Abstract:
The present invention discloses a support system for thermoplastic pipe which includes two sleeves each securable to one of two pipe ends, each encompassing a portion of the pipe and having a connection member spaced apart from the pipe and interconnected between the sleeves. The system minimizes stress on the pipe and fittings associated with thermal expansion and contraction of the pipe.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of design application Ser. No. 800,393, filed Nov. 27, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is directed to pipe supports and pipelines and, in one aspect to a novel support system for thermoplastic piping (e.g. HDPE) which is suitable for use above grade. This system is particularly useful in supporting piping placed in pipe racks or connected to process equipment without causing stress on the equipment or pipe fittings. With such systems design requirements for structural support is reduced. 
     High density polyethylene (HDPE) and other thermoplastic materials have been formed into piping. Such piping has provided effective solutions to many material handling problems. Typically such piping is used to handle hazardous materials, such as corrosive fluids. Units or lengths of such piping are generally connected with flanges or welding. Overland pipelines often suffer from thermal expansion which causes the pipe to &#34;snake&#34; or &#34;roll&#34; and the pipe fittings to fail at their mitered welds due to over stressing. Thermal expansion in thermoplastic piping is aggravated in above ground piping (i.e. overland pipelines) by the use of plastic additives, such as carbon black, to block the degradation caused by exposure to ultraviolet light. For example, carbon black filled polyethylene piping can expand 0.25 inch (in.) per 100 feet (ft.) of length per each 10° F. rise in temperature. Typically this type of piping is buried underground to control or mitigate the thermal expansion and contraction of pipe due to changes in temperature. The Driscopipe Systems Design (1988), and Engineering Characteristics of Driscopipe, No. 1159-88A17, both by Philips Driscopipe, Inc., discuss methods used in the industry to control the &#34;snaking&#34; or &#34;rolling&#34; caused by thermal expansion. For above ground piping systems that contact the ground, anchoring the pipe at specific intervals or allowing the pipe to move between two rows of pylons anchored in the ground restricts lateral movement. Above ground systems that are supported in pipe racks or suspended in the air present a more difficult problem since the support system must be able to support the weight of the pipe and materials in the pipe. The support system must also withstand the forces exerted by the piping during expansion and contraction. 
     Continuous support may be used where support structures can handle the stress caused by expansion and contraction of the pipe and the weight of the continuous support, in the form of an external casing or other suitable method. Continuous support may be suitable for piping less than 12 inches in diameter, but the cost of such a structure is prohibitive for large diameter piping. Another prior art method involves insulating the pipe to maintain it at a relatively constant temperature to avoid expansion or contraction due to changes in ambient temperatures. Continuous support and insulation are expensive and result in higher initial costs and in higher maintenance costs if a leak occurs. If a leak occurs, the support or insulation must be removed in order to find and repair the leak. This is difficult, time consuming and costly. 
     The problems associated with above ground piping along a linear pipe segment are compounded when a system involves interconnected three dimensional piping and tank systems. The continuous support and insulation techniques mentioned above are not suited for use in such a three dimensional situation, particularly when vertical pipe runs are required. The connecting points that join vertical piping to tanks are severely stressed when the pipe expands or contracts. 
     Various approaches have been used to keep pipe joints from separating due to internal or external pressures. One approach uses threaded pipe sections (U.S. Pat. No. 1,680,499 assigned to S. R. Dresser Manufacturing). Clamping rings in conjunction with a coupling sleeve have been used to reinforce screwed joints. U.S. Pat. No. 1,941,358 (assigned to The Elk River Concrete Products Co.), utilizes clamping rings connected by wire cables spaced around the pipe as a connecting truss to overcome movement caused by shifting soil. Use of support plates, interlocked to keep them from moving relative to each other is taught by U.S. Pat. No. 3,819,210 (assigned to Johns-Manville Corporation) as a means of overcoming internal thrust forces in a pressurized fluid. U.S. Pat. No. 3,252,192 discloses the use of clamps which grip the wall of the pipe, the clamps connected by screw elements, to position and hold adjacent ends of piping together. U.S. Pat. Nos. 3,863,182 (assigned to Owens-Illinois, Inc.), 4,492,391 (assigned to Star Industries, Inc.), 4,602,810 and 4,635,970, each incorporated herein by reference, also disclose systems which utilize thrust rods and couplings to hold pipe sections together. 
     U.S. Pat. No. 3,930,675 (assigned to Chemiebau Dr. A. Zieren GmbH &amp; Co.) addresses the expansion or contraction of pipe systems by use of expansion compensators to absorb stresses. Use of this method requires that the compensators be compatible with the materials to be carried in the piping and be able to withstand flexing at the bellows without failing or leaking. Metal is usually used in such applications due to its ability to flex without losing the ability to contain the material in the pipeline. Thermoplastic materials ordinarily used in piping do not have the resilience required to flex and maintain structural integrity. 
     None of the patents cited above, however, satisfactorily address the problems caused by thermal expansion or contraction of thermoplastic piping and there is generally a strong economic and performance preference for above ground thermoplastic piping, particularly when piping corrosive or toxic fluids. 
     SUMMARY OF THE INVENTION 
     The present invention in one embodiment discloses a novel support system for thermoplastic piping which is suitable for use in above grade piping systems. The support system includes a thermoplastic pipe having a first pipe end and a second pipe end, the support system comprising a first sleeve for disposition about the first pipe end, a first securement means for securing the first sleeve to the first pipe end, a second sleeve for disposition about the second pipe end, second securement means for securing the second sleeve to the second pipe end, and connection means for connecting the sleeves together exteriorly of the pipe. 
     A second aspect of this invention is a support system for a plastic pipe, the pipe having a first pipe end and a second pipe end and each pipe end having a pipe flange, the support system comprising a first sleeve for disposition about the first pipe end, first securement means for securing the first sleeve to the corresponding pipe flange on the first pipe end, a second sleeve for disposition about the second pipe end, second securement means for securing the second sleeve to the corresponding pipe flange on the second pipe end, and connection means for connecting the sleeves together exteriorly of the pipe. 
     Another embodiment is a support system for a plastic pipe, the pipe having a first pipe end and a second pipe end and each pipe end having a pipe flange, the support system comprising a first sleeve having a pipe flange for disposition about the first pipe end, first securement means for securing the first sleeve flange to the corresponding flange on the first pipe end, a second sleeve having a pipe flange for disposition about the second pipe end, second securement means for securing the second sleeve flange to the corresponding sleeve flange on the second pipe end, and connection means for connecting the sleeves together exteriorly of the pipe. 
     In another embodiment this invention is a pipeline comprising a first pipe with two ends, a second plastic pipe with two ends, a third pipe with two ends, the three pipes joined together with an end of the first pipe joined to an end of the second pipe, and the other end of the second pipe joined to an end of the third pipe, and a support system for the second pipe, the support system comprising a first sleeve for disposition about a first end of the second pipe, first securement means for securing the first sleeve to the first end of the second pipe, a second sleeve for disposition about a second end of the second pipe, a second sleeve securement means for securing the second sleeve to a second end of the second pipe, and connection means for connecting the sleeves together exteriorly of the pipe. 
     In another aspect a system according to this invention has longitudinal extended supports with tension members connecting the two sleeves together and tension members connecting each sleeve to grade or to a support structure. 
     In another embodiment a system according to this invention includes a method of supporting thermoplastic pipe by use of rigid longitudinal supports which does not require the use of tension members between the sleeves or to connect the sleeves to grade. 
     Certain systems according to this invention eliminate or substantially reduce the stress on tanks and other equipment to which vertical piping is attached. Such systems are relatively inexpensive. Repair of a pipeline is facilitated by easy access to thermoplastic pipe. Replacement of a segment is also facilitated by using a system according to this invention. Additional objects, features and advantages will be apparent in the written description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side, perspective view of a system according to this invention. 
     FIG. 2 is a side, perspective view of a system according to this invention. 
     FIG. 3 is a cross-sectional view of a sleeve portion according to this invention. 
     FIG. 4 is a expanded side view of a system with a support ring. 
     FIG. 5 is a expanded side view of the clamp portion of the invention with tension members. 
     FIG. 6 is a side perspective view of a system according to the present invention with a vertical tension supposed position shown with potions of the piping connecting to a tank. 
     FIG. 7 is a side perspective view of a system according to the present invention with a vertical rigid supported position shown with potions of the piping connected to a tank. 
     FIG. 8 is a side perspective view of a system according to the present invention with multiple fittings. 
     FIG. 9 is a side perspective view of a system according to this invention utilizing an alternate clamp potion. 
     FIG. 10 is a cross-sectional view of the clamp potion according to FIG. 9. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain presently preferred embodiments of this invention may be more fully understood by reference to the drawings. 
     FIG. 1 is a side view of a support system according to this invention for high density polyethylene piping, synthetic resinous piping and thermoplastic piping which is suitable for use above grade. In this embodiment, a thermoplastic pipe 10, has a flange adapter 11, commonly called a stub end, welded to the pipe 10. A metallic sleeve 12, is fitted over the pipe leaving sufficient space for a wear pad 13, inserted between the pipe 10, and the sleeve 12. A backing flange 14, is welded to the sleeve and butts against the flange adapter 11. The backing flange 14 is attached to another adjacent backing flange with the backing flanges spaced apart from each other by the stub-ends upon tightening the bolts 15 therethrough or any other means used in the art. The adjacent backing flange 18 may be connected to an adjacent unit or a standard steel backing flange 18. At least two circumferentially spaced lugs 16 are welded into the sleeve 12. Each lug 16 has an interconnecting member 17 which connects it with an identical lug on a sleeve system on the opposite end of the pipe 10. The interconnecting member 17 is equipped with an attaching means 19 for attaching the interconnecting member 17 to the lug. 
     The embodiment shown in FIG. 2 is similar to that in FIG. 1 but the interconnecting member is replaced with similar tension connectors. Each lug 16 has a tie rod or cable 21 which connects it with an identical lug on a sleeve system on the opposite end of the pipe 10. The rod or cable 21 is equipped with a means for tightening 20 the cable or rod 21. The tightened rod or cable 21 keeps the thermoplastic pipe 10 in longitudinal compression and absorbs thrust created by thermal expansion of the pipe. While the tension rods or cables inhibit pipe movement due to thermal expansion, anchors used at various intervals and preferably at straight run terminations control movement due to thermal contraction of the pipe. Anchor cables 25 and anchor points 26 are attached to the metallic sleeve 12 by use of a lug 27. The anchor cables 25 may be attached to anchor points 26 such as grade or other structures which can withstand the load created by the contracting pipe 10. The anchor points 26 may also be provided by a pipe rack if the rack is capable of withstanding the forces exerted by the system. In a given length of pipe incorporating one or more sections of pipe utilizing this invention, anchor points 26 may be used for any given length. The distance between anchor points will be determined by good engineering practices and convenience. In one embodiment for a section of pipe 36 inches in diameter and 640 feet long, two anchor points were used each, one at each end of the run. It can be seen that in certain embodiments in which rigid members are used to support the pipe instead of cables, anchor points are usually not required since rigid members resist both thermal expansion and contraction of the pipe 10. 
     FIG. 3 presents a cross-sectional end view of a sleeve portion of the invention. At least two circumferentially spaced lugs 16 are welded into the sleeve 12. Each lug has a tie rod, cable or rigid member which connects it with a (generally identical) lug on a sleeve system on the opposite end of the pipe. When several pipe sections are used in conjunction with each other at least two additional lugs 30 are used in conjunction with cable, tie rods or rigid members which are used as shown in FIGS. 1 and 2. At least two shoes 22 are connected to the sleeve 12. A bolt 15 may be used to connect these shoes 22 to a structural support 23, such as an above grade pipe rack. Bolting of the shoes 22 to a support is not required to carry out the objects of this invention. One preferred method, includes connecting the shoes 22 to the structural support 23 by use of a guide 24 which is bolted to the structure. Use of guides 24 allows quick installation or removal of the support system without lining up bolt holes. The use of a guide prevents thermally induced loads from being transmitted to the underlying support. 
     Another preferred embodiment uses support rings 29, as shown in FIG 4. The distance between the rings 29 and the sleeves 12 will be determined by good engineering practices and convenience. The rings 29 have sufficient space for a wear pad 13 to be inserted between the pipe 10 and the ring 29. Wear pads are preferably made of steel or a synthetic resinous material. Preferably the wear pads are made a thermoplastic or more preferably from HDPE. Lubrication of the wear pads is not required but may be use where dictated by good engineering practices. 
     FIG. 5 is a side view of a clamp portion of an embodiment of the invention with rigid members 28 instead of tension members such as rod or cable 21 as shown in FIG. 2. The rigid members may be any structural material that resists thermal contraction and expansion such as metal pipe, metallic wide flanges or other materials having similar properties. The forces created by both the thermal expansion and contraction of the pipe 10 in the system of FIG. 5 are absorbed in substantial part by the rigid members 28 unlike the tension system of FIG. 2, in which the force caused by thermal expansion is absorbed in substantial part by the tie rod or cable 21 and the force caused by thermal contraction is absorbed in substantial part by the anchor cables 25 and anchors 26. 
     Another embodiment of this invention utilizes both tension and rigid supports. A combination of supports may be used when it is desired to relieve stress on members of the piping. For example, for vertical and horizontal piping runs connecting to a vessel such as a tank or a reactor, it is undesirable to place stress on a connection between the piping and the vessel connection. In the embodiment of this invention shown in FIG. 6, use of a rigid members 28 transfers the weight of the piping support system to grade. When using tension members such as rod or cable 21 to absorb thermal stress, the anchor cable 25 transfers forces caused by contraction of the pipe 10 to the anchor point 26 which may be a vessel wall or any convenient structure rather than to the welded joint located between the vessel and the inlet pipe. 
     In situations where low anchor loads are necessary, rigid members may be used in place of tension members as shown in the embodiment of the present invention depicted in FIG. 7. The tension cables are replaced by rigid members 28 which in substantial part absorb the forces caused by thermal contraction of the pipe 10. 
     Certain embodiments of this invention may be used to restrain the movement of pipe in areas where space limitations prevent the use of metallic sleeves. An example of such a system is shown in FIG. 8 in which multiple pipes 31 tee off a short run of pipe 32 located between two sections of pipe supported by a system according to this invention. Use of, as an interconnecting member, a rigid member 28 or cable or rod connected to the adjacent metallic sleeves 12 at opposite ends of the short run, restrains the pipe from movement. 
     Another embodiment of this invention uses the optional means of attaching the sleeve to the pipe as shown in FIG. 9. The sleeve may be attached at any location on the pipe with the distance between sleeves dictated by good engineering practice. A preferred embodiment would be to attached the sleeve at each end of a section of pipe. The sleeve 33 consists of two members connected by bolts 15 or any other means used in the art. At least two circumferentially spaced lugs 16 are welded into the sleeve 33. Each lug 16 has a interconnecting member 17 which connects it with an identical lug on a sleeve system on the opposite end of the pipe 10. The interconnecting member 17 is equipped with an attaching means 19 for attaching the interconnecting member 17 to the lug 16. 
     FIG. 10 presents a cross-sectional end view of a clamp portion of FIG. 9. At least two circumferentially spaced lugs 16 are welded into the sleeve 32. Each lug has a tie rod, cable or rigid member which connects it with a (generally identical) lug on a sleeve system on the opposite end of the pipe.