling into intermediate spaces 16 of bellows 10. Generally, roller type tools do not work satisfactorily, since the surface of the band is very sticky and the band adheres to the roller. 
     In order to achieve the partial interjection of the wrap, according to the invention, a specified sequence of manufacture is provided. The manufacture comprises the steps of: (1) stretching the bellows; (2) winding the wrap; and (3) compressing the bellows. The step of winding the wrap further includes the step of winding rubber layer 26, then winding PE carrier layer 24. Additionally, the method also includes the step of applying an adhesive to promote the rubber-metal bond between bellows 10 and connections 12, 14 and wrap 22. 
     As a result of the indicated method of manufacture, covering/wrap 22 becomes partially bellows shaped as shown in FIGS. 1 and 5. Any axial extension in bellows 10, and, in turn, the wrap can, thus, be absorbed by the corrugated wrap, similar to the way it is absorbed in the metal bellows. The maximum for axial extension of wrap 22 is considerably greater than that of the uncorrugated material itself, due to the bellows type corrugated profile. The permissible extension of the covering is increased with particular advantage by means of this form, that is, it substantially corresponds to the permissible extension of corrugated pipe/bellows 10. 
     A complete interjection of the covering into the free spaces (i.e., eliminating intermediate spaces such as intermediate space 16) is not required and not expedient. In underground laying of pipe it is taken into consideration that eventually send and earth fill substantially all voids surrounding the device. As such, a wrap that is completely interjected into the corrugation/intermediate space 16 has the disadvantage that the sand fills in the corrugations, and any movement during axial compression of the compensators is impeded. On the other hand, with only a partially interjected wrap, the volume of the sand proximate the corrugations is considerably smaller due to the larger intermediate space 16, and, as a result the bellows/wrap can move slightly outwardly or inwardly during a compression. 
     Upon complete extension of the flexible elements, namely the sliding of wrap 22 and the movement of the bellows 10, the wrap construction facilitates the full axial extension of the bellows. 
     Width 28 of wrap 22, as shown in FIG. 3, should be at least the width of a corrugation of bellows 10 in order to prevent a complete falling into intermediate space 16 of the corrugation. 
     Overlap width 30 of the wrap 22, as shown in FIG. 3, influences the extendibility of the wrap. If overlap width 30 is small, there will only be a short path for sliding and the winding will readily open up. If overlap 30 is large, the carrier layer of the band will extend greatly and finally tear before any significant sliding occurs. 
     The width 28 of the wrap 22 and the overlap width 30 should be selected such that with the maximum extension of the flexible elements the wrap seal remains intact; and such that the shear forces in the rubber layer that occur upon extension of the flexible elements are slightly smaller than the force required to tear the carrier layer. 
     The optimal overlap width 30 (denoted as bk in the equations) can be determined by tests, or can be calculated if the material characteristics are known, as shown below: 
     τk is the shearing stress upon flow of the rubber layer 
     δt is the tearing force of the carrier layer, st is the thickness of the carrier layer. 
     The forces equilibrium in the axial direction 
     is 
     
         τk·bk·d=δt·st·d 
    
     resulting in 
     
         bk=δt·st/τk 
    
     The overlap width can be derived from this as 
     
         bk&lt;δt·st/τk 
    
     It is particularly advantageous to utilize the maximum possible extensibility for each band winding of wrap 22. 
     Furthermore, as a result of using corrugated pipe or bellows 10 with the applied bellows-like wrap 22 according to the invention, the total extension of the flexible supply line is uniformly divided along the length by means of the overlay of the covering on the corrugation peaks. Accordingly, no small section needs to take up a large extension. 
     As a particular advantage, the above indicated invention facilitates bellows of virtually any diameter to be wound with wrap 22. The contemplated widths start at approximately DN 50 and end at DN 1600, while it is also contemplated that the wrap would work with pipes that are both larger and smaller. The ease of warehousing the covering material, that is, wrap 22, also results in cost advantages during the manufacturing process and rapid availability of the wrap, and therefore rapid availability for the customer. 
     The foregoing description and drawings merely explain and illustrate the invention and the invention is not limited thereto except insofar as the appended claims are so limited, as those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.