Anti-extrusion elements for pressure-containing seals

Abstract

The present invention relates to a composite member (10) for use in the production of an anti-extrusion element for a pressure-containing seal. The composite member (10) comprises: an elongate outer coiled spring (12) defining an inner cavity (13), an elongate inner spring (14), the elongate inner spring (14) being positioned within the inner cavity (13) of the elongate outer coiled spring (12), and an elastomeric material (16), wherein the elastomeric material (16) fills the inner cavity (13) of the elongate outer coiled spring (12), wherein the elongate outer coiled spring (12) is formed from a flat tape.

Description

[0001] Anti-extrusion elements for pressure-containing seals

[0002] Field of Invention

[0003] The present invention relates to an anti-extrusion element for a seal. In particular, the present invention relates to a composite member used to produce anti-extrusion elements for pressure-containing seals.

[0004] Background

[0005] Anti-extrusion elements are used alongside seals or packing devices in a multitude of applications, wherein at least a portion of the sealing device is subjected to extrusion forces. For example, anti-extrusion elements are commonly used in valves and cylinder bodies such as for hydraulic circuits, chemical pumps, injection moulding machines, adhesive dispensing valves, presses, agricultural machines, and oil and gas wellhead equipment.

[0006] When sealing two components together, for example a wellhead and wellbore casing, the deformable material of a seal may be squeezed into clearances being sealed between these two components. Accordingly, over time, the seals will progressively lose material and eventually fail. Therefore, anti-extrusion elements are used alongside sealing or packing devices to prevent this loss of sealing material. However, this risk of extrusion increases with increased clearance gap size, increased temperature, and increased pressure. Typically, under these conditions, conventional anti-extrusion elements may fail.

[0007] Typical anti-extrusion elements are made from hard and less deformable materials to make elements that are more extrusion-resistant. As anti-extrusion elements are harder than the sealing device in order to reduce extrusion, a problem that can arise is that the anti-extrusion device may cause damage to the sealing counterfaces and this can be very problematic in sealing systems. The risk of damage increases as the system pressure also increases. The damage to the sealing counterfaces has larger consequences as it can further result in damage to the seals themselves and can also cause poor sealing performance by forming leak paths along the main sealing contact area.

[0008] Additionally, the present inventors have found that imperfections, gaps or voids in an anti- extrusion elements surface or design can cause air bubbles to become trapped during manufacture of a sealing device. Furthermore, under high pressure conditions, especially in combination with elevated temperatures, gases in the area surrounding a seal can be absorbed into the seal over time. If the system pressure is then quickly released, the sudden pressure difference will cause any trapped gases to expand, which can then damage the seals. This is called rapid gas decompression (RGD) and is an issue with seals and anti-extrusion elements, especially when used in high-pressure conditions.

[0009] US 4,379,558 describes a packing member containing an anti-extrusion element for use in dynamic or static applications. As illustrated in Figure 1 , the anti-extrusion element 1 is formed from a tubular spring member 2 with overlapping contiguous elements. A second coiled helical spring 3 is arranged within the tubular spring member 2. However, this inner coiled helical spring is not fixed and so cannot support the outer helical spring effectively. The overlapping contiguous elements of the outer tubular spring member 2 prevent extrusion of the packing member between spring convolutions. However, the overlapping contiguous elements of the outer tubular spring member provides an uneven surface, which contacts the sealing surface with a small surface area. This small contact area leads to an increased pressure being exerted on the sealing counterfaces, resulting in a higher probability of damage. Furthermore, the extrusion element is an enclosed element that contains gas, increasing the risk of rapid gas decompression. Additionally, the overlapping elements create multiple triangular areas in the perimeter of the anti-extrusion element, which the inventors have appreciated could allow the seal material to bypass the antiextrusion element leading to loss of material from the body of the seal and therefore increasing the risk of failure.

[0010] Therefore, there is a need for an anti-extrusion element with improved anti-extrusion capabilities, particularly when used with large clearance gaps, high pressure and / or high temperatures.

[0011] Summary of Invention

[0012] According to a first aspect of the invention, there is provided a composite member for use in the production of an anti-extrusion element for a pressure-containing seal, the composite comprising: an elongate outer coiled spring defining an inner cavity; an elongate inner spring; the elongate inner spring being positioned within the inner cavity of the elongate outer coiled spring; and an elastomeric material, wherein the elastomeric material fills the inner cavity of defined by the elongate outer coiled spring.

[0013] The composite member of the first aspect of the invention can be used to form antiextrusion elements according to the second aspect of the invention. These anti-extrusion elements can then be an integral component of or used in addition with a pressurecontaining seal to prevent damage to these seals from extrusion forces. A sign that the seal is being damaged due to extrusion is where the part of the seal that lies against the extrusion gap begins to flake away, which in extreme cases can result in an uneven sealing surface. It has been found that pressure-containing seals used with or containing an antiextrusion element made from a composite member according to embodiments of the present invention possess a number of advantages in comparison with seals that include other forms of reinforcement, such as conventional toroidal round wire springs.

[0014] The present invention provides a composite member for use in the production of an antiextrusion element for a pressure-containing seal. The composite member comprises an elongate outer coiled spring defining an inner cavity; an elongate inner spring; wherein the elongate inner spring is positioned within the inner cavity of the elongate outer coiled spring. The composite member further comprises an elastomeric material, which fills the inner cavity of the elongate outer coiled spring. That is, the elastomeric material fills the inner cavity of the elongate outer coiled spring such that the elongate inner spring is encased within the elastomeric material. Such encasement of the inner spring ensures that there are no gaps or voids in the anti-extrusion element.

[0015] In preferred embodiments, the elongate inner spring comprises a coiled spring defining an inner cavity, and the elastomeric material fills both the inner cavities of the elongate outer coiled spring and the elongate inner spring. This ensures that the elongate inner spring is encased within the elastomeric material thus avoiding the formation of gaps or voids in the anti-extrusion element.

[0016] The elastomeric material provides the elongate inner and outer coiled springs with support whilst also allowing for deformation of the composite member. This means that the material is able to conform better to the spaces where it is being used. This is possible due to the elastomeric material being elastically deformable but also incompressible, as it fills the inner cavities of both the elongate inner and outer coiled springs. As such, the elastomeric material aids elastic deformation of the springs whilst preventing the springs from being crushed or collapsing and so permanently deforming. Therefore, the composite member is suitable for use at high pressures.

[0017] The composite member of the present invention can also be used in anti-extrusion elements that are particularly suitable for use with large extrusion gaps, for example in excess of those recommended for conventional elastomeric seals such as in accordance with ISO 3601-2. In sealing systems, the clearance gap (or extrusion gap) is defined as the space between the two components. For example, in a piston configuration, the clearance gap would be the space between the piston and bore. The clearance gap can be expressed in terms of the diametral clearance or radial clearance, where the radial clearance is equal to half of the diametral clearance, in systems where the two components are radially separated. Alternatively, the clearance gap can be expressed in terms of the linear clearance, where the two components are linearly separated.

[0018] Generally, the larger the clearance gap, the higher the stresses that the seal must be able to withstand, and accordingly many current anti-extrusion elements and seal are unsuitable for use with systems that have large clearance gaps. However, as the composite member has an elongate inner spring and elastomeric material supporting the elongate outer coiled spring, the composite member is able to withstand higher stresses, and so is suitable for use in systems with large clearance gaps. For example, the elastomeric seal systems containing an anti-extrusion element of the present invention may be used to seal diametral gaps of up to 20 mm and axial gaps of up to 16 mm.

[0019] Suitable types of springs include those formed from, amongst others, flat tape, square wire or round wire, or combinations thereof. The coils may be right-hand wound and / or lefthand wound. Preferably, the elongate outer coiled spring may be formed from a flat tape. This provides a more even surface structure to the composite member and thus causes less damage to the sealing surface of the components when the composite member is used in an anti-extrusion device. Optionally, the flat tape may have a thickness from 0.05 mm to 2.5 mm, preferably from 0.075 mm to 2 mm. Furthermore, the flat tape may have a width from 0.5 mm to 20 mm, preferably from 0.5 mm to 16 mm.

[0020] The elongate outer coiled spring may be formed as a closed coiled spring or an open coiled spring. For example, the elongate outer coiled spring may comprise a series of gaps between consecutive coils, which provides an open structure to the coiled spring. Where the elongate outer coiled spring contains a series of gaps between consecutive coils, the gap width may be up to 2 mm, preferably up to 1 .5 mm, and most preferably up to 1 mm.

[0021] When the elongate outer coiled spring comprises a series of gaps between consecutive coils, it is preferable that the elastomeric material may be present within the series of gaps, even more preferably wherein the elastomeric material is present within each gap. Where there is elastomeric material within each gap, the elastomeric material is able to deform to the shape of the counterface while in use to provide a continually flat surface against the sealing face, which ensures even distribution of load across the sealing face. In this way, the composite member aids in the reduction of potential damage to the counterface sealing surface.

[0022] Furthermore, the use of an outer elongate coiled spring comprising gaps between consecutive coils allows for easier insertion of elastomeric material and thus provides for more consistent filling of the composite member.

[0023] The elongate outer coiled spring may also not have gaps between consecutive coils, which provides a closed coil structure. However, it is preferable that the elongate outer coiled spring does not contain overlapping coils, i.e. , wherein the gap between consecutive coils is less than zero. When the coils are overlapping, it is more difficult to provide the elastomeric material within the inner cavity. Furthermore, when the coils are overlapping, there is an uneven surface structure that results in a higher probability of damage occurring to the counterface sealing surfaces, due to high surface pressure occurring at the areas of overlap.

[0024] A wider flatter contact area may be achieved by forming the outer spring from a flat tape or from using an open coiled spring and filling the gaps between each consecutive coil with elastomeric material. This wider flatter contact area of embodiments of the present invention significantly reduces the contact pressure on the sealing counterfaces and thus significantly reduces any damage caused by the interaction.

[0025] The elongate inner spring prevents the elongate outer coiled spring from collapsing, particularly when the composite member is used under high pressure conditions. The elongate inner spring may be a leaf spring or a coiled spring. When the elongate inner spring comprises a coiled spring, the coiled spring may be formed from a flat tape, a round wire or a square wire, or combinations thereof. Optionally, the flat tape may have a thickness from 0.05 mm to 2.6 mm, preferably from 0.075 mm to 2 mm. Furthermore, the flat tape may have a width from 0.5 mm to 20 mm, preferably from 0.5 mm to 16 mm. The round or square wire may have a diameter or width of from 0.3 mm to 3.5 mm, preferably from 0.3 mm to 3.0 mm. Additionally, the coiled elongate inner spring may also have either an open or closed coil structure.

[0026] The elongate outer coiled spring may comprise carbon steel, stainless steel, corrosion resistant alloys, aluminium alloys, copper, copper alloys, polyether ether ketone polymers, or polytetrafluoroethylene polymers, or combinations thereof.

[0027] The elongate inner spring may comprise carbon steel, stainless steel, corrosion resistant alloys, aluminium alloys, copper, copper alloys, polyether ether ketone polymers, or polytetrafluoroethylene polymers, or combinations thereof.

[0028] The elongate outer coiled spring or the elongate inner spring may comprise a coated or treated material. For example, the material may be treated using a low-friction surface treatment or coated with an anti-corrosion coating. Other exemplified coatings include PEEK coated tape or silver-plated tape.

[0029] In particular, suitable grades of stainless steel comprise, but are not limited to, UNS S31600 (Grade 316); UNS S30400 (Grade 304); and UNS S30200 (Grade 302).

[0030] In particular, suitable grades of corrosion resistant alloys comprise, but are not limited to, UNS N06625 / W; UNS N07750 / W; UNS N10276; UNS N04400; and UNS R30003.

[0031] In particular, suitable types of polytetrafluoroethylene polymers may comprise, but are not limited to, carbon / graphite filled materials; glass fibre filled materials; bronze filled materials; and synthetic aromatic polyester resin filled materials.

[0032] When the elongate inner spring comprises a coiled spring, the coiled spring may have a cross-sectional diameter of the outer diameter of the spring from 0.5 mm to 28 mm, preferably from 1 mm to 19 mm.

[0033] The elongate inner spring is contained within the elongate outer coiled spring and accordingly the outer diameter of the coiled elongate inner spring must be smaller than the inner diameter of the elongate outer coiled spring. Preferably, the elongate inner spring has an outer diameter that is from 2.0 % to 25.0 % smaller than an inner diameter of the elongate outer coiled spring, preferably from 2.5 % to 20.0 % smaller. Providing a gap between the elongate outer coiled spring and the elongate inner spring allows for elastomeric material to sit between the two coiled springs and support both springs to make the composite member more resiliently deformable and to prevent collapse.

[0034] The composite member may have a cross-sectional diameter of from 1 to 30 mm, preferably from 1.5 mm to 20 mm. However, suitable sizes of the composite member will vary depending on the end application of the anti-extrusion element.

[0035] The elongate inner spring and the elongate outer coiled spring may have similar thermal expansion coefficients. This is particularly helpful when the composite member will be exposed to high temperatures because it reduces the risk of separation.

[0036] The elongate inner spring and the elongate outer coiled spring may be substantially axially aligned. This means that the elongate inner and outer coiled springs have substantially the same central axis. Being substantially axially aligned means that the elongate inner coiled spring provides more uniform support to the elongate outer coiled spring. However, the elongate inner spring may also not be centrally aligned with the inner cavity of the elongate outer coiled spring. These differences may arise due to different manufacturing methods.

[0037] Furthermore, the composite member may comprise more than one elongate inner spring. These additional springs may be positioned within the inner cavity of the elongate outer coiled spring to provide a radially extended system of springs. These additional springs may provide increased support, resulting in a stiffer anti-extrusion element. Alternatively, the composite member may comprise multiple elongate inner springs axially arranged so as to fill the length of the composite member. This may be advantageous when making longer sections of composite member, for ease of manufacturing. For the same reason, the composite member may also comprise multiple elongate outer coiled springs axially arranged so as to fill the length of a composite member.

[0038] The elastomeric material may comprise nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, carboxylated nitrile butadiene rubber, fluoroelastomer, perfluoroelastomer, tetrafluoroethylene propylene, silicone, fluorosilicone, chloroprene, butyl rubber, ethylene propylene diene monomer rubber, natural rubber, polyether urethane, or polyester urethane, or combinations thereof.

[0039] Materials that have a high elastic modulus are harder to deform, whereas more deformable materials have a low elastic modulus. Preferably, where the composite member is being used in an anti-extrusion device for larger clearance gaps, the elastomeric material has a lower elastic modulus and thus is easier to deform. However, typically, the elastic modulus is between 4MPa and 11 MPa at 50% elongation as measured under BS ISO 37.

[0040] According to a further aspect of the invention, there is provided a method of manufacturing a composite member of the present invention, the method comprising the steps of: i) providing an elongate outer coiled spring having an inner cavity; ii) providing an elongate inner spring; iii) positioning the elongate inner spring within the inner cavity of the elongate outer coiled spring; and iv) filling the inner cavity of the elongate outer coiled spring with an elastomeric material.

[0041] In some embodiments, the elongate inner spring comprises a leaf spring. In other embodiments, the elongate inner spring comprises a coiled spring having an inner cavity. Where the elongate inner spring is a coiled spring, step iv includes filling the inner cavity of the coiled elongate inner spring with an elastomeric material.

[0042] The method may be performed within a mould. Accordingly, the elongate inner spring is positioned within the elongate outer coiled spring and both can be placed within a mould. The mould may be cylindrical in shape and the mould may be sized so as to be the same size as the outer diameter of the elongate outer coiled spring. However, the skilled person will appreciate that alternative shapes and sizes may be suitably used.

[0043] In some embodiments, the mould is pre-filled with elastomeric material and the elongate outer coiled spring and the elongate inner spring are immersed into the elastomeric material in order to fill the inner cavity of the elongate outer coiled spring or the inner cavities of both springs. Alternatively, the springs may be immersed into the elastomeric material outside of a mould and then the elastomeric material can be removed from the outer surface of the elongate outer coiled spring. The elastomeric material may be heated to reduce the viscosity prior to filling the cavity / cavities of the elongate springs. Filling the coiled springs in such a manner is possible even with a closed outer coiled spring as the spring can be stretched minorly during the process and then when the elastomeric material hardens and solidifies, the spring will be retracted back into a closed coil position. Solidifying the elastomeric material may be achieved using known techniques, such as curing or cooling.

[0044] In alternative embodiments, the inner cavity of the elongate outer coiled spring or the cavities of both the elongate outer coiled spring and the coiled elongate inner spring may be filled with elastomeric material by injection, preferably by injection moulding. Alternatively, the method may be performed using vacuum forming.

[0045] The steps of the method may not be performed in the order described. For example, in some embodiments, in a first step the elongate inner spring is encased in an elastomeric material, followed by curing of the elastomeric material to form a solid encased structure. The elongate outer coiled spring can then be formed around the elastomeric encased elongate inner spring. For example, a flat tape can be wrapped around the encased structure to form the elongate outer coiled spring.

[0046] According to further aspect of the invention, there is provided an anti-extrusion element for a pressure-containing seal comprising a composite member according to the present invention.

[0047] The anti-extrusion elements provided herein provide superior anti-extrusion properties and are particularly suitable for use in systems that include large clearance gaps and are suitable for use in high pressure and / or at high temperature conditions.

[0048] The present anti-extrusion element is particularly resistant to degradation via rapid gas decompression because the inner cavity of the elongate outer coiled spring is filled with elastomeric material and thus there are minimal air gaps within the anti-extrusion element that can cause damage. Furthermore, the elongate outer coiled spring means that there is a low surface area of gas permeable materials at the surface of the anti-extrusion element, preventing gas from being absorbed into the anti-extrusion element of the present invention.

[0049] Another key benefit of the anti-extrusion elements made from the composite member is that embodiments of the anti-extrusion elements of the present invention are nondamaging. These anti-extrusion elements sit between two components which are being sealed together, typically under pressure. It is known that conventional, already-known anti-extrusion elements may cause damage to the sealing faces that they are held against. This is particularly problematic where there is movement between the sealing faces. These problems have hitherto been overcome in the art by using additional fabric reinforcements, such as aramid fibres, to reduce the damage caused by the anti-extrusion elements. Other proposals such use of softer materials result in a notable decrease in pressure resistance, as well as a reduction in the size of gap which can be sealed.

[0050] However, as detailed above, the anti-extrusion elements described herein can be considerably less damaging on the sealing counterfaces, and therefore can remove the need for, for example, additional fabric reinforcements.

[0051] The anti-extrusion element may be formed into a continuous loop. This may be a circular shape, an obround shape, an elliptical shape or an oval shape or any other suitable continuous shape. The anti-extrusion element may have a diameter or other dimension of between 10 mm and 3000 mm, preferably from 12 mm to 2500 mm.

[0052] This continuous loop may be formed by joining a first end of a composite member with a second end of the same composite member to form the continuous loop. The composite member may contain multiple either elongate outer coiled and / or inner springs. Furthermore, the composite member may be made from multiple smaller segments connected together to form a single extended composite member. The first end of the composite member may be joined to a second end of the composite member using adhesive, welding, brazing or soldering techniques, or other suitable joining techniques. The joining technique may preferably be laser welding. It will be appreciated that the present invention does not encompass a system containing a single spring where the ends are joined in an overlapping manner, such as by securing one end of the single spring within the cavity defined by the other end of the single spring, but instead the present invention is directed to a system containing two springs - both an inner spring and an outer coiled spring.

[0053] These joining techniques may be used to join the elongate outer coiled spring at the first end with the elongate outer coiled spring at the second end of the composite member. However, they may also be used when the elongate inner spring is coiled to bind two ends of the elongate inner coiled spring. Alternatively, the continuous loop may be formed by attaching two ends of the elastomeric material together.

[0054] Alternatively, joining the first end of the composite member with the second end of the composite member may be achieved by placing an insert within a first and second end of the elongate inner spring to form the continuous loop, for example within the inner cavity of the elongate inner spring. In some embodiments, this insert may be formed integrally with the elongate inner spring. In an embodiment, the coiled elongate inner spring may be formed as a conical coil at a first end. This conical end may be formed with a thread so that the conical coil can be screwed into an inner surface of the coiled elongate inner spring at the second end.

[0055] According to yet a further aspect of the invention, there is provided a method of manufacturing an anti-extrusion element of the present invention, the method comprising the steps of: i) providing a composite member as described above; and ii) joining a first end of the composite member with a second end of the composite member to form a continuous loop.

[0056] Step (ii) of the method may involve forming a join between the first and second ends of the composite member. In particular, this may be joining the first and second ends of the elongate outer coiled spring. This join may be achieved using adhesive, welding, brazing or soldering. Preferably, the join may be made from laser welding.

[0057] Alternatively, or in addition to, the joining step may involve inserting an insert into a first and second end of the inner elongate inner spring, for example where it is a coiled spring, into the inner cavity. These joining steps may be performed as described above.

[0058] According to an alternative aspect of the invention, there is provided a method of manufacturing an anti-extrusion element of the present invention, wherein the method involves the step of: i) providing an elongate outer coiled spring having an inner cavity; ii) providing an elongate inner spring; iii) positioning the elongate inner spring within the inner cavity of the elongate outer coiled spring; iv) joining at least a first end of one or more of the elongate outer coiled and inner springs with a respective second of the one or more elongate outer coiled and inner springs; and v) filling the inner cavity of the elongate outer coiled spring with an elastomeric material.

[0059] In some embodiments, the elongate inner spring comprises a leaf spring. In other embodiments, the elongate inner spring comprises a coiled spring having an inner cavity. Where the elongate inner spring is a coiled spring, step (v) may include filling the inner cavity of the coiled elongate inner spring with an elastomeric material.

[0060] The step of joining a first end of one or more of the elongate outer coiled and inner springs may be performed as already outlined above. For example, the join may be achieved using adhesive, welding, brazing or soldering. Preferably, the join may be made from laser welding.

[0061] Alternatively, or in addition to, where the elongate inner spring comprises a coiled spring having an inner cavity, the joining step may involve inserting an insert into a first and second end of the inner cavity of the elongate inner spring.

[0062] The step of filling the inner cavity of the elongate outer coiled spring or the inner cavities of both the elongate outer coiled and inner springs may also be performed as outlined above. For example, the method may be performed using a mould. The mould may be pre-filled with elastomeric material, or the springs may be arranged within the mould and then filled with elastomeric material.

[0063] According to a fifth aspect of the invention, there is provided an elastomeric seal system comprising an anti-extrusion element according to the present invention and a pressurecontaining seal.

[0064] Typically seal bodies are formed from materials that deform under certain conditions, such as under compression, temperature change or other triggers. Accordingly, the seals may get damaged due to extrusion forces. The anti-extrusion element provides the seals with a greater durability and prevents damage to the seals. The pressure containing seal may be either a static seal or a dynamic seal.

[0065] The anti-extrusion device may be an integral element of the pressure-containing seal. This means that the anti-extrusion device may be formed within the seal to provide the seal with the benefits outlined herein.

[0066] In some embodiments, the anti-extrusion element is pre-formed and then moulded into the pressure-containing seal. For example, the anti-extrusion element may be formed and placed into a mould and then the seal forming material can fill the mould surrounding the anti-extrusion element, forming the seal around the anti-extrusion element. A chemical bonding agent may be applied to the anti-extrusion element prior to the moulding operation to provide a strong chemical bond between the two elements.

[0067] Alternatively, in some embodiments, the anti-extrusion element and pressure containing seal can be formed together in situ. For example, elongate outer coiled and inner springs can be provided and arranged in a mould such that the elongate inner spring is positioned within a cavity defined by elongate outer coiled spring. The elastomeric material can then fill the mould to form both the extrusion element and the pressure containing seal simultaneously.

[0068] Alternatively, the anti-extrusion element can be pre-formed and assembled together with a pre-formed pressure containing seal to act as a barrier between the pre-formed seal and the extrusion gap. The anti-extrusion element can be used with any suitable seals.

[0069] There may be two anti-extrusion elements present in the system, one at an upper end and one at a lower end of the pressure-containing seal. However, the skilled person would readily understand that some systems may only require a single anti-extrusion element. Furthermore, some systems may include more than two anti-extrusion elements.

[0070] The anti-extrusion element of the present invention may be inserted into the sealing space between two components by deforming the anti-extrusion element, typically into a crescent shape, and positioning it within the sealing space. Once positioned, the anti-extrusion element will reform its original shape. This allows for the anti-extrusion element to be positioned into a groove in a housing.

[0071] The anti-extrusion element of the present invention can also be positioned in this manner when it is integrally formed in a seal or assembled with a seal. Typical anti-extrusion elements are too hard or rigid to be fitted this way, however the present anti-extrusion element can be beneficially placed in this manner. According to a sixth aspect of the invention, there is provided the use of an anti-extrusion element according to the present invention in combination with a pressure-containing seal.

[0072] These seals may be a static seal or a dynamic seal.

[0073] These anti-extrusion elements of the present invention are particularly suitable for use in high pressure conditions. For example, the anti-extrusion element is particularly suited for use with a seal at pressures exceeding 10 MPa, and more particularly suited for use at pressures exceeding 69 MPa. For example, the seals may be used in systems exceeding 10 MPa, such as exceeding 15 MPa, exceeding 30 MPa, exceeding 50 MPa, or exceeding 69 MPa.

[0074] The temperature range that the anti-extrusion elements can be used is dependent on the elastomeric material used, however the anti-extrusion element typically may be used at a temperature from -50 °C to 350 °C. The anti-extrusion element is particularly suited for use with high temperature conditions, for example over 100 °C, such as from 100 °C to 200 °C, particularly 140 °C to 200 °C.

[0075] These seals and anti-extrusion elements can be used in many different applications. For example, the anti-extrusion element and pressure-containing seal may be used for sealing gaps between a casing and a well-head of an oil or gas well. Furthermore, these antiextrusion elements and seals can be used with rough casing of the oil well, without requiring any smoothing of the casing surface. It is known that the surface of rough casing in a wellhead system is challenging to ensure a secure seal against because it has significant defects on the surface that provide leak paths. Typically, for rough surfaces, softer seal materials are required to ensure a tight seal and prevent risk of leaking. However, in a wellbore, the pressures and temperatures may both be incredibly high and therefore seal materials will soften with the heat and so are highly likely to extrude and damage the seal. Therefore, developing suitable seals for use with a rough casing in a wellbore is extremely challenging. However, the elastomeric seal system and the antiextrusion elements of the present invention are able to provide a suitable seal without extrusion of the seal material. This has been shown in Example 1 , outlined below, where the seals were tested against a surface that has a rough finish of up to 350 RMS. RMS is the Root Mean Square of a surfaces measured microscopic peaks and valleys and the higher the value, the rougher the surface. However, the skilled person will also appreciate that these anti-extrusion elements may be used with a variety of seals in a variety of applications.

[0076] These anti-extrusion elements may be used with seals to seal diametral gaps of up to 20 mm. They also may be used to seal axial gaps of up to 16 mm.

[0077] Aspects of the present inventions will now be described by way of example and with reference to the figures below.

[0078] Brief Description of the Figures

[0079] Figure 1 shows an elevational view of a prior art anti-extrusion element according to US 4,379,558 with portions cut away to show details of its construction.

[0080] Figures 2A to 2D are schematic partial side views of embodiments of the composite member of the present invention.

[0081] Figure 3A is a schematic diagram depicting an elastomeric seal system according to an embodiment of the present invention, wherein two anti-extrusion elements are integrally formed within a pressure-containing seal.

[0082] Figure 3B is a schematic diagram depicting an elastomeric seal system according to an embodiment of the present invention, wherein two pre-formed anti-extrusion elements are assembled with a pressure-containing seal.

[0083] Figure 4 shows an elastomeric seal system according to an embodiment of the present invention after having undergone the test procedure outlined in Example 1.

[0084] Figure 5 shows the elastomeric seal system of Figure 3 before having undergone the test procedure outlined in Example 1.

[0085] Figure 6 shows an seal containing a prior art anti-extrusion element after having undergone one cycle of the test procedure outlined in Example 1.

[0086] Figure 7 shows another aspect of the seal containing a prior art anti-extrusion element of Figure 6 after having undergone one cycle of the test procedure outlined in Example 1.

[0087] Figure 8 shows the seal containing a prior art anti-extrusion element of Figures 6 and 7 before having undergone one cycle of the test procedure outlined in Example 1. Figure 9 shows the seal containing a prior art anti-extrusion element of Figure 8 having undergone the reduced pressure test procedure outlined in Example 1.

[0088] Figure 10 shows an elastomeric seal system according to an embodiment of the present invention after having undergone the test procedure outlined in Example 2.

[0089] Figure 11 shows a seal containing a prior art anti-extrusion element after having undergone the test procedure outlined in Example 2.

[0090] Figure 12 shows an elastomeric seal system according to an embodiment of the present invention after having undergone the test procedure outlined in Example 3.

[0091] Figure 13 shows the elastomeric seal system of Figure 12 before having undergone the test procedure outlined in Example 3.

[0092] Detailed Description

[0093] Figures 2A-D provide schematic sectional views of a composite member 10 according to various embodiments of the present invention. The composite member 10 comprises an elongate outer coiled spring 12 which defines an inner cavity 13. Within the inner cavity 13, is an elongate inner coiled spring 14, which itself defines an inner cavity 15. The composite member 10 further comprises an elastomeric material 16, which fills both of the inner cavities 13,15.

[0094] In Figures 2A and 2C, the elongate outer coiled spring 12 is formed from a flat tape. The use of a flat tape results in an open coil spring, where there is a series of gaps between consecutive coils with elastomeric material within each gap. The wider flatter contact area of this embodiment resulting from the use of a flat tape outer coiled spring significantly reduces the contact pressure on the sealing counterfaces and thus significantly reduces any damage caused by the interaction.

[0095] The elongate outer coiled spring 12 may also not have gaps between consecutive coils, which provides a closed coil structure.

[0096] In Figures 2A and 2B, the elongate inner coiled spring 14 shown is formed from a flat tape to provide either an open (Fig. 2A) or closed (Fig. 2B) coiled spring. However, again the skilled person would appreciate that springs formed from other materials will also be suitable, such as round wire shown in Figures 2C and 2D. In Figures 2A and 2B, the elongate outer coiled spring 12 and the elongate outer coiled spring are formed from a flat tape with a tape thickness of 0.08 mm and a tape width of 2.5 mm. The outer diameter of the elongate outer coiled spring 12 is 3.1 mm and the outer diameter of the elongate inner coiled spring 14 is 2.8 mm. In Figure 2A, the series of gaps between consecutive coils of the elongate outer coiled spring 12 are 0.15 mm wide and filled with elastomeric material 16 and the series of gaps between consecutive coils of the elongate inner coiled spring 14 are 0.225 mm wide.

[0097] In Figures 2C and 2D, the elongate outer coiled spring 12 is formed from a flat tape with a tape thickness of 0.25 mm and a tape width of 3.175 mm. The outer diameter of the elongate outer coiled spring 12 is 6mm. In Figure 2C, the series of gaps between consecutive coils are 0.2 mm wide and filled with elastomeric material 16. The elongate inner coiled spring 14 of Figures 2C and 2D is formed from a wire with a wire diameter of 0.9 mm and the series of gaps between consecutive coils are 0.225 mm wide. The elongate inner coiled spring 14 has an outer diameter of 5mm.

[0098] Figure 3 shows a schematic diagram depicted an elastomeric seal system according to embodiments of the present invention, where the elastomeric seal system is sealing a gap between two components. Figure 3A shows an elastomeric seal system 20, wherein the anti-extrusion elements 22 are integrally formed within the pressure-containing seal 24. Figure 3B shows an elastomeric seal system 20, wherein the anti-extrusion elements 22 are pre-formed and then assembled with a pre-formed pressure-containing seal 24. The clearance gap is shown by the box labelled 30 and it can be clearly seen that the antiextrusion elements are positioned to prevent contact of the seal material with the clearance gap, to reduce the risk of extrusion. There are two anti-extrusion elements present in both systems depicted in Figure 3, one at the upper end 26 and one at the lower end 28 of the pressure-containing seal 24.

[0099] It will be understood that the present invention has been described above purely by way of example, and modification of details can be made within the scope of the invention. Each feature disclosed in the description and, where appropriate, the claims and drawings may be provided independently or in any appropriate combination.

[0100] Examples Seals comprising anti-extrusion elements of the invention were constructed and tested to assess the performance properties of the anti-extrusion elements of the invention.

[0101] Example 1 - Seal Test 1

[0102] A casing seal incorporating an anti-extrusion element according to an embodiment of the present invention was tested using a modified API 6A PR2F test procedure at 103 MPa (15000 psi). The seal with the anti-extrusion element was tested with a casing having a diameter of 243 mm and a diametral clearance of 4.7 mm. The casing sealing surface had been roughened to replicate the surface on a API 5CT rough Casing.

[0103] The anti-extrusion element that was tested had a stainless steel elongate outer coiled spring and elongate inner coiled spring, and the elastomeric material was hydrogenated nitrile butadiene rubber. The elongate outer coiled spring was formed from a flat tape into an open coiled spring. The elongate inner coiled spring was formed from a round wire into an open coiled spring. The following dimensions were used:

[0104] The modified test involved three separate hour-long pressure holds at 103 MPa (15000 psi) and 149 °C under dry nitrogen gas as the test media, followed by a hold at ambient temperature and lower pressure. In between each hold, the pressure and temperature was dynamically cycled between low temperatures and pressures, as follows.

[0105] The seal completed all of the pressure holds without incident and within the criteria defined in the API 6A PR2F test procedures. Furthermore, the seal containing the anti-extrusion element according to the present invention showed an improved performance when compared to the same seal design tested with a toroidal wire spring anti-extrusion element.

[0106] Figure 4 shows the seal tested with an anti-extrusion element according to the present invention after the test. The seal demonstrated significant improvement in seal performance and also minimal loss of seal material. The recorded weight after the test showed that the seal lost only 0.4 g of elastomer, which is a 0.093% loss, a significant reduction to previous tests with commercially available anti-extrusion elements. Thus, the seal has a greater lifespan when compared to seals containing known anti-extrusion elements. This is illustrated by comparison of Figures 4 (seal and anti-extrusion element post-test) and 5 (seal and anti-extrusion element pre-test) where no substantial difference can be seen.

[0107] Figures 6 and 7, on the other hand, show a seal tested under the same conditions using a conventional commercial toroidal round wire spring anti-extrusion element. Figures 6 and 7 show the seal condition after one cycle (at 103 MPa (15000 psi) and 149 °C), afterwhich, the seal suffered a catastrophic failure. It can be seen that the seal suffered significant damage through loss of material due to extrusion of the seal material. For comparison, Figure 8 shows the same seal before testing.

[0108] T o further highlight the increased performance of seals containing anti-extrusion elements according to the present invention, a further test was performed on a seal containing a conventional commercial toroidal round wire spring anti-extrusion element. The same seal design was tested at a lower pressure of 60 MPa (10000 psi) and at a temperature of 149 °C. The seal was able to complete testing at this reduced pressure, however a significant amount of extrusion damage was present, as seen in Figure 9. Accordingly, extended use of such a seal would likely result in failure due to extrusion damage.

[0109] Example 2 - Seal Test 2 seal incorporating an anti-extrusion element according to an embodiment of the present invention was tested using a high pressure high temperature (HPHT) rig with a nominal groove axial depth of 14.7 mm and radial width of 6.29 mm. The diametral clearance gap was 0.4 mm.

[0110] The anti-extrusion element that was tested had a cobalt-chromium-nickel alloy elongate outer coiled spring and elongate inner coiled spring, and the elastomeric material was hydrogenated nitrile butadiene rubber. Both the elongate outer and inner coiled springs were formed from a flat tape into an open coiled spring. The following dimensions were used:

[0111] The test involved three separate holds at pressures of 34 MPa, 69 MPa and 103 MPa using Shell Heat transfer Oil as the test media, with a test media temperature of 150 °C and a test media pressure of 103 MPa (15000 psi). The seal was tested using the following test parameters:

[0112] Steps 1 and 2 are performed at ambient temperature conditions, i.e. » 25°C.

[0113] The seal completed all of the pressure holds without incident. Furthermore, the seal containing the anti-extrusion element according to the present invention showed an improved performance when compared to the same seal design tested with a toroidal wire spring anti-extrusion element.

[0114] Figure 10 shows the seal tested with an anti-extrusion element according to the present invention after the test. The seal demonstrated significant improvement in seal performance and also minimal loss of seal material compared with the seal using the traditional anti-extrusion element shown in Figure 11 . Thus, the seal has a greater lifespan when compared to seals containing known anti-extrusion elements.

[0115] Example 3 - Seal Test 3

[0116] A casing seal incorporating an anti-extrusion element according to an embodiment of the present invention was tested using an API 6A PR2 Annex F test procedure. The seal with the anti-extrusion element was tested with a casing having a diameter of 243 mm and a diametral clearance of 4.7 mm. The casing sealing surface had been roughened to replicate the surface on an API 5CT rough Casing.

[0117] The anti-extrusion element that was tested had a stainless steel elongate outer coiled spring and elongate inner coiled spring, and the elastomeric material was hydrogenated nitrile butadiene rubber. The elongate outer coiled spring was formed from a flat tape into an open coiled spring. The elongate inner coiled spring was formed from a round wire into an open coiled spring. The following dimensions were used:

[0118] The Test conditions were as follows:

[0119] The seal completed all of the pressure holds without incident and within the criteria defined in the API 6A PR2 Annex F test procedure. Furthermore, the seal containing the antiextrusion element according to the present invention showed an improved performance, particularly in regard to extrusion resistance when compared to the same seal design tested with a toroidal wire spring anti-extrusion element.

[0120] Figure 12 shows the seal tested with an anti-extrusion element according to the present invention after the test. The seal demonstrated significant improvement in seal performance and also no loss of seal material. The recorded weight after the test showed that the seal lost none of its elastomeric body (there was a small amount of frayed elastomer still attached as can be seen in Figure 12, a significant reduction to previous tests with commercially available anti-extrusion elements). Thus, the seal has a greater lifespan when compared to seals containing known anti-extrusion elements. This is illustrated by comparison of Figures 12 (seal and anti-extrusion element post-test) and 13 (seal and anti-extrusion element pre-test) where no substantial difference can be seen. Figures 6 and 7, on the other hand, show a seal tested under the same conditions using a conventional commercial toroidal round wire spring anti-extrusion element. Figures 6 and 7 show the seal condition after one cycle (at 103 MPa (15000 psi) and 149 °C), afterwhich, the seal suffered a catastrophic failure. It can be seen that the seal suffered significant damage through loss of material due to extrusion of the seal material. For comparison, Figure 8 shows the same seal before testing.

[0121] T o further highlight the increased performance of seals containing anti-extrusion elements according to the present invention, a further test was performed on a seal containing a conventional commercial toroidal round wire spring anti-extrusion element. The same seal design was tested at a lower pressure of 60 MPa (10000 psi) and at a temperature of 149 °C. The seal was able to complete testing at this reduced pressure, however a significant amount of extrusion damage was present, as seen in Figure 9. Accordingly, extended use of such a seal would likely result in failure due to extrusion damage.

Claims

Claims1. A composite member for use in the production of an anti-extrusion element for a pressure-containing seal, the composite comprising: an elongate outer coiled spring defining an inner cavity; an elongate inner spring; the elongate inner spring being positioned within the inner cavity of the elongate outer coiled spring; and an elastomeric material, wherein the elastomeric material fills the inner cavity of the elongate outer coiled spring; wherein the elongate outer coiled spring is formed from a flat tape.

2. A composite member according to Claim 1 , wherein the flat tape has a thickness from 0.075 mm to 2 mm, and / or wherein the tape has a width from 0.5 mm to 20 mm.

3. A composite member according to any preceding claim, wherein the elongate outer coiled spring comprises a series of gaps between consecutive coils, and preferably wherein the gap width is up to 1 .5 mm.

4. A composite member according to Claim 3, wherein the elastomeric material is present within the series of gaps between consecutive coils, and preferably wherein elastomeric material is present within each gap.

5. A composite member according to any preceding claim, wherein the elongate outer coiled spring comprises carbon steel, stainless steel, corrosion resistant alloys, aluminium alloys, copper, copper alloys, polyether ether ketone polymers, or polytetrafluoroethylene polymers, or combinations thereof.

6. A composite member according to any preceding claim, wherein the elongate inner spring comprises carbon steel, stainless steel, corrosion resistant alloys, aluminium alloys, copper, copper alloys, polyether ether ketone polymers, or polytetrafluoroethylene polymers, or combinations thereof.

7. A composite member according to any preceding claim, wherein the elongate inner spring comprises a leaf spring.

8. A composite member according to any preceding claim, wherein the elongate inner spring comprises a coiled spring defining an inner cavity, and wherein the elastomeric material fills the inner cavity of the elongate inner spring.

9. A composite member according Claim 8, wherein the elongate inner spring is formed from a flat tape, a round wire, or a square wire.

10. A composite member according to Claim 9, wherein the elongate inner spring is formed from a wire, and preferably from a wire having a diameter of from 0.3 mm to 3.5 mm.11 . A composite member according to any preceding claim, wherein the elongate inner spring has a cross-sectional outer diameter from 0.5 mm to 28 mm.

12. A composite member according to any preceding claim, wherein the elongate inner spring has an outer diameter that is from 2 % to 25 % smaller than an inner diameter of the elongate outer coiled spring.

13. A composite member according to any preceding claim, wherein the elongate inner spring and the elongate outer coiled spring are substantially axially aligned.

14. A composite member according to any preceding claim, wherein the composite member has a cross-sectional diameter of from 1 mm to 30 mm.

15. A composite member according to any preceding claim, wherein the elastomeric material comprises nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, carboxylated nitrile butadiene rubber, fluoroelastomer, perfluoroelastomer, tetrafluoroethylene propylene, silicone, fluorosilicone, chloroprene, butyl rubber, ethylene propylene diene monomer rubber, natural rubber, polyether urethane, or polyester urethane, or combinations thereof.

16. An anti-extrusion element for a pressure-containing seal comprising a composite member according to any one of Claims 1 to 15.

17. An anti-extrusion element according to Claim 16, wherein the anti-extrusionelement is formed into a continuous loop.

18. An anti-extrusion element according to Claim 17, wherein a diameter of the antiextrusion device is from 12 mm to 2500 mm.

19. An anti-extrusion element according to Claim 17 or 18, wherein a first end of the composite member is joined to a second end of the composite member to form the continuous loop.

20. An anti-extrusion element according to Claim 19, wherein the first end of the composite member is joined to a second end of the composite member using adhesive, welding, brazing or soldering.

21. An anti-extrusion element according to Claim 20, wherein the first end of the composite member is joined to a second end of the composite member using laser welding.

22. An anti-extrusion element according to any one of Claims 16 to 21 , wherein a first end of the composite member is joined to a second end of the composite member using an insert in the first and second ends of the elongate inner spring.

23. A method of manufacturing a composite member according to any one of Claims 1 to 15, the method comprising the steps of: i) providing an elongate outer coiled spring having an inner cavity; ii) providing an elongate inner spring; iii) positioning the elongate inner spring within the inner cavity of the elongate outer coiled spring; and iv) filling the inner cavity of the elongate outer coiled spring with an elastomeric material.

24. A method of manufacturing a composite member according to Claim 23, wherein the elongate inner spring is a coiled spring having an inner cavity, and wherein step iv) includes filling the inner cavity of the elongate inner spring with an elastomeric material.

25. A method of manufacturing a composite member according to Claims 23 or 24,wherein the method is performed within a mould.

26. A method of manufacturing a composite member according to any one of Claims 23 to 25, step (iv) comprises immersion of the springs into the elastomeric material.

27. A method of manufacturing a composite member according to any one of Claims 23 to 25, wherein the inner cavity of the elongate outer coiled spring is filled with the elastomeric material by injection.

28. A method of manufacturing a composite member according to any one of Claims 23 to 25, wherein in a first step the elongate inner spring is encased in an elastomeric material followed by curing of the elastomeric material, followed by a step of forming an elongate outer coiled spring around the elastomeric encased elongate inner spring.

29. A method of manufacturing an anti-extrusion element according to any one of Claims 16 to 22, the method comprising the steps of: i) providing a composite member according to any one of Claims 1 to 15; and ii) joining a first end of the composite member with a second end of the composite member to form a continuous loop.

30. A method of manufacturing an anti-extrusion element according to Claim 29, wherein step (ii) involves: a) inserting an insert into first and second ends of the elongate inner spring; and / or b) forming a join between the first and second ends of the composite member, such as first and second ends of the elongate outer coiled spring.

31. A method of manufacturing an anti-extrusion element according to Claim 30, wherein forming a join between the first and second ends of the composite member comprises using adhesive, welding, brazing or soldering, and preferably includes laser-welding.

32. A method of manufacturing an anti-extrusion element according to any one of Claims 16 to 22, wherein the method involves the step of: i) providing an elongate outer coiled spring having an inner cavity;ii) providing an elongate inner spring; iii) positioning the elongate inner spring within the inner cavity of the elongate outer coiled spring; iv) joining at least a first end of one or more of the elongate outer coiled and inner springs with a respective second of the one or more elongate outer coiled and inner springs; and v) filling the inner cavity of the elongate outer coiled spring with an elastomeric material.

33. A method of manufacturing an anti-extrusion element according to Claim 32, wherein the elongate inner spring comprises a coiled spring having an inner cavity and wherein step (v) further includes filling the inner cavity of the elongate inner spring with an elastomeric material.

34. A method of manufacturing an anti-extrusion element according to Claims 32 or 33, wherein step (iv) involves: a) inserting an insert into first and second ends of the inner cavity of the elongate inner spring; and / or b) forming a join between first and second ends of the elongate outer coiled spring.

35. A method of manufacturing an anti-extrusion element according to Claim 34, wherein forming the join comprises use of adhesive, welding, brazing or soldering, and preferably includes laser-welding36. A method of manufacturing an anti-extrusion element according to any one of Claims 32 to 35, wherein the method is performed using a mould.

37. An elastomeric seal system comprising an anti-extrusion element according to any one of Claims 16 to 22 and a pressure-containing seal.

38. An elastomeric seal system according to Claim 37, wherein the pressure-containing seal is a static seal or a dynamic seal.

39. An elastomeric seal system according to Claims 37 or 38, wherein the antiextrusion element is an integral element of the pressure-containing seal.

40. An elastomeric seal system according to Claim 39, wherein the extrusion element is pre-formed and moulded into the pressure-containing seal.

41. An elastomeric seal system according to Claim 39, wherein the extrusion element and pressure-containing seal are formed in situ.

42. An elastomeric seal system according to Claims 37 or 38, wherein the antiextrusion element is pre-formed and assembled with a pre-formed pressurecontaining seal.

43. An elastomeric seal system according to any one of Claims 37 to 42, wherein the elastomeric seal system does not comprise a fabric reinforcement.

44. Use of an anti-extrusion element according to any one of Claims 16 to 22 in combination with a pressure-containing seal.

45. Use of an anti-extrusion element according to Claim 44, wherein the use comprises withstanding pressures in excess of 10 MPa, such as in excess of 15 MPa, preferably in excess of 30 MPa, more preferably in excess of 50 MPa, most preferably in excess of 69 MPa.

46. Use of an anti-extrusion element according to Claims 44 or 45, wherein the use comprises operating at temperatures of -50°C to 320°C, for example at temperatures of 100 °C and above.

47. Use of an anti-extrusion element according to any one of Claim 44 to 46, wherein the pressure-containing seal is a static seal or a dynamic seal.

48. Use of an anti-extrusion element according to any one of Claims 44 to 47, wherein the anti-extrusion element and pressure-containing seal are positioned between a casing and a well-head of an oil or gas well.

49. Use of an anti-extrusion element according to any one of Claims 44 to 48, wherein a diametral gap to be sealed is up to 20 mm.

50. Use of an anti-extrusion element according to any one of Claims 44 to 49, whereinan axial gap to be sealed is up to 16 mm.

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