GB2224333A - Fail-sale valve - Google Patents

Abstract

A fail-safe valve suitable for a sub-sea oil production module has a valve 1 fitting within a valve block of the module, an actuator 5 and a mechanical leaf spring 4 to move the valve to the fail-safe position in the event of any malfunction of the actuator. The use of a leaf spring gives the potential for producing a module with smaller overall dimensions than hitherto without sacrificing spring power. <IMAGE>

Description

FAIL-SAFE VALVE This invention relates to a valve on an oil production module, and in particular to a fail-safe mechanical spring system to move the valve to a preferred position, i.e. to open or close the valve in the event of any failure or emergency. It is particularly suitable for sub-sea oil production modules, but could equally be used on land-based modules, or on fixed or floating platforms.

Sub-sea oil production modules are being increasingly used to control the production of oil and/or gas from sub-sea wells. The modules may be positioned directly above a well or be separate from it. They may receive oil or gas from more than one well. The modules may also be used to control the injection of fluids (e.g. water injection or gas re-injection) into the wells and the term "oil production module" is to be understood as including any sub-sea module for the control of any sub-sea operation.

Flow of fluid out of or into a well is controlled by valves within a valve block forming part of the module. Conventionally there are valves to isolate and control the production and annulus flows.

These main valves may be duplicated in each flow. There may be other smaller valves to control other fluid flows.

The valve blocks within a sub-sea module fit into a suitable template and the main valves are normally placed horizontally with axes at 180 , in vertical bores extending up through the blocks. The blocks themselves can be relatively small but the valve actuators have to extend horizontally beyond the blocks thereby increasing the overall module dimensions. The valves are normally actuated hydraulically but electro-hydraulic or electrical actuation would be possible.

In addition the valves have mechanical springs large enough and strong enough to move the valves to a prefered position in the event of a failure or malfunction of the control system. Traditionally, coiled springs have been used around the valve stems. However, this further increases the distance the valve actuation assemblies have to project from the valve block, thereby further increasing the overall dimensions of the module. More recently, some reduction in the overall dimensions has been achieved by having valve stems projecting from each valve on either side of the block with the actuator on one side and the spring on the other. Nevertheless the overall dimensions are still considerable and, on a sub-sea system with several modules, the size of the modules limit the closeness that one module can be positioned relative to another.This in turn increases the bulk and weight of the templates which are needed to position and hold the modules.

As the water depths at which oil is produced tend to increase, there is an increasing benefit from keeping the dimensions of oil production modules to a minimum. The present invention is concerned with reducing the overall diameter of valve blocks by replacing a fail-safe coiled spring with a leaf spring.

According to the present invention, a fail-safe valve suitable, for example, for a sub-sea oil production module comprising a valve fitting within a valve block, an actuator for the valve and a mechanical spring against which the actuator operates, said spring being adapted to move the valve to a fail-safe position in the event of any malfunction of the actuator, is characterised in that the spring is a leaf spring.

The invention is applicable to any type of valve, but particularly to gate valves. The actuator can be hydraulically operated, but could equally be electro-hydraulically or electrically operated.

The leaf spring could be positioned on the same side of the valve block as the actuator, but is preferably on the opposite side. It may have its own housing sealing it from the hydrosphere and the housing may be filled with a suitable oil.

The spring may be fixed to a valve stem extending from the valve in any convenient manner and it may be H-shaped in plan view. The ends of the spring may be held by rollers which can move to take up the change in length of the spring as it is compressed.

The valve stem fixed to the leaf spring can have a travel sensor (e.g. a sealed linear voltage differential transformer within it) with a cable from the sensor to a control unit or other monitoring system.

The invention is illustrated with reference to the accompanying drawings in which: Figure 1 is a partly-sectioned plan view of a valve with a leaf spring.

Figure 2 is an enlarged, partly-sectioned plan view of part of Figure 1 showing more detail, and Figures 3 and 4 show side elevations of a valve block at right angles to each other.

In Figure 1, a gate 1 of a gate valve has a valve stem 2 extending sideways from it. Gate 1 can slide within block 3. The end of valve stem 2 is fixed to a leaf spring 4, which is within a spring housing 9. The ends of the spring wrap around and are held by rollers 27. There is a travel sensor 7 at the end of stem 2, with a travel sensor line 8 from it.

A gasket test line 10 and a seal monitoring line 11 lead to a gland assembly around valve stem 2 and a spring housing oil line 12 leads into housing 9 so that the housing can be filled with oil. The oil acts to protect and dampen the spring.

On the other side of valve block 3 opposite leaf spring 4 is a valve actuator 5 with an ROV vertical override 6.

In Figure 1 the valve is shown in the closed position with leaf spring 4 in its bowed, pre-energised state. Opening 32 in gate 1 is shown not over bore 33 within which the valve operates. To open the valve actuator 5 has to move gate 1 against the force of leaf spring 4, further compressing the spring. Any failure of the actuator relinquishing this holding force thus allows spring 4 to move gate 1 and shut the valve quickly and firmly.

Figure 2 is an enlargement of Figure 1 in the area around valve stem 2. The same reference numerals are used for the major components as in Figure 1.

Figure 2 shows how the gland assembly seals valve stem 2 and prevents any leakage from the valve. The gland assembly is made up of a gland seal 37, and the gland itself 13 which is screwed into gland housing 14. Stem bushing 15 is held within gland 13 by ring 34. BX gasket 16 seals gland housing 14 with respect to valve body 3. Dotted lines within gland housing 14 show how gasket test line 10 and seal monitoring line 11 connect to the areas around gasket 16 and seal 37 respectively.

Various other ring seals sealing the gland 13 with respect to the stem 2 and housing 14 are shown but not numbered.

At the other end of valve stem 2, the stroke of which is shown by the arrowed line 35, leaf spring 4 is fixed to the stem by load plate 17 which is screwed onto the end of valve stem 2. Stop ring 18 also acts to hold the stem to the spring.

Within a hollow in the end of stem 2 is a travel sensor 7. This is formed, in known manner, of a linear voltage differential transformer (LVDT). Cap 19 and split lock ring 20 hold the LVDT within stem 2. The LVDT itself consists of a piston 24, which is internally spring loaded by spring 23 and which supports a core 21.

Windings 22 in the annulus around piston 24 are connected to travel sensor line 8, formed of an electrical cable encased in a pressurised line filled with dielectric fluid.

Finally Figure 2 shows some of the tie bolts 25 which hold the leaves of the spring together.

Figure 3 is a side view of a dual block with the valve of Figure 1, again using the same main reference numerals. Figure 3 shows that leaf spring 4 is H-shaped, with two arms on either side. It also shows how the ends of the leaf spring are wrapped around a shaft 26.

The right hand shaft and roller are shown sectioned in Figure 3 to illustrate this more clearly. Roller 27 is also around shaft 26 in the space between the arms of the spring with spacing washers 28 at either side of the roller 27. As seen also in Figure 1, roller 27 rests on the base of housing 9 but is not fixed, so that the spring ends are free to move in and out as the spring is relaxed and compressed.

Figure 3 also shows how the valve of Figure 1 relates to other parts of the valve block 3. Valve block 3 is fixed within a module by screws 36. Valve block 3 is shown with two large and two small valve units positioned on it. Thus Figure 3 shows two housings 29 of smaller valve units functioning across smaller bores of valve block 3. Another large valve unit 31 similar in size to that of Figure 1 is shown functioning across the other main bore of the valve block 3.

Since this valve unit 31 is at 180 to the main valve unit, Figure 3 shows the actuator end of the unit rather than the spring and spring housing end. Although Figure 3 shows two large and two small valve units, it will be appreciated that there could be more or less of each type of valve unit.

Figure 3 shows two large valve units positioned adjacent to one another, with two smaller valve units 29 for the smaller bores of the valve block 3 at either end of the valve block. This particular arrangement of large and small valve units produces the most compact overall block. However an alternating valve unit arrangement with the smaller valve units 29 alternating with the longer valve units 31 would be possible. Both the large and small valve units have leaf springs to ensure fail-safe operation.

Figure 4 which is an elevation at right angles to Figure 3 shows particularly the benefit of valves of the present invention in keeping the overall dimensions of a valve block within reasonable limits. It will be seen that leaf spring housings 9 project less than the actuators 5. With the main production and annulus valves positioned, in conventional manner, 180 on either side of the valve block, this means that the overall dimensions of the valve block are determined by the size of the valve actuators rather than that of the valve springs. Further there is room for the actuator ROV vertical overrides to extend up above the valve block without them fouling or having to be diverted around the spring housings.

Although, as shown by Figure 3, spring housings 9 do extend sideways of the valve block in the plane at right angles to Figure 4, the overall dimensions of the valve block are still no greater in this plane than they are in the plane of Figure 4.

Claims (6)

Claims

1. A fail-safe valve suitable for a sub-sea oil production module comprising a valve fitting within a valve block, an actuator for the valve and a mechanical spring against which the actuator operates, said spring being adapted to move the valve to a fail-safe position in the event of any malfunction of the actuator, characterised in that the spring is a leaf spring.

2. A fail-safe valve as claimed in claim 1 wherein the valve is a gate valve.

3. A fail-safe valve as claimed in claim 1 or 2 wherein the leaf spring and actuator are on opposite sides of the valve block.

4. A fail-safe valve as claimed in claims 1, 2 or 3 wherein the leaf spring is enclosed in a housing which seals it from the hydrosphere and which is filled with oil.

5. A fail-safe valve as claimed in any of claims 1 to 4 wherein the leaf spring is H-shaped in plan view.

6. A fail-safe valve as claimed in any of claims 1 to 5 wherein the ends of the spring are held by rollers which can move to take up the change in length of the spring as it is compressed.