The present invention relates to a monitoring apparatus and method. In particular, but not exclusively, the present invention relates to the monitoring of strain or load in a flexible riser installation for transporting production fluids such as oil and gas.

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, say 1000 metres or more) to a sea level location. The pipe may have an internal diameter of typically up to around 0.6 metres. 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 metallic and polymer layers.

A flexible pipe is an assembly of a portion of a 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 may be formed from a combination of layered materials that form a pressure- containing conduit. Although a number of particular layers are illustrated in Fig. 1 , pipe body structures may include two or more coaxial layers manufactured from a variety of possible materials. For example, the pipe body may be formed from metallic layers, composite layers, or a combination of different materials. The layer thicknesses are shown for illustrative purposes only.

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. Pipe body may be used without a carcass layer (i.e. smooth bore) or with a carcass (rough bore). 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 (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 as 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.

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 metallic 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 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. 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. A 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. 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.

A cross-section of a known end fitting 300, such as disclosed in WO2007/144552 or EP1867907, is shown in Figure 3. The end fitting 300 includes an end fitting body 301 , which includes an internal bore 302 running along its length, and a jacket or casing 305, which is secured via one or more bolt or other such securing mechanism to the end fitting body. The jacket acts as a housing and is sealed to the outer sheath 108 of the flexible pipe body via an outer sealing ring 309. The end fitting body is made from steel or other such rigid material. At a first end of the end fitting body 301 there is defined an open mouth region 303 into which an end of a segment of flexible pipe body 100 is located and then terminated. At a further end of the end fitting body 301 is a connector 304. This is formed as a substantially disk-like flared region on the end fitting body. The connector can be connected directly to a matching connector of a further end fitting body of an adjacent segment of flexible pipe. This can be done using bolts or some other form of securing mechanism. In such a configuration the end fittings would be located in a back-to-back configuration. This may be termed an intermediate connection or midline connection. Alternatively the connector 304 may be connected to a floating or stationary structure such as a ship, platform or other such structure. This may be termed the top connection or hang off point, and the end fitting would have a hang off assembly added to enable the pipe to structurally locate at the moon pool of the vessel, or equivalent position on a platform, etc. As used herein, the term end fitting assembly is used to describe either an end fitting or an end fitting plus any ancillary components such as a hang off. Various layers of flexible pipe body are introduced to the end fitting assembly, cut to appropriate length, and sealingly engaged with a particular portion of the end fitting. An end fitting assembly may form part of either a top connection (hang off point) or a midline connection.

In use, an end fitting assembly is subject to various forces including high tension and compressions loads, for example. These forces can be due to environmental factors including temperature and pressure fluctuations and underwater currents. The weight of a flexible pipe terminated in an end fitting can also cause increased stresses and strains in the end fitting assembly.

Throughout the lifetime of a riser installation, many of the structural components and ancillary equipment (such as the hang off) included in the riser can experience high levels of stress and strain. This is particularly so at the region of the top connection (including the area under a bend stiffener), which experiences high tension due to the weight of the riser, but also occurs lower down a riser assembly particularly at points where the riser is freely suspended. In order to monitor such stresses and strains, numerical analysis and experimental tests may be performed on the components. Such analysis and testing is both time consuming and difficult and does not provide real time data. Because of this, the flexible pipe may be overly conservative in the structural features to ensure adequate strength and safety, which itself adds further weight and cost to the assembly.

WO 2009/109745 discloses a fatigue monitoring system adapted to be fit onto a flexible pipe system having a bend stiffener, and having instrumentation to monitor fatigue close to the bend stiffener. The fatigue monitoring system is operable to determine pipe fatigue near the bend stiffener during use. The system comprises a composite sleeve that is clamped onto the flexible pipe and as such the sleeve itself could cause extra stress on the pipe.

According to a first aspect of the present invention there is provided an apparatus for monitoring strain in a flexible riser, comprising at least one sensor for measuring a mechanical parameter of the flexible riser, the at least one sensor operably connected to an end fitting assembly of the flexible riser and arranged to provide data corresponding to the parameter to a data acquisition system. According to a second aspect of the present invention there is provided a method for measuring strain in a flexible riser, comprising operably connecting at least one sensor for measuring a mechanical parameter of the flexible riser to an end fitting assembly of the flexible riser, and providing data corresponding to the parameter to a data acquisition system.

According to a third aspect of the present invention there is provided an apparatus substantially as herein described with reference to the drawings.

According to a fourth aspect of the present invention there is provided a method substantially as herein described with reference to the drawings.

Certain embodiments of the invention provide the advantage that real time monitoring of particular areas of a flexible pipe may be provided. Certain embodiments provide the advantage that data may be generated that is representative of actual field data, enabling a reduction in conservatism in the design of pipe layers for controlling tension, and thus enabling lighter and more cost effective pipe structures to be designed.

Certain embodiments of the invention provide the advantage that tension monitoring at and/or in an end fitting assembly can be provided.

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 assembly;

Fig. 3 illustrates an end fitting;

Fig. 4 illustrates a perspective view of a known hang off;

Fig. 5 illustrates a cross section of a known hang off;

Fig. 6 illustrates a cross section of a hang off;

Fig. 7 illustrates a perspective view of the hang off of Fig. 6; Fig. 8 illustrates a cross section of another hang off;

Fig. 9 illustrates a perspective view of the hang off of Fig. 8;

Fig. 10 illustrates a perspective view of a hang off;

Fig. 1 1 illustrates an enlarged view of a portion of Fig. 10;

Fig. 12 illustrates a cross sectional view of the hang off of Fig. 10 attached to an end fitting;

Fig. 13 illustrates an enlarged view of a portion of Fig. 12;

Fig. 14 illustrates a cross sectional view of an intermediate connector;

Fig. 15 illustrates an enlarged view of a portion of Fig. 14;

Fig. 16 illustrates a cross sectional view of another intermediate connector;

Fig. 17 illustrates a cross sectional view of another intermediate connector; and Fig. 18 illustrates a cut away view of the connector of Fig. 17.

In the drawings like reference numerals refer to like parts.

In view of the above-mentioned problems relating to the measuring of tension loads in a flexible pipe, the present inventors have used various structural portions of a riser itself, to provide real-time measurements representative of tension in the flexible pipe, heretofore previously only used as purely mechanical components of the pipe.

When an end fitting is used at the end of a flexible pipe for connection to a floating facility, a "hang off" assembly is attached to the end fitting 300. The assembly includes an annular hang off collar, which is often formed from two sections that bolt together around the end fitting and provide a widened mechanical flange around the circumference of the pipe to sit over or be fastened to a moon pool of a ship or an opening in a platform, for example. A hang off assembly is shown in Fig. 4, and a cross-sectional view is illustrated in Fig. 5. Fig. 5 shows a flexible pipe body 100 connected to an end fitting 300 and a hang off 400 attached to the end fitting body. The hang off includes a hang off body 402 and a hang off collar 404. In a first embodiment of the present invention, a plurality of recesses or cavities 602 are formed in the base 604 of a hang off assembly 600, as shown in Figs. 6 and 7. The hang off assembly 600 is shown attached to an end fitting 606. The hang off base 604 is the lower section of the hang off, and in use the lower surface of the hang off base would contact (sit on) the floating facility, in this case a platform.

One or more of the plurality of recesses 602 houses a compressive load washer sensor 608. In this case 4 sensors are housed within the hang off at equally spaced locations. Compressive load washer sensors are themselves known, and will not be described here in detail. Each sensor 608 has an accompanying cable 610 enabling data acquisition from the sensor to a data acquisition system (not shown). The sensor 608 acts as a compressive load cell, and is located at the junction between the hang off and the platform. As such, the sensor can monitor the tension load that is applied to the hang off. The sensor can also feed real time data to the data acquisition system about the tension loads experienced whilst the riser is in use.

It will be appreciated that the sensor 608 is external to the end fitting. In use the sensor 608 is positioned in the recess 602 on the surface of the hang off assembly and is adjacent to the surface of the floating facility.

To help balance the hang off loads equally, the remainder of the recesses 602 that are not housing a sensor are each filled with a dummy washer. Figs. 6 and 7 also show a plurality of bolts 612 for securing the hang off 600 to the platform.

Figs. 8 and 9 illustrate another embodiment of the present invention. A hang off 800 includes a hang off body 802, and is attached to an end fitting 806. As shown in Fig. 9, in a recessed surface 804 of the hang off body 802, a strain gauge sensor 808 is affixed to the surface 804 of the hang off body.

The sensor 808 is therefore arranged such that it is located on an external surface of the end fitting assembly. With this arrangement the sensor may easily be incorporated into a preinstalled hang off body and will require minimal changes to the existing manufacturing process. Strain gauges are themselves known, and will not be described here in detail. The sensor 808 has an accompanying cable 810 enabling data acquisition from the sensor to a data acquisition system (not shown). The sensor 808 acts to measure local deformation at the position where affixed to the surface of the hang off body. As such, the sensor can monitor the tension load at that point of the hang off. The sensor can also feed real time data to the data acquisition system about the tension load experienced whilst the riser is in use.

Figs. 10 to 13 illustrate yet another embodiment of the present invention. Fig. 10 shows a perspective view of a hang off 1000. Fig. 12 shows a cross section of the hang off 1000 attached to an end fitting 1006. As shown in the enlarged view of Fig. 13, the hang off has a recess 1002 formed on its internal surface 1004. In the recess, a split collar insert 1010 is located. The recess is aptly provided at a location adjacent a joining portion of the hang off, so as to ensure minimal alterations to the machining of the hang off. The recess is also aptly provided to meet an inner shoulder region 1016 of the hang off. On a surface of the insert 1010, in this case a vertical surface (in the orientation shown), there are provided six strain gauges 1008 at equal spacing around the circumference of the hang off. Each strain gauge is provided adjacent a longitudinal cavity 1012 extending from the radially inner surface to the radially outer surface of the hang off. A sensor cable 1014 connects each strain gauge 1008 to a data acquisition system (not shown). Alternatively, compressive load sensors may be utilised, on a horizontal surface of the collar insert (in the orientation shown).

The sensors 1008 are provided in the inner shoulder region 1016 of the hang off. This inner shoulder region will receive a relatively large amount of compressional loading due to the weight of the end fitting and flexible pipe body hanging therefrom.

The sensors 1008 can be operable to act as a compressive load cell for measuring the loads at the inner shoulder region of the hang off. The sensors can also feed real time data to the data acquisition system about the tension loads experienced whilst the riser is in use.

A further embodiment of the present invention is illustrated in the cross sectional view of Figs. 14 and 15. Rather than the hang off assembly being used to incorporate sensors, here an intermediate connection 1400 is employed. Fig. 14 shows two end fittings 1402, 1404 in a back-to-back configuration. It is known to use fasteners such as bolts to attach connector flanges of end fittings together. In this embodiment, two fasteners 1406 have been adapted to include a strain gauge 1408 applied to the outer surface of the fastener, so as to be located within the body of the end fitting upon assembly.

The connector flange 1410 has also been adapted to provide a narrow channel 1412 within which can run a cable 1414 to connect the sensor 1408 to a data acquisition system (not shown). This is shown in the enlarged view of Fig. 15. The cable may be provided in a protected housing (not shown) to prevent damage to the cable, as it is likely to run from an intermediate connector of a riser to the surface.

This embodiment enables the acquisition of the tensile loads being applied to the flexible pipe intermediate connector in real time. In addition, the arrangement may be used to detect leakage from the flexible pipe. This is because, leakage from a pipe is likely to cause a noticeable change in strain. Thus, if the 'normal' load is known (within a set range), the sensors 1408 can be used to indicate a change in load, which indicates a possible leak situation. The data acquisition system may be linked with an alarm or other indicator.

A further embodiment of the invention is shown in Fig. 16, in which four strain gauges 1608 are attached to the outer surface of an end fitting body 1602. Each sensor 1608 has an accompanying cable 1614 enabling data acquisition from the sensor to a data acquisition system (not shown). The sensor 1608 acts to measure local deformation at the position where affixed to the surface of the end fitting body. As such, the sensor can monitor the tension load at that point of the end fitting. The sensor can also feed real time data to the data acquisition system about the tension load experienced whilst the riser is in use.

Since the strain gauges 1608 are located on an outer surface of the flexible pipe, a protective housing 1616 is attached to the end fitting body so as to cover the strain gauge. The housing is a polymeric cover that is clamped or strapped around the end fitting in this example. As such, the sensors 1608 are considered external to the end fitting assembly.

Figs. 17 and 18 illustrate a further embodiment of the present invention. As mentioned above, it is known to use fasteners such as bolts to attach connector flanges of end fittings together. The fasteners are usually accompanied by a washer on either side of the connector flange to help prevent wear between the bolt head and the connector flange. In this embodiment, four washers of an end fitting 1702 are replaced with four compressive load washer sensors 1708 respectively. The sensors have an accompanying data cable 1714 for sending real time data to a data acquisition system.

The sensors 1708 are external to the end fitting 1702. The sensors 1708 can easily replace existing washers and therefore require minimal alteration to the current manufacturing processes.

In a similar manner to the sensors 608 described above, data can be gathered to measure the compression loading at the area of the sensors 1706. With a predetermined number of fasteners 1706, the remaining fasteners without compressive load washer sensor can each have a dummy washer.

In addition, the arrangement may be used to detect leakage from the flexible pipe. This is because, leakage from a pipe is likely to cause a noticeable change in strain. Thus, if the 'normal' load is known, the sensors 1708 can be used to indicate a change in load, which indicates a possible leak situation. The data acquisition system may be linked with an alarm or other indicator.

Various modifications to the detailed designs as described above are possible. For example, although the above embodiments have been described with one, two, four or six sensors for reading compression or tension loads, any number of sensors may be used. Aptly, the sensors are spaced approximately equal distances around the circumference of the pipe. Of course additional sensors will produce further information, though one sensor may be sufficient in some circumstances. Aptly, four sensors each at 90 degrees give readings from four sides of the pipe, which may be useful if the pipe is bending for example. Whilst separate embodiments have been described above, any or all of the embodiments may be used in combination.

Although the embodiment of Fig. 16 describes a polymeric cover, the housing could be of any suitable material, such as a metallic cover that is welded to the end fitting, for example. Although the embodiments described above illustrate the sensors to be located at various particular locations on the end fitting assembly, the sensors may be located at other specific locations on the end fitting assembly to suit the requirements of a particular project.

In many of the above-described embodiments, a sensor is provided on an external portion of an end fitting assembly. As used herein, the term 'external' should be understood as having a broad interpretation, for example including the sensors being: provided on an external surface, used with at least partly external fasteners, or embedded in a cavity on an external surface.

The apparatus of above described embodiments act to monitor tension in an end fitting assembly. Each embodiment measures tension in the end fitting assembly at the position of the sensor and can feed real time data to a data acquisition system about the tension loads experienced whilst the riser is in use, and the variations of these at different circumferential locations around the flexible pipe.

With the present invention, a sensor may be provided on and/or in an end fitting assembly.

With the present invention, a sensor may be configured to measure strain and/or load in an end fitting assembly.

With the above-described invention apparatus for monitoring strain is provided within structural components of a flexible riser installation. Minimal alteration to the structural components is necessary, making the invention cost effective and effective to install. The arrangements monitor real time active compressive and tensile loads that are applied to structural components of the riser installation during field service. The data acquired may be used to calculate the tensile and compressive forces occurring at the specific points on the riser installation. That is, data representative of the load experienced may be fed via a cable or electrical connection to a data acquisition device. Then, the data may be used to calculate the strain at the location of the sensor. Aptly, the strain monitoring sensors can be calibrated before the riser assembly is deployed.

By capturing real time data of stress, compression, and/or strain occurring within a flexible pipe, this will enable a more accurate picture to be built up. Future flexible pipe designs may then be made with a higher accuracy of the strength of materials required to tolerate the loads, which will inevitably allow a less conservative approach to the amount of material required.

In addition, the data may be used to calculate the top angle, i.e. the angle at which the riser lies off vertical at the hang off area, by monitoring the differences in strain at various circumferential locations.

The data may also be used to detect the presence of a possible leak by comparison of strain to previous measurements, with an anomaly of predetermined amount as an indicator of a possible leak.

The data may then be used to calculate further information such as fatigue loading on the flexible pipe.

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.