GB2226103A - Pipeline gate valve - Google Patents

Abstract

A top entry gate valve for a pipeline comprises an elongate housing 1 for straddling the pipeline horizontally and at right angles thereto to provide a through passage between pipeline sections upstream and downstream thereof, the housing containing at least two gating sections 7, 11, 13 and associated means 4 for achieving linear displacement of the gating sections within the housing, at least one 11, 13 of which sections is a gate for closing the valve, which sections are releasably coupled together, each being capable of entering the position of the through passage, the housing comprising at least one top entry opening 2a, 2b having closure means therefor and positioned laterally with respect to the position of the through passage and being sized sufficiently to allow the removal therethrough of the gating section which has been displaced to be thereunder. <IMAGE>

Description

PIPELINE GATE VALVE This invention relates to a pipeline gate valve and more particularly to a gate valve able to serve as a main valve for controlling and shutting down an oil or gas pipeline, particularly one used in a sub-sea environment.

Valves employed for controlling and shutting down oil and gas pipelines fall into two basic categories, namely ball valves and gate valves, each type having its own particular merits. With both it is possible to achieve a full, round smooth bore which does not restrict flow and will permit the passage of pipeline pigs and spheres. Typical examples which are commercially available are the applicant's C-B5 ball valve and C-G4 gate valve.

In general, a gate valve has the particular advantage of being top entry so that internal components can be exchanged without removing the valve from the line. Not only does this reduce the work involved, but it avoids the problem that when a valve is removed, the ends of the pipeline are no longer anchored and reinstallation of the valve may then turn out to be difficult. This is a particular problem in a submarine environment and would occur with a ball valve. Despite these advantages of gate valves it is found in practice that ball valves rather than gate valves are more commonly used for pipeline duty.

While top entry ball valves have been available for many years, they have found little favour mainly on account of increased size, weight and cost when compared with the standard "side entry" ball valve. It has generally been the practice to use valves designed for land purposes when working underwater. The adaptations needed for underwater use have generally made it desirable to have available valves specially designed for underwater use. The lack of such valves has tended to limit the extent to which valves are incorporated in underwater pipes. The result is that if problems arise and the entire system needs to be shut down, then this may take a significant amount of time resulting in considerable danger to operatives on offshore platforms as well as environmental pollution as spillage into the sea takes place.

Notwithstanding the aforementioned limitations of top entry ball valves, they have found increasing favour recently, particularly for critical valves offshore and on underwater pipelines where the removal and replacement of a complete valve otherwise poses problems. An improvement in design which has taken place with such valves is the inclusion of an internal rotating sleeve which is capable of blocking the pipeline in both directions while the internal parts of the valve are replaced. Nevertheless, there are significant operating advantages in employing gate valves which provide top entry into the valve housing. When a gate valve is in the closed position, pipeline pressure acts on the full area of the gate pressing it into its downstream seat thereby generating high contact forces capable of producing a tight seal.However, the force required to slide the gate to "crack" the valve remains relatively small and the stress is uniformly distributed across the valve stem. In addition suitable devices used to create the required thrust, such as hydraulic cylinders and mechanical springs are highly efficient. With a ball valve, fluid pressure can also act over the full pipe bore area on the ball pressing it into the downstream seat to create a tightly sealing valve. This type of valve is then known as a "floating" ball valve. The problem which then arises is that a relatively high torque is needed to operate the valve due to the wedging action of the ball in its seats. Rotary action is required and this necessitates the use of actuators which are less efficient than those employed with gate valves.

A further problem is that torsion must be applied. This does not have a uniform stress distribution and either stronger materials or larger components need to be employed to cope with the peak stresses. The result is that the floating ball valve design becomes completely impracticable for larger pipeline ball valves due to the size of actuator which would need to be employed.

A solution to this latter problem is to change to a "trunnion mounted" design. In this case, the ball is fitted with internal or external trunnions and rotates in bearings so that the torque required to operate the valve is reduced to a feasible level. However, the ball is no longer thrust into a downstream seat producing a tight seal as it is held in the centre of the valve and the trunnions resist the thrust created by the pipeline pressure. Instead, the seals float axially on springs and are pressed against the ball with a light force forming a relatively delicate seal. By its nature, a gate valve will thus tend to be a tighter sealing valve than a trunnion mounted ball valve and thus to obtain equivalent performance with trunnion mounted ball valves the valve design has to be much modified with respect to for example, seals before use in oil and gas pipelines.

It is thus an object of this invention to provide a pipeline valve for use in underwater environments, in particular, a pipeline valve which can be shut down rapidly without there being any significant restrictions as to size or pressure, and which enables the internal parts of the valve to be exchanged readily.

According to the present invention, there is provided a top entry gate valve for a pipeline which comprises an elongate housing for straddling the pipeline horizontally and at right angles thereto to provide a through passage between pipeline sections upstream and downstream thereof, the housing containing at least two gating sections and associated means for achieving linear displacement thereof within the housing, at least one of which sections is a gate for closing the valve, which sections are releasably coupled together, each being capable of entering the position of the through passage, the housing comprising at least one top entry opening positioned laterally with respect to the position of the through passage and being sized sufficiently to allow the removal therethrough of a gating section which has been displaced to be thereunder.

The gate valve of the invention offers the advantages of the aforementioned ball valves, that is the ability to close off the pipeline rapidly for repair of pipeline or gate or its seals. The valve has a good seal coupled with the top entry facility of gate valves in general, while allowing ready replacement of defective valve components without the need for removal from the pipeline of the complete valve. Various designs of valve embodying the invention are possible, each providing at least one benefit not attainable with prior art gate valves and ball valves.Before describing these various advantages, reference will now be made by way of example only to the accompanying drawing wherein: FIGURE 1 is a vertical cross-section lengthwise through one form of gate valve embodying the invention; FIGURE 2 is a perspective view from above and to one side showing, to a smaller scale, the valve of Figure 1 in place in a pipeline; FIGURE 3 is an exploded perspective view showing a gate of the valve of Figure 1 mounted in the valve and separately, the end of a piston rod to engaged therewith; FIGURE 4A shows an end face of a second gate while Figure 4B is a perspective view from an opposite direction of the end face of a gating member to be engaged therewith; FIGURE 5 is a like view to that shown in Figure 1 through an alternative form of gate valve embodying this invention; and FIGURE 6 is a vertical cross-section lengthwise through a simplified form of gate valve embodying the invention.

The accompanying drawings show a preferred gate valve embodying the invention in a purely schematic representation which enables nevertheless the essential constructional features according to the invention to be appreciated readily. The valve comprises a pressure containing valve body 1 to be disposed horizontally with its axis at right angles to the axis of an oil or gas pipeline which is to be equipped therewith. Adjacent the ends of the valve body 1 are sealed hatches 2a and 2b which are bolted or clamped to the valve body but which are removable when access to the interior is required.

Fitted to one end of the valve body is a linear valve actuator 4 housing a valve stem 3 which is constructed as a piston with a piston head 5 and passing through a sealed aperture 6 in the valve body 1. The valve stem 3 is in engagement with the first of three gating members which are coupled to each other. The central gating member shown is a valve member 7 having a dirt seal against ingress of debris or sediment in the valve body but which cannot act as a pressure seal, the valve member 7 forming in effect an open gate and having a bore 8 matched to the bore of the pipeline comprising upstream and downstream sections 9 and 10 respectively (see Figure 2 - naturally it is arbitrary for purposes of illustration which of the pipeline sections is upstream and which is downstream).To the left of the valve member 7 is a primary gate 11 which is designed to be pulled to the right to occupy the position shown in Figure 1 by the valve member 7 during an emergency shutdown to block and seal the pipeline flow. The primary gate 11 is fitted with integral valve seats 12 on either side housing high pressure spring actuated sealing rings for providing an effective seal against outflow of oil or gas on either the upstream or downstream side of the primary gate 11. To the right of the valve member 7 and coupled to the valve stem 3 is a secondary gate 13, the length of the valve body 1 being such that it can be pushed into position to block the pipeline and permit a faulty primary gate to be removed for, for example, seals comprised thereby to be replaced. Access for such purpose would be through hatch 2a.Likewise, hatch 2b is positioned to allow removal of the secondary gate 13.

The secondary gate 13 is likewise provided with a valve seat 14 on either side for housing an integral pressure seal to be effective during an emergency shutdown. The valve gating members 7, 11 and 13 are suspended by rails 15 at a height which will be clear of any pipeline debris or sediment trapped in the valve body thereby to allow free running of the gating sections in the valve body 1.

Alternatively, however, the gating members may simply be pushed or pulled over the floor of the valve body 1.

Although not shown, there may be provided means for purging the valve body to remove, for example, sea water which enters when the hatches 2a,2b are opened.

In the configuration of Figure 1, the valve member 7 is fitted with dirt seals only and will not be able to seal pipeline pressure. This valve member is intended to stay in place during the entire operating life of the valve. However it is feasible within the present invention for valve member 7 to be fitted with full pressure seals (see Figures 5 and 6) in which case, with suitable positioning of removal hatches, valve member 7 can be removed for repair in the same way as the primary or secondary gate of the valve of the accompanying drawings.Such a configuration has the advantages that: (a) the pipeline would remain sealed during the removal and replacement of the valve actuator even with the valve in the open position; and (b) the valve would have the capability of being able to bleed the valve body with the pipeline pressure contained therein, in both the closed and open positions.

Turning next to Figure 3, the secondary gate 13 can be seen to be provided at one end with a "T"-sectioned slot cavity - providing member 16 which has a maximum width at top and bottom and with angled end faces 17a and 17b. The valve stem 3 terminates in a neck 18 surmounted by a circular member 19 whose diameter is matched to the width of the cavity provided by member 16.

The member 16 has an opening 20 whose width is matched to the diameter of the neck 18. The valve stem is thus able to enter into engagement with the secondary gate 13 by passage of neck 18 down slot 20 and this engagement ensures that thrust from the stem either in or out is transmitted to the gate. The stem 3 and valve actuator 4 may be removed without disturbing the secondary gate 13.

For this purpose, with the valve closed by means of the primary gate 11 the valve actuator is merely unbolted from the exterior of the valve body 1 and by pivoting the valve stem in the aperture 6 it can be lifted out of the opening in member 16 and then withdrawn from the valve body. The tapered entry to member 16 from top or bottom means that whether it is valve stem 3 or secondary gate 13 which is removed, ready self alignment occurs to aid the reverse operation.

Turning next to Figures 4A and 4B, the former shows one end edge region of valve member 7 and the latter shows the edge region of primary gate 11 to be coupled therewith. The valve member 7 is formed along a vertical edge 21 with a channel member 22 providing a T-slot 23 running along a part of its length and having a widened entry zone or entry funnel 28. The adjacent vertical edge 24 of the valve member 7 is provided with a T-shaped tongue 25 which is to enter the slot 23 and which has a taper 29 at the bottom to aid location in the entry funnel 28. Similar engagement means is provided between the valve member 7 and the secondary gate 13.To assist removal of gates 11 and 13 through hatches 2a and 2b respectively, lifting lugs or equivalent members (not shown) are provided on the top surfaces 26 of runners 27 to assist removal of the gating members from rails 15 and hence from the valve body, and reinstallation.

The above described valve arrangement thus provides a smooth passage contiguous with pipeline internal surfaces both upstream and downstream thereof during operation of the pipeline with the valve in the open position when the valve member 7 is in the position shown in Figure 1. In the event for example of rupture of the pipeline, the primary gate 11 can be drawn into position to shut off the pipeline extremely rapidly by means of the linear valve actuator 4 which is typically powered hydraulically in both directions by a double acting piston or is hydraulically driven in one direction and spring operated in the other direction utilising the spring as a stored energy device. The use of a double acting piston means that a hydraulic accumulator may be used as a stored energy source.Actuation may be implemented from a remote location on receipt of a suitable signal which could typically be electrical, acoustic or simply loss of control pressure. Local operation by a diver or ROV (Remotely Operated Vehicle) is also feasible. In the event that the primary gate requires examination and possible replacement in whole or part it is merely necessary for the valve to be placed in the closed position by displacement of secondary gate 13 to block the pipeline whereupon primary gate 11 can readily be lifted out of engagement with rails 15 and with the adjacent valve member 7 and taken out of the valve body through hatch 2a. Should it be desired for secondary gate 13, to be lifted out of hatch 2b in like manner, it is automatically lifted out of engagement with valve stem 3 as well as valve member 7. Primary gate 11 will then block off pipeline flow. Such removal of gates is likely to take place if the gate and/or its seals have become defective due for example to wear, corrosion or mechanical damage.

Control of the extent of displacement executed by the gating members takes place as follows. As already indicated, the valve is shown in Figure 1 in the open position with a full round bore presented to pipeline flow. The valve is shut by the stem 3 being withdrawn from the valve body. If this is achieved by the type of actuator illustrated, it would result in application of hydraulic pressure to the annular face of the piston 5.

A mechanical stop (not shown) in either the valve or the valve actuator positions the primary gate 11 to block the pipeline flow. The valve is reopened by reverse operation, hydraulic pressure on the full bore side of the piston acting until a mid-position mechanical stop (not shown) is reached. If it is found that the gate and seals have become defective and are to be replaced, then the mid-position stop is released from the outside of the valve and the valve members moved so that the secondary gate 13 is blocking the pipeline. The mid-position stop is reset after the replacement of the defective parts has taken place and the appropriate hatch has been reinstalled and the valve has been returned to the open or closed position.

Although the above described embodiment illustrates a high degree of flexibility which may be achieved with a valve embodying the invention, there are alternative configurations embodying the invention. In the first instance, when providing primary and secondary gates as well as a valve member 7 providing a full round bore, these gating members can be rearranged in any other possible combination, possibly with repositioning of hatches appropriate to such combination which will allow removal of one gate while the other is blocking off the pipeline. Thus in Figure 5 in which like reference numerals denote like parts in the preceding figures and construction is generally as previously described, the primary gate 11 with integral i.e. pressure seals is intermediate the valve member 7 and the secondary gate 13 with integral seals.This results in the sealed hatches 2a and 2b for removal of gates 11 and 13 respectively being closer together which is less satisfactory than the arrangement of Figure 1 insofar as the performance of valve body 1 as a pressure vessel is concerned.

Moreover valve member 7, in this embodiment has integral pressure seals 30. This means that servicing of the primary gate 11 and/or the valve stem 3 can take place when the pipeline is open to fluid flow, i.e. the valve, instead of being as shown in Figure 5 with the primary gate 11 placing it in the closed position, has the valve stem fully retracted so that valve member 7 providing a full round bore, occupies the position shown for the primary gate 11 in Figure 5. The pipeline is thus sealed to the environment but not blocked.

The valve member 7 in Figure 5 will need to have the facility for its removal from the valve body 1 for servicing. The valve member 7 is shown in Figure 5 below hatch 2a and it is through this hatch it is to be removable. Separable engagement of adjacent gating members will be basically like that shown in Figures 4a and 4b. However, because the central gating member, primary gate 11, unlike valve member 7 in Figure 1, is to be removable for servicing, T-slot 23 on each edge of this central gating member, here member 11, will have an entry funnel 28 at each end and T-shaped tongue 25 which will be on the inner vertical edges of valve member 7 and secondary gate 13 has a taper 29 at top and bottom. In this way, whichever of the gating members is being lowered into position, it will readily locate and enter into engagement with its neighbouring gating member(s).

It is not even essential for there to be three gating members as such. A shorter cheaper valve may be achieved by dispensing with the valve member 7 so that a through round conduit is not in fact achieved. The valve body will then only house primary and secondary gates which when drawn to the right in the sense of Figure 1 will provide a through passage between upstream and downstream sections of the pipeline and displacement to the left will enable the pipeline to be blocked off by the primary gate when the secondary gate is to be removed and by the secondary gate, when the primary gate is to be removed.

Indeed even the secondary gate may be omitted for reasons of cost but in this case the feature of being able to block and seal the pipeline when the primary gate is being changed will be lost. Such a configuration is shown in Figure 6 in which like reference numerals again denote like parts in Figures 1 to 4. However, the pipeline can remain sealed to the environment, and vice versa although open to oil or gas throughflow, when the primary gate 11 is being changed because, as in Figure 5, the valve member 7 is fitted with pressure seals, here shown at 30. Figure 6 shows the valve in the open position. The valve member 7 may then need to be removed for replacement of its seals. Hatch 2b is available for this purpose while hatch 2a is available for removal of gate 11. If simplicity, size and cost saving are major factors, then this configuration is to be preferred.No mid-position mechanical stops are required. If for example for structural strength reasons, the valve body requires that the two hatches be positioned further apart, then this can be achieved without increasing their size by installing a third valve member of the required width to act merely as a spacer between members 7 and 11.

The primary gate 11 and seals integral therewith are designed to withstand the forces generated on operating the valve as fast as dictated by ESD (Emergency Shut Down) practice. The gate and its seals should withstand the forces generated during the closing operation by the pipeline contents flowing up to the maximum possible velocity. Finally the primary gate and the seals integral therewith are to block the pipeline and seal the static pressure in both directions up to the rated maximum.

A secondary gate 13, when present, could be constructed to function in identical manner to the primary gate 11 and therefore would be able to cope with the same operating conditions. This would provide additional back-up to the ESD function of the primary gate 11 and a "two valves in one" capability.

Alternatively, if the secondary gate is not used for ESD, advantage could be taken of the reduced service requirements of the secondary gate which is not required to operate quickly and is to seal properly at only low pressure differentials. (The main function of the gate is to provide valve closure during non-critical conditions, when the primary gate is to be serviced).

The seals of the secondary gate could nevertheless be designed for the longest possible life to reduce the possibility of having to change the components in service. If it is decided that the secondary gate 13 and its seals remain in place for the installation life of the valve, then one service hatch could be omitted and the secondary gate together with the valve member 7 could be formed as a single component.

A valve embodying the invention has the advantage that the components most likely to fail in service can be removed and replaced without disturbing the valve actuator. Compared with changing the valve internals on a conventional pipeline gate valve, the components being handled are relatively small, light and rigid. These factors are important when the valve is installed in a hostile environment e.g. under water.

The gate is a relatively small member to handle when it is removed through the valve body because it separates from the member which gives the valve the through conduit capability, that is full smooth round pigable bore. A result of this is that the surface hatch(es) on the valve body is/are also relatively small.

This assists the design of the body as a pressure and load bearing vessel, ensuring that it is as small, light and economical to manufacture as possible. Any opening in the valve body 1 requires reinforcement and reduces the overall strength of the body. The bigger the aperture size the greater the reduction in strength. In addition, the valve body must be designed to resist pipeline stresses which can subject the valve to generation of tension, compression, bending and torsion.

Generally, these are resisted by the central section of the valve and the small size of the surface hatch permits this feature which weakens the vessel to be located away from this area.

The fact that while the gate is being replaced, a second gate may block and seal the pipeline has the advantage that the pipeline contents and the environment are protected during a changing of valve gate and seat seals. For example, crude oil is prevented from leaking into the seal or seawater from entering a crude oil or gas pipeline.

Finally, the valve actuator is capable of being replaced without disturbing the position of the gate.

This is of considerable advantage since the actuator too may need replacement during the service life of the valve. During this operation the gate remains in position to block and seal the pipeline.

Claims (14)

Claims:

1. A top entry gate valve for a pipeline which comprises an elongate housing for straddling the pipeline horizontally and at right angles thereto to provide a through passage between pipeline sections upstream and downstream thereof, the housing containing at least two gating sections and associated means for achieving linear displacement of the gating sections within the housing, at least one of which sections is a gate for closing the valve, which sections are releasably coupled together, each being capable of entering the position of the through passage, the housing comprising at least one top entry opening having closure means therefor and positioned laterally with respect to the position of the through passage and being sized sufficiently to allow the removal therethrough of the gating section which has been displaced to be thereunder.

2. A valve as claimed in claim 1, wherein one gating section provides an open gate when positioned transverse to said pipeline sections.

3. A valve as claimed in claim 2, wherein said one gating section comprises an integral valve seat providing an effective seal against outflow of oil or gas from the pipeline.

4. A valve as claimed in any preceding claim, wherein a said gate for closing the valve comprises an integral valve seat providing an effective seal against outflow of oil or gas on either the upstream or the downstream side thereof.

5. A valve as claimed in any one of claims 1 to 4, comprising a linear valve actuator attached to one end of the housing, which actuator houses a valve stem which is constructed as a piston having a piston head and which passes through a sealed aperture in the housing to be in engagement with a said gating member.

6. A valve as claimed in any one of claims 2 to 5 which comprises two gating sections providing gates for closing the valve separated by a gating section providing a said open gate.

7. A valve as claimed in claim 6, which comprises two top openings spaced apart by a distance equal to the combined lengths of said gates.

8. A valve as claimed in claim 5 and any one of claims 2 to 4, which comprises two gating sections providing gates for closing the valve positioned adjacent one another, with the valve stem being attached to one such gate and an open gate being attached to the other valve closing gate at a position remote from the position of attachment of the valve stem to said one valve closing gate, there being two top entry openings separated by a span of said housing equal in width to the length of a said gate positioned therebetween located centrally along the length of the elongate housing.

9. A valve as claimed in any preceding claim, wherein adjacent gating sections are in vertical sliding engagement with one another.

10. A valve as claimed in claim 9, wherein said sliding engagement is achieved by provision of a "T" section slot cavity on the margin of one gate and an elongate "T" sectioned projection on the adjacent gate sized for sliding travel therein.

11. A valve as claimed in claim 5 or any one of claims 6 to 10 when appendant to claim 5, wherein the valve stem comprises an end formation comprising a projecting portion of reduced diameter capped by an end portion of increased width and the adjacent margin of a gate to which the valve stem is to be attached is formed with a "T"-sectioned slot cavity engaged by the formation on the end of the valve stem for sliding travel therein.

12. A valve as claimed in any preceding claim, wherein said gates travel on rails extending lengthwise of the housing.

13. A top entry gate valve for a pipeline, substantially as hereinbefore described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.

14. A top entry gate valve for a pipeline, substantially as hereinbefore described with reference to Figures 3 to 5 or Figures 3, 4 and 6 of the accompanying drawings.