SPANSWICK PETER (GB)
KELL JOHN MARTIN (GB)
SANDERSON ALLAN (GB)
SPANSWICK PETER (GB)
KELL JOHN MARTIN (GB)
FR2315045A1 | 1977-01-14 | |||
US2401108A | 1946-05-28 | |||
GB1370442A | 1974-10-16 | |||
GB2074489A | 1981-11-04 |
1. | An annular seal assembly comprising a stretchable annular seal member; and an actuating assembly to which the seal member is mounted, the actuating assembly being adapted to move the seal member between a sealing position and a retracted position in which the seal member is moved radially outwardly and stretched relative to its sealing position. |
2. | An assembly according to claim 1, wherein the actuating means comprises a number of pivoted flaps circumferentially spaced around the assembly, and at least one actuator for moving the flaps between the sealing and retracted positions. |
3. | An assembly according to claim 2, wherein the flaps are shaped such that in the sealing position they form a substantially continuous plate. |
4. | An assembly according to claim 2 or claim 3, wherein the or each actuator comprises an hydraulic or pneumatic actuator. |
5. | An assembly according to any of claims 2 to 4, wherein the seal member is wrapped around a radially inner edge of each flap. |
6. | An assembly according to any of claims 2 to 5, wherein the flaps have a low friction surface on their radially inner edges. |
7. | An assembly according to claim 6, wherein the radially inner edge is defined by a nylon material. |
8. | An assembly according to any of the preceding claims, wherein the seal member comprises a number of separate, subsidiary members. |
9. | An assembly according to claim 8, when dependent on any of claims 2 to 7, wherein each subsidiary member is located on one or a pair of flaps. |
10. | An assembly according to any of the preceding claims, wherein the seal member takes up a frustoconical form in the sealing position. |
11. | An assembly according to any of the preceding claims, wherein the seal member is made of an elastomer material. |
12. | An assembly according to claim 11, wherein the elastomer is rubber. |
13. | An annular seal assembly according to any of the preceding claims, the assembly being in the form of a module which can be mounted on or dismounted from a supporting apparatus. |
14. | Radiation beam welding apparatus incorporating an annular seal assembly according to any of the preceding claims. |
15. | Apparatus according to claim 14, comprising two annular seal assemblies according to any of claims l to 13, the seal assemblies being arranged substantially coaxially and spaced apart. |
16. | Apparatus according to claim 14 or claim 15, the apparatus being mounted on a vessel. |
17. | A method of laying a pipeline using apparatus according to claim 15 or claim 16, the method comprising positioning a trailing end of the pipeline in one seal assembly; positioning a pipe section in the other seal assembly and in contact with the pipeline; actuating the seal assemblies; substantially evacuating the space between the seal assemblies; welding the pipe section to the trailing end of the pipeline; repressurising the space between the seal assemblies; retracting the seal assemblies; and extracting the pipeline from the apparatus. |
The invention relates to an annular seal assembly for sealing a cylindrical body to a housing, where the seal may be required to be retracted an appreciable distance from the cylindrical wall to allow free movement of the cylindrical body with respect to the housing.
The most common form of sealing against differential pressures for cylindrical objects comprises a close fitting continuous ring of compressible material, known as an "0 M ring. The containment space for the ring is so ordered that under the differential pressure the ring is biased against a housing and the cylindrical object to effect a barrier between the cylindrical object and a corresponding housing, such as a shaft in a plain bearing housing. This "O" ring is generally arranged to be well-fitted to the cylindrical object and hence does not allow free axial movement when not required to maintain a differential pressure. Another similar continuous ring seal is formed from an inflatable tube which expands to fill the containment cavity and press against the cylindrical object and its associated housing. To some extent when deflated the inflatable ring is free from its containment cavity, but normally still remains attached to the cylindrical object, preventing free axial movement. This follows since when inflated the tubular ring expands outwardly and thus reduces its inward contact with its associated cylindrical object. A further known development involves the use of fibre reinforcement to a tubular ring in an endeavour to constrain the natural outward movement of such a ring when inflated. Some control of relative expansion is obtained but this is limited and it is difficult to ensure that a loose fitting inflatable ring will produce inward movement sufficient to cause the loose fitting ring to close down onto the cylindrical object and provide a sufficient seal.
Thus when relaxed the ring does not lift off the cylindrical object to any significant extent. Moreover, the presence of embedded fibres or mesh with an inflatable elastomer leads to differential movement and rapid wear together with the developing separation between the elastomer and the reinforcing fibres. Hence such a reinforced ring has a very limited operating life.
In accordance with one aspect of the present invention, an annular seal, for example for sealing a cylindrical body to a housing, comprises a stretchable annular seal member; and an actuating assembly to which the seal member is mounted, the actuating assembly being adapted to move the seal member between a sealing position and a retracted position in which the seal member is moved radially outwardly and stretched relative to its sealing position.
The present invention provides a seal which is both close fitting to a cylindrical body, such as a shaft, under operating conditions and which can be freed from the cylindrical body to allow complete freedom of movement of the latter both axially and rotationally, for example to permit radially outwardly extending flanges on a pipe to pass through the assembly. The invention is particularly suitable for use as a vacuum seal on cylindrical bodies such as shafts or tubes to allow free access and/or axial or rotational movement of the shafts or tubes when the vacuum condition is released. In some cases, the cylindrical body could move e.g. rotate when sealed to the housing, provided its surface was reasonably smooth. It is important to note that with this invention, the seal member is stretched when in its retracted position. This is completely contrary to known seals which are typically stretched in their sealing position. The advantage of the present approach is that when the seal member is retracted, it will not buckle due to the stretching action. When the seal member is moved to its sealing position, its location is controlled by the
actuating assembly and does not rely on any inherent resilience within the seal member. In the sealing position, the seal member is not likely to be fully relaxed. The invention enables a seal to be constructed which can be retracted from the cylindrical body by a significant amount radially such as more than 10mm and preferably more than 100mm where the cylindrical body has a diameter of the order of 0.5m and greater. The invention can also provide a retraction of such a seal by some 2% radially and preferably more than 20% radially for a cylindrical body of at least 0.1m diameter.
Typically, the retractable, flexible, circumferential seal member can withstand a pressure difference of the order of 1 atmosphere at least and can accommodate a degree of lack of circularity of the cylindrical body such as a radial error of ±lmm and greater.
Conveniently, the actuating means comprises a number of pivoted flaps circumferentially spaced around the assembly, and at least one actuator for moving the flaps between the sealing and retracted positions. In other examples, non-pivoted members could be used to constitute the actuating means but the use of pivoted flaps is preferred. Although the flaps could define spaces in the circumferential direction between them when in the sealing position, preferably the flaps are shaped such that in the sealing position they form a substantially continuous plate. This ensures that the seal member is fully urged towards its sealing position.
Typically, the or each actuator comprises an hydraulic or pneumatic actuator, although other forms of actuator such as solenoid operated spindles and the like could be used. In order to secure the seal member to the actuating means, preferably the seal member is wrapped around a radially inner edge of each flap.
It is important that relative sliding movement can take place between the flaps and the seal member during movement between the retracted and sealing positions. Conveniently, this is achieved by providing the flaps with a low friction surface on their radially inner edges. For example, the radially inner edge may be defined by a nylon material. In addition, or alternatively, the flaps could be lubricated to assist the sliding action. For neoprene rubber, a suitable lubricant would be silicone grease. In some examples, the seal member comprises an integral, continuous annular member. For ease of manufacture and use, however, the seal member preferably comprises a number of separate, subsidiary members. Where the actuating means comprises a number of pivoted flaps, each subsidiary member is preferably located on one or a pair of the flaps.
Typically, the seal member takes up a frusto-conical form in the sealing position. However, in some cases the base angle of the frusto-conical seal could approach zero. In this case, supports would be required on the lower pressure side of the seal to prevent the seal being pushed through.
The seal member is preferably made of an elastomer material such as rubber although other suitable materials could be used instead. For the seal to operate over a maximum range, the seal membrane needs to be made from a very elastic material. Neoprene rubber is currently preferred although for seals which are not required to stretch as much the following elastomers could be used: ethylene-propylene diene terpolymer (EPDM) rubber, nitrile rubber, natural rubber and silicone rubber.
One of the major advantages of this invention is that the seal assembly can be manufactured in the form of a module which can be mounted on or dismounted from a supporting apparatus. Thus, if the seal member has to be changed, it is a relatively simple matter to dismount the
module from the remaining supporting apparatus without disassembling the supporting apparatus.
The seal member may be made of a material sufficiently elastic to accommodate surface roughness including scratches or grooves to allow pump down to pressures of the order of l millibar or less using conventional mechanical booster pumps together with conventional so-called roughing pumps of known construction and design.
Typically, the seal member will have a relatively smooth surface but could be formed with surface features such as circumferential peripheral ridges to improve the surface contact or dimples to facilitate spreading of the elastomer and better contact with the cylindrical body.
An example of an application of the invention is sealing on the outer surface of a tube or pipe to allow the creation of a local vacuum to permit circumferential radiation beam, particularly electron beam, welding to be conducted.
For example, in accordance with a second aspect of the invention, a method of laying a pipeline comprises positioning a trailing end of the pipeline in one seal assembly; positioning a pipe section in another seal assembly and in contact with the pipeline; actuating the seal assemblies; substantially evacuating the space between the seal assemblies; welding the pipe section to the trailing end of the pipeline; repressurising the space between the seal assemblies; retracting the seal assemblies; and extracting the pipeline from the apparatus.
These and other aspects of the invention are described and contrasted with known seals with reference to the accompanying diagrams, in which:-
Figures 1A-1C are cross-sections through part of a conventional "O" ring seal of the prior art;
Figures 2A-2C are cross-sections through part of a known form of tubular or inflatable ring seal;
Figure 3 is a plan of an example of an annular seal assembly according to the invention with the seal member omitted;
Figure 4 is a section taken on the line A-A in Figure 3 but also showing flaps in their retracted position;
Figure 5 illustrates part of electron beam welding apparatus incorporating two seal assemblies similar to that shown in Figures 3 and 4;
Figure 6 illustrates an alternative method of actuating the seal assembly;
Figure 7 illustrates schematically a pipe laying application utilising a seal assembly according to the invention; and,
Figure 8 illustrates the welding arrangement shown in Figure 7 in more detail.
The conventional practice for a cylindrical shaft or tube utilising an "0" ring seal is illustrated in Figure 1 in which the ring 1 of elastomer material is set in a suitable cavity recess (2 ' in Figure IA) in one or other of the components between which a seal is desired. As shown in Figure IB, the "O" ring 1 is compressed between a shaft
3 and the housing 2, the "O" ring naturally projecting beyond the cavity 2' (Figure IA) by a significant amount.
Alternatively, the "0" ring can be set in a suitable recess 3' in the cylindrical component 3 as shown in Figure IC.
The ring serves to separate regions 10 and 11 which have a pressure differential. Note that the existence of a pressure difference tends to cause leakage between the ring and the flat surface of the shaft 3 or housing 2 respectively.
An inflatable ring 4 is illustrated in Figure 2 where the ring 4 lies in a similar recess 2' or 3' between the housing 2 and shaft 3. With this arrangement, the ring does not need to protrude from the cavity before it is pressurised. However, in practice, it is difficult to obtain a suitable seal in the arrangement of Figure 2C where the ring is required to expand radially inwards
compared with the arrangement in Figure 2B where the ring naturally expands radially outwards.
Figures 3 and 4 illustrate a self-contained seal assembly module comprising an annular frame 20 having circular upper and lower flanges 21,22 and a tubular central member 23 welded to the flanges. Secured to the member 23 is an annular support ring 24 to which is pivoted a set of eight metal flaps 25. Each flap 25 can be pivoted between a sealing position shown in solid lines in Figures 4 and 5 and a retracted position shown by dashed lines at
25' in Figure 4. In the sealed position, the flaps 25 cooperate together to define a closed, frusto-conical form.
A lug 26 is mounted on each flap 25, each lug being coupled to a piston/cylinder actuator 27 via a spindle 28 which extends through an aperture 29 in the member 23 into a protective tube 30. Each piston/cylinder actuator 27 is connected to a control system (not shown) which actuates the arrangements 27 to move the flaps 25 between their sealing and retracted positions. Each flap 25 carries a nylon member 31 at its leading edge to provide a low friction surface.
The seal member has been omitted from Figures 3 and 4 for clarity but is shown in the enlarged detail in Figure 5. As can be seen in this enlarged detail, a rubber seal member 32 is located along the surface of the ring 24 and the flap 25 and extends around the end of the flap 25 where it defines a reentrant fold or bulb 33. When mounted as shown in Figure 4, the portion 34 of the seal member 32 adjacent the ring 24 is sandwiched between the ring 24 and the annular member 23. In this way, the end is anchored in place, the other end being anchored about the nylon edge member 31.
For better sealing, particularly for rough pipe surfaces, a softer rubber could be bonded to the bulb 33. In addition, the seal bulb 33 could be covered in a suitable media such as vacuum grease or a pliable sealing compound to improve sealing.
In the sealing position shown in Figure 4 and the enlarged detail of Figure 5, the rubber seal member 32 is either relaxed or slightly stretched while in the retracted position shown in dashed lines in Figure 4, the rubber will be in a more stretched condition. This arises because of the increased circumferential length defined around the flaps 25 in the retracted position. In this way, there is little risk of the seal member buckling as it is retracted. The main section of Figure 5 illustrates two seal assembly modules of the types shown in Figures 3 and 4 indicated at 40 and 41 mounted in a workpiece supporting apparatus 42 for use with an electron beam welding system (not shown) . The upper module 40 is attached to a support structure 43 via bearings 40A which is attached in turn to the lower module 41 via bearings 41A. The module 41 is bolted on a base 44. A pair of tubular members to be welded are shown at 45A,45B located within the apparatus and extending between the upper and lower modules 40,41. The tubular members 45A,45B are positioned in place by two sets of three equiangularly positioned piston/cylinder arrangements, two of which 46,47 are shown. A window 48 is provided in the supporting apparatus 43 through which an electron beam can be injected.
Prior to insertion of the tubular members 45A,45B into the apparatus 42, the flaps 25 of the modules 40,41 are in their retracted position as shown for the module 41. The tubular members 45A,45B are then inserted and then the actuators 27 of both modules 40,41 are operated to pivot the flaps 25 into their sealing positions, this being shown with the module 40. In the sealing position, the seal member 32 at the leading end of the flaps 25 engages the surface of the respective tubular members 45A,45B and thus seals the volume between the modules 40,41 allowing this volume to be evacuated for electron beam welding. In the seal position, it will be appreciated that additional strength is achieved by virtue of the pressure differential which exists across the flaps.
Typically, the contact zone defined between each tubular member 45A,45B and the seal member 32 will have an axial length of at least 3mm and this will extend under the influence of the pressure differential across the flaps 25. During movement of the flaps 25 between their sealing and retracted positions, the sealing member 32 will slide relative to the flaps 25 and this sliding movement is enhanced by the use of the nylon members 31 providing a low friction surface. The tubular members 45A,45B are then welded at 45C by an electron beam passing through the window 48. In the preferred arrangement an electron beam gun (not shown) fixed relative to the support structure 43 orbits, together with the support structure 43, about the tubular members 45A,45B.
Typically, the diameter of the member 23 is 1000mm while the typical radial dimension of each flap 25 is about 160mm. The arrangement illustrated in Figures 3 to 5 is suitable for cylindrical workpieces of the order of 0.5m diameter and greater and gives a radial clearance of more than 50mm. It should be noted that the flaps radial dimension is dependent on the diameter of pipe to be welded. If this increases or decreases beyond the sealing tolerance or another critical dimension then it will mean that the flaps will either need to be larger or smaller in radial dimension to accommodate that change.
Figure 6 illustrates an alternative approach for actuating the flaps 25. In this example, a circular, tubular ring 50 is positioned at the hinge end of the flap 25 and is in fluid communication through a conduit 51 of the member 23 with a source of liquid or air pressure (not shown) . When the space 52 within the ring 50 is pressurised, it forces the flaps 25 into their sealing position as shown. When pressure is removed, the flaps 25 are retracted. This is accomplished as follows. The ring 50 is secured to the back of the flaps 25 by either direct bonding onto the diaphragm or using a lug. When the air or
liquid is removed via conduit 51, the retraction of the ring 50 would pull the flaps 25 back into the open position. A negative pressure in the ring 50 would need to be maintained to keep the flaps 25 in the open position. Releasing that pressure would allow the diaphragm to return to its natural shape as shown in Figure 6.
Other forms of actuator (not shown) may be used. For example, the flap may be attached to a tubular ring on the outside or the inside of the flap and when pressurised the expanding ring raises the flap away from the cylindrical component. In another example, a tension spring may be placed within the tubular ring 50 to first compress the diaphragm flap 25 against the cylindrical component 45 when the tubular ring is not pressurised. Activated metal flaps could in this case be used to combat spring tension and provide adequate seal clearance when retracted.
This overall arrangement provides adequate seals on solid cylindrical components or tubular components of dimensions in excess of O.lm diameter or even in excess of 0.5m in diameter and provides a seal for low pressure or vacuum use better than 1 millibar in spite of normal surface roughness and light corrosion as is commonly found on steel pipes. The large clearance between the circumferential housing and the cylindrical component enables the latter to be rapidly positioned within the vacuum or low pressure zone and subsequently translated to a subsequent zone. In particular, this system has been used in conjunction with an electron beam heat source heating at partial pressure within the evacuated zone for welding tubular components of wall thickness upwards of 10mm and even upwards of 40mm.
An application in which the invention is particularly useful is in pipeline welding. Figure 7 illustrates a pipe laying barge 60 floating on a surface 61 above the seabed at 62. A pipe 63 is to be laid in the so-called "J" mode by welding together separate pipe sections using electron beam welding. A pipe support tower 64 is mounted on the
barge above a conduit 65 through which the pipe 63 is lowered into the water. A stock of pipe sections 66 is provided which can be individually loaded into the top of the pipe support tower 64 using a crane 67. Figure 8 illustrates the welding apparatus in more detail. This comprises apparatus similar to that shown in Figure 5. Those parts which are similar to parts shown in Figure 5 have been given the same reference numerals and will not be described in further detail. The upper and lower modules 40,41 are anchored to parts of the barge.
A gear ring 74 is mounted to the lower section 41 so as to be fixed relative to the barge support structure and this engages a pinion 73 connected to a drive motor 72 which in turn is mounted on the rotatable, central section 43. An electron gun 70 is also mounted to the central section 43 via a support plate 71 and has a beam guide tube 83 which extends through the window 48. A high voltage cable 84 is connected the electron gun 70 and is coiled within an electrical cable drag chain housing 68. A vacuum pump 85 is connected via tube 86 to the chamber between the sealing modules 40,41.
In use, the trailing end of a pipe 63 is held by the piston/cylinder 47 within the welding apparatus and the seal member within the sealing module 41 is actuated (by means not shown) to seal against the pipe. The crane 67 then lifts a pipe member 66 from the store and inserts this into the top of the welding apparatus as shown in Figure 8. The seal member within the sealing module 40 is then actuated to its sealing position and then the chamber between the two sealing modules is evacuated using the vacuum pump 85.
The welding process then commences by activating the electron gun 70 and the motor 72. Rotation of the pinion 73 causes the electron gun slowly to rotate with the central section 43 of the welding apparatus, around the joint 87 between the pipe section 68 and the pipeline 63.
Once welding has been completed, the chamber between modules 40,41 is repressurised by venting to atmosphere.
The seal members within each sealing module 40,41 are then released and the pipeline is drawn through the apparatus and laid onto the seabed.
In the examples described, the electron beam gun rotates with the central support structure 43. Other arrangements are possible, however. For example, the structure 43 and gun could be non-rotatably fixed to the modules 40,41 and the pipe sections 45A,45B rotated. In a second example, the window 48 may extend completely around the structure 43 which is non-rotatably bolted to the modules 40,41. In this case, the electron beam gun can be rotated around the structure 43. Alternatively, the electron beam gun could be maintained stationary while the apparatus itself is rotated.