DEVICE AND METHOD FOR COUPLING PIPES

Abstract: A composite pipe coupling has a liner (16), which seals pipes (10,12) to be coupled by the utilization of heat recover­ able metallic drivers (18 to 26), and a complementary exter­ nal support structure (28) that allows high tensile loading of the coupling. A pair of complementary heat recoverable metallic tensile rings (118,130) may further supplement the tensile strength of the liner (16;132).

Description: ,VICE AND METHOD FOR COUPLING PIPES DESCRIPTION This invention relates to a composite pipe coupling using heat recoverable metallic material. In the past, heat-recoverable metal couplings have been developed for joining pipes together for such applications as aircraft hydraulic systems. See for example U.S. Patent No. 4,135,743. As discussed in said patent, couplings have been made entirely out of heat recoverable metal and are referred to generally as monolithic couplings. Composite couplings have also been made, using a liner which is driven by heatrecoverable metal to effect sealing. when such a composite pipe coupling having a liner is utilized, the tensile strength characteristics of the coupling itself depend primarily upon the thickness or crosssectional area of the liner as well as other factors. It can be understood, therefore, that an increase in tensile load strength requires an increase in thickness of the liner and correspondingly a greater driving force to crush the liner to seal with respect to the pipes being coupled. It must be undertood that even if the heat-recoverable metal driver is unitary it will carry only a nominal amount of tensile load since it is only in frictional contact with the liner. The major portion of said tensile load is carried by the liner. If the driver is not unitary, e.g if it is a plurality of ring segments, it would obviously be incapable of carrying any tensile load. Such prior art devices are therefore limited in tensile strength and utility. In accordance with the present invention, there is provided a composite pipe coupling comprising; liner means capable of receiving therein the ends of pipes to be connected; driver means of heat-recoverable metallic material mounted around said liner means, said driver means being arranged to constrict inwardly upon heat recovery to grip said liner means and to deform said liner means to effect sealing with the pipes to be connected; and support means mounted around said driver means and said liner means to support said liner means axially. In one embodiment, the support means is mounted concentrically around said driver means and acts -longitudinally inwardly of the coupling on, and preferably directly contacts, each end of said liner means. The tensile strength of the composite coupling is not limited by the tensile strength of the liner means, since high independent coupling strength is provided by the support means. In a further embodiment, the coupling comprises two tensile rings of heat-recoverable metallic material, said tensile rings being axially mounted adjacent respective ends of said liner means and being arranged to constrict inwardly upon heat recovery to grip respective ones of said pipes. In this embodiment, the tensile strength of the composite coupling is not limited by the tensile strength of the liner means, since the tensile rings and complementary support means can be arranged to provide high overall coupling strength independent of liner strength. Furthermore, the galvanic corrosion potential and exteral contamination may be reduced. The driver means may comprise a plurality of ring-like segments distributed axially along and over the liner means, and may have a varying degree of heat recovery therealong so as to exert an axially variable gripping force on the liner means. The support means may comprise heating means for effecting recovery of the driver means. The composite pipe coupling of the present invention is suitable for a wide variety of diameter pipe, and especially for large diameter pipe utilized in undersea gas and oil transport. The coupling is capable of withstanding high hydraulic or pneumatic pressure internally and high stresses created by movement of undersea piping by the sea itself during operation. Furthermore, the pipe coupling provides a high tensile loading coupling suitable for subsea installation requiring no subsea welding and not employing flanges, which are leak prone. Several embodiments of composite pipe coupling and methods of coupling two pipes together, all in accordance with the present invention, will now be described by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 show first and second embodiments of the coupling respectively; Figure 3 shows a modification of Figure 1; Figures 4 and 5 show third and fourth embodiments of the coupling respectively; and Figure 6 shows a modification of Figure 4. With reference to the drawings, Figure 1 illustrates a cross-section of a composite pipe coupling connecting pipes 10 and 12. In operation, the pipes 10 and 12 are positioned within the composite pipe coupling shown generally at 14 through an over-sized hollow, tubular liner 16. Liner 16 is thin in cross-section and is preferably made from a material that is resistant to corrosive fluids or gases that are being pumped through pipes 10 and 12, and to external pipe corrosive atmosphere. Drivers 18, 20, 22, 24 and 26 are positioned concentrically around liner 16. The drivers are made from a heat-recoverable metal. As shown, a plurality of drivers in the form of rings are utilized, but it is understood that a one-piece or unitary driver may be utilized. Preferably the centrally located driver, driver 22, has less recovery than the outer drivers, drivers 18, 20, 24 and 26, because it is not desirable to subject the ends of pipes 10 and 12 to such compressive forces which might tend to deform and bend the pipes and thereby constrict flow within the pipes or weaken the connection. It is understood that the degree of recovery of memory type metals is controllable and depends upon the amount of deformation it is subjected to in its martensitic state. It is also understood that any number of rings may be used. It is important to note that segmenting the driver means has several advantages. One such advantage is the ease of manufacture as for example by ring rolling of individual segments such as drivers 18, 20, 22, 24 and 26, which would not be possible if the driver means were unitary. Ring rolling the individual segments improves the mechanical properties and performance of each segment. Ring rolling will develop an orientation or texture in a preferred manner with respect to the direction of maximum strain. Since this direction is the same (tangential) as the hoop stresses developed in the rings during their expansion and recovery the ring rolling process will improve the mechanical properties of the rings. It is also more economical to control the driver thickness along its length by segmenting rather than by machining a one piece driver. One of the most important advantages of the segmented design is that the final coupling is inherently more reliable. Specifically, if any one segment should fail the coupling will generally remain operable. The drivers 18, 20, 22, 24 and 26 are made from heat-recoverable metals which are commonly called memory alloys. These ring-like members have been deformed from an original configuration and retain their deformed configuration until they are heated, at which time they will recover toward their original configuration. These alloys exhibit a so-called martensitic transformation from a low temperature form to high temperature form and it is this transformation which produces the memory effect. Among such alloys there may be mentioned for example, various alloys of titanium and nickel which are described in U.S. Patent Nos. 3,174,851, 3,351,463, 3,753,700, 3,759,552, British Patent Nos. 1,327,441, and 1,327,442 and NASA Publication SP 110, "55-Nitinol-The Alloy with a Memory, etc. (U.S. Government Printing Office, Washington, D.C. 1972). The property of heatrecoverability is not confined to such titanium nickel alloys. Thus for example, various beta-brass alloys have been demonstrated to exhibit this property in for example, N. Nakanishi et al., Scipta Metallurgica 5, 433-440 (Pergamon Press, 1971) and such materials may be alloyed to lower their transition temperatures to cryogenic regimes by known techniques. Similarly, type 304 stainless steels have been shown to enjoy such characteristics (see E. Enami et al., ibid at pages 663-668). As shown in Figure 1, the drivers have been heated and have constricted radially inwardly and gripped the liner to cause the liner to seal on to the pipes. The tensile load capability of the liner is greatly increased by use of external support arrangement 28, which comprises two half-shells (only one is shown) that are coupled together by flange members 30 and bolts 32. The support arrangement 28 contacts the ends of the liner 16 at the periphery of the opening therethrough. The liner 16 is contained radially by the drivers 18, 20, 22, 24 and 26 and axially by the support arrangement 28. Tensile loads on the liner 16 created by pipes 10 and 12 are transmitted by the radially contained liner 16 axially through its ends to the external support arrangement 28, said liner 16 therefore acting as a compression member. Of the total tensile load of the coupling, a much greater portion is carried by the external support arrangement 28 than by the liner 16. The ratio of the tensile load carried between the support arrangement 28 and the liner 16 depends upon the modulus of elasticity, yield strength and cross section area of the respective components. It is understood that the support arrangement 28 may comprise any number of segments. There is preferably a slight force fit between the support arrangement 28 and the liner 16 to ensure that the liner 16 will not elongate under tensile load without the support arrangement also elongating. Note also that there is a small amount of axial space 34 between the outer ends of the driver 16 and the inside of the external support arrangement 28 to accommodate some axial swelling of the driver when it returns to original shape and moves into engaging contact with pipes 10 and 12. The amount of spacing between the support arrangement 28 and the driver 16 may be varied generally to place some load on the external support arrangement, if desired. It can be seen in Figure 1 that the inside surface of the liner 16 has continuous ring-like teeth 36 which cut into the pipes 10 and 12. In the embodiment shown in Figure 1 the liner 16 has teeth of generally square cross-section positioned on the inside thereof at points generally axially centered under the drivers 18, 20, 24 and 26. The configuration, size and number of such teeth or serrations may be varied. It can also be seen that the liner 16 and the drivers 18, 20, 22, 24 and 26 are a close fit. The relative dimensions of these components must be such that the driver can slide over the liner 16 during assembly but yet not be so loose in tolerance as to defeat the desired constricting and gripping forces generated by the driver when it returns to its original shape. In the embodiment of Figure 2 the external support arrangement comprises a canister 37 and a complementary lid 38. The canister 37 has a generally cylindrical side wall and an end wall having an opening therethrough to accommodate one of the pipes to be coupled. Likewise the lid 38 has an opening therethrough to accommodate the other pipe to be coupled. The lid 38 is attached to the canister by conventional means, as for example by threading. Other fastening means such as flanges and bolts, welding, adhesives, etc., may be employed. Furthermore, the configuration of the canister may be varied from cylindrical to cubical, spherical, etc., as may be desired. It is important to note that lid 38 and canister 37 interface may be sealed by an "O" ring 40 as shown, to keep out external contamination such as sea water. Figure 3 illustrates an alternative embodiment wherein the coupling shown in Figure 1 is supplemented by a controllable heating device. A heater may be desired when a memory metal element with austenitic start temperature above ambient is utilised. An electrical heating element 42 is placed in the cavity between the external support arrangement and the driver. Thermal insulation 44 is placed between the heating element 42 and the support arrangement to increase the efficiency of the heating element. Power leads 46 connect the heating element 42 to a power source (not shown) to energize the heating element as desired. In the case where the transformation temperature is below the ambient temperature the heater will accelerate the transformation. Other heating means may be used in the cavity between the external support arrangement and the driver, e.g chemical reaction heating devices, etc., or to provide an externally heated medium which is pumped through the coupling cavity. Figure 4 illustrates a cross-section of a further embodiment of composite pipe coupling for connecting pipes 10 and 12. In operation, the pipes 10 and 12 are positioned within the composite pipe coupling. The composite pipe coupling comprises an external support arrangement shown generally at 113, a pair of tensile rings 118 and 130, a liner 132, and a driver arrangement for said liner. Liner 132 is thin in cross section and is preferably made from the same material as the pipes 10 and 12 in order to minimize process fluid corrosion. The driver arrangement for said liner preferably comprises drivers 120, 122, 124, 126 and 128, which are positioned concentrically around liner 132. These drivers are made from heat-recoverable metal. Driver 124 has less recovery than drivers 120, 122, 126 and 128 for the reason given above with reference to the driver 22. The pair of tensile rings 118 and 130 are positioned concentrically around pipes 10 and 12. The rings 118 and 130 are positioned axially outside liner 132 and drivers 120, 122, 124, 126 and 128. Furthermore the rings 118 and 130 are positioned axially within and are in contact with external support structure members 116 and 114, respectively. The tensile rings, like the drivers discussed above, are also made from heat-recoverable metal memory alloy. As shown in Figure 4, drivers 120, 122, 124, 126 and 128 have been heated and they have constricted radially on the liner 132 and have caused the liner 132 to seal with respect to pipes 10 and 12. Likewise, the tensile rings 118 and 130 have been heated and they have also constricted radially on pipes 10 and 12 and their continuous ring-like teeth 136 cut into the pipes 10 and 12. As they constrict, they also drive the sealing lips 134 of the external support structures 114 and 116 radially to contact pipes 10 and 12 and cause the teeth on sealing lips 134 to seal with respect to pipes 10 and 12. It is important to note that external support structures 114 and 116 are likewise made from material similar to pipes 10 and 12 to minimize or eliminate the galvanic corrosion potential. The external support structure illustrated in Figure 4 is a canister 116 and a complementary lid 114. The canister 116 has a generally cylindrical sidewall and an end wall having an opening therethrough to accommodate one of the pipes to be coupled. It can be seen in Figure 4 that the canister 116 is made from a sleeve 117 and threaded end 119 which is welded at 121 to the sleeve 117. Likewise the lid 114 has an opening therethrough to accommodate the other pipe to be coupled. The lid 114 is attached to the canister by conventional means, as for example, by threading as can be seen in Figure 5. Other fastening means such as flanges and bolts, welding, adhesives, etc., may be employed. Furthermore, it will be appreciated that the configuration of the canister may be varied from cylindrical to cubical to spherical, etc., as may be desired. It is also possible to make the external support arrangement in the form of two shells which could be coupled together by flanges and bolts. It is important to note that the lid 114 and tensile ring 130 may be sealed with respect to each other by a metal to metal tooth seal 140 to keep out external contamination such as sea water. A similar seal utilizing a tooth seal 140 is made between tensile ring 118 and canister 116 as can be seen in Figure 4. It can be seen in Figure 4 that the inside surface of the liner 132 is provided with teeth 138 which cut into the pipes 10 and 12 for the purpose of sealing and for carrying some tensile load. Most of the tensile load, however, is carried by the pair of tensile rings 118 and 130 and is transferred to the external support structures 116 and 114. The pair of tensile rings and complementary external support structures provide superior coupling tensile strength independent of the tensile strength capabilities of the liner and driver. Therefore, the main function of the liner 132 remains the maintenance of a good seal with pipes 10 and 12. By this arrangement, even at high tensile loads, the liner 132 remains unaffected and able to maintain a good pipe seal. It can be seen in Figure 4 that liner 132 axially abutts tensile rings 118 and 130 and therefore is capable of transmitting compression loads to tensile rings 118 and 130 and therefore to the external support structure. It is however also envisaged that the liner 132 may be spaced axially from the tensile rings, which together with the complementary external support structure provide by far the majority of the tensile strength of the composite pipe coupling. During assembly of the coupling, it is preferred to tighten the external support structure lid 114 to set the tooth seal 140 and to hold tensile rings 118 and 130 and liner 132 in position. It is also preferred to seal threads 143 at assembly with a conventional seal such as a sealing tape, etc. An #O" ring 141 is shown sealing the threads. Later when the coupling is installed it is possible to fill the coupling cavity through an external port (not shown) with a filler. Such a port can also be used for pressure testing the installed coupling assembly. Figure 6 illustrates an alternative arrangement wherein the device shown in Figure 4 is supplemented by a controllable heating device similar to that described with reference to Figure 3. An electrical heating element 142 is placed in the cavity between the external support and the driver arrangement. Insulation 144 is placed between the heating element 142 and the external support to increase the efficiency of the heating element. Power leads 146 connect the heating element 142 to a power source (not shown) to energize the heating element as desired. It will be appreciated that the present invention provides a composite pipe coupling capable of high tensile loading that is substantially independent of the tensile strength of the liner. Furthermore, the coupling may be installed rapidly, does not employ flanges, which are leak prone, and, since it requires no welding, is particularly advantageous in subsea applications.

Claims: WHAT WE CLAIM IS: 1. A composite pipe coupling comprising: liner means capable of receiving therein the ends of pipes to be connected; driver means of heat-recoverable metallic material mounted around said liner means, said driver means being arranged to constrict inwardly upon heat recovery to grip said liner means and to deform said liner means to effect sealing with the pipes to be connected; and support means mounted around said driver means and said liner means to support said liner means axially. 2. A composite pipe coupling as claimed in Claim 1, wherein said driver means comprises a plurality of ringlike segments distributed axially along and over said liner means. 3. A composite pipe coupling as claimed in Claim 1 or 2, wherein the driver means has a varying degree of heat recovery axially of the coupling, whereby the gripping forces of said driver means are variable. 4. A composite pipe coupling as claimed in any preceding claim, comprising heating means disposed within said support means for effecting recovery of the driver means. 5. A composite pipe coupling as claimed in any preceding claim, wherein said support means comprises a closed, generally cylindrical canister having an axial opening through the ends thereof, one end of said canister being detachable from the remainder of the canister for assembly of the coupling. 6. A composite pipe coupling as claimed in any preceding claim, wherein said support means is mounted concentrically around said driver means and acts longitudinally inwardly of, preferably in direct contact with, the coupling on each end of said liner means. 7. A composite pipe coupling as claimed in any of Claims 1 to 4, comprising two tensile rings of heat-recoverable metallic material, said tensile rings being axially mounted adjacent respective ends of said liner means and being arranged to constrict inwardly upon heat recovery to grip respective ones of said pipes. 8. A composite pipe coupling as claimed in Claim 7, wherein said support means is mounted around said liner means, said driver means and said tensile rings to contain and support said tensile rings axially. 9. A composite pipe coupling as claimed in Claim 7 or 8, wherein said support means acts longitudinally of the coupling on, and preferably in direct contact with, respective ends of said tensile rings. 10. A composite pipe coupling as claimed in any of Claims 7 to 9, wherein said support means has a sealing lip at each end thereof, said lips respectively extending axially inwardly toward said tensile rings and having a portion thereof extending under the tensile rings, said tensile rings being arranged to constrict radially upon recovery to grip said sealing lips and pipes to seal said support means to the pipes to be connected. 11. A method of coupling two pipes together, wherein liner means is positioned over the ends of the pipes and heat-recoverable metallic driver means is recovered inwardly to grip said liner means and to deform said liner means into sealing engagement with the pipes, and wherein a support arrangement is mounted around said driver means and said liner means to provide axial support for the liner means. 12. A method of coupling two pipes together, wherein liner means is positioned over the ends of the pipes and heat-recoverable metallic driver means is recovered radially inwadly to grip said liner means and to deform said liner means into sealing engagement with the pipes, and wherein a support arrangement, at least a portion of which is heat-recoverable, is positioned to enclose said liner means and driver means for strengthening the coupling. 13. A method of coupling two pipes together employing a composite pipe coupling according to any of Claims 1 to 10.

Inventors: BROYLES, HARRY CLIFTON, SZALVAY, LASZLO
Applicants: RAYCHEM CORPORATION
Application year: 1980
Main classification: F16L13
IPC codes: F16L13