DE2609011A1 - SEAL PIPE CONNECTION - Google Patents

Description

Tight Pipe Joints The invention relates to pipe joints.

The conventional construction of a pipe connection provides flanges at the two ends of the pipes to be connected, the are bolted together. A suitable sealing ring is located between the flanges in order to achieve a sealing effect. For an effective seal, this structure requires high strength bolts and high bolt and washer loads. If such conventional bolted flange connections are used for low-temperature applications, occurs during commissioning a particular problem.

When a flange connection changes from room temperature to very

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ORIGINAL INSPECTED

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low temperatures, such as the working temperature the evaporator is cooled by liquefied natural gas, the flanges cool down and shrink faster than that Screw bolts. This means that the bolts no longer hold the flanges tight enough because the connection loosens, so that a Leak occurs. One way to reduce this effect is to use screw bolts with an extremely low coefficient of expansion to be used so that the tension of the bolt is always maintained. Alloys with very low expansion coefficients are however expensive; this means that the flange connections become expensive. After a period of time, though the entire flange connection has cooled down, the leakage stops the conventional bolted flanges, since the Shrinkage of the Eolzen seals the flange connection and creates a sealing effect.

Although the invention particularly relates to the creation of pipe connections in connection with at very low temperatures If the pipes used are used, the flange connection can also be used at other temperatures.

As an alternative to the conventional sealing ring flange connections, In which a sealing ring is located between the flanges, a flange connection is proposed has been (see e.g. GB-PS 7 573 36), which uses a cylindrical sealing element with beveled surfaces, which with corresponding cooperate beveled surfaces on the pipe ends. To make the connection, the pipe ends are under Force brought together and the sealing element against the

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deformed beveled surfaces at the pipe ends. The connection is made by bringing the pipe ends together to form the To surrender to poetry.

The invention provides a pipe joint comprising two pipe ends and a tubular sealing cylinder which extends into the two pipe ends and with its ends with the insides of the two pipe ends

represents an interference fit, the tubular sealing cylinder is flexible at the ends so that it is radial within the pipe ends in use under the pressure of the fluid is pressed outwards and creates a sealing effect between the pipe ends.

The pipe ends can have essentially the same diameter. The cylinder can be slightly constricted and are slightly larger in diameter at their opposite ends than at the center.

The cylinder may have an annular outer bead in the center which fits between the pipe ends and forms a positive fit for the pipe ends; the outer bead also serves to form a stable central part. He can have a groove on its outer surface.

Preferably, the outside diameter of the cylinder at the ends is somewhat larger than the inside diameter of the pipe ends.

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The material of the cylinder preferably has essentially the same coefficient of thermal expansion as the material of the Pipe ends.

Furthermore, the pipe ends and the cylinder are preferably made of the same material.

The pipe ends may have outer flanges that can be bolted together to keep the pipe ends in alignment. The pipe ends can be machined to form recesses ^z u which receive the tubular seal cylinder. The cylinder preferably has a circular cross-section. The cylinder and / or the recesses can be coated with a substance with a low coefficient of friction, preferably polytetrafluoroethylene or molybdenum disulfide.

The invention also provides a pipe connection which has two pipe ends and a metallic sealing element, which extends into both pipe ends and a fluid-tight one in between Forms sealing element; it is characterized in that each of the pipe ends is a substantially cylindrical having inner sealing surface and that the metallic sealing element is a one-piece, substantially cylindrical is tubular member extending into the pipe ends, each of the outer portions of the tubular member

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forms an interference fit with one of the inner sealing surfaces and wherein the tubular member is flexible at its ends so that, in use, it will be exposed to the pressure of the fluid is pushed radially outward within the pipe ends and creates a seal between the pipe ends.

The invention also provides a pipe joint having two pipe ends with passages that are in axial alignment are to each other, and a metallic sealing element that extends into both pipe ends and between one results in a fluid tight seal; the pipe connection is characterized in that the pipe ends each have a substantially cylindrical inner sealing surface that a one-piece tubular sealing cylinder with an annular outer bead in the center and flexible at the ends Having sections, each flexible outer section being telescopically received by one of the pipe ends, the ends of the outer portions form an interference fit with the inner sealing surface and the tubular sealing cylinder under, in use the pressure of the fluid within the pipe connection is pressed radially outward and a seal between the Causes pipe ends.

The two end sections can be fixed or movable relative to one another. The tubular element can be im central portion have an outer annular bead.

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The invention is explained in more detail below with reference to the drawing of exemplary embodiments.

Fig. 1 shows a cross section of a first embodiment according to the invention.

2A shows a cross section of a second according to the invention Embodiment.

Fig. 2B shows a cross section of a conventional connection.

3 shows a cross section of a third exemplary embodiment according to the invention.

As shown in Fig. 1, a connection is made between the ends 1 and 2 of pipes. A little Flange 3 is welded to pipe end 1 and a corresponding flange 4 is welded to pipe end 2. The inner bores the pipe ends 1 and 2 are precisely machined and form cylindrical Recesses 5 and 6, which have an exact diameter and also have a smooth surface. Inside the recesses 5 and 6 is a tubular cylinder 7, which the actual sealing element forms. The cylinder 7 is sufficiently flexible that it moves radially under the action of the internal pressure can expand. On the outer surface of the cylinder 7 is located

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an annular bead 8 which serves to hold the cylinder exactly within the recesses 5 and 6. The bead 8 forms also "a stable middle part, so that the outer parts can bend away from the middle part. The cylinder points at its outer ends 9 and 10 have a slightly larger diameter than at its central portion 11 when the cylinder is outside the pipe ends. The bead 8 has a circumferential groove 12 to allow the cylinder to be withdrawn from one end of the tubes to facilitate when the connection is disassembled. Because the ends 9 and 10 have an interference fit within the recesses 6 and 5, it would be difficult to remove ^ the cylinder if the groove were not provided to allow sufficient leverage can achieve on the bead. The flanges 3 and 4 have an annular trough 13 for receiving the annular Bead 8. The connection is established simply by the Cylinder 7 is brought into the end of a pipe either by hand or with the help of a suitable tool and then the another tube is brought over the free end of the cylinder. Bolts, such as the screw bolts 14, are then inserted through the holes in the flange to keep the pipe ends in working contact. The sealing element then acts simply so that it expands to the outside by the internal pressure of the fluid inside the pipe.

The material from which the cylinder 7 is preferably made has the same coefficient of thermal expansion as the material of the pipes. If so, the poetry remains

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effective regardless of temperature changes. To get the best results To achieve, the seal and the pipe ends are made of the same material, so that the expansion coefficients are identical are. When the cylinder is brought into the pipe ends it forms because of the interference fit between the outer surface of the ends ·. 9 and 10 and the inner diameter of the recesses 5 and 6 of the pipe ends at the same time a seal. Increasing the Pressure inside the pipe only increases the sealing effect. Therefore, the bolts 14 only need to hold the assembly together and absorb the internal pressure, but not create a further sealing pressure. Consequently, compared to a conventional bolted flange connection requires far fewer bolts; these bolts themselves can be smaller, lighter, weaker and be cheaper.

Since the flexible sealing element is thin, it lets heat quickly through the walls; that means that the Connection is not influenced by heat transfers and rapid temperature changes. About the resilience of the connection To test for heat transfers, a stainless steel unit with a diameter of 50 mm was made up of a cylinder stainless steel with pipe ends made of stainless steel, tested in a system that maintains a constant pressure of 2 to 3 at was maintained within the connection. The temperature in the compound was like during a cycle of 120 seconds follows changed. The temperature was increased from 75 ° C in 10 seconds

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5OO ° C increased. ^{It was held at 500 °} C. for 80 seconds and then reduced to 75 ° C. in 10 seconds. The temperature was held at this level for 20 seconds, completing the cycle. It can be seen that this is an extreme thermal cycle arrangement; the connection withstood more than 1000 cycles without errors. The test of the seal after 700 cycles, the system was stopped, the seal was dismantled and examined - showed that none of the sealing surfaces was scuffed or chafed; the seal was found to be satisfactory.

In order to facilitate the assembly of the seal, it can have a layer of polytetrafluorethylene on its surface, which is applied by simply rubbing the outer surfaces of the cylinder 7 with a block of polytetrafluorethylene can be. Since polytetrafluorethylene has a low Has coefficient of friction, this facilitates the assembly of the seal.

In the representation of FIGS. 2 A and 2 B (the

For easier understanding of the invention, the same parts of the invention are given the same reference numerals as in Fig. Mistake. Referring first to Figure 2B, it shows a conventional pipe joint of the type that has flanges and one Has sealing ring. A solid flange 15 is on the pipe end 1 welded on; a similar flange 16 is on the pipe end 2 welded on. A sealing ring 17 is located between

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the flanges; a number of bolts 18 and 19 are tightened around the periphery of the flanges to accommodate the inside of the Connection to withstand prevailing pressures. The pressure exerted by the bolts consists of two main components, the pressure load and the sealing load of the sealing ring. The sealing load of the sealing ring, which the axial force required to create the seal is much higher than the compressive load; it depends on the geometry of the flange and on the material used for the sealing ring; it can be over three times larger be than the pressure load. The flanges and bolts must therefore be very massive to withstand the pressures applied. The connection shown in Fig. 2B has the same pressure capacity as that according to the invention shown in Fig. 2A Connection on. It can be seen that the compound according to the invention is very'much, smaller than the conventional connection. In addition, it is not necessary to use unusual and expensive materials in making the connection.

In Fig. 2A, the sealing element 11 is inside of the recesses 5 and 6 of the pipe ends 1 and 2 in the same way as described above with reference to FIG is. An outer circular ring 20 or 21 is welded to the respective pipe end. The ring 20 is at 22 provided with a screw thread. You can see that the Bead 8 is received within the rings 20 and 21, which are machined after welding, so that the end faces the pipe ends 1 and 2 with the rings 20 and 21 flush

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are. An outer circular cylindrical holding part 23 has an inner flange 24 attached to the end face -25 of the ring 21 rests. The inner surface of the holding part 23 is provided with a screw thread at 26 so that it is as shown 2 A can be screwed onto the ring 20 from the right. A threaded locking pin 27 can then be screwed in, which prevents the holding part 23 from loosening, but a relative rotation of the holding part 23 relative to the ring 21 allows. It can be seen that this annular part, the pipe ends 1 and 2 in axial alignment with one another holds.

In Fig. 3 a slidable connection is shown which forms a suitable expansion connection. A sliding one Element 28 is welded at one end 29 to a pipe end 2. Somewhat away from it is located on the element 28 an outer, annular bead 28a; the outermost section of the Element 28 is a flexible metal cylinder 30 which is formed in one piece with the remainder of the element 28. The end of the pipe 1 has a smooth inner surface 5 on which the metal cylinder 30 can be moved. A holding part 31 has a near inward flange 32; it is screwed at 33 to an outwardly directed annular shoulder 34. A the locking pin 27 of Fig. 2a similar pin can be used if necessary. It can be seen that the element 28 is relatively Can be moved to the end of the pipe 1 by a distance equal to the sum of the lengths 35 and 36. This forms an effective

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sliding connection in which the seal between the end of the cylinder 30 and the inner surface 5 is made. The seal is maintained by the action of the pressure within the joint.

The compound of the invention is much smaller than conventional connections; in addition, it has a very smooth, uninterrupted interior and is capable of very much greater pressures resist. A connection made as shown in Fig. 1 with 100 mm diameter was with a conventional Compound of the type shown in Fig. 2B "with the same diameter. The flanges and bolts were made of aluminum (N8; ASA class 150). Using conventional sealing rings of the type shown in Fig. 2B the pressure that could be held by the connection was about 18 at (1 attelOO kPa} jSurn comparison: the connection as shown in Fig. 1 was subjected to a pressure of 85 atm without leaking. The pressure was then reduced to zero and the bolts 14 and nuts were unscrewed a little so that the bolts had a play of about 1.5 mm. The connection was again placed under a pressure of 85 at: it still remained tight. The pressure was maintained for 1 hour preserved, the connection remained tight. The pressure was then released, after which the connection was again pressurized was set by 128 at. The connection was still tight.

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A connection made of aluminum was used to test the resistance of the connection to bending moment loads of the 50 mm diameter type shown in Fig. 2A with a 50 mm joint of the type shown in Fig. 2B Diameter connected; the tube 2 was supported in a clamp so that bending moment loads could be applied the pipe end to the left of the connection shown in Fig. 2 A weights could be added. First, a pressure of 280 at was applied to the arrangement, at which the pressure shown in FIG The connection according to the invention was tight, while the conventional connection as shown in FIG. 2B failed. In the The connections shown in FIGS. 2A and 2B are to scale so that it can be seen that the solid connection 2B before the smaller connection according to the invention became faulty. A new sealing ring 17 was made; the conventional one The connection according to FIG. 2B was disassembled and reassembled, after which a pressure of 70 atm was applied to the arrangement. Weights were added, which caused a bending moment of 550 Nm on the connection according to the invention. The connection was tight. The pressure was released, the connection was rotated, after which the pressure was re-applied; it was found that the connection was tight again. The bending moment was then increased to a value of 27.5 Nm, with the connection according to the invention leaked. During dismantling, it was found that the connecting part or receiving part 23 was not screwed on sufficiently tightly has been. The sealing cylinder was then re-aligned slightly so that its opposite sections 9 and 10 were slightly expanded outwards, after which the connection

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was reassembled. A pressure of up to 70 at was again applied to the arrangement; it was found to be tight. Then, weights were attached to the pipe, which increased the bending moment to 1250 Nm, the connection remained tight, the test was interrupted at that stage because it was impossible to put a greater number of weights in the fixed to the tube pan _Z u. It can therefore be seen that the connection according to the invention is very resistant to bending moment loads and also that it does not transmit any torque because it is freely rotatable.

It can therefore be seen that the connection is not only much smaller than conventional connections, but also has a greater resistance to internal pressure.

It is an important feature of the invention that the tubular sealing cylinder is formed from a material that over a long period of time, for example 3 months Hooke's law obeyed.

In a material subject to Hooke's law, Stress and strain are proportional to each other. Thus, if a steel wire is within its elasticity range with a If the amount X is loaded, then there is an expansion of Y. If the loading is 2 χ, the expansion is 2Y. If the

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Load X is hanging on the wire for a period of 3 months, the expansion is still Y.

In contrast, rubber and plastic materials do not obey the Hcoke ¹ See Law for a long period of time. Although a rubber or plastic tape ^{may satisfy Hooke's 1} law at room temperature for short-term loads, it would not be obeyed over a long period of time. Thus, if a load A causes an immediate expansion B of the rubber band, an expansion after the load has been applied for three months would be greater than B because of the flow of the material under the sustained effect of the applied load. It is similar to placing a rubber block under a weight: the block would gradually deform over time as a result of flowing, so that the thickness of the block would gradually decrease. It is entirely possible that the block will return to its original shape after the load is removed.

When the tubular metal sealing cylinder of the invention is inserted into the pipe ends, it is subject to one Pressure load, i.e. that the opposite sections of the cylinder are constantly exerting strong pressure against the inner walls of the Pipe ends are subject. Therefore, when the pressure is applied, there is an immediate sealing effect, which is caused by the action of the internal pressure is increased and the sealing load is increased. When the tubular seal cylinder is made of rubber or

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a plastic material, it would be - although it is subject to pressure load after installation, it warps (creeps) if it is not used for a few months whereby the tension would be reduced or even disappear completely. So the fluid might when the pressure is applied between the cylinder and the wall of the tube and a pressure equalization between the two Make sides of the tubular seal cylinder. if Once this situation is reached, the seal can no longer function and will always leak.

Since the original seal is so important, it is clearly beneficial that the pipe ends have a smooth interior surface exhibit; this is preferably set with reference to the roughness (center line mean). Preferably the roughness for the inner surface of the pipe ends and the outer surface of the cylinder is less than 1.6 µm and preferably in the range from 0.8 µm to 1.6 µm. It is clear that the smoother the surfaces, the better; It is of course becoming progressively more expensive to produce smoother surfaces because of the machining time required.

In order to facilitate the removal of the sealing cylinder from the connection, the bead 8 can be axial and to the central axis of the Sealing cylinder have parallel bores into which bolts can be inserted to the sealing cylinder

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to force out of the pipe end.

The pipe connection shown is actually on pipes with a circular cross-section, as these pipes are the same as in are common in practice.

One of the pipe ends can be blocked to form a seal for a pressure vessel.

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Claims (28)

Claims ί 1.,. Pipe connection which has two pipe ends and a metallic sealing element which extends into the pipe ends and creates a fluid-tight seal, characterized in that each of the pipe ends (1,2) has a substantially cylindrical inner sealing surface (5,6) and that the metallic sealing element (11) is a one-piece, substantially cylindrical tubular element (7) extending into the pipe ends with each of the opposing portions (9,10) of the tubular element being an interference fit with one of the inner sealing surfaces and the tubular element on its ends is flexible, so that it is pressed radially outwardly within the pipe ends under the pressure of the fluid during operation and causes a seal between the pipe ends. 2. Pipe connection, the two pipe ends that have passages, axially aligned with one another and having a metallic sealing element extending into the pipe ends and forms a fluid-tight seal between them, characterized in that the pipe ends (1,2) each have a substantially cylindrical inner sealing surface (5,6), that a one-piece tubular sealing cylinder (7) a central, outer annular bead (8) and flexible 609838/0297 opposing sections (9,10), each flexible opposing section telescopically within one of the Pipe ends is received and the end of each of the opposing sections is an interference fit with the inner sealing surface forms and the tubular sealing cylinder under during operation the pressure of the fluid within the pipe connection is pressed radially outward and a seal between causes the pipe ends. 3. Compound according to claim 1 or 2, characterized in that that the two end sections are fixed relative to each other. 4. A compound according to claim 1 or 2, characterized in that that the two end sections are movable relative to one another. 5. A compound according to claim 1 or 2, characterized in that that the tubular element (7) has an outer, annular bead (8) at its central portion, the a forced fit between the pipe ends (1,2) and forms a rigid central section. 6. A compound according to claim 5, characterized in that the outer bead (8) has a groove (12) on its surface. 7. A compound according to any one of claims 1 to 6, characterized in that the opposite ends (9,10) of the 609838/0297 Cylinder (7) have a slightly larger outer diameter than it is the inside diameter of the pipe. 8. A compound according to claim 7, characterized in that the outer diameter at the opposite ends of the cylinder (7) is slightly larger than the outer diameter of the central portion of the cylinder, excluding the annular bead (8). 9. A compound according to any one of claims 1 to 8, characterized in that the outer surface of the cylinder (7) and the tubular inner surface of the pipe ends (1,2) are smooth and have a surface treatment, the Roughness is not greater than 1.6 μπι. 10. A compound according to claim 9, characterized in that the roughness is in the range from 0.8 pm to 1.6 pm. 11. A compound according to any one of claims 1 to 10, characterized in that the material of the cylinder (7) has a coefficient of thermal expansion which is essentially the same as that of the material of the pipe ends (1,2). 12. A compound according to claim 11, characterized in that the pipe ends (1,2) and the cylinder (7) are made of the same Material are formed. 13. A compound according to any one of claims 1 to 12, characterized characterized in that the pipe ends (1,2) have outer flanges (3,4) which are bolted together and the pipe ends 609838/0297 - 21 - 26U90] 1 keep them in alignment with each other. 14. A compound according to any one of claims 1 to 13, characterized characterized in that the pipe ends (1,2) are machined and form recesses (5,6) which the tubular Pick up the sealing cylinder (7). 15. A compound according to any one of claims 1 to 14, characterized in that the cylinder (7) has a circular cross-section having. 16. A compound according to any one of claims 1 to 15, characterized characterized in that the cylinder (7) and / or the recesses (5,6) is coated with a material that has a low Has coefficient of friction, preferably polytetrafluoroethylene or molybdenum disulfide. 17. Pipe connection, the two pipe ends and a metallic one Has sealing element which connects the pipe ends and forms a fluid-tight seal between them, thereby characterized in that the metallic sealing element (28, 30) is a substantially cylindrical tubular member which is sealingly connected to one of the pipe ends (2) and in a substantially cylindrical inner sealing surface (5) at the other end of the pipe (1) it is sufficient that the outermost section of the tubular element is connected to the inner sealing surface Forms a tight fit and that the tubular element is flexible at its outer end, so that it is in operation under the pressure 609838/0297 a fluid is pressed radially outward within the pipe ends and causes a seal between the pipe ends. 18 .. Connection according to Claim 17, characterized in that that the tubular metallic sealing element (28) is firmly connected to one pipe end (2). 19. A compound according to claim 17, characterized in that that the sealing element (28) is firmly connected to the pipe end (2) by means of welding or screwing or from a Piece with the pipe end. 20. A compound according to claim 17, characterized in that both pipe ends (1,2) are substantially cylindrical inner sealing surface (5) have that the tubular sealing element extends into both inner sealing surfaces, and that it is flexible at both ends, so that it is pressed radially outwards by the internal pressure during operation and with both Pipe ends is sealingly connected. 21. A compound according to any one of claims 17 to 19, characterized characterized in that the tubular member (28) is operable to slide within the inner sealing surface and forms an expansion joint. 22. A compound according to claim 21, characterized in that the tubular sealing element (28) has an outer 609838/0297 " ²³ " 26U9011 having annular bead (28a) which is displaceable within an outer holding part (31), the holding part having a Forms stop on both sides of the bead. 23. A compound according to any one of claims 1 to 12 or according to claim 20, characterized in that an annular outer holding element (23) is provided which is screwed to one of the pipe ends (1) and against an outer bead portion (21) at the other end of the pipe (2) so that the two pipe ends are in in a fixed alignment. 24. A compound according to claim 23, characterized in that a fixed 11 screw (27) is provided, which is the outer Element (23) holds and prevents its rotational movement after assembly. 25. A compound according to any one of claims 1 to 24, characterized in that the pipe ends (1,2) are made of aluminum and that the sealing element (11,28) is made of aluminum. 26. A compound according to any one of claims 1 to 24, characterized in that the sealing element (11, 28) is made of steel and that the pipe ends (1,2) are made of steel. 27.- A compound according to claim 2, characterized in that the outer annular bead (8) has a plurality of holes distributed around its periphery. 28. A compound according to claim 27, characterized in that 609838/0297 the holes are screw-threaded. 609838/0297 ORIGINAL INSPECTED