The invention relates to a coolable joint for interconnecting pipe sections.

More particularly the invention relates to a coolable joint for connecting a pipe section to a coolable pipe section which has co-axial fibre reinforced inner and outer walls and a cooling fluid channel formed between said walls.

Coolable double-walled plastic pipe sections are disclosed in European Patent Specification No. 0281689. Such coolable plastic pipe sections are light-weight, fire resistant and are substantially maintenance free and are therefore suitable for use in pipeline systems on decks of ships and on offshore structures.

The cooling fluid channels of adjacent pipe sections known from said prior art reference are interconnected via U-shaped connection tubes of which one leg is screwed to the outer wall of one pipe section and has an inlet opening that passes through the outer wall of said one pipe section into a fluid channel formed between the inner and outer walls of that pipe section and the other leg is screwed to the outer wall of the other pipe section and has an outlet opening that passes through the outer wall of said other pipe section into a fluid channel formed between the inner and outer walls of said other pipe section.

Disadvantages of the application of the known U- shaped connection tubes are that they require labour intensive installation procedures and that, once installed, the tubes can be easily damaged. Furthermore, the known U-shaped connection tubes hamper the interconnected pipe sections to slide relative

to each other as a result of thermal expansion or contraction which may initiate significant thermal stresses when the pipe sections are surrounded by a fire. In the event of a fire any cooling fluid flowing through the U-shaped connection tubes will furthermore warm up significantly and the U-shaped connection tubes do not provide a uniform flow path for cooling fluid which evenly cools those external surfaces of the joint and coolable pipe which are exposed to the fire. An object of the present invention is to remedy these disadvantages.

The pipe joint according to the invention thereto comprises a tubular section having co-axial inner and outer walls and a cooling fluid channel formed between said walls, which channel is connectable in fluid communication with said cooling fluid channel of said coolable pipe section such that the joint allows the interconnected pipe sections to slide relative to each other and maintains a uniformly distributed flow path of cooling liquid throughout a substantial part of the cooling fluid channels of the coolable pipe section and of said tubular section of the joint irrespective of said sliding motion.

Preferably the cooling fluid channel between the walls of the joint is provided with cooling fluid flow distribution means which evenly distribute the flow of cooling fluid throughout said channel. It is also preferred that, when in use, said cooling fluid channel is separated by sealing rings from both the interior and the exterior of the pipe sections interconnected thereby. In a first embodiment of the joint according to the invention the joint is designed to interconnect a pair of said coolable pipe sections and the cooling channel formed between the walls of the joint has an annular shape and is at least partly filled with a structural but

permeable core, which core forms part of said cooling fluid distribution means.

In said first embodiment of the joint according to the invention the tubular section may be formed by a sleeve having a cylindrical inner surface which fits co- axially around the ends of the pipe sections that are to be interconnected by the joint which sleeve is provided at each end with a solid end ring to which the inner and outer walls of the sleeve are connected, the inlet section is provided by a series of circumferentially distributed inlet openings in the inner wall of the sleeve adjacent to one end ring and the outlet section is provided by a series of circumferentially distributed outlet openings in the inner wall of the sleeve adjacent to the other end ring.

Alternatively, in said first embodiment of the joint according to the invention the tubular section consists of a male and a female part, each part being connected to one of the pipe sections to be interconnected such that the part forms an end piece of the pipe section, the male part having an inner wall comprising a cylindrical end section which protrudes beyond the outer wall of said part and which has an outer diameter that is substantially equal to the inner diameter of at least the end section of the inner wall of the female part; and the female part having an outer wall comprising a cylindrical end section which protrudes beyond the inner wall of said part and which has an inner diameter that is substantially equal to the outer diameter of at least the end section of the outer wall of the male part.

A pipe section adapted to be coupled to other pipe sections by a joint comprising a male and female part as described hereinbefore may comprise at one end thereof said female part and at another end said male part.

Sometimes it is desirable to connect a double-walled plastic pipe to a conventional steel pipe. Thus, there is a need for a transition joint that is suitable for making such a connection. Such a transition joint should provide a thermal barrier which protects the plastic pipe from overheating in the event the metallic pipe is engulfed in a fire and heat is transmitted via the wall of the metallic pipe and the transition joint and optionally via the interior thereof to the walls of the plastic pipe.

Moreover, such a joint should be cooled and provide an entrance or discharge for cooling fluid that may be pumped through the annular cooling fluid channel provided between the walls of the plastic pipe. In a second embodiment of the joint according to the invention the joint forms a transition joint for interconnecting a metallic and a coolable double-walled plastic pipe.

The transition joint according to the invention comprises a first tubular section which is securable in fluid communication with the metallic pipe and which is secured by a ring-shaped transition section in fluid communication with a second tubular section. The second tubular section is fittable co-axially around or within the double-walled plastic pipe and is formed by a double- walled sleeve. The sleeve has an annular cooling fluid channel formed between the walls. In the inner or outer tubular wall of the sleeve which faces in use a wall of the plastic pipe one or more perforations are present that are connectable in fluid communication with one or more perforations in the adjacent wall of the plastic pipe in order to create in use a fluid communication between the annular cooling fluid channel formed between the walls of the sleeve and an annular cooling fluid channel formed between the walls of the plastic pipe. The

sleeve is further provided with a cooling fluid passage for feeding or discharging cooling fluid into or from the annular fluid channels.

Preferably, the second tubular section has a larger width than the first tubular section and the ring-shaped transition section is formed by a double-walled frusto- conical pipe-section of which the inner and outer wall are each at one end thereof secured to the outer circumference of the first tubular section and at the other end thereof to the inner and outer walls, respectively, of the sleeve.

It is furthermore preferred that the transition joint is predominantly made of metal.

It is also preferred that the second tubular section is fittable around a coolable double-walled plastic pipe and that said perforations are arranged in the inner wall of the sleeve. In such case the inner wall of the sleeve is equipped at its inner circumference with one or more sealing rings at each side of said perforation or perforations.

It is observed that Netherlands patent specification 8205037 discloses a stab-in joint for interconnecting dual passageway plastic pipes such that fluid channels passing through the pipe wall are interconnected via an annular chamber. This chamber is provided with a bleeding valve which may be used to take samples of the fluid from the channels. Although the chamber is connected to the channels any fluid which enters the chamber is essentially stagnant, unless the bleeding valve is opened. Hence the known chamber is not designed to be used for cooling purposes.

Other joints for dual passageway pipes are disclosed in German patent specifications 2537924 and 2249449, US patent specification No. 4149739 and in French patent specification 2362330. The joints known from these prior

art references are not designed for interconnecting coolable plastic pipes and the known joints contain screw connections or flanges that are bolted together to secure the interconnected pipe sections to each other which may lead to significant thermal stresses when the pipe sections expand or compact as a result of temperature variations.

The invention will now be described in more detail and by way of example with reference to the accompanying drawings, in which

Figure 1 shows a longitudinal sectional view of an upper half of the first embodiment of a joint according to the invention;

Figure 2 shows a longitudinal sectional view of an upper half of an alternative configuration of the first embodiment of a joint according to the invention;

Figure 3 is a cross-axial section of the joint of

Figure 2 along line III-III when seen in the direction of the arrows; and Figure 4 shows a longitudinal sectional view of the second embodiment of the joint according to the invention in which the joint is used as a transition joint for interconnecting a coolable plastic pipe and a metallic pipe. Referring now to Figure 1 there is shown the upper half of a joint 1 which consists of a male part 1A and a female part IB.

The male part 1A has co-axial fibre reinforced plastic inner and outer walls 11 and 12, respectively, which are connected to the co-axial fibre reinforced plastic inner and outer walls 21 and 22, respectively, of a first pipe section 2 via a tapered transition section 3 such that the male part 1A forms an integral end piece of the first pipe section 2.

The female part IB has co-axial fibre reinforced plastic inner and outer walls 13 and 14, respectively, which are connected to the co-axial fibre reinforced inner and outer walls 31 and 32, respectively, of a second pipe section via a tapered transition section 4 such that the female part IB forms an integral end piece of the second pipe section 3.

The inner wall 11 of the male part 1A comprises a cylindrical end section 15 which protrudes beyond the outer wall 12 of said part 1A whereas the outer wall 13 of the female part IB comprises a cylindrical end section 16 which protrudes beyond the inner wall 14 of the female part.

The cylindrical end section 15 of the male part 1A has an outer diameter which is slightly smaller than the inner diameter of the end of the inner wall 14 of the female part IB and O-ring seals 17 are located in grooves at the outer circumference of said outer wall 14 to provide a fluid tight seal between said end section 15 and wall 14.

The cylindrical end section 16 of the female part IB has an inner diameter which is slightly larger than the outer diameter of the outer wall 12 of the male part 1A and O-ring seals 17 are located in grooves at the outer circumference of said outer wall 12 to provide a fluid tight seal between said end section 16 and wall 12.

Between the inner and outer walls 11 and 16, respectively, of the male part 1A an annular cooling fluid channel 18 is formed which is connected in fluid communication with an annular cooling fluid channel 20 between the inner and outer walls 21 and 22, respectively, of the first pipe section 2 via an annular inlet opening 23 which is formed between the co-axial walls of the tapered transition section 3.

Between the inner and outer walls 14 and 13, respectively, of the female part IB an annular cooling fluid channel 19 is formed which is connected in fluid communication with an annular cooling fluid channel 30 between the inner and outer walls 31 and 32, respectively, of the second pipe section 3 via an annular inlet opening 33 which is formed between the co-axial walls of the tapered transition section 33.

The male part 1A and female part IB of the joint 1 are mated by sliding the parts towards each other in longitudinal direction relative to the central axis I. After mating of the parts 1A and IB the fluid channels 18 and 19 of these parts are interconnected and a continuous annular flow path is formed by the channels 20, 18, 19 and 30 through which cooling fluid can be pumped in the direction of arrow A or vice versa. In the mated position the O-ring seals 17 provide fluid tight seals between the cooling fluid channels 20, 18, 19 and 30 and both the pipe interior 34 and pipe exterior 35. Optionally, the sealing rings 17 are cooled in case of a fire by inducing fluid to flow through the annular space (not shown) between the sealing rings 17 and the outer walls 12 and 16. This may be accomplished by arranging a polyvinylchloride (PVC) plug (not shown) in a hole through the outer wall 16 of the female part 1A near the bottom of the area between the sealing rings 17 and by drilling one or more holes (not shown) through the outer wall 12 of the male part 1A near the top of the area between the sealing rings 17. In case of a fire the PVC plug will melt away and some cooling fluid will then enter into the annular space between the sealing rings 17 via the openings in the male part 1A and will flush away from said annular space to the pipe enterior via the opening in which the PVC plug was present.

Referring now to Figure 2 there is shown a joint which comprises a sleeve 50 having co-axial fibre reinforced plastic inner and outer walls 51 and 52, respectively. The sleeve 50 surrounds the ends of the pipe sections

60 and 70 that are to be interconnected by the joint.

The sleeve 50 is at each end provided with a solid fibre reinforced plastic end ring 53 to which the inner and outer walls 51 and 52 are connected. One of the end rings 53 is secured to the outer wall 61 of the pipe section 60 by a locking ring 63. This ring 63 fits within a groove formed in said wall 61 and serves to lock the sleeve 50 in a predetermined axial position relative to the end of the pipe section 60 such that a series of circumferentially spaced inlet openings 54 in the inner wall 54 of the sleeve 50 surround a series of circumferentially spaced openings 64 in the outer wall 61 of the pipe section 60. Two sets of O-ring seals 65 are provided at each side of the series of openings 54, 64 to provide fluid tight seals between the pipe interior 68, the pipe exterior 69 and the cooling fluid channel formed by the openings 54, 64 and the annular spaces 56 and 66 between the co-axial walls 51 and 52 of the sleeve 50 and between the co-axial walls 61 and 62 of the pipe section 60.

Near the end ring 53 at the right side of Figure 2 a series of circumferentially spaced outlet openings 57 are formed in the inner wall 51 of the sleeve 50. These outlet openings 57 surround one or more openings 77 in the outer wall 71 of the pipe section 70. Two sets of O- ring seals 75 are provided at each side of the series of openings 57, 77 to provide fluid tight seals between the pipe interior 68, the pipe exterior 69 and the cooling fluid channel formed by the openings 57, 77 and the annular spaces 56 and 76 between the co-axial walls 51

and 52 of the sleeve 50 and between the co-axial walls 71 and 72 of the pipe section 70.

The assembly of annular spaces 56, 66 and 76 and openings 54, 64, 57 and 77 provide a channel through which cooling fluid can be pumped in the direction of the arrows B or vice-versa.

Air escape openings 58 are provided in the outer wall

52 of the joint through which air may be allowed to escape when the cooling fluid channel is filled with an aqueous cooling fluid, which openings are closed off by bolts 59 when all air has escaped from the channel.

In Figure 2 the pipe sections 60, 70 and joint 50 are shown in the coupled position where a small gap 80 is left between the ends of the pipe sections 60 and 70 to allow the sections to thermally expand or contract whereby the pipe section 70 will axially slide within the sleeve 50.

The pipe section 70 can be disconnected from the joint by pulling the section 70 out of the sleeve 50 in longitudinal direction relative to the central axis II of the sleeve 50.

Figure 3 shows that the annular space 56 formed between the inner and outer walls 51 and 52 of the sleeve

50 shown in Figure 2 is filled with a permeable but structural core 81 of rectangular tubular elements or strut elements as described in European patent

No. 0281689, which core serves to enhance the strength and stiffness of the inner and outer walls 51 and 52 of the sleeve 50. It will be understood by those skilled in the art that numerous modifications may be made to the joints illustrated in Figures 1 and 2 without departing from the spirit of the invention.

Thus it will understood that the sleeve as shown in Figure 2 may be bent or may have three or more branches

if it is used to interconnect three or more pipe sections.

It will be also understood that instead of providing the sleeve 50 with a series of circumferentially spaced inlet and outlet openings 54 and 57 as shown in Fig. 2 the sleeve may also be provided with a single inlet opening 54 and a single outlet opening 57. In such case it is preferred that the tubular elements of the core 81 are arranged in such a pattern that they provide a flowguide which evenly distributes cooling fluid throughout the annular space 56. This may be accomplished by arranging the tubular elements in a helical pattern within the annular space 56 such that cooling fluid is induced to swirl through said space 56. The transition joint shown in Fig. 4 comprises a first tubular section 101 and a second tubular section 102, which forms a sleeve having co-axial inner and outer walls 102A and 102B, respectively. A ring-shaped transition section 103 having co-axial frusto-conical inner and outer walls 103A and 103B, respectively interconnects the first and second section 101 and 102 of the joint. The walls 103A and 103B of the transition section 103 and the walls 102A and 102B of the sleeve 102 are made of a stainless steel and welded together. These walls 102A, 102B, 103A and 103B are coolable by means of the annular space between them which provides a cooling fluid channel. Also the end part 101A of the first tubular section 101 is made of a stainless steel. This end part has a smaller thickness than the other parts of this section 101 that are made of a mild steel.

The metallic tubular section 101 is equipped with a flange 105 for connecting the joint to a conventional steel pipe (not shown) .

The second tubular section 102 surrounds an end of a double-walled plastic pipe 106 of which the inner and

outer walls 106A and 106B are spaced apart, thereby creating an annular cooling fluid channel 107 between these walls.

The outer wall 106B of the plastic pipe 106 and the inner wall 102A of the second tubular section 102 comprise openings 108 and 109, respectively, which provide a fluid communication between the annular cooling fluid channel 107 of the pipe and an annular cooling fluid channel 110 formed between the inner and outer walls 102A and 102B of the sleeve.

Sealing rings 111 are arranged between the outer wall 106B of the plastic pipe 106 and the inner wall 102A of the second tubular section 102 at each side of the openings 108 and 109 in order to seal off the cooling fluid channels 107 and 110 from the pipe interior and exterior. The inner surface of the inner wall 102A of the section 102 and the inner surface of the tubular section 101 are provided with a nylon coating (not shown) which serves as a fire and corrosion protection of said wall 102A and the sealing rings 111.

The outer wall 102B of the sleeve is provided with an opening 112 which forms, together with a conduit 113 that is secured to the rims of the opening 112, a cooling fluid passage. As illustrated by the arrows in the example shown cooling fluid flows from the annular cooling fluid channel 107 of the pipe 106 via openings 108 and 109 into the cooling fluid channel 110 of the second tubular section 102 and is then discharged via the opening 112 in the outer wall 102B of said section 102 into the conduit 113.

It will be understood that at another end of a string of double-walled plastic pipes 106 a similar transition joint may be present which comprises a conduit similar to conduit 113 via which cooling fluid is supplied to the

annular cooling fluid channels of the plastic pipe string and the sleeve of the latter transition joint.

A flow distribution system 116 comprising a series of tapered flow guide fences 117 is arranged within the annular cooling fluid channel 110 of the section 102. The flow guide fences 117 are perforated in the area of the opening 109 in the inner wall 102A of the section 102 to allow cooling fluid to flow from said opening 109 into the annular fluid channel 110. The system 116 serves to induce cooling fluid that enters the annular fluid channel 110 via the opening 109 to be evenly circulated around the annular fluid channel and also between the inner and outer walls 103A and 103B of the frusto-conical section 103 before it is discharged into the conduit 113. In this way the entire surface of the walls 102A, 102B and 103A, 103B of the sections 102 and 103 is evenly cooled by the cooling fluid.

An air bleeding opening 118 is arranged in the transition section 103 of the joint for bleeding air from the pipe interior. During normal operation of the joint this discharge opening 118 is sealed off by a bleeder plug 119. The outer wall 102B also comprises an air bleeding opening 120 which during normal operation of the joint is sealed off by a bleeder plug (not shown) . An end ring 121 seals off the end of the annular cooling fluid channel 110 of the sleeve, which ring is welded to both the inner and outer wall 102A and 102B of the section 102.

In the embodiment shown the conduit 113 is arranged at the lower side of the section 102 whereas the cooling fluid inlet opening 109 is arranged at the upper side of the section 102. This arrangement ensures a uniform flow of cooling fluid throughout the annular channel 110 of the annular space 110 if the space is initially filled

with gas and subsequently a liquid cooling fluid, such as water, is pumped into the annular channel 110.

The space between the inner and outer wall 103A and 103B of the conical transition section 103 is in fluid communication with the annular cooling fluid channel 110 of the sleeve. In this way it is accomplished that the cooling fluid also cools the walls 103A and 103B of the transition section 103 so that also the transition section 103 acts as a heat buffer which prevents radiation and conduction of heat from the first section 101 towards the other parts of the joint and the plastic pipe 106 if the first section 101 and adjacent steel pipe (not shown) are engulfed in a fire.

The outside walls 101, 101A, 102B, 103B, 113 and 121 are all provided with a glass reinforced plastic or similar water resistant coating (not shown) to prevent direct impingement of the fire onto the surface of the transition joint and to provide a measure of thermal insulation.