GB2188708A - Fire-safe ball valve - Google Patents

Abstract

A side-entry ball valve, for gas and oil wells and chemical plants, has a fire-safe sealing assembly comprising, on each side of the ball 12, an inner seat ring 46, an outer spring urged (68) seat ring 50, a spring holding ring 42, a first cylindrical collar 94 and a second spring urged (118) cylindrical collar 108, these elements housing sealing gaskets 60, 88, 112, refractory masses 96, 124, spacers 122, 126, 128, and a gasket 82 with porous back-up rings 84, 85. Differential fluid pressure applied to gasket 82 and step 78 of ring 46 biases gasket 60 onto the ball 12. During a fire, elements 60, 82, 88, 112, 122, 126, 128 are destroyed, seat ring 46 moves towards the ball and metal lip 62 thereof seals with the ball, and collars 108 and 94 move towards the ball and compress masses 124 and 96 to form seals. <IMAGE>

Description

SPECIFICATION Improved ball valve for control of fluids fitted with a device providing tightness in case of fire and with 2-directional pistonwise moving seal seats DESCRIPTION The present invention relates to valves for the control of fluids of the so-called ball type made up of an external body which houses a moving part or plug of a substantially spherical form against which rest two seal seats.

When said valves are employed for the control of fluids highly contaminated with solid particles or corrosive substances it is necessary now and then to remove the plug from the body of the valve for maintenance or repairs, especially for the replacement of worn gaskets. Said removal can be done in two directions, one parallel to the longitudinal axis of the valve body and the other perpendicular to said axis, representing two basic types of valves termed by those skilled in the art 'side entry' and 'top entry' valves.

In particular the present invention relates to an improved ball valve of the 'side entry' type fitted with moving 2-directional piston seal seats containing a device providing tightness of said valve in case of destruction of the gaskets due to overheating as in a fire.

Ball valves are widely used in several fluid control applications even of contaminated or dangerous fluids such as corrosive or inflammable fluids present in chemical plants, in petroleum product extraction units such as natural gas wells, crude petroleum wells, etc. and especially wells in particular environments such as offshore wells.

It is known that petroleum products issue from wells contaminated by several foreign substances which may include solid abrasive substances such as sand and scale from the storage rock containing them, corrosive liquid substances such as sea water or brackish water and even gaseous substances such as hydrogen sulfide (H2S) and carbon dioxide (CO2) which alone or combined with other substances can have quite harmful effects on piping and valves which convey and control them.

As a consequence of this fact it is sought to eliminate said contaminants in a location as near as possible to the well to limit as far as possible the employment of materials having high resistance to abrasion and corrosion and therefore particularly expensive. For this reason in the immediate proximity of extraction wells there are placed installations perfoming a first decontamination of the extracted products and in particular separation from the natural gas or petroleum of the gaseous contaminants mentioned above.

In the case of offshore wells serviced by platforms said decontamination installations are usually installed thereon and since said platforms are densely occupied by service and control personnel all the installations and their components must meet quite severe safety requirements.

One of the safety requirements which must be met by components of said installations and in particular by the ball valves which are the object of the present invention is the ability to maintain sufficient tightness to permit closing in case of overheating due for example to fires which result in destruction of gaskets sensitive to heat. Said ability is known to those skilled in the art by the term 'fire safe', i.e safety in case of fire.

There is already a fire-safe system for ball valves of the type having a plug insertable or removable along the direction of the longitudinal axis of the valve body, commonly termed 'side entry' by those skilled in the art. Said system makes it possible to provide adequate tightness between the plug, the body and the sealing points of a ball valve when, due to overheating caused by fire, the soft gaskets placed between the plug and the valve seats housed between the body and the sealing points are destroyed, transferring the tightness of the gaskets by means of the action of springs placed between the sealing points and the seats to special surfaces of the seats shaped complementarily to the valve plug and appropriately finished to provide said tightness.But in said fire safe system the seats do not move pistonwise against the ball plug because, as the springs which push the seats against the ball plug rest directly against the closing flanges of the valve, tightness between the seats and the closing flanges must be provided by a gasket housed in a circumferential recess of the seat against which the pressure of the fluid does not exert any force to move the seats pistonwise.

For this reason an object of the present invention is to provide sufficient tightness of a side entry valve in case of overheating due to fire, causing complete destruction of the soft gaskets engaged between the plug and the seats, by employing original seats which provide said tightness between the ball plug and the seats and between the seats and the valve closing flanges.

Another object is to provide pistonwise movement of said seats against said ball plug.

To achieve the above objects the valve in accordance with the present invention consists of a substantially spherical plug supported by supports in a valve body having the form of a hollow cylinder connectable by its bases to two closing flanges prolonged by tubular unions which serve to connect the valve to the pipes of the installation in which they are to be inserted.

Between said ball plug, said valve body and said flanges there are inserted two valve seats made up of a first internal seat-ring consisting of a hollow cylindrical element having on the base facing the ball plug a groove designed to house a soft gasket and ending in an outward turned flange against which there rests an external seat-ring with a lip turned inward and faced against said ball plug and contributing to form the groove for said soft gasket, said external seat-ring having the form of a hollow cylinder fitting tightly on the outward turned flange of the internal seat-ring and ending in a base perpendicular to its axis serving as a rest for springs arranged circumferentially and housed in cylindrical recesses in a spring-holding ring resting against a front seat of one of the closing flanges of the valve and bearing a projection toward the interior forming with a descending step of the external surface of the inner seat-ring a recess designed to house a gasket to permit pistonwise movement of said seat against said ball plug, said inner seat-ring having a projection on the base opposed to the one facing the ball plug designed to fit in a corresponding recess of a cylindrical element having an inside diameter equal to that of said inner seat-ring and outside diameter equal to an inside diameter of the valve-closing flange cavity, said cylindrical element having an external surface stepping down with a first step with an inclined bottom and a second step with a flat bottom such that on this stepped down surface are fitted corresponding internal surfaces of a subsequent element pushed by springs housed in recesses machined in said closing flange and having externally a circumferential recess housing a gasket.

According to a preferred embodiment of the present invention the recess between the inner seat-ring and the spring-holding ring is an annular recess with rectangular cross section having two pairs of adjacent sides sliding reciprocally and housing a seal assembly formed by an O-ring held in place between two backup rings of rigid material porous or permeable to fluids.

In accordance with another preferred embodiment of the invention between the inner seat-ring and the following cylindrical element there is placed a spacer made of material yielding and/or volatilizable at high temperatures and in the recess of the following cylindrical element corresponding to the projection of the innner seat ring there is placed a mass of fibrous material substantially refractory at high temperatures, such as graphite fibre braid such as to form a sealing gasket when it is compressed by said projection in case of yielding of said spacer.

In accordance with another preferred embodiment of the present invention the step with inclined bottom of said following cylindrical element contains near the descending shoulder a spacer element yielding and/or volatilizable at high temperatures and resting thereon a mass of fibrous material virtually refractory at high temperature of the type described above such that, when compressed, it forms a sealing gasket while the step with flat bottom contains a spacer yielding and/or volatilizable at high temperatures which permits compression of the fibrous material contained in the above step.

The above and other objects of the invention together with other advantages and characteristics will be made clear by the following detailed description of a nonlimiting example of a preferred embodiment thereof accompanied by the annexed drawings wherein: FIG. 1 represents a cross section along its longitudinal axis of a side-entry valve in accordance with the present invention, and FIG. 2 represents an enlarged cross-section of part of a plug and seat assembly in accordance with the present invention having the characteristics described above.

With reference to the figures a side-entry valve in accordance with the present invention comprises a body 10 in the form of a thick collar housing in its interior a ball plug 12 with a through hole 14. Said valve body 10 has in its top part a hole 15 designed to permit passage of a shaft 16 for operation of the plug 12. Around said shaft 16 there is a sealing collar 22 which by means of gaskets 23 provides tightness between the shaft 16 and the valve body and a closing plate 18 which by means of a set of screws or bolts 20 fixes the collar 22 to the valve body 10. Said valve body 10 is also pressed between two closing flanges 24 and 25 which are held against said body by a set of tightening means such as stud bolts 26 appropriately fitted with nuts.

From the flanges 24 and 25 there emerge tubular unions 28 ,and 29 respectively having internal opening 30 of a diameter virtually equal to that of the through hole 14 of the ball plug 12. Inside the valve body 10 there is housed a ball support 32 having through holes 34 and 36 for the operating shaft 16 of the ball plug 12 and the journal 38 of said plug respectively.

Two seat assemblies 40 and 41 fit in the closing flanges 24 and 25 of the valve and provide tightness between the ball plug 12 and said flanges 24 and 25. Said seat assemblies 40 and 41 are fitted with external rings 42 and 43 respectively resting on respective front seats of the flanges 24 and 25 and housing pins 44 and 45 which have the function of holding steady the ball support 32 in relation to the flanges 24 and 25 and hence in relation to the valve body 10.

Now examining FIG. 2 it is seen that the seat 40 contains an inner ring 46 fitted on the side toward the ball plug with a flange 48 turned outward and on which there is fitted with minimal gap an outer seat-ring 50 having a flange 52 turned inward. Said flange ends with a lip 54 formed as a portion of a spherical surface complementary to that of the ball plug 12 followed by a bevel 56 which together with a groove 58 on the base of the inner seat-ring 46 forms a seat for a soft elastic gasket 60 having the function of providing complete tightness between the ball plug 12 and the seat 40, said gasket 60 protruding sufficiently to hold separate from the surface of the ball plug the lip 54 of the outer seat-ring 50 and a similar lip 62 of the inner seat-ring 46.

Said outer seat-ring 50 rests against the flange 48 turned inward by means of a split ring 64 optionally locked against undesired rotations by an elastic pin 66 fitted in a hole passing through the outer seat-ring 50 and thrust by a set of springs 68 housed in and guided by seats 70 in the outer ring 42 and resting against a plane 72 forming part of the inner face of the closing flange 24, which is better seen in FIG. 1. Said outer ring 42 also has a central cylindrical recess 74 fitting with minimal gap on the outer surface of the inner seat-ring 46 and ending in a flange 76 turned inward. The inner seat-ring 46 has a descending step 78 ending in a cylindrical surface 80 having a diameter substantially equal to that described by the inward turned flange 76.

Between the cylindrical recess 74, the inward turned flange 76, the step 78 and the cylindrical surface 80 there is formed an annular cavity of rectangular cross section having the function of housing an elastic gasket 82 such as an O-ring and two back-up rings 84 and 85 made of a material substantially rigid but porous and permeable to the fluids to be controlled by the valve. An annular recess 86 on the rear face of the outer ring 42 houses a sealing gasket such as the O-ring 88 having the function of providing tightness between the inside and the outside of the seat 40 in such a manner as to not have infiltration of fluid from the seat behind the outer ring 42.

The inner seat-ring 46 is provided on the rear with a projection 90, also annular, which couples with a similar recess 92 made in a base of an element 94 with cylindrical collar placed behind the inner seat-ring 46 and housing a fibrous mass of material substantially refractory at high temperature such as felt or graphite fibre braid. Said element 94 with cylindrical collar has a first descending step 98 followed by a tapered or conical surface 100 continuing with a cylindrical surface 102 which ends with a second descending step 104 followed by a cylindrical surface in which the element 94 with cylindrical collar ends.

Above the cylindrical surfaces 102 and 106 are fitted corresponding surfaces of a second cylindrical collar element 108 having externally a circumferential recess 110 housing a gasket 112 and ending in a base 114 fitted with an inward turned flange 116 which serves to receive the thrust of the springs 118 housed in cylindrical guide recesses 120.

Between the cylindrical collar 94 and the cylindrical collar 108 there are formed a first space housing a spacer 122 and a mass 124 of fibrous material substantially refractory at high temperatures and a second space housing a spacer 126 yielding and/or volatilizable under heat.

Another spacer 128, also yielding under heat, is inserted in a chamber 130 placed between the inner seat-ring 46 and the cylindrical collar element 94, said chamber 130 communicating with the interior of the seat 40 through a duct 132 for the purpose explained below.

To understand the operation of the present invention reference is made to FIG. 2 in which it is clearly seen that the seat 40 is pressed between the plane 72 of the closing flange 24 against which it rests by means of the springs 68 and the ball plug 12, against which it usually rests by means of the soft elastic gasket 60.

The pistonwise movement of the two seats 40 and 41 illustrated with reference to FIG. 2 for the seat 40 is provided by the duct 132 which through the chamber 130 and the recess 92 puts the interior of the seat 40 in communication with the annular space containing the gasket 82 with the porous support rings 84 and 85. The pressure of the fluid in the seat 40 is applied to the gasket 82 and then through the back-up ring 84 to the descending step 78 of the inner seat-ring 46.

As fluid pressure of the seat 40 applied between the inner wall of the inner ring 46 and the gasket 60 pushes the seat to the right with a certain force while the same pressure applied to a surface equivalent to that between the inner wall and the gasket 60 with in addition the surface corresponding to the descending step 78 pushes the seat to the left against the ball plug 12 with greater force because of the greater surface offered by the descending step 78 the seat 40 receives a total thrust toward the ball plug 12 proportional to the fluid pressure controlled in such a manner that the tightness of the gasket 60 is enhanced by the thrust of the seat 40 against the ball plug.

If due to a leak of the gasket between the seat 41 and the ball plug 12 fluid enters under pressure around the outer ring of the seat 52 said fluid also penetrates into the annular space containing the gasket 82 with the backup rings 84 ard 85 and the seat thus receives thrust to the right caused by the pressure of the outer seat-ring 52 and a thrust to the left caused by the same pressure on an equivalent surface of the outer ring 52 and in addition on the surface corresponding to the step 78 in such a manner that in this second case also the seat 40 receives a total thrust against the ball plug 12 proportional to the pressure of the controlled fluid. There is thus obtained the so-called double piston effect, i.e. a thrust of the seats against the ball plug always linked to the fluid pressure.

Finally, if the fluid pressure is too low a thrust of the seats against the ball plug is always provided by springs such as the spring 68 which in all cases push the outer seat-ring and, because of the lock ring 64, the inner seat-ring 46 toward the ball plug 12 also, holding the gasket 60 pressed.

Again with reference to FIG. 2 it is understood also how the device providing tightness in case of fire operates.

As the soft elastic seat gasket 60 and the other elastic O-rings 82, 88 and 112 and the spacers 122, 126 and 128 lose consistency in the presence of high temperatures, melting and even volatilizing, it happens that in case of overheating from a fire all the elements listed above disappear from the seats. Disappearance of the soft elastic gasket 60 allows the inner seat-ring 46 to slide forward and, under the thrust of the springs 68 transmitted by the outer seat-ring 50 to the inner ring 46 through the lock ring 64 engaged between thereof, bring the lip 62 to rest against the spherical surface of the plug 12, increasing the tightness between the metal surfaces and thus partially compensating for the loss of tightness caused by disappearance of the gasket 60.

Yielding and possible disappearance of the spacer 126 causes the cylindrical collar to advance under the thrust of the springs 118 and press the fibrous mass or refractory tow 124 which occupies the narrower front space left free by the disappearance of the spacer 122, becoming substantially impenetrable to the fluids which pass through the valve so as to assume the sealing functions of the gasket 112 jeopardized by overheating.

In the same manner the yielding and possible disappearance of the spacer 128 permits advancement of the cylindrical collar 94 pushed by the rearward cylindrical collar 108 and causing compression of the fibrous mass or refractory tow 96, which also becomes quite impenetrable to the fluids passing through the valve so as to provide a certain tightness between the inside and outside of the seat, thus remedying the loss of tightness caused by damage to the O-rings 82 and 88.

Thus in case of fire said sealing device provides a certain limitation of leaks from the valve so as to meet applicable safety regulations.

Loosening of the nuts 27 screwed on the stud bolts 26 (FIG. 1) permits, in addition to removal of the valve body 10 from between the two closing flanges 24 and 25 and then removal of the ball plug 12 from the body 10, extraction of the seats 40 and 41 with associated outer rings 42 and 43 from their housing in the closing flanges 24 and 25 for maintenance and/or repair purposes, especially after a fire has destroyed all the heat-affected parts of the valve.

Indeed, in observing the seat 40 and the associated outer ring 42 represented in FIG. 1 and in greater detail in FIG. 2 it is seen that once the valve body 10 is removed with the associated ball support 32 and the ball plug 12 said seat 40 and the associated outer ring 42 can be withdrawn freely from the housing in the closing flange 24 and disassembled in all their component parts for the purpose of cleaning or replacement of gaskets and spacers, allowing restoration of the seat 40 and the ring 42 to their functions.

Mere replacement of the seat 40 and the outer ring 42 in their housings in the flange followed by replacement of the valve body 10 containing the ball support 32 and the ball plug 12 permits complete reassembly of the valve in accordance with the present invention.

The above description of an embodiment of the invention is given as an example and equivalent full or partial solutions can occur to those skilled in the art from reading of the present description.

It is accordingly intended to cover all of said fully or partially equivalent solutions.

Claims (5)

1. Improved ball valve fitted with a sealing device in case of fire and sealing seats moving pistonwise in two directions consisting of a substantially spherical plug backed up by supports in a valve body in the form of a hollow cylinder which can be coupled by its bases to two closing flanges prolonged with tubular unions which serve to connect the valve to the pipes of the installation in which they are to be inserted characterized in that between said ball plug, said valve body and said flanges there are inserted two valve seats made up of a first internal seat-ring consisting of a hollow cylindrical element having on the base facing the ball plug a groove designed to house a soft gasket and ending in an outward turned flange against which there rests an outer seat-ring having a lip turned inward faced against said ball plug and contributing to form a groove for said soft gasket, said outer seat-ring having the form of a hollow cylinder fitting with minimal gap on the outward turned flange of the inner seat-ring and ending in a base perpendicular to its axis serving as a rest for springs arranged circumferentially and housed in cylindrical cavities of a spring-holding ring which rests against a front seat of one of the closing flanges of the valve and bears an inward projection forming with a descending step of the outer surface of the inner seat-ring a recess designed to house a gasket to permit pistonwise movement of said seat against said ball plug, said inner seat-ring having a projection on the base opposite to that facing the ball plug designed to fit in a corresponding recess of a cylindrical element having an inside diameter equal to that of said inner seat-ring and an external diameter equal to an inside diameter of a cavity in a closing flange of the valve, said cylindrical element having a stepped down outer surface with a first step with an inclined bottom and a second step with a flat bottom such that on said stepped down surface there fit corresponding inner surfaces of a following element pushed by springs housed in cavities in said closing flange and having a circumferential cavity outside housing a gasket.

2. Improved ball valve as in claim 1 characterized in that the recess between the inner seat-ring and the spring-carrying ring is an annular recess with a rectangular cross section having two pairs of adjacent sides sliding reciprocally and housing a seal assembly made up of an O-ring retained betwaeen two back-up rings made of a material rigid but porous or permeable to fluids.

3. Improved ball valve as in claims 1 and 2 characterized in that between the inner seatring and the following cylindrical element there is placed a spacer made of material yielding and/or volatilizable under high temperatures and in the recess of the following cylindrical element corresponding to the projection of the inner seat ring is placed a mass of fibrous material substantially refractory at high temperatures, such as graphite fibre braid, so as to form a sealing gasket when it is compressed by said projection in case of yielding of said spacer.

4. Improved ball valve as in the above claims characterized in that the step with inclined bottom of said following cylindrical element contains near the descending shoulder a spacer element which is yielding and/or volatilizable under high temperatures and resting thereon a mass of fibrous material virtually refractory at high temperatures of the type decribed above such that when it is compressed it forms a sealing gasket while the step with flat bottom contains a spacer yielding and/or volatilizable at high temperatures which permits compression of the fibrous material contained in the above step.

5. A ball valve substantially as hereinbefore described with reference to the accompanying drawings.