The present invention relates to a venting apparatus and method. In particular, but not exclusively, the present invention relates to a venting apparatus suitable for use in a subsea flexible pipe, for venting annulus gases out of the pipe body.

Traditionally flexible pipe is utilised to transport production fluids, such as oil and/or gas and/or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location (which may be deep underwater) to a sea level location. The pipe may have an internal diameter of typically up to around 0.6 metres (e.g. diameters may range from 0.05 m up to 0.6 m). Flexible pipe is generally formed as an assembly of a flexible pipe body and one or more end fittings. The pipe body is typically formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses that impair the pipe’s functionality over its lifetime. The pipe body is generally built up as a combined structure including polymer, and/or metallic, and/or composite layers. For example, a pipe body may include polymer and metal layers, or polymer and composite layers, or polymer, metal and composite layers. The annulus is often said to be an inner part of the multi-layer pipe, sandwiched between the internal pressure sheath and the outer sheath.

API Recommended Practice 17B provides guidelines for the design, analysis, manufacture, testing, installation, and operation of flexible pipes and flexible pipe systems for onshore, subsea and marine applications.

API Specification 17J titled“Specification for Unbonded Flexible Pipe” defines the technical requirements for safe, dimensionally and functionally interchangeable flexible pipes that are designed and manufactured to uniform standards and criteria.

Unbonded flexible pipe has been used for deep water (less than 3,300 feet (1 ,005.84 metres)) and ultra deep water (greater than 3,300 feet) developments. It is the increasing demand for oil which is causing exploration to occur at greater and greater depths where environmental factors are more extreme. For example in such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature that may lead to pipe blockage. Increased depths also increase the pressure associated with the environment in which the flexible pipe must operate. For example, a flexible pipe may be required to operate with external pressures ranging from 0.1 MPa to 30 MPa acting on the pipe. Equally, transporting oil, gas or water may well give rise to high pressures acting on the flexible pipe from within, for example with internal pressures ranging from zero to 140 MPa from bore fluid acting on the pipe. As a result the need for high levels of performance from the layers of the flexible pipe body is increased.

Flexible pipe may also be used for shallow water applications (for example less than around 500 metres depth) or even for shore (overland) applications.

The end fittings of a flexible pipe may be used for connecting segments of flexible pipe body together or for connecting them to terminal equipment such as a rigid sub-sea structures or floating facilities. As such, amongst other varied uses, flexible pipe can be used to provide a riser assembly for transporting fluids from a sub-sea flow line to a floating structure. In such a riser assembly a first segment of flexible pipe may be connected to one or more further segments of flexible pipe. Each segment of flexible pipe includes at least one end fitting. Figure 2 illustrates a riser assembly 200 suitable for transporting production fluid such as oil and/or gas and/or water from a sub-sea location 201 to a floating facility 202.

When a production fluid is conveyed through a flexible pipe, gases such as carbon dioxide and hydrogen sulphide for example can permeate the internal pressure sheath. These gases then accumulate in the pipe annulus. This may result in a corrosive environment when associated with water present in the annulus. The corrosive environment is known to lead to pipe failure due to stress corrosion cracking of the metallic pipe layers for example. It is known to construct the metallic pipe layers from complex metal alloys to mitigate the failure mode associated with the corrosive annulus gas.

A build-up of annulus gases can cause over pressurization and mechanical failure of the flexible pipe. It is known that gas venting is required to reduce the excessive build-up of permeated gases in the annulus of subsea flexible pipe. Traditionally venting occurs by creating a continuous flow path laterally through the pipe annulus to valves in the end fittings of said pipes. For a flexible riser connected to a floating platform, the gas venting system is often linked to the flaring system.

Current venting systems rely on end fittings to expel the gas; thus, a gaseous build up at a position far from an end fitting is most likely. Gaseous diffusion along a lateral venting pathway to an end fitting is slow. A corrosive environment in the annulus is created regardless of the addition of mechanical vents on an end fitting.

There is limited space on each end fitting for vents (typically three may be incorporated into each end fitting), and as such the number of vents that can be configured in a section of flexible pipe is limited. The obstruction of the vent mechanism can result in riser outer sheath failure due to over-pressurisation.

Annulus venting systems are comprised of mechanical vents (non-return valves) which rely on a gaseous build up behind the cap, said cap is opened once the pressure of the gas provides sufficient lifting force (the differential in pressure across the non-return valve seal overcomes the mechanical resistance of the spring(s) holding the seal shut). These venting systems are placed at end fittings as traditionally the flexible pipe must be integrally sealed along it’s length (by means of the sealed outer sheath layer of the pipe body), to prevent ingress of sea water into the pipe annulus where it will lead to corrosion of the reinforcing elements (armouring wires etc.). Mechanical vents allow the movement of materials in all phases.

Non-gaseous particles can build up within the vent passages, and in the mechanical vents themselves, resulting in blockages. Examples of materials which can lead to blockages include, but are not limited to, wax, oil corrosion products, and salt. Such blockages can result in pipe polymer shield (outer sheath) failure. Mechanical vents therefore often have vent monitoring systems in place to monitor for such blockages, and have some redundancy through the number of vent ports on each end fitting, however those systems cannot identify where a blockage is, just that the flow of annulus fluid has been restricted or prevented from exiting the end fitting through the valves.

FR3045770 and EP2356361 disclose flexible pipes including venting arrangements.

It is an object of the present invention at least partly mitigate the above-mentioned problems.

According to a first aspect of the present invention there is provided a venting apparatus for a subsea flexible pipe, comprising a venting conduit configured for positioning through a polymer shield layer of a flexible pipe body, the venting conduit providing a venting passage therethrough; and a vent cap provided in operable connection with the venting conduit, the vent cap for positioning on a radially outer side of the polymer shield layer, the vent cap comprising a one-way fluid valve for allowing fluid to flow in a direction from the vent passage out of the one-way fluid valve.

According to a second aspect of the present invention there is provided a method of installing a venting apparatus to a flexible pipe body, wherein the method comprises positioning a venting apparatus through the polymer shield layer of a flexible pipe body to provide a venting passage therethrough, wherein the venting apparatus comprises a venting conduit extending through the polymer shield layer, and a vent cap provided in operable connection with the venting conduit, the vent cap positioned on a radially outer side of the polymer shield layer, and wherein the vent cap comprises a one-way fluid valve for allowing fluid to flow in a direction from the vent passage out of the one-way fluid valve. Certain embodiments provide the advantage that a venting apparatus is provided that is suitable for positioning on a polymer shield layer. In this way, vents can be placed at any point along the pipe body.

Certain embodiments provide for venting apparatus that can be retrospectively fitted to a pipe body either during storage or service.

Certain embodiments reduce the chance of blockages in a flexible pipe body.

Embodiments of the invention are further described hereinafter with reference to the

accompanying drawings, in which:

Fig. 1 illustrates a flexible pipe body;

Fig. 2 illustrates a riser system;

Fig. 3 illustrates a cross section of a venting apparatus attached to a layer of flexible pipe body;

Fig. 4 illustrates a cross section of the venting apparatus of Fig. 3;

Fig. 5a illustrates a vent attached to a flexible pipe;

Fig. 5b illustrates a top view of the venting apparatus of Fig. 5a;

Fig. 6a is a top view of a venting apparatus attached to a flexible pipe;

Fig. 6b is a top view of a venting apparatus attached to a flexible pipe;

Fig. 7 illustrates a vent conduit with a self-tapping cutting edge;

Fig. 8 illustrates the venting apparatus of Fig. 4 configured to create a venting pathway;

Figs. 9a-e illustrate the method for attaching the venting apparatus to the flexible pipe body.

In the drawings like reference numerals refer to like parts.

Throughout this description, reference will be made to a flexible pipe. It will be understood that a flexible pipe is an assembly of a portion of pipe body and one or more end fittings in each of which a respective end of the pipe body is terminated. Fig. 1 illustrates how pipe body 100 is formed in accordance with an embodiment from a combination of layered materials that form a pressure-containing conduit. Although a number of particular layers are illustrated in Fig. 1 , it is to be understood that the pipe body is broadly applicable to coaxial structures including two or more layers manufactured from a variety of possible materials. For example, the pipe body may be formed from polymer layers, metallic layers, composite layers, or a combination of different materials. It is to be further noted that the layer thicknesses are shown for illustrative purposes only. As used herein, the term “composite” is used to broadly refer to a material that is formed from two or more different materials, for example a material formed from a matrix material and reinforcement fibres.

As illustrated in Fig. 1 , a pipe body includes an optional innermost carcass layer 101. The carcass provides an interlocked construction that can be used as the innermost layer to prevent, totally or partially, collapse of an internal pressure sheath 102 due to pipe decompression, external pressure, and tensile armour pressure and mechanical crushing loads. The carcass layer is often a metallic layer, formed from stainless steel, for example. The carcass layer could also be formed from composite, polymer, or other material, or a combination of materials. It will be appreciated that certain embodiments are applicable to ‘smooth bore’ operations (i.e. without a carcass layer) as well as such ‘rough bore’ applications (with a carcass layer).

The internal pressure sheath 102 acts as a fluid retaining layer and comprises a polymer layer that ensures internal fluid integrity. It is to be understood that this layer may itself comprise a number of sub-layers. It will be appreciated that when the optional carcass layer is utilised the internal pressure sheath is often referred to by those skilled in the art as a barrier layer. In operation without such a carcass (so-called smooth bore operation) the internal pressure sheath may be referred to as a liner.

An optional pressure armour layer 103 is a structural layer that increases the resistance of the flexible pipe to internal and external pressure and mechanical crushing loads. The layer also structurally supports the internal pressure sheath, and typically may be formed from an interlocked construction of wires wound with a lay angle close to 90°. The pressure armour layer is often a metallic layer, formed from carbon steel, for example. The pressure armour layer could also be formed from composite, polymer, or other material, or a combination of materials and may be bonded to the underlying internal pressure sheath 102.

The flexible pipe body also includes an optional first tensile armour layer 105 and optional second tensile armour layer 106. Each tensile armour layer is used to sustain tensile loads and internal pressure. The tensile armour layer is often formed from a plurality of wires (to impart strength to the layer) that are located over an inner layer and are helically wound along the length of the pipe at a lay angle typically between about 10° to 55°. The tensile armour layers are often counter-wound in pairs. The tensile armour layers are often metallic layers, formed from carbon steel, for example. The tensile armour layers could also be formed from composite, polymer, or other material, or a combination of materials. The flexible pipe body shown also includes optional layers of tape 104 which help contain underlying layers and to some extent prevent abrasion between adjacent layers. The tape layer may be a polymer or composite or a combination of materials.

The flexible pipe body also typically includes optional layers of insulation 107 and an outer sheath 108, which comprises a polymer layer used to protect the pipe against penetration of seawater and other external environments, corrosion, abrasion and mechanical damage.

Each flexible pipe comprises at least one portion, sometimes referred to as a segment or section of pipe body 100 together with an end fitting located at at least one end of the flexible pipe. An end fitting provides a mechanical device which forms the transition between the flexible pipe body and a connector. The different pipe layers as shown, for example, in Fig. 1 are terminated in the end fitting in such a way as to transfer the load between the flexible pipe and the connector.

Fig. 2 illustrates a riser assembly 200 suitable for transporting production fluid such as oil and/or gas and/or water from a sub-sea location 201 to a floating facility. For example, in Fig. 2 the sub-sea location 201 includes a sub-sea flow line. The flexible flow line 205 comprises a flexible pipe, wholly or in part, resting on the sea floor 204 or buried below the sea floor and used in a static application. The floating facility may be provided by a platform and/or buoy or, as illustrated in Fig. 2, a ship 200. The riser assembly 200 is provided as a flexible riser, that is to say a flexible pipe 203 connecting the ship to the sea floor installation. The flexible pipe may be in segments of flexible pipe body with connecting end fittings.

It will be appreciated that there are different types of riser, as is well-known by those skilled in the art. Embodiments may be used with any type of riser, such as a freely suspended (free, catenary riser), a riser restrained to some extent (buoys, chains), totally restrained riser or enclosed in a tube (I or J tubes).

Fig. 2 also illustrates how portions of flexible pipe can be utilised as a flow line 205 or jumper 206.

Fig. 3 shows a venting apparatus 300 positioned in a subsea flexible pipe body 350. In the arrangement shown, the venting apparatus is positioned on an outer layer of the flexible pipe body. In the pipe body shown, there is an outer polymer shield layer 352, a tensile armour layer 354, a pressure armour layer 356 and an internal pressure sheath 358. In this embodiment the internal pressure sheath is the inner layer of the flexible pipe body, which contains any fluid in the bore 360 of the tubular pipe body. The pressure armour layer 356 and the tensile armour layer 354 are formed from metallic materials. The diffused gases form a corrosive environment in the spaces within and surrounding the pressure armour layer 356 and the tensile armour layer 354; these spaces are known as the annulus region within the art.

The venting apparatus 300 includes a venting conduit 302 that is positioned through the polymer shield layer 352. The venting conduit 302 is a tube or stem that is, in this case, hollow. The venting conduit has a length that is sufficient to extend all the way through the polymer shield layer 352. The venting conduit may be formed from stainless steel, corrosion resistant alloy (e.g. nickel alloy), ceramic, or polymer composite. The venting conduit 302 may even be an open lumen formed from drilling a hole in the polymer shield layer 352.

The venting conduit 302 is at least 1 mm in diameter, however may be as large as 20mm diameter, although it is preferable to keep the size below 10mm diameter.

The venting apparatus 300 also includes a vent cap 304 positioned on the radially outer side of the polymer shield layer 352. The venting cap 304 contains a material permeable to annulus gases 306. The permeable material 306 provides a venting pathway for annulus gases to passively discharge the flexible pipe body 100. The venting cap may comprise a mesh and/or layers of hydrophobic material and/or a material comprising micro or nano passageways, to form a one-way fluid valve, allowing fluid (gas) to flow in a direction from the vent passage 302 out of the one-way fluid valve. The permeable material 306 may comprise nano-foamed ceramic materials through which there are tortuous micro- or nano passages small enough for gas to escape through but not so large as to allow liquid water through. Alternatively, the permeable material 306 may comprise aligned micro- or nano tubes, (too fine to allow liquid water through, even under pressure), the micro- or nano- tubes being glued or sintered together, or in a matrix material such as a polymer or epoxy resin. The permeable material 306 provides a diffusion gradient across the polymer shield layer 352, allowing gases to continually discharge from the annulus to the pipe exterior through the polymer shield layer 352. The flow of the gases from the bore to the annulus and then to the pipe exterior is a substantially direct path, radially outwardly from the bore.

The vent cap 304 is formed from a vent seat 308 adhered or sealed against the outer surface of the polymer shield layer 362, and a vent cover 305 extending radially outwards from the vent seat 308. The vent seat 308 includes an inner central portion and extended portions 314 _a-b extending from the inner central portion. The vent seat 308 includes a first side 31 S _{a¬ f} a seated against the polymer shield layer 352 and a second side 317 _a-b opposite to the first side and distal from the polymer shield layer 352. The vent cover 305 extends over the inner central area of the second side of the seat portion, and an outer area of the second side of the seat portion forms the extended portions of the vent seat 314 _a-b . Optionally the vent cover 305 comprises a screw thread to enable it to be attached to the valve seat 308 and seal between the two, optionally using a sealing gasket or O-ring. Additional strapping 312 can be placed over the extended portions of the vent seat 314 _a-b to help secure the vent seat 308 in position. The vent cap 304 comprises a hydrophobic material treated with fluoropolymer such as PTFE (an example of this is well known to many as Gore-Tex® - a trade-mark of W.L. Gore and Associates) to prevent sea water from entering the layers of flexible pipe body, while allowing gas out. There are other structures incorporating PTFE infused layers which are useful also for this purpose, such as described in U.S. Patent 4,194,041. The fluoropolymer is applied sometimes as nano-particles, and may be deposited using vapour deposition techniques. Other hydro-phobic materials may alternatively be incorporated, or infused into layers making up the vent cap 304; these include trimethylsilyl functionalized silica nanoparticles, cellulose, and carbon nanotubes.

Advantageously a copper or copper alloy mesh or woven fabric may be incorporated into the vent cap 304, as an outer layer, to inhibit marine life growth, and thereby prevent blockage of the vent cap from the outside or damage to layers of the vent cap from the marine organisms.

The vent cap 304 is installed on a vent seat 308 which is connected onto the outer surface of the polymer shield layer 362. The vent seat 308 is secured against the polymer shield layer 352 by seat protrusions 310. The vent seat comprises a material which may either be rigid, secured against a flattened section of the outer surface of the polymer sheath layer, or may comprise a compliant material which may be bent around the circumference of the outer sheath layer.

The seat protrusions 310 engage with the polymer shield layer 352 to a set depth forming a seal between the vent cap 304 and the outer surface of the polymer shield layer 362. The protrusions are sized to ensure that when engaged against the polymer shield layer 362 they achieve at least 5% compression into the surface of the polymer, and preferably at least 10% compression, and aptly over 12.5% compression. Compression is a measure of the reduction in thickness of the polymer shield layer resulting from the imposition of a protrusion into its outer surface. This degree of compression is intended to ensure that the seal is maintained when the polymer is acted on by the external hydrostatic head of water at great depths.

The evenly spaced undulations that extend around the venting conduit in a concentric pattern against the face of the polymer shield layer. However, the protrusions could alternatively be linear to form lines across the vent seat, or some other pattern of protrusions. The protrusions help to form a sealing engagement between the vent seat and the polymer shield layer and also help to secure the venting apparatus 300 at the location of the vent passage 302 axially and circumferentially on the pipe body. The shape of the undulations in cross-section could be V-shaped (as in Figure 3) or semi-circular, or another more complex shape, depending on the notch sensitivity of the polymer sheath material employed in the design of the pipe body 100.

Optionally, strapping 312 can be applied to the extended portions of the vent seat 314 _a-b to help securely attach the venting apparatus 300 to the outer surface of the polymer shield layer 362. The strapping may be of high strength, corrosion resistant material, such as titanium or nickel alloy, or of composite material.

The vent seat 308 may also include flange portions 320 _a-b on an outer edge, which extend radially outwardly from the extended portions of the vent seat 314 _a-b . The flange portions 320 _a-b can help to retain the optional strapping 312 in position on the vent seat 308.

Fig.4 shows the venting apparatus 300 without attachment to the flexible pipe. The vent cap 304 is located on the vent seat 308. The venting conduit 302 leads to the permeable material 306 contained in the vent cap 304. Optionally, the outer surface of the vent cap can be covered in a coating for preventing marine growth 318. The coating can be formed from copper or copper alloy (for instance phosphor bronze).

The venting apparatus 300 is manufactured as a separate entity to the flexible pipe body 100 and may be fitted to the pipe body retrospectively, for example while the pipe body is in being installed, or even when in service.

The size of the vent cap typically is in the range 15 - 35mm diameter (when circular) while the vent seat size will depend on the use or otherwise of straps 312 and the dimensions of those straps.

Fig. 5a shows an example of the venting apparatus 300 attached to an outer surface of the polymer shield layer 562 of a portion of flexible pipe body 100 with strapping 512. In this embodiment the strapping 512 extends all of the way around venting apparatus and at least partly over the vent seat (so the venting apparatus is supported around it’s circumference) and passes around the outside of the flexible pipe body. In this embodiment the strapping 512 aptly has a width greater than the width or diameter of the venting cap 304. Aptly the strapping 512 is configured with an aperture the same width or diameter as the vent cap 304 in which the vent cap protrudes radially through.

The strapping can be formed from woven composite material, or a high strength corrosion resistant alloy, such as a nickel alloy, or titanium. Fig. 5b shows the same configuration of Fig. 5a in plan view. Fig. 6a shows a plan view of a similar arrangement to that shown in Figure 5a. The strapping 612a and 612b pass either side of the vent cap and secure the vent seat 608 (which in this case is elongate and curves at least part way around the pipe body 100). The strapping 612 helps to provide a strong seal against the surface of the polymer shield layer 662.

Fig. 6b shows a similar version of the apparatus as shown in Fig. 6a but with a slightly different shaped vent seat 608 designed for another pipe size - it generally being ovoid in shape rather than circular.

Fig. 7 shows an example of the vent conduit 702 of the venting apparatus 700. The vent conduit 702 has a self-tapping edge 704. The self-tapping edge 704 is for attachment of the venting apparatus to the flexible pipe body. The self-tapping edge 704 of the vent conduit 702 allows the stem itself to form the hole in the flexible pipe body for the vent conduit 702 to sit in. The self-tapping edge forms the hole as the vent conduit 702 is screwed into position through the polymer shield layer.

The self-tapping edge 704 protrudes radially from and extends helically around the vent conduit 702. The self-tapping edge provides improved sealing between the vent conduit 702 and the polymeric shield layer. The self-tapping edge allows the vent conduit to create its own aperture (passage or hole) through the polymer shield layer, without the need for a pilot hole formation. This can result in faster installation and stronger sealing and locational securing between the vent conduit and the polymer shield layer.

The self-tapping edge effectively defines a complex path from an inner side to an outer side of the polymeric shield layer around an outer surface of the vent conduit 702. This helps to prevent fluid from entering the polymeric shield layer around the outside of the vent conduit 702. The vent conduit 702 and self-tapping edge 704 are formed from relatively strong materials, for example stainless steel or moulded polymer composite. The materials are aptly configured to withstand the force of insertion into the polymer shield layer without failure.

The self-tapping edge 702 may typically protrude around 0.2 - 1 5mm from the vent conduit 704 depending on the depth of the polymer shield layer and the material comprising it.

The self-tapping edge 704 is preformed onto the vent conduit 702 prior to the assembly of the venting apparatus 300. It will be understood the self-tapping edge and the vent conduit can be formed together as one body (i.e. integrally). Similarly, it will be understood that the vent conduit may be formed integrally with the vent seat (not shown in Fig. 7).

Fig. 8 shows a first venting apparatus 800 in fluid connection with a second venting apparatus 801 to form an extended venting pathway through a plurality of layers of flexible pipe. The first venting apparatus 800 and second venting apparatus may be substantially the same venting apparatus as those described above and are not described again for brevity.

In the arrangement shown, the first venting apparatus 800 is positioned on an outer layer of the flexible pipe body. The pipe body of this example includes, from the outermost layer to the innermost layer, an outer polymer shield layer 852, an insulation layer 851 , a second outer shield layer 853, a first tensile armour layer 854, a second tensile armour layer 866, an anti-birdcaging tape layer 855, a pressure armour layer 856, an internal pressure sheath 858, a wear layer 862 and a carcass layer 864.

The first venting apparatus 800 and second venting apparatus 801 form an extended venting pathway for gases to passively diffuse from the annulus region to the exterior of the flexible pipe body. The second venting apparatus 801 is positioned internally within the pipe providing a venting pathway across the second outer shield layer 853 to the insulation layer 851. The difference between the apparatus 800 and the apparatus 801 may be that the thickness of the apparatus 801 may be reduced both because there is less space for the apparatus in the insulation layer 851 , and also because during normal operation sea water at the external hydrostatic pressure will not act directly on the outside of the apparatus, so fewer layer are required in the design of the vent.

Figs. 9a-e show the installation of a venting apparatus 900 through a polymer shield layer 952 of flexible pipe body.

Prior to positioning the venting apparatus 900 through the polymer shield layer 952, the thickness A of the polymer shield layer is determined. The thickness A is measured by means of calibrated ultrasound measurement (UT). The vent passage 902 is then shortened to a length equating to the outer sheath 952 thickness A.

The venting apparatus 900 is positioned through the polymer shield layer 952 of a flexible pipe body to provide a venting passage from the annulus of the flexible pipe body to the exterior of the flexible pipe body. The venting passage allows for the passive discharge of annulus gases from the annulus layers of the flexible pipe body.

The venting apparatus 900 includes a vent conduit 902. The vent conduit 902 has a length approximately equal to the thickness of the polymer shield layer 952. In other words, the vent conduit 902 extends through the polymer shield layer 952 and is of sufficient length to pass through the polymer shield layer without extending into the next radially inner layer.

Positioned in operable connection with the vent conduit 902 is a vent cap 904. The vent cap 904 is positioned on a radially outer side of the polymer shield layer 952. The vent cap 904 is formed from a one-way fluid valve for allowing fluid to flow in a direction from the vent passage out of the one-way fluid valve, for example to the outside of the flexible pipe body or towards a radially outer layer of the pipe body.

In this example, once the thickness A of the polymer shield layer 952 has been determined, a pilot hole 950 is formed through the polymeric shield layer 952. The pilot hole 950 is drilled to the thickness A of the polymer shield layer such that the pilot hole 950 extends through the entire thickness of the polymer shield layer 952. The pilot hole 950 is configured to have a diameter substantially equal to the vent conduit 902 to provide a tight sealing between the vent conduit 902 and the walls of the pilot hole 950. The tight sealing helps to prevent fluid from the exterior of the pipe body entering the layers of pipe body. As such, the integrity of the outer sheath is maintained.

In another example, similar to that described in Fig. 7, the vent conduit 902 may include a self-tapping edge mitigating the need for a pilot hole. As such, the vent conduit 902 may act as the drilling apparatus due to a self-tapping edge. The self-tapping edge helps to increase the sealing ability between the vent conduit 902 and the polymer shield layer 952.

The venting apparatus 900 is fitted retrospectively to the polymer shield layer 952 (i.e. after the polymer shield layer 952 is formed). In this example, the vent conduit 902 is positioned through the pilot hole 950 (or, in an example having a self-tapping edge, the vent conduit 902 is screwed directly into the polymer shield layer 952). In this example having a pilot hole, the venting apparatus 900 is screwed into the pilot hole 950. Adhesive may be applied to the surface of the polymer shield layer 962 which contacts the underside of the venting apparatus 964. Suitable adhesives may include silicone based sealants, acrylates, polyurethanes, or epoxy resin, but selection will depend on the compatibility and suitability of each with the materials of the polymer sheath layer, the vent seat and the vent conduit.

Once the vent conduit 902 is fully inserted in the pilot hole 950 or the self-tapping vent conduit 902 is fully screwed into the polymer shield layer, the venting apparatus 900 is in close contact with the outer surface of the polymer shield layer 962. A vent seat 908 forms close contact between the venting apparatus 900 and the outer surface of the polymer shield layer 962. The vent seat 908 includes at least one seat protrusion 910 for engaging and sealing against the polymer shield layer 952 when the venting apparatus 900 is in position. The at least one seat protrusion 910 extends into the outer surface of the polymer shield layer 962, thereby helping to grip the polymer shield layer 962.

An optional further step (not shown in Fig. 9) is to attach strapping to the seat portion 908 of the vent apparatus 900. The seat portion 908 is strapped to the polymer shield layer 952 the strapping helps to hold the vent seat 908 and the outer surface of the polymer shield layer 962 in close connection providing a secure attachment of the venting apparatus 900 to the pipe body.

The vent seat portion 908 and vent cover portion 904 form an enclosed space in fluid communication with the vent conduit 902. The enclosed space includes a permeable material to provide a continuous venting pathway for annulus gases to discharge from the flexible pipe. The vent cap 904 is formed from a hydrophobic material which prevents water from entering the annulus from the outside of the pipe body via the vent passage 902.

The vent seat portion 908 may be curved to correspond to the curve of the outer surface of the polymer shield layer 962. In another example, the valve seat portion 908 may be substantially flat and a corresponding substantially flat area can be formed on the surface of the polymer shield layer 962, by sanding the area for example.

Optionally, the vent cap is coated with a layer of material for preventing marine growth. In this example the material for preventing marine growth comprises phosphor bronze. This can help to reduce blocking of the vent cap by external marine growth.

Various modifications to the detailed arrangements as described above are possible. For example, while the venting conduit has been described as hollow, it could have gas permeable material provided within the conduit.

Whilst the coating for preventing marine growth has been described as covering the whole vent cap, the coating may partially cover the vent cap or may cover a plurality of parts of the vent cap.

The additional strapping may be used to attach a plurality of venting apparatus to the flexible pipe body.

The vent may be attached through any pipe body layer and is not limited to polymeric sealing sheaths.

The venting apparatus may be attached to the polymer shield layer without formation of a pilot hole, the self-tapping edge penetrates the polymer shield layer as the venting apparatus is driven into place. As such, the venting conduit forms a hole as it is inserted to the polymer shield layer.

The vent conduit may be slightly larger diameter at the outer surface of the polymer shield layer than at the inner surface of the polymer shield layer, in order to both assist the insertion of the tapped vent conduit, and to increase the lateral compression into the polymer shield layer near the outer surface of the polymer shield layer, improving sealing. This makes the vent conduit slightly conical in shape. The venting apparatus may not be screwed into position but inserted in some other manner.

Throughout the drawings and description, the venting apparatus has been described as predominantly circular or ovoid in shape, it will be understood that the venting apparatus may be of any shape suitable for use as a venting apparatus, for example square or rectangular in nature.

As shown in Fig. 8 a plurality of venting apparatus can be positioned in line across multiple layers, however the venting apparatus may not be directly in line but may be spaced apart circumferentially and/or longitudinally along the pipe body.

Adhesive may be placed on the underside of the venting apparatus for contact with the outer surface of the polymer shield layer. Adhesive may alternatively be placed on both the outer surface of the polymer shield layer and the underside of the venting apparatus.

With the above-described arrangement the continuous discharge of annulus gases reduces or mitigates the need for vent monitoring systems. Multiple venting apparatus can be placed along the pipe body such that a blockage in one venting apparatus will not cause pipe failure. The venting apparatus allows constant diffusion of gases from the pipe annulus and therefore reduces pressure build up in the annulus, which could cause pipe failure.

The above-described arrangement provides the advantage that the venting of annulus gases is a continuous and a passive process. This means there is very little build-up of gases in the annulus reducing the risk of a corrosive environment forming in the pipe annulus. By reducing the corrosiveness of the annulus region, the risk of stress corrosion cracking is diminished. The venting of the annulus gas further provides the advantage that the operable lifetime of the flexible pipe is increased.

With the above-described arrangement, the venting apparatus can be attached at any point along the pipe body. The venting apparatus of the above described arrangement can be fitted to the flexible pipe body retrospectively, either in service or in storage. The venting apparatus can therefore be fitted to existing pipelines.

The venting apparatus could be used in combination with known end fitting apparatus, for example at points along the flexible pipe body where an annulus gas build-up is common or at regions far from an end fitting having a known venting apparatus.

This provides the advantage that multiple vents can be placed along the pipe body to result in multiple venting points. The multiple venting points reduce the distance the annulus gas must travel to be discharged to the pipe exterior. Thus, reducing the overall volume of gases within the annulus region and thereby also reducing the corrosion in the annulus region and extending the lifetime of the pipe. The venting apparatus of the above-described arrangement provides a further advantage that the vent could be fitted to a portion of flexible pipe body that is susceptible to a build-up of annulus gases and as such reduces the need for replacement of an entire section of flexible pipe body.

The placement of multiple vents along the pipe body provides the advantage that the risk of over pressurization caused by a build-up of annulus gases is greatly reduced. That is, if one vent becomes blocked the gases can travel a short distance through the annulus to an alternative vent to be discharged. Furthermore, the placement of vents is not limited to a small area of the flexible pipe such as an end-fitting. Therefore, a large number of vents may be attached to the pipe body if required.

The above-described arrangement provides the advantage that as the venting apparatus can be attached anywhere along the length of flexible pipe body, the flexible pipe body length is not limited by requirement of venting annulus gas at an end fitting.

The vent seat projections and vent conduit self-tapping cutting edge of the above-described arrangement provide the advantage of a tight seal between the perforated layer and the venting apparatus reducing the risk of leaking and maintaining structural integrity of the flexible pipe.

A further advantage of the above described arrangement is that the venting pathway is significantly shorter than vents placed at an end fitting. A shorter venting pathway allows for faster venting of the annulus gases and as such there is less time for an annulus gas to corrosively attack the armouring wires within the pipe body annulus.

A further advantage of the above described arrangement is that the reduction in the corrosive environment means the formation of metallic layers from expensive corrosion resistant metal alloys is not required.

Previously, it had been thought that to discharge gas from the annulus directly to the pipe exterior was not possible without weakening the integrity of the flexible pipe. Previously the perforation of an outer sheath has been avoided as a perforation would allow water to travel in and/or out of the vent. The above described apparatus negates these problems.

It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be applicable interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention. Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean“including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.