WO2020249931A1

WO2020249931A1 - Hybrid metal ceramic ball valve

Info

Publication number: WO2020249931A1
Application number: PCT/GB2020/051375
Authority: WO
Inventors: Stephen Thompson
Original assignee: Morgan Technical Ceramics Australia Pty Ltd; Morgan Advanced Materials Plc
Priority date: 2019-06-12
Filing date: 2020-06-05
Publication date: 2020-12-17
Also published as: AU2020290781A1; GB201908364D0

Abstract

A ball valve for controlling the flow of a fluid comprising a housing (1) comprised of a metallic material; said housing comprising an inlet and an outlet of a fluid passageway (7) extending therethrough; an actuation mechanism for moving the ball valve housing (1) from an open position to a closed position; a valve seat (9) for sealing the inlet from leakage of the fluid; wherein the ball valve further comprises a sealing dome comprising a ceramic sealing face (2) adapted to circumferentially seal against the valve seat (9) when the ball valve is in the closed position and a metal cap (4).

Description

HYBRID METAL CERAMIC BALL VALVE

FIELD OF THE INVENTION

The present invention relates to ball valves for the controlling the flow of fluids, including slurries. More particularly, the invention relates to a ball valve that has both good

mechanical and chemical resistance properties

BACKGROUND

Many industrial processes consume, or make use of, fluids that may be either highly corrosive, highly erosive, or both. Corrosive fluids include a broad array of chemicals that may be corrosive to both ferrous and nonferrous metals and metal alloys, as well as other materials. Erosive fluids include slurries comprising a primary fluid or fluid mixture in which solid particulate matter is suspended. Particles of contaminates carried by an otherwise non- erosive fluid may also cause erosion. Also, industrial applications often necessitate the delivery of corrosive and/or erosive fluids at high flow rates, high temperature and/or high pressures. Industrial processes, as well as scientific or laboratory applications, consuming or making use of corrosive or erosive fluids - particularly, at high flow rate or high temperature - require fluid delivery systems adapted to function in severe operating environments.

Industrial fluid delivery systems routinely include one or more fluid valves configured to control the rate of, or completely terminate, fluid flow through the system. These fluid shut off and control valves must be constructed of components adapted to withstand the severe operating environments created by corrosive and/or erosive fluids flowing at high

temperature or high flow rate or pressure drop. High temperatures may increase the rate at which a fluid chemically attacks (i.e. , corrodes) internal components of a valve, and high temperatures may also subject a valve to thermal stresses, especially in conjunction with thermal cycling. Process conditions in the fluid may dictate high pressure drops or high flow rates, subjecting the valve to higher stresses.

Ball valves have traditionally been employed in such applications due to their durable and reliable characteristics and their ability to provide a reliable shutoff of process fluids.

However, ball valves are prone to entrained solids becoming trapped by the seat or in crevices adjacent thereto. Additionally as the valve is almost closed high process velocities can occur which increases erosion rates and results in“wire drawing” material erosive failure for metal and metal alloy valve balls and seats.

US6,367,774 partially addressed this problem by improving the abrasive and chemical resistance of the valve by inserting a cylindrical shaped ceramic fitting within the valve to define the fluid passageway.

US9,470,320 also partially addressed this deficiency through the implementation of ceramic wipers to create a mechanical joint with the external surface of the ball component and prevent/inhibit contaminants from embedding within, scoring, corroding or otherwise abrading the valve seat.

Despite these improvements to ball valve design, there is still a need to further improve ball valve design, particularly high diameter valve sizes, to facilitate reliable and durable operation.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a ball valve for controlling the flow of a fluid comprising a ball comprising a housing comprised of a metallic material; said housing comprising an inlet and an outlet of a fluid passageway extending

therethrough; an actuation mechanism for moving the ball valve ball housing from an open position to a closed position; a valve seat for sealing the inlet from leakage of the fluid; characterised in that the ball further comprises a sealing dome comprising a ceramic component comprising a ceramic sealing face adapted to seal against the valve seat when the ball valve is in the closed position; and a metal cap.

The ball may be a sphere or a segment thereof (e.g. vee ball valve or camflex™ valve).

The ball valve may further comprise the features of the dependent claims appended hereto.

The metal cap preferably comprises a fastening mechanism to attach the sealing dome to the housing (e.g. threaded bolts).

The formation of a ceramic seal when the ball valve is closed reduces/mitigates the risk of fluid leakage by providing a seal with increased mechanical hardness and chemical resistance to withstand extreme fluid processing environment, particularly in the

transportation of slurries.

The ceramic component comprising a ceramic sealing face preferably comprises an annular shaped ceramic component sealingly abutting against the metal cap. The sealing dome components are preferably discrete from and connect to the metallic ball valve housing. The use of an annular shaped ceramic component (also known as a wear ring) enables beneficial properties of the ceramic material to be located where they are most critical: on and around the sealing interface with the valve seat.

The ceramic annular component comprising the ceramic sealing face preferably has a circumferential length (i.e. the length of the ceramic sealing face 2 when travelling along the circumference of the housing 1 from the drive slot 3 to the bolts 8 in Figure 3) of at least 5mm, more preferably at least 10mm, even more preferably at least 30mm, yet even more preferably at least 50mm or at least 100mm or at last 200mm or at least 400mm. The ceramic annular component comprising the sealing face preferably comprises at least 5%, more preferably at least 10%, even more preferably at least 20%, yet even more preferably at least 40% and most preferably at least 50% of the circumferential surface area of the dome cap. The greater the ceramic coverage the greater the resistance the ball valve seating surface and seats have to the fluid, particularly when the ball valve is in the closed position. The optimal configuration and proportion of the ceramic and metal cap will depend upon the specific operational conditions of the process, including the fluid characteristics (corrosive and erosive nature) and the flow regime (e.g. Reynold’s number).

In some embodiments ceramic annular component comprising the ceramic sealing face comprises less than 80% or less than 70% of the circumferential surface area of the metal cap. The remaining circumferential area preferably comprises metal. Preferably, the metal forms part of a fastening mechanism for fastening the sealing dome to the housing.

In some embodiments, the ball valve comprises a further sealing dome at the opposing valve outlet (i.e. 180° from the first sealing dome). This enables the valve to operate in reverse direction, whilst still maintaining its resilience to erosive and corrosive flow.

Preferably, the metallic body of the housing comprises a different metal or coating thereof to the metallic material of the metal cap. By having a discrete sealing dome which has the specific function of sealing the fluid passageway in the closed position, the materials of constructions can be tailored to this purpose. As such, a higher grade metal (i.e. more chemical resistant and/or abrasive resistant) may be used relative to the other metal components of the housing which do not come into direct contact with the fluid; or do not come into direct contact with the fluid for long periods of time or not directly in the fluid path (e.g. housing which is exposed to the fluid when the ball valve is been moved from an open position to a closed position or vice versa). Where the ball valve will be subjected to large temperatures variations (e.g. > 100°C or 200°C) then the thermal co-efficient of expansion of the materials (metal and ceramics) should preferably be matched (e.g. preferably within 20% or within 10% or within 5% of each other). For example, zirconia may be suitably matched with suitable grades of steel; steel alloys or titanium. In one embodiment, the fastening mechanism (e.g. bolts) comprises a different metal composition to the housing.

The ball valve of the present invention has advantages over completely ceramic ball valves as the metallic components are more easily machined and able to be scaled up into increasing larger diameters. The use of a metal ceramic hybrid construction enables ball valves sizes with ceramic seals to be increased compared to exiting monolithic ceramic construction methodologies, thereby filling a growing unmet demand in the market.

The internal fluid passageway diameter of the ball valves are preferably at least 200mm, more preferably at least 250mm, even more preferably at least 400mm, and yet even more preferably at least 500mm. However, the minimum and maximum diameter of the ball valve is only limited by the constraint of existing manufacturing technology.

The metal cap preferably comprises a fastening mechanism to fasten the metal cap to sealing dome of the housing. The sealing dome may be fastened to the housing by any suitable means known to those skilled in the art, including by adhering, brazing or mechanically fastening. In a preferred embodiment, the sealing dome is fastened to the housing through mechanical means, such as one or more fastening bolts, which threadingly connect the sealing dome to the housing.

The metal cap preferably forms part of a sealing surface between the dome and the housing. The metal cap is preferably configured such that the fastening means sandwiches the ceramic component comprising the sealing face between the metal cap and the body of the valve (i.e. housing). The metal cap preferably has a sealing lip which extends over part of the ceramic component to clamp the ceramic sealing face/component against the ball valve body.

The fastening means preferably comprises metal. The use of metal fasteners (e.g. threaded bolt) to connect a metal portion of the sealing dome 4 to the metal housing 1 is preferred over ceramic - metal seals, as metal - metal seals provide a more resilient seal which is less likely to loosen or crack, thereby lowering the risk of corrosive liquid or slurry

penetrating into the seal area leading to premature mechanical failure. Preferably, the metals are the same composition or have a similar co-efficient of thermal expansion (e.g. preferably within 10% of each other or within 5% of each other). The sealing dome is preferably releaseably fastened to the housing. This enables the sealing dome or the annular ceramic component to be conveniently replaced, if damaged or worn, or changed if a different material grade was required for a different operating environment. The use of releasable fasteners also enables a resilient polymeric seal to be used and replaced between the sealing dome and the housing. The use of a resilient polymeric seal is particularly beneficial in maintaining a positive force between the ceramic component and the underside of the sealing lip, thereby increasing resistance of the sealing lip - ceramic seal surface interface to ingress from corrosive fluids/slurries. The seal is protected from exposure to the corrosive environment by the positive forces that it applies to the adjacent seals which prevent the ingress of corrosive fluids. The seal may be periodically inspected and replaced during routine maintenance, or as required, particularly when used in combination with a releasable fastening system.

The polymeric seal is preferably annular, such as an O-ring. The polymeric seal is preferably disposed within a groove or channel of the housing and/or the ceramic sealing surface. The polymeric seal may be made of any suitable resilient chemical resistant polymer, such as PTFE (e.g. Teflon®). The use of an O-ring, particularly partially embedded within the housing in combination with a metal cap with a fastening mechanism provides a robust and reliable seal arrangement which is particularly suitable for high pressure, high temperature and/or corrosive environments. Furthermore, the robustness of the sealing mechanism is particularly suited to high diameter passageways (e.g. at least 250mm or at last 400mm or at least 500mm diameter) where higher stresses are experienced on the sealing mechanism. Fastening mechanisms relying on adhesive bonding or fastening systems overly relying on a ceramic sealing mechanism are more prone to seal failure in such harsh operating environments.

The use of ceramic material for corrosive resistance in combination with metal for robustness/crack resistance in the fastening/sealing mechanisms (optionally aided by the resilience of a polymeric seal) has been found to overcome the deficiencies of conventional ball valves used in harsh operating environments.

The metallic ball valve housing preferably further comprises a ceramic insert to define the fluid passageway. The ceramic insert preferably forms a seal with the seat valve when the ball valve is in the open position. In some embodiments, the ceramic insert is a cylindrical shape which covers the circumference of the fluid passageway immediately adjacent the inlet to the ball valve fluid passageway. The width of the cylindrical ceramic insert is preferably sufficient to enable the ceramic insert to form a seal with the valve seat.

Preferably the width of the ceramic cylinder is at least 5mm, more preferably at least 10mm and even more preferably at least 20mm. However, there are no constraints upon the size of the ceramic cylinder other than limitations of existing manufacturing techniques. The insert is typically at least 0.1 mm. 1.0 mm or 3.0mm thick and more preferably at least 10.0 mm thick. The minimum thickness of the cylinder is governed by the mechanical performance of the insert required in fitting the cylinder and/or the material performance requirement for the application. In embodiments, in which the cylindrical ceramic insert does not cover the complete length of the fluid passageway of the ball valve, in the section not covered by the ceramic insert, the bore diameter of the housing is increased by the thickness of the ceramic insert, such that cylindrical ceramic insert when fitted into the fluid passageway forms a flush surface with the adjacent metallic fluid passageway. In one embodiment, the ceramic insert is placed at the inlet end of the fluid passageway and optionally also at the outlet end of the fluid passageway.

The valve seat may be made of suitable metallic, ceramic or polymeric materials (e.g. PTFE) or any other suitable material as known in the art.

The seal formed between the ball valve in the open or closed position and the valve seat may be a metal - ceramic, a ceramic - ceramic or a ceramic - polymer seal. In

embodiments in which the valve seat comprises or consists of a ceramic material, the valve seat preferably comprises a (part) spherical, bevelled or tapered edge to increase the sealing surface between the valve seat and the valve housing.

The housing preferably comprises a cavity to receive the sealing dome. The cavity is preferably positioned at an angle of about 90° from the inlet of the fluid passageway, although other configurations are also covered within the scope of the invention.

The actuation mechanism preferably comprises a cavity defining an external surface of the housing to securely receive an actuation shaft. Alternative actuation mechanisms may also be used as known in the art. Preferably, the actuation mechanism is integral with the metallic housing to enable the high actuation torque to be used relative to actuation mechanisms made using ceramic materials.

The metallic material used for the ball valve ball (including the valve seat) is preferably selected from the group consisting of stainless steel, hardened alloys, carbon steel, nickel copper alloy such as Inconel, Monel™, titanium or titanium alloy and tantalum. Depending upon the functional requirements of a specific application, the metallic material may be coated with ceramics, such as tungsten carbide which may be applied using a HVOF thermal spray process or the like. Polymer/polymers coatings may also be applied including fluoropolymers (e.g. PTFE) or polyethylene.

A wide variety of ceramic materials may useful employed in practicing this invention.

Preferably, the ceramic material has a high strength and high toughness. Suitable ceramics include zirconia (including toughened or stabilised zirconia), silicon carbide, tungsten carbide, titanium carbide, alumina and/or silicon nitride

Preferably, the flexural strength of the ceramic material is at least 200 MPa, more preferably at least 400 MPa and even more preferably at least 600 MPa (ASTM test FA 17-78).

Preferably the ceramic material has a Weibull modulus of greater than 10, more preferably greater than 20 and most preferably greater than 30. Preferably, the compressive strength of the ceramic material is at least 500 MPa, more preferably at least 1000 MPa and even more preferably at least 1750 MPa (ASTM test C773-82).

Preferably, the hardness of the ceramic material is at least 5 GPa, more preferably at least 10 GPa and even more preferably at least 12 GPa.

Preferably, the fracture toughness of the ceramic material is a least 2 MPa.m⁰⁵, more preferably at least 2 MPa.m⁰⁵ and even more preferably at least 11 MPa.m⁰⁵.

In another aspect of the present invention, there is provided a ceramic sealing face adapted to circumferentially seal against a valve seat when the ball, as previously defined, is in the closed position.

In another aspect of the present invention, there is provided use of the ceramic sealing face of second aspect of the present invention, in a ball valve of the first aspect of the present invention, in controlling the flow of a fluid. The control preferably includes stopping the flow of the fluid.

There is also provided a ball for a ball valve, the ball being as defined above.

It will be understood that the term metal cap may be inclusive of a metal fastening mechanism used to fasten the sealing dome to the housing.

It will be understood that while the sealing dome typically forms part of a spherical ball in the valve ball (i.e. spherical cap), the sealing dome be of any shape (e.g. planar face) which still enables the valve ball to rotate from an open position to a closed position and vice versa.

A spherical or substantially spherical ball may be preferred. To provide a spherical or substantially spherical ball, the ball valve ball may comprise a metal cap. The sealing dome may have a part spherical surface matching that of a partially or substantially spherical housing. The metal cap may have a part spherical surface matching that of a partially or substantially spherical housing. Including a metal cap may be advantageous. In particular, including the metal cap may allow a seal to be provided against a valve seat when rotating the housing between an open position and a closed position.

A significant benefit of using this invention is the fact that the working faces of the ball valve are ceramic where it is most needed but the most highly stressed features of the valve namely the drive slot in the ball (and preferably the sealing dome fastening mechanism) preferably remain metallic (relative to prior art metallic ball valve designs). This enables the high actuation torque to be used when the valves are operated with a high pressure drop (resulting from upstream pressure pushing the ball onto the seat) or become jammed due to extended periods of use between actuation operations. Previously using a solid ceramic ball has resulted in either failure at the drive slot under these extreme conditions resulting in valve users avoiding the use of ceramics for these applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1a is a plan view of a ball valve ball in an embodiment of the present invention. Figure 1b is a sectional view (B-B) of the ball valve ball of Figure 1a.

Figure 1c is a sectional view (A-A) of the ball valve ball of Figure 1a.

Figure 2 is a perspective view of the ball valve ball of an embodiment of the present invention.

Figure 3 is a sectional view of the ball valve ball of an embodiment of the present invention. Figure 4 is a sectional view of the ball valve ball of Figure 3 with a valve seat in a closed position.

Figure 5 is a sectional view of the ball valve ball and seat of an embodiment comprising a resilient seal which applies a positive force to the ceramic component against the valve seat. Figure 6a is a plan view of a vee ball valve ball of a further embodiment of the present invention.

Figure 6b is a sectional view (A-A) of the vee ball valve ball of Figure 6a.

Figure 7 is a perspective view of the vee ball valve ball of Figure 6. Figure 8 is a sectional view of the vee ball valve ball of Figure 6 with a valve seat in a closed position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

There is provided a ball valve for controlling the flow of a fluid comprising a housing (1) comprised of a metallic material; said housing comprising an inlet and an outlet of a fluid passageway (7) extending therethrough; an actuation mechanism for moving the ball valve housing (1) from an open position to a closed position; a valve seat (9) for sealing the inlet from leakage of the fluid; and characterised in that the ball valve further comprises: a sealing dome comprising: a ceramic sealing face (2) adapted to circumferentially seal against the valve seat (9) when the ball valve is in the closed position; and a metal cap (4). Referring to Figures 1a-1c, there is provided a ball valve ball comprising a housing 1 which is made of steel. The specific composition and grade of metal may vary depending upon the particular application the ball valve is being used. For example, the spherical housing 1 may comprise titanium or a titanium alloy, a nickel alloy such as Monel™ 400, Inconel™ 600, or Incoloy™ 800, or a stainless steel such as type 316, type 17-4ph, or type 317, tantalum or any other (corrosion resistant) metal or alloy that is known in the art.

The housing 1 is generally spherical in shape 5 and, in this embodiment, has a diameter of 425mm. The housing 1 comprises a cylindrical bore 7 defining a fluid passageway extending through the housing 1. The bore 7 is lined with a ceramic insert 12 made of zirconia, partially stabilised with magnesia, such as Nilcra® (Weibull modulus of greater than 30) which is available from Morgan Advanced Materials (Melbourne). It will be appreciated that different ceramic materials may be also used depending upon the specific requirements of the application. The ceramic insert 12 provides exceptional strength and toughness together with erosion and corrosion resistance compared to metallic materials. The material’s properties make it ideal for use with slurries generated in mineral processing as well as erosive mineral particles and sand encountered in oil & gas extraction and processing.

The metal bore 7 preferably has an outside diameter that is at least as large as the desired outside diameter of the housing 1. The bore 7 also has an interior circumferential surface that has been formed to a desired surface finish and a uniform inner diameter that is smaller than an outside diameter of the ceramic insert 12. Preferably, the inner diameter of the metal bore is 10 to 400 microns smaller than the outside diameter of the ceramic insert 12.

Preferably, the ceramic insert 12 is a ceramic cylinder, e.g. a hollow ceramic cylinder.

To fit the ceramic insert 12 during manufacturing, the metal bore 7 is heated to a

temperature sufficient to expand the metal bore 7 such that the inner diameter of the metal bore 7 is at least equivalent or slightly larger in dimension relative to the outside diameter of the ceramic insert 12. To expand the metal bore 7, the bore 7 may be heated to a

temperature sufficient to expand the metal bore 7 such that the ceramic insert 12 can be inserted into the metal bore 7 to form a metal-ceramic cylinder assembly. The metal bore 7 and ceramic insert 12 are then allowed to cool, shrinking the metal bore 7. As the metal bore 7 shrinks in diameter, the interior circumferential surface of the metal bore 7 imparts compressive forces on the outer circumferential surface of the ceramic insert 12, thereby retaining the ceramic insert 12 in place within the metal cylinder.

The outer circumferential surface of the ceramic insert 12, the interior circumferential surface of the metal bore 7, or both, may include a surface coating or a surface treatment. If either or both of the ceramic insert 12 and metal bore 7 includes a surface coating or treatment, the outer circumferential surface of the ceramic insert 12 may not necessarily be in direct contact with the interior circumferential surface of the metal bore 7. A surface coating on either of the outer circumferential surface of the ceramic insert 12 or the interior circumferential surface of the metal bore 7 may be used to facilitate adhesion there between, as well as to improve other structural or chemical characteristics of the housing 1.

The ball valve ball further comprises a metal cap 4 which comprises a steel body and an annular ceramic ring defining a peripheral rim 2 which sealingly interfaces with the housing 1. The ceramic ring may be made of the same material as the ceramic insert 12 lining the bore 7 described above. To ensure the required tolerances to the spherical circumference are achieved, where desired, the dome cap may be machined in situ, preferably after the steel cap is fastened to the housing.

A drive slot 3 is embedded into the housing 1. The drive slot is shaped (e.g. hex-shaped) to receive an actuation shaft (not shown) forming part of an actuation mechanical to open and close the ball valve. The actuation mechanism may comprise any suitable structure as known in the art capable of securing the actuation shaft to the housing 1 , which generally includes a female in the housing 1 into which a male coupling of the actuation shaft is inserted. Alternatively, a male protrusion may be formed with or joined to the housing 1.

As illustrated in Figures 2 & 3, the metal cap 4 is mechanically fastened to the housing 1 through four threaded bolts 8. The bolts are counter sunk into the metal cap 4. The bolts are generally flush to the peripheral surface of the housing 1. Alternatively, the bolts may be recessed relative to the peripheral surface of the housing 1. In some embodiments, the heads of the bolts may be covered with a ceramic cover (not shown) to protect the bolt heads from corrosion. The ceramic covers are preferably configured to be flush with the peripheral surface of the metal cap and may be adhered to the sealing dome using adhesive or brazing methods as known in the art.

As illustrated in the section view of Figure 3, the annular ceramic ring, including ceramic sealing face 2, sits within a groove within the metallic housing 1 , with the bolts acting to clamp the metallic dome 4 sealingly tight against the ceramic ring. As illustrated in Figure 4, the ball valve further comprises a valve seat 9 which functions to seal the fluid passageway 7 open or closed. The valve seat 9 may be any conventional valve seat, which typically has the form of an annular ring which is able to sealingly couple the ball valve to associated pipework defining a fluid passageway. The valve seat typically couples the ball valve upstream and downstream from the fluid passageway 7. The fluid passageway of the valve seat generally has a diameter similar that of the fluid passageway 7 of the ball valve ball.

In the open position, the valve seat 9 forms a seal against the inlet end of the cylindrical ceramic insert 12 illustrated in Figures 1a-1c.

During operation, the ball housing 1 , including the metal cap 4, rotates with the actuation shaft which exhibits approximately zero angular deviation, such that the housing 1 is in sealing contact with the valve seat 9 as the housing 1 rotates, approximately 90°, from an open position to a closed position.

Figure 4 illustrates the ball valve in the closed position. The annular ceramic component comprising sealing face 2 sealingly contacts the inner bore of the valve seat 9. The annular ceramic component comprising sealing face 2 maintains the integrity of the seal against the erosive and corrosive properties of the fluid in the inlet passageway. The fluid may comprise highly alkaline or acidic liquids carrying highly abrasive particles. The act of rotating the ball valve housing 1 from open to closed position results in the sealing face 2, 4 being exposed to harsh conditions. These conditions are particularly harsh at the sealing circumference as the suspended particles are impacted against the annular ceramic ring including sealing face 2. Conventional metal housings are prone to corrosion, particularly at the sealing interface between the valve seat and the ball housing. Maintaining the seal integrity for slurries is in particular difficult in metal - metal seals as the abrasive particles of the slurries can pit the metal surface, increasing the surface area and grain boundaries for chemical attack by the fluid. The use of a ceramic seal is better able to prevent leaks due to its combination of mechanical hardness and chemical resistance, which enables the ceramic seal to better maintain its shape.

Figure 5 illustrates a preferred embodiment in which the ceramic component comprising sealing face 2 is partially sunken within a groove 10 of the housing 1. The groove 10 stabilises the position of the component comprising sealing face 2 and prevents lateral movement of the ceramic seal across the dome - housing sealing surface 15. An O-ring 20 is disposed within a groove 25 of the housing 1 , with the cross-sectional diameter of the O- ring being greater than the depth of the groove, such that the O-ring exerts a force upon the ceramic component comprising sealing face 2 and onto the underside of a sealing lip 30. Suitable O-rings include Viton ® fluorocarbon elastomer O-rings. The size of the O-ring will vary depending upon the size of the annular ceramic component comprising ceramic sealing face 2 (e.g. 5 inch, 10 inch, 20 inch diameter or greater). The cross-sectional diameter of the O-ring will also vary according to application, however are typically in the range of 1mm to 20 mm. The O-ring also exerts a positive force upon the valve seat 9. The maintenance of a positive force between the ceramic component including ceramic sealing face 2 and the underside of the sealing lip 30 further prevents the penetration of corrosive liquids and slurries into the sealing interface between the sealing dome 4 and housing 1.

The ceramic component including ceramic sealing face 2 has bevelled edges 35 to form only obtuse angles enabling the ceramic component to be securly fitted within the valve housing 1 without the ceramic component 2 being prone to chipping. The bevelled edges 35 are also more resistant to chipping or cracking due to stress formed from different thermal expansion coefficients between the ceramic component 2, the housing 1 and the metal cap 4.

In some embodiments, the valve seat 9 is also ceramic such that a ceramic-ceramic seal 40 is created. The valve seat 9 may comprise a tapered or spherical inner bore 40, such that the surface contact between the ceramic component comprising the ceramic sealing face 2 and the valve seat 9 is increased, thereby producing an increased sealing area to further minimise the probability of seal leakage. Further details of a ceramic valve seat which may be used in combination with the present invention are provided in US5, 183,068.

It will be appreciated that the ball valve ball may further comprise a further sealing dome and valve seat corresponding to the outlet side of the ball valve. A ball valve with a further sealing dome comprising a ceramic sealing face may be beneficial in situations in which corrosive fluid may remain in the fluid passageway in contact with the ball valve housing, even when the ball valve is in the closed position.

In another embodiment, the ball valve may comprise a segmented ball. Such a ball valve including a segmented ball or ball segment is illustrated in Figures 6 to 8, wherein like reference numerals are used with the addition of 100. It will be appreciated that features of the ball valve described with reference to Figures 1 to 5 may be employed to advantage with the ball valve described with reference to Figures 6 to 8 and vice versa.

Within this embodiment, the segmented ball, such as a vee ball segment, rotates within an outer housing. The outer housing in combination within the internal surface of the segmented ball forms the fluid passageway, when the ball valve is in the open position. The outer housing may be any dimension which enables the segmented ball valve to rotate between a closed and an open position, although the inner surface of the outer housing preferably has a radial arc which the segmented ball sealingly rotates into, when in the open position.

Referring to Figures 6a, 6b, and 7, there is provided a ball valve vee ball segment comprising a housing 101 which is has the shape of a segmented sphere 105. A metallic dome 104 is bolted onto the housing 101 with four bolts 108 which are sunken below the spherical outline of the metallic dome 104. Two hexagonal shaped drive slots 103 circumferentially extend from opposing sides of the housing, with a central axis aligning the hexagonal drive slots within an outer housing component (not shown). The segmented housing 101 is able to rotate through rotation of an actuation shaft (not shown), within the outer housing component, which has a spherical walls to accommodation inner housing 101. In the open position, the housing forms part of the fluid passage (not shown).

The vee valve or ball segment configuration enables the weight of the valve to be

significantly decreased thereby reducing stresses generated during actuation of the valve. The vee height 107 may be at least 100 mm or at least 200 mm or at least 300 mm. The diameter of the vee valve 106 may be at least 250 mm or at least 350 mm or at least 450 mm.

Figure 8 illustrates the vee ball valve ball segment in the closed position, with the ceramic sealing face 102 of the ceramic component sealing against the valve seat 109, with the metallic dome 104 protruding into the fluid passage 107. In addition or alternatively to the four bolts 108, the metallic dome 104 forms a female / male connection 111 , 112 with the housing 101. The opposing side to the metallic dome is“V” shaped 113, which forms the internal surface of the ball segment. In the open position, the“V” shaped housing 113 may partially protrude into the fluid passage, with the“V” shaped housing 113 forming part of the fluid passage. It will be appreciated that the shape of the internal surface of the ball segment may vary.

The foregoing detailed description and accompanying drawings are only illustrative and not restrictive. They have been provided primarily for a clear and comprehensive understanding of the present invention and no unnecessary limitations are to be understood therefrom. Numerous additions, deletions, and modifications to the preferred embodiment, as well as alternative arrangements, may be devised by those skilled in the art without departing from the spirit of the present invention and the scope of the appended claims.

Claims

1. A ball valve for controlling the flow of a fluid comprising: a ball or ball segment comprising a housing (1 , 101) comprised of a metallic material; said housing comprising, or partially forming, a fluid passageway (7, 107) comprising an inlet and an outlet, and extending therethrough; an actuation mechanism (3, 103) for moving the ball valve housing (1 , 101) from an open position to a closed position; a valve seat (9, 109) for sealing the inlet from leakage of the fluid; and characterised in that the ball or ball segment further comprises: a sealing dome (2, 4, 102, 104) comprising: a ceramic component comprising a ceramic sealing face (2, 102) adapted to seal against the valve seat (9, 109) when the ball valve is in the closed position; and a metal cap (4, 104).

2. The ball valve according to claim 1 , wherein the ceramic component is annularly shaped.

3. The ball valve according to claim 1 or 2, wherein the metal cap (4, 104) comprises a different metallic material to the metallic material of the housing.

4. The ball valve according to claim 1 , 2, or 3, wherein the metal cap (4, 104) comprises a sealing lip (30) which extends over the ceramic component, such that a portion of the ceramic component is disposed between the housing (1 , 101) and the sealing lip (30).

5. The ball valve according to any preceding claim, wherein the sealing dome (2, 4,

102, 104) is mechanically fastened (8, 108) to the housing (1 , 101).

6. The ball valve according to any preceding claim, wherein a resilient seal (20) is disposed between the ceramic component and the housing (1 , 101).

7. The ball valve according to claim 6, wherein the resilient seal (20) is an O-ring.

8. The ball valve according to claims 6 or 7, wherein the resilient seal (20) is disposed within a groove (25) in the housing (1 , 101) and/or the ceramic component.

9. The ball valve according to any of claims 6 to 8, when directly or indirectly dependent upon claim 4, wherein the resilient seal (20) is disposed between the ceramic component and the housing (1 , 101) such that the resilient seal exerts a force upon the ceramic component against the sealing lip (30).

10. The ball valve according to any preceding claim, wherein the sealing dome (2, 4,

102, 104) is releaseably fastened to the housing (1).

11. The ball valve according to any preceding claim, further comprising a ceramic insert (12), wherein the ceramic insert (12) defines at least a portion of the fluid passageway.

12. The ball valve according to claim 11 , wherein the ceramic insert (12) seals against the valve seat (9) when the ball valve is in the open position.

13. The ball valve according to any preceding claim, wherein the valve seat (9) comprises a valve seat ceramic component such that seal between the valve seat ceramic component and the housing (1 , 101) and/or the sealing face (2, 102) is a ceramic - ceramic seal in at least one of the open position and/or the closed position.

14. The ball valve according to any preceding claim, wherein the housing (1 , 101) comprises a cavity and/or planar face for receiving the sealing dome (2, 4, 102, 104), said cavity and/or planar face being positioned at an angle of about 90° from the inlet of the fluid passageway.

15. The ball valve according to any preceding claim, wherein the actuation mechanism (3, 103) comprises a cavity defining an external surface of the housing for securely receiving an actuation shaft.

16. The ball valve according to any preceding claim, wherein the ceramic component comprises zirconia (e.g. stabilised zirconia, partially stabilised zirconia and/or toughened zirconia), silicon carbide, tungsten carbide, titanium carbide, alumina and/or silicon nitride.

17. The ball valve according to any preceding claim, wherein the housing (1 , 101) and/or metal cap (4, 104) comprises a stainless steel, a hardened alloy, a carbon steel, a nickel copper alloy such as Monel™, titanium and/or a titanium alloy.

18. A ball or ball segment for a ball valve, the ball being as defined in any preceding claim.