Pipeline apparatus and method of monitoring a pipe

Abstract

There is provided a pipeline apparatus (300) to transport production fluids, such as oil, gas or water. The apparatus (300) comprises a flexible pipe (302) comprising first and second body sections (304), (306). First and second pairs (324), (328) of electrically conductive members extend at least partially along the lengths of the first and second pipe body sections (304), (306), respectively. The electrically conductive members in each pair (324), (328) are electrically isolated from one another. The apparatus (300) comprises first and the second sets of leads (332), (334) connected to the first and second pairs (324), (328) of electrically conductive members, respectively, such that the impedance of the first pair (324) of electrically conductive members and the impedance of the second pair (328) of electrically conductive members are independently measurable via the first and second sets of leads (332), (334). There is also provided a further pipeline apparatus and methods of monitoring a pipe.

Description

[0001] PIPELINE APPARATUS AND METHOD OF MONITORING A PIPE

[0002] The present invention relates to a pipeline apparatuses and methods for monitoring a pipe. In particular, but not exclusively, the present invention relates to detecting defects in a Pipe.

[0003] Traditionally, a 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.

[0004] 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.

[0005] Regardless of measures taken to improve the performance of layers within a pipe, there remains a risk of defects arising within the pipe. A defect may comprise damage to an outer wall of a flexible pipe body resulting in the ingress of seawater into an annulus within the pipe body such that seawater fills voids between the armouring elements, such as wires or ligaments, and other structural elements of the pipe. Armouring elements are typically manufactured from steel or other metallic materials, which are vulnerable to accelerated corrosion upon contact with seawater. If such a defect is not detected promptly then the structural integrity of the pipe body can be compromised.

[0006] Certain embodiments of the invention provide the advantage that a defect within a pipe body can be detected without requiring periodic visual inspection and the defects may be monitored over time. Defects can then be repaired, or the pipe body replaced.

[0007] According to an aspect of the invention there is provided a pipeline apparatus comprising: a pipe comprising: a first pipe body section, a second pipe body section and an end fitting connected to a first end of the first pipe body section; wherein the second pipe body section is coupled to a second end of the first pipe body section; a first pair of electrically conductive members extending at least partially along the length of the first pipe body section, wherein the first pair of electrically conductive members are electrically isolated from one another; a second pair of electrically conductive members extending at least partially along the length of the second pipe body section, wherein the second pair of electrically conductive members are electrically isolated from one another; and a first set of leads for a measurement of impedance of the first pair of electrically conductive members and a second set of leads for a measurement of impedance of the second pair of electrically conductive members, wherein the first and the second sets of leads are connected to the first and second pairs of electrically conductive members, respectively, such that the impedance of the first pair of electrically conductive members and the impedance of the second pair of electrically conductive members are independently measurable via the first and second sets of leads.

[0008] The first and second sets of leads allow independent impedance measurements to made in the first and second pipe sections, his is advantageous because if a breach occurs in the first pipe body section, this does not affect the monitoring of the second pipe body section.

[0009] The first and second set of leads may each extend from the end fitting to the first and second pairs of electrically conductive members, respectively.

[0010] The pipeline apparatus may comprise a cable extending from the end fitting to the second pipe body section. The cable comprise the first and second sets of leads and being configured to deliver the first set of leads to the first pair of electrically conductive members and to deliver the second set of leads to second first pair of electrically conductive members.

[0011] The pipeline apparatus may comprise an impedance monitor. The pipeline apparatus may comprise the impedance monitor arranged to measure or determine the impedance of the first pair of electrically conductive members via the first set of leads and to measure or determine the impedance of the second pair of electrically conductive members vis the second set of leads.

[0012] The first and second sets of leads may extend from the end fitting to the impedance monitor.

[0013] The pipeline apparatus may comprise a processor configured to determine if the impedance between each pair of electrically conductive members is indicative of a defect in the pipe body section. A defect may be indicated by a reduction in the impedance. A short circuit between a pair of electrically conductive members indicates a defect whereas an open circuit between the members indicates there is no defect.

[0014] Each of the first and second sets of leads may each comprise a pair of current force leads and a pair of voltage sense leads. One of the current force leads and one of the force sense leads may be connected to each of the respective pair of electrically conductive members.

[0015] The impedance monitor may comprise a current source configured to apply an alternating current to the pairs of current force leads and a voltage monitor configured to measure a voltage between the pairs of voltage sense leads such that impedance monitor is configured to measure impedance by four terminal sensing.

[0016] In certain embodiments, the pipe may be a flexible pipe.

[0017] The first and second pipe body sections may each comprise a polymer fluid barrier surrounding at least one pair of tensile armour layers. Each tensile armour layer may comprise a plurality of helical armouring elements.

[0018] The plurality of helical armouring elements may be a plurality of helically wound steel ligaments or wires.

[0019] One of the tensile armour layers in the first pipe body section may comprise the first pair of electrically conductive members and one of the tensile armour layers in the second pipe body section comprises the second pair of electrically conductive members. That is, each of the electrically conductive members may be a helical armouring element. According to an aspect of the invention, there is provided a method for monitoring a flexible pipe, the method comprising: providing the above-described pipeline apparatus; connecting an impedance monitor to the first pair of electrically conductive members and measuring the impedance between the first pair of electrically conductive members; and connecting the impedance monitor to the second pair of electrically conductive members and measuring the impedance between the second pair of electrically conductive members.

[0020] The method may comprise sequentially connecting the impedance monitor to the first and second pairs of electrically conductive members.

[0021] The method may comprise determining if the impedance is indicative of a defect in the first or second pipe body section.

[0022] According to an aspect of the invention, there is provided a pipeline apparatus comprising: a flexible pipe comprising: a pipe body section; a pair of electrically conductive members extending at least partially along the length of the pipe body section, wherein the pair of electrically conductive members are electrically isolated from one another; and a pair of current force leads and a pair of voltage sense leads connected to the pair of electrically conductive members such that one of the current force leads and one of the force sense leads is connected to each electrically conductive member; and an impedance monitor connectable to the current force leads and the voltage sense leads, the impedance monitor comprising a current source to provide an alternating current to the current force leads and a voltage monitor arranged to monitor the voltage between the voltage sense leads such that the impedance monitor is configured to measure the impedance between the pair of electrically conductive members by four terminal sensing.

[0023] Using four terminal sensing to measure the impedance may advantageously improve the accuracy of the impedance measurement. The measured impedance is independent of the impedance of the leads when the impedance is measured using four terminal sensing. This is particularly advantageous when measuring the impedance of a pipe body section that is a large distance from the impedance monitor.

[0024] The impedance monitor may comprise an energy limiter, the energy limiter comprising: a first circuit connectable between the pair of current force leads and the current source, at least one Zener diode arranged in parallel with the current source and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members; and a second circuit connectable between the pair of voltage sense leads and the voltage monitor, at least one Zener diode arranged in parallel with the voltage monitor and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members.

[0025] The first circuit may comprise a fuse arranged on either side of the current source, between the current source and the at least one Zener diode.

[0026] The second circuit may comprise a fuse arranged on either side of the voltage monitor, between the voltage monitor and the at least one Zener diode.

[0027] The resistors in the first circuit may each have a resistance of between 5 and 20 ohms.

[0028] The resistors in the second circuit may each have a resistance of between 75 and 200 ohms.

[0029] In each of the first and second circuits the at least one Zener diode may comprise a pair of Zener diodes arranged in series with each other and facing in opposite directions.

[0030] The pipeline apparatus may comprise processor configured to determine if the impedance measured between the pair of electrically conductive members is indicative of a defect in the pipe body section.

[0031] Optionally, the current source may be configured to provide an alternating current at a plurality of frequencies between 10 Hz and 100 kHz.

[0032] The pipe body section may comprise a polymer fluid barrier surrounding at least one pair of tensile armour layers. Each tensile armour layer may comprise a plurality of helical armouring element.

[0033] Optionally, one of the tensile armour layers in the pipe body section may comprise the pair of electrically conductive members. The plurality of helical armouring elements may be a plurality of helically wound steel ligaments or wires.

[0034] According to an aspect of the invention there is provided a method for detecting defects within a flexible pipe. The method comprising: coupling an impedance monitor to a pair of current force leads and a pair of voltage sense leads of a pipe body section of a flexible pipe, wherein the pair of current force leads and the pair of voltage sense leads are connected to a pair of electrically conductive members extending at least partially along the length of the pipe body section; generating an test current at the impedance monitor and applying the test current to the current force leads; measuring at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current; determining the impedance of the electrically conductive members based on the measured voltage and the test current; and determining if the impedance is indicative of a defect in the pipe body section.

[0035] The method may comprise: applying the test current to the current force leads at a plurality of frequencies; measuring at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current at each of the plurality of frequencies; determining the impedance of the electrically conductive members based on the measured voltage and the test current at each of the plurality of frequencies; and if the impedance indicates a defect in the pipe, evaluate the distance of the defect along the pipe body section from a variation in the determined impedances across the plurality of frequencies.

[0036] In certain embodiments, evaluating the distance to a defect along the pipe may comprise performing a fit to the determined impedances as a function of frequency.

[0037] The plurality of frequencies may comprise at least 10 different frequencies between 10 Hz and 100 kHz.

[0038] In certain embodiments, the method may comprise sequentially coupling the impedance monitor to a pair of current force leads and a pair of voltage sense leads of a plurality pipe body sections, wherein each pair of current force leads and each pair of voltage sense leads are connected to a pair of electrically conductive members extending at least partially along the length of the pipe body section.

[0039] For each of the plurality of pipe body sections, the method may comprise: generating an test current at the impedance monitor and applying the test current to the current force leads; measuring at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current; determining the impedance of the pair of electrically conductive members based on the measured voltage and the test current; and determining if the impedance is indicative of a defect in the pipe body section.

[0040] In certain embodiments, the method may comprise providing the above-described pipeline apparatus.

[0041] According to an embodiment to the invention, there is provided an energy limiter for connection to an impedance monitor having a current source and a voltage monitor. The energy limiter may comprise: a first circuit connectable between the pair of current force leads and the current source, at least one Zener diode arranged in parallel with the current source and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members; and a second circuit connectable between the pair of voltage sense leads and the voltage monitor, at least one Zener diode arranged in parallel with the voltage monitor and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members.

[0042] The first circuit may comprise a fuse arranged on either side of the current source, between the current source and the at least one Zener diode.

[0043] The second circuit may comprise a fuse arranged on either side of the voltage monitor, between the voltage monitor and the at least one Zener diode.

[0044] The resistors in the first circuit may each have a resistance of between 5 and 20 ohms. The resistors in the second circuit may each have a resistance of between 75 and 200 ohms.

[0045] In each of the first and second circuits the at least one Zener diode may comprise a pair of Zener diodes arranged in series with each other and facing in opposite directions.

[0046] DESCRIPTION OF FIGURES

[0047] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0048] Figure 1 schematically illustrates a perspective cut-away view of a flexible pipe;

[0049] Figure 2 schematically illustrates a riser assembly suitable for transporting production fluid;

[0050] Figure 3 schematically illustrates a pipeline apparatus according to an embodiment of the invention;

[0051] Figure 4 schematically illustrates an energy limiter according to an embodiment of the invention; and

[0052] Figure 5 illustrates a method according to an embodiment of the invention.

[0053] In the drawings like reference numerals refer to like parts.

[0054] DETAILED DESCRIPTION

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] 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 I helical armouring elements (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.

[0060] 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.

[0061] 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.

[0062] 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 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.

[0063] 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.

[0064] 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).

[0065] Fig. 2 also illustrates how portions of flexible pipe can be utilised as a flow line 205 or jumper 206.

[0066] As noted above, defects in a flexible pipe body can compromise the structural integrity of the pipe body. In particular, a breach or rupture of an outer seawater resistant layer can allow seawater ingress into the pipe body annulus between an innermost barrier layer and the outer seawater resistant layer. With reference to Fig. 1 the outer seawater resistant layer may comprise the polymer outer sheath 108 and the innermost barrier layer may comprise the internal pressure sheath 102. The pipe body annulus is occupied by metallic structural components such as the tensile armour layers 105, 106 of Fig. 1. Such components are frequently formed from steel or other metals and are susceptible to rapid corrosion in the presence of seawater. There will now be described embodiments of the present invention which can detect a breach of an outer resistant layer of a flexible pipe body. Figure 3 schematically shows a pipeline apparatus 300 according to an embodiment of the invention. The pipeline apparatus 300 is not shown to scale. The pipeline apparatus 300 is for monitoring a pipe 302 and, in particular, for detecting defects within the pipe 302. The pipeline apparatus 300 advantageously allows different sections of the pipe 302 to be monitored independently and improves the accuracy of detecting defects within the pipe 302.

[0067] As shown in the embodiment in Figure 3, the pipeline apparatus 300 comprises a pipe 302. The pipe 302 may be a flexible pipe. The pipe 302 comprises a first pipe body section 304, a second pipe body section 306 and an end fitting 308 (i.e. a first end fitting). The first end fitting 308 connected to a first end 310 of the first pipe body section 304.

[0068] The second pipe body section 306 is coupled to a second end 312 of the first pipe body section 304. That is, to the opposing end of the first pipe body section 304 to the first end fitting 308. The pipe 302 may comprise further end fittings to couple the second pipe body section 306 to the first pipe body section 304. As shown in the embodiment in the Figures, the pipe 302 may comprise a second end fitting 314 connected to the second end 312 of the first pipe body section 304 and a third end fitting 316 connected to a first end 318 of the second pipe body section 306. The second and third end fittings 314, 316 may be connected together to couple the first and second pipe body sections 304, 306 together. The second pipe body section 306 may comprise a fourth end fitting 320 at a second end 322. Whilst not shown, the second pipe body section 306 may be coupled to a third pipe body section (not shown). The pipe 302 may therefore comprise two or more pipe body sections. The skilled person will appreciate that any suitable end fittings known in the art may be used in the pipe. As such, the features of the end fittings will not be described further.

[0069] Each of the pipe body sections 304, 306 may comprise a polymer fluid barrier such as the outer sheath 108 of Figure 1. The polymer fluid barrier surrounds at least one pair of tensile armour layers such as tensile armour layer 105 of Figure 1. Each tensile armour layer may comprise a plurality of helical armouring elements. The plurality of helical armouring elements may be a plurality of helically wound steel ligaments or wires. Each of the pipe body sections 304, 306 may have substantially the same structure as described above with reference to Figure 1, or different structures optimised for their position in the pipe 302, for instance a lower pipe body section 306 may be designed for ultra-deep water with enhanced collapse resistance, while the upper pipe body section 304 may be designed with axial tension capacity optimised. The pipe 302 comprises a first pair 324 of electrically conductive members extending at least partially along the length of the first pipe body section 304. As shown in the embodiment in Figure 3, the first pair 324 of electrically conductive members extending along the entire length of the first pipe body section 304. The first pair 324 of electrically conductive members are electrically isolated from one another. The first pipe body section 304 may comprise an insulating material 326 arranged to electrically isolate the first pair 324 electrically conductive members from one another and from tensile armour wires in that pipe layer. In the same manner, the pipe 302 comprises a second pair 328 of electrically conductive members extending at least partially along the length of the second pipe body section 306. As shown in the embodiment in Figure 3, the second pair 328 of electrically conductive members extending along the entire length of the second pipe body section 306. The second pair 328 of electrically conductive members are electrically isolated from one another. The second pipe body section 306 may comprise an insulating material 330 between the second pair 328 of electrically conductive members to electrically isolate the electrically conductive members from one another and from tensile armour wires in that pipe layer.

[0070] The first pair 324 of electrically conductive members is electrically isolated from the second pair 328 of electrically conductive members. This may be achieved via the coupling between the first and second pipe body sections 304, 306 by second and third end fittings 314, 316. The pairs 324, 328 of electrically conductive members may also be electrically isolated from the end fittings 308, 314, 316, 320 of the respective pipe body section 304, 306.

[0071] The pairs 324, 328 of electrically conductive members are disposed in the respective pipe body section such that fluid entering the pipe body section (i.e. the pipe body section annulus) due to a breach of or defect in the pipe body section, for example a breach in the polymer outer sheath 108, can come into contact with the electrically conductive members. That is, the insulating materials 326, 330 may not entirely surround one of the electrically conductive members. As such, in the first pipe body section 304, when there are no defects in the pipe body section, the first pair 324 of electrically conductive members are electrically isolated from one another (and the armour wires in the that layer) i.e. there is an open circuit between the first pair 324 of electrically conductive members. However, when fluid enters the first pipe body section 304 due to a breach, the fluid closes a circuit between the first pair 324 of electrically conductive members so that they are no longer electrically isolated from one another i.e. there is a short circuit between the first pair 324 of electrically conductive members. It is the same for the second pipe body section 306 and second pair 328 of electrically conductive members. As described above, in certain embodiments the pipe 302 may comprise a third pipe body section. In such embodiments, each pipe body section comprises a pair of electrically conductive members in the same manner as the first and second pipe body sections 304, 306.

[0072] As shown in the embodiment in the Figures, one of the tensile armour layers in the first pipe body section 304 may comprise the first pair 324 of electrically conductive members and one of the tensile armour layers in the second pipe body section 306 may comprise the second pair 328 of electrically conductive members. That is, the electrically conductive members may be helical armouring elements. The helical shape of the electrically conductive members is shown in Figure 3. Providing the electrically conductive members as helical armouring elements reduces the number of modifications required to implement the invention in pipe because the electrically conductive members are formed from features present in a conventional pipe body section.

[0073] In each of the first and second pipe body sections 304, 306, one of the pair of electrically conductive members may be provided by a first helical armouring element and the other of the pair of electrically conductive members may be provided by one or more of the other helical armouring elements in the same tensile armour layer. In the embodiment shown in Figure 3, only two of the helical armouring elements are shown for simplicity. However, the skilled person will appreciate that each pipe body section comprises additional helical armouring elements that are not illustrated. The first helical armouring element in each pipe body section may be electrically isolated from the other helical armouring elements by the insulating material 326, 330. The insulating material 326, 330 may be disposed on either side of the first helical armouring element to separate and electrically isolate the first helical armouring element from the other helical armouring elements in the tensile armour layer. The insulating material 326, 330 may therefore be disposed between the first helical armouring element and the other helical armouring elements in the tensile armour layer. In certain embodiments, the insulating material 326, 330 may comprise a polymer. The insulating material 326, 330 may comprise tape layers. The tape layer may be positioned between helical armouring elements.

[0074] The pipeline apparatus 300 comprises a first set of leads 332 for a measurement of impedance between the first pair 324 of electrically conductive members. The first set of leads 332 are connected to the first pair 324 of electrically conductive members. As shown in the embodiment in Figure 3, the first set of leads 332 may extend at least partially through the first end fitting 308 for connection with the first pair 324 of electrically conductive members. The first set of leads 332 may be connected to the first pair 324 of electrically conductive members at the first end fitting 308. As described above, if there are no defects in the first pipe body section 304, there is an open circuit between the first pair 324 of electrically conductive members and a measured impedance between the first pair 324 of electrically conductive members will be very high, if not infinite. However, if there is a breach in the first pipe body section 304 the measured impedance between the first pair 324 of electrically conductive members will be lower due to a short circuit between the first pair 324 of electrically conducting members.

[0075] In a similar manner, the pipeline apparatus 300 comprises a second set of leads 334 for a measurement of impedance between the second pair 328 of electrically conductive members. The second set of leads 334 are connected to the second pair 328 of electrically conductive members. Each set of leads is represented by a dashed line in Figure 3. In embodiments where the pipe comprises more than two pipe body sections, the apparatus comprises a set of leads connected to the pair of electrically conductive members in each of the pipe body sections.

[0076] As shown in the embodiment in Figure 3, the second set of leads 334 may extend through the first end fitting 308. The first and second sets of leads 332, 334 are electrically isolated and / or separate from each other. The second set of leads 334 may extend from the first end fitting 308 to the second pipe body section 306 for connection with the second pair 328 of electrically conductive members. That is, the second set of leads 334 extend along the length of the first pipe body section 304. The second set of leads 334 may extend through the second end fitting 312 and may be connected to the second pair 328 of electrically conductive members at the third end fitting 314.

[0077] The first and second sets of leads 332, 334 enable the impedance between the first pair 324 of electrically conductive members and between the second pair 328 of electrically conductive members to be measured independently. Therefore, the impedance in each pipe section 304, 306 can be independently monitored. This is advantageous because if a breach or defect occurs in the first pipe body section 304, this does not affect the monitoring of the second pipe body section 306.

[0078] The pipeline apparatus 300 may comprise a cable 336 for housing the sets of leads. The cable 336 may be configured to deliver the sets of leads to the respective pipe body sections. The cable 336 may comprise a plurality of sections.

[0079] As shown in the embodiment in Figure 3, the cable 336 may comprise a first section 336a. The first section 336a comprises (i.e. encloses) the first and second sets of leads 332, 334. As such, the first and second sets of leads 332, 334 may be enclosed in and protected by the first section 336a of the cable 336. The first section 336a of the cable 336 may deliver the first and second sets of leads 332, 334 to the first end fitting 308. The first section 336a of the cable 336 may be connected to the first end fitting 308 by a connector 338. The connector 338 may facilitate the electrical connection of the first set of leads 332 with the first pair 324 of electrically conductive members at the first end fitting 308.

[0080] The cable 336 may comprise a second section 336b extending from the first end fitting 308 to the second pipe body section 306. The second section 336b of the cable 336 therefore extends along the length of the first pipe body section 304. The second section 336b of the cable 336 may extend from the first end fitting 308 to the second end fitting 312. The second section 336b of the cable 336 comprises (i.e. encloses) the second set of leads 334. The second section 336b of the cable 336 is configured to deliver the second set of leads 334 to the second pipe body section 306.

[0081] The pipeline apparatus 300 may comprise connectors 340, 342 for connecting each end of the second section 336b of the cable 336 to the first and second end fittings 308, 312. The connector 342 at the second end fitting 312 may facilitate the electrical connection of the second set of leads 334 with the second pair 328 of electrically conductive members.

[0082] In embodiments where the pipe body comprises a third pipe body section, the first and second sections, 336a, 336b of the cable 336 may comprise a third set of leads 344. The cable 336 may also comprise a third section 336c extending along the length of the second pipe body section 306. The third section 336c of the cable 336 may comprise the third set of leads 344. The third section 336c of the cable 336 may extend from the third end fitting 316 to the fourth end fitting 320. The third section 336c of the cable 336 may be connected to the third end fitting 316 and the fourth end fitting 320 by connectors 346, 348. The third section 336c of the cable 336 may be configured to deliver the third set of leads 344 to the third pipe body section for connection to a pair of electrically conductive members in the third pipe body section in the same manner as described above for the first and second sets of leads 332, 334.

[0083] Each lead in the sets of leads 332, 334, 344 may be continuous (i.e. a continues piece of material without interruption). Alternatively, each lead in sets of leads 332, 334, 344 may comprise a plurality of connected sections. Each lead may be divided into a plurality of sections such that each section 336a, 336b, 336c of the cable 336 and each connector 338, 340, 342, 346, 348 comprises a different section of the lead. The plurality of sections of the leads are electrically connected to one another to form one continual lead. Dividing the leads into a plurality of sections may improve assembly of the pipeline apparatus 300. It will be understood that the cable 336 may be optionally helically wound around the pipe, similar to how the electrically conductive members are integrated into a layer of pipe body. The cable 336 may be integrated into the pipe structure or the cable 336 may be otherwise attached or wrapped around the pipe.

[0084] Each of the connectors 338, 340, 342, 346, 348 may be substantially the same as each other. The connectors 338, 340, 342, 346, 348 may facilitate the electrical connection between the sections of each lead.

[0085] The pipeline apparatus 300 may comprise an impedance monitor 350. The impedance monitor 350 may be housed in a monitoring apparatus 352. The impedance monitor 350 is configured to measure or determine the impedance of the pairs 324, 328 of electrically conductive members.

[0086] The impedance monitor 350 is arranged to measure the impedance of the first pair 324 of electrically conductive members via the first set of leads 332 and to measure the impedance of the second pair 328 of electrically conductive members via the second set of leads 334. To this end and as shown in the embodiment in Figure 3, the monitoring apparatus 352 may be connected to the first section 336a the cable 336. The first section 336a of the cable 336 may be connected to the monitoring apparatus 352 by a connector 354. The first and second sets of leads 332, 334 therefore extend between the monitoring apparatus 352 and the first end fitting 308. The first and second sets of leads 332, 334 may extend through the first end fitting 308 for connection to the impedance monitor 350.

[0087] The impedance monitor 350 may be configured to measure the impedance by any suitable means. However, in certain embodiments, the impedance monitor 350 may be configured to measure impedance by four terminal sensing. Using four terminal sensing to measure the impedance improves the accuracy of the impedance measurement. The measured impedance is independent of the impedance of the first and second set of leads 334 when the impedance is measured using four terminal sensing. This is particularly advantageous when measuring the impedance between the second pair 328 of electrically conductive members in the second pipe body section 306 because the length of the second set of leads 334 would be significant.

[0088] To measure the impedance using four terminal sensing, each of the first and second sets of leads 332, 334 may each comprise a pair of current force leads 356 and a pair of voltage sense leads 358. The current force and voltage sense leads 358 are shown in Figure 4. One of the current force leads 356 and one of the voltage force leads 358 may be connected to each member of the respective pair 324, 328 of electrically conductive members. The first set of leads 332 may therefore comprise four leads. The four leads include a pair of current force leads 356 (i.e. a first current lead and a second current lead) and a pair of voltage sense leads 358 (i.e. a first voltage lead and a second voltage lead). The first current and first voltage leads are connected to one member of the first pair 324 of electrically conductive members and the second current lead and the second voltage lead are connected to the other member of the first pair 324 of electrically conductive members. The second set of leads 334 is connected to the second pair 328 of electrically conductive members in the same way.

[0089] The impedance monitor 350 may comprise a current source 360 and a voltage monitor 362. The current source 360 is configured to apply an alternating current to each pair of current force leads 356. The current source 360 may be configured to provide an alternating current at a plurality of frequencies between 10 Hz and 100 kHz. The voltage monitor 362 is configured to measure a voltage between each pair of voltage sense leads 358 in response to the applied current. The voltage monitor 362 may be configured to measure a voltage between each pair of voltage sense leads 358 at each frequency of the applied current. The impedance monitor 350 may measure or determine the impedance of or between the pair of electrically conductive members from the ratio of the measured voltage to the applied current.

[0090] The impedance monitor 350 is configured to be connected to both the first and second set of leads 334. The monitoring apparatus 352 may comprise a plurality of relays 364 for connecting the first and second set of leads 334 to the current source 360 and voltage monitor 362. As such, the first and second sets of leads 332, 334 may be sequentially connected to the current source 360 and voltage monitor 362, one set at a time. For example, the impedance of the first pair 324 of electrically conductive members may therefore be measured first and the impedance of second pair 328 of electrically conductive members may then be measured second. The measurements may be repeated to monitor both the first and second pipe body sections 304, 306 over time.

[0091] The pipeline apparatus 300 may comprise a processor 366 configured to determine if the impedance of a or each pair of electrically conductive members is indicative of a defect in the pipe body section 304, 306. The processor 366 may be configured to determine if the impedance is indicative of a defect in the pipe body section 304, 306 by determining if the measured impedance indicates an open circuit or a short circuit between the pair of electrically conductive members. As described above, a short circuit indicates that there is a breach of defect in a pipe body section 304, 306. The processor 366 may be configured to determine if the impedance is indicative of a defect by, for example, comparing the measured impedance to a threshold. If the impedance indicates a defect in the pipe body section 304, 306, the processor 366 may be configured to evaluating the distance of the defect along the pipe body section 304, 306 from a variation in the determined impedances across the plurality of frequencies. Evaluating the distance to a defect along the pipe body section 304, 306 may comprise performing a fit to the determined impedances as a function of frequency as described further below in relation to Figure 5.

[0092] The processor 366 may be configured to receive the impedance measurements from the impedance monitor 350. The processor 366 may be connected to the impedance monitor 350 via a wired connection for receiving the impedance measurements. In certain embodiments, the processor 366 may be at a remote location from the impedance monitor 350.

[0093] The pipeline apparatus 300 may comprise an energy limiter 368. The impedance monitor 350 may be connected to the first and second sets of leads 332, 334 via the energy limiter 368 as shown in Figure 3. The monitoring apparatus 352 may comprise the energy limiter 368. The energy limiter 368 is configured to minimise the risk of or prevent electrostatic discharge being created in the monitoring apparatus 352. This is advantageous when the pipe 302 is used for transporting hydrocarbons. An area near the pipe 302 where is it would be ideal to position the monitoring apparatus 352may be an area in which an explosive gas atmosphere is likely to occur in normal operation due to the presence of hydrocarbons. However, the energy limiter 368 enables the monitoring equipment to be safely located in this area near the pipe 302. As mentioned above, the processor 366 may be remote from the impedance monitor 350. The processor 366 may be located outside the area in which an explosive gas atmosphere is likely to occur in normal operation.

[0094] The energy limiter 368 is shown in detail in Figure 4. The energy limiter 368 comprising a first circuit 370 connectable to a pair of current force leads 356 and a second circuit 374 connectable to a pair of voltage sense leads 358. The first circuit 370 and second circuit 372 may be connected to the current force leads 356 and voltage sense leads 358, respectively, of each of the first and second sets of leads 332, 334 by the plurality of relays 364. The relays 364 may be positioned between the energy limiter 368 and the first and second set of leads 334. For ease of understanding, the relays 364 are not shown in Figure 4 and the energy limiter 368 will be described as if connected to the first set of leads 332. However, the energy limiter 368 may be connected to either of any set of leads via the plurality of relays 364.

[0095] The first circuit 370 is configured to be connected to the current source 360 of the impedance monitor 350. In Figure 3, the first circuit 370 is shown connected to the current source 360 of the impedance monitor 350. The first circuit 370 comprises at least one Zener diode 384 arranged in parallel with the current source 360. The use of at least one Zener diode 374 stabilises the voltage in the energy limiter 368 and limits the power thereby preventing the voltage from getting too higher and, consequently, preventing electrostatic discharge. The Zener diode 374 enable the energy limiter 368 to be placed in an explosive gas atmosphere.

[0096] The first circuit 370 comprises a resistor 376 arranged in series with each of the current force leads 356 in the first set of leads 332. Each resistor 376 is therefore arranged in series with one of the electrically conductive members in the first pair 324 of electrically conductive members. The first circuit 370 may comprise a fuse 378 arranged on either side of the current source 360. As shown in Figure 4, the fuses 378 are positioned between the current source 360 and the at least one Zener diode 374. The fuses 378 limit the current provide to the Zener diode 374 thereby preventing the Zener diode 374 from overheating and becoming damaged.

[0097] The second circuit 372 is configured to be connected to the voltage monitor 362 of the impedance monitor 350. In Figure 3, the second circuit 372 is shown connected to the voltage monitor 362 of the impedance monitor 350. In a similar manner to the first circuit 370, the second circuit 372 comprises at least one Zener diode 380 arranged in parallel with the voltage monitor 362. The second circuit 372 also comprises a resistor 382 arranged in series with each of the voltage sense leads 358 in the first set of leads 332. Each resistor 382 is therefore arranged in series with one of the electrically conductive members in the first pair 324 of electrically conductive members. In the same manner as the first circuit 370, the second circuit 372 comprises a fuse 384 arranged on either side of the voltage monitor 362. As shown in Figure 4, the fuses 384 are positioned between the voltage monitor 362 and the at least one Zener diode 380.

[0098] The resistors 374, 382 in the first and second circuits 370, 372 limit the energy in the circuits thereby reducing the reducing the likelihood of electric sparks being created. The resistors 374 in the first circuit 370 may each have a resistance of between 5 and 20 ohms. The resistors 382 in the second circuit 372 may each have a resistance of between 75 and 200 ohms. The inventors found that the resistors having these values sufficiently limit the energy in the first and second circuits 370, 372 without significantly affecting the measurements.

[0099] In each of the first and second circuits 370, 372 the at least one Zener diode 374, 380 may comprise a pair of Zener diodes arranged in series with each other and facing in opposite directions as shown in Figure 4 thereby improving the voltage stabilisation provided by the Zener diodes in view of the alternating current provided by the current source 360. As shown in the embodiment in Figure 4, the pair of Zener diodes arranged may be arranged back-to-back. An infallible track 386 may be disposed between the pair of Zener diodes to connect the diodes to one another in both the first and second circuits 370, 372.

[0100] As shown in the embodiment in Figure 4, each of the first and second circuits 370, 372 comprises three pairs of Zener diodes 374, 380 arranged in series with each other and facing in opposite directions. Each of the pairs of the Zener diodes 374, 380 are arranged in parallel with either the current source 360 or voltage monitor 362. Three pairs of Zener diodes 374, 380 are used for redundancy in the first and second circuits 370, 372.

[0101] Figure 5 shows a method 400 according to an embodiment of the invention for monitoring pipe body sections. The method 400 may be used to detect defects in one or more pipe body sections. The method 400 may be performed using the pipeline apparatus 300 shown in Figure 3 but is not limited to the pipeline apparatus 300 shown in Figure 3. However, for ease of understanding the method 400 will be described with reference to the pipeline apparatus 300 shown in Figure 3.

[0102] The method 400 comprises coupling 402 an impedance monitor 350 to a pair of current force leads 356 and a pair of voltage sense leads 358 of a pipe body section 304, 306 of a pipe 302. The pipe 302 may comprise multiple pipe body sections 304, 306 as shown in the embodiment in Figure 3. Alternatively, the pipe 302 may comprise only one pipe body section. The pair of current force leads 356 and the pair of voltage sense leads 358 are connected to a pair 324, 328 of electrically conductive members extending at least partially along the length of the pipe body section 304, 306. The energy limiter 368 may be connected between the impedance monitor 350 and the leads.

[0103] The method 400 comprises generating 404 a test current at the impedance monitor 350 and applying the test current to the current force leads 356. The test current may be generated by the current source 360. The method 400 comprises measuring 406 at the impedance monitor 350 the voltage between the pair of voltage sense leads in response to the test current. The voltage may be measured by the voltage monitor 362.

[0104] The method 400 comprises determining 408 the impedance of the pair of electrically conductive members based on the measured voltage and the test current. The impedance may be determined 408 based on the ratio of the measured voltage to the applied current.

[0105] The method 400 comprises determining 410 if the impedance is indicative of a defect in the pipe body section 304, 306. Determining if the impedance is indicative of a defect in the pipe body section 304, 306 may comprise determining if the measured impedance indicates an open circuit or a short circuit between the pair 324, 328 of electrically conductive members. An open circuit indicates that there is no breach or defect in the pipe body section 304, 306 and a short circuit indicates a breach. The method 400 there uses four terminal sensing to find the impedance improves the accuracy of the impedance measurement as described above.

[0106] The method 400 may be repeated to determine the impedance between the electrically conductive members in the pipe body section 304, 306 over time. As such, the time at which a defect develops in a pipe body section 304, 306 may be identified. The method 400 may be repeated to determine the impedance between the pairs 324, 328 of electrically conductive members in a particular pipe body section 304, 306 at set time intervals.

[0107] The method 400 may be used to monitor a plurality of pipe body sections. The method 400 may therefore comprise sequentially coupling the impedance monitor 350 to a pair of current force leads 356 and a pair of voltage sense leads 358 of a plurality pipe body sections 304, 306. Each pair of current force leads 356 and each pair of voltage sense leads 358 are connected to a pair 324, 328 of electrically conductive members extending at least partially along the length of the pipe body section 304, 306. Sequentially coupling the impedance monitor 350 may comprise a pair of current force leads 356 for the current source of the impedance monitor 350 and a pair of voltage sense leads 358 to the voltage monitor of the impedance monitor 350. The impedance monitor 350 may be sequentially coupled to the first and second sets of leads 332, 334 by the relays 364.

[0108] The plurality of pipe body sections may be multiple pipe body sections of the same pipe such as the first and second pipe body sections 304, 306 of the embodiment in Figure 3. As such, the method may comprise connecting the impedance monitor 350 to the first pair 324 of electrically conductive members and measuring the impedance of the first pair 324 of electrically conductive members, and then connecting the impedance monitor 350 to the second pair 328 of electrically conductive members and measuring the impedance of the second pair 328 of electrically conductive members. Additionally or alternatively, the plurality of pipe body sections may comprise pipe body sections may be pipe body sections of different pipes. The method 400 may there comprise connecting the impedance monitor to the pair of electrically conductive members of pipe body sections in different pipes and measuring the impedance of the electrically conductive members.

[0109] For each of the plurality of pipe body sections 304, 306, the method 400 comprises: generating a test current at the impedance monitor 350 and applying the test current to the current force leads 356; measuring at the impedance monitor 350 the voltage between the pair of voltage sense leads in response to the test current; determining the impedance of the between the pair of electrically conductive members based on the measured voltage and the test current; and determining if the impedance is indicative of a defect in the pipe body section. Measuring the impedance and determining if the impedance is indicative of a defect in the pipe body section 304, 306 may be done in the same way for each pipe body section of the plurality of pipe body sections.

[0110] The method 400 may be used to sequentially monitoring the plurality of pipe body sections 304, 306. The method 400 may be repeated so that each pipe body section of the plurality of pipe body sections is monitored at a set time interval.

[0111] In certain embodiments, the test current may be applied to the current force leads 356 at a plurality of frequencies. That is, the method may comprise generating 402 the test current at a plurality of frequencies. For example, the test current may be applied to the current force at least 10 different frequencies between 10 Hz and 100 kHz. In such embodiments, the method 400 may comprise measuring at the impedance monitor 350 the voltage between the pair of voltage sense leads in response to the test current at each of the plurality of frequencies. As such, a plurality of voltage measurements are made.

[0112] The impedance of the pair of electrically conductive members may then be determined 408 based on the measured voltage and the test current for each of the plurality of frequencies. That is, an impedance of the electrically conductive member is determined for each of the plurality of frequencies.

[0113] If the measured impedance indicates a defect in the pipe, the method 400 may comprise evaluating 412 the distance of the defect along the pipe body section 304, 306 from a variation in the determined impedances across the plurality of frequencies. Evaluating 412 the distance to a defect along the pipe body section 304, 306 may comprise performing a fit to the determined impedances as a function of frequency. The distance to the defect may be useful to ascertain where the pipe body section 304, 306 needs to be repaired. If a pipe body section 304, 306 has a defect the distance to the breach may be monitored over time to ascertain if or how the size of the breach is changing and, therefore, when the pipe body section 304, 306 needs to be repaired. The distance to the breach, for example, may change as the amount of fluid entering the pipe body section or annulus increases. Using four terminal sensing to determine the impedance may improve the accuracy of the distance of the breach along the pipe body section 304, 306.

[0114] In the method 400, and also the apparatus of Figure 3, the electrically conductive members can be treated as having a distributed characteristic impedance with a resistance, R, inductance, L, capacitance, C, and conductance, G, per unit length. The electrically conductive members can be modelled as a transmission line having a characteristic impedance, Zo, of: where > is the frequency of the current and j the imaginary unit.

[0115] The resistance, inductance, capacitance and conductance may vary with frequency. In particular, the resistance per unit length of the electrically conductive members varies with the frequency of the applied current due to the skin effect. That is, an alternating current in a conductor the current density in the conductor is greatest next to the surface of the conductor and decreases with depth into the conductor. The current flows mainly between the outer surface of the conductor and a level called the skin depth. Skin depth depends on the frequency of the alternating current. As frequency increases, current flow becomes more concentrated near the surface resulting in a smaller skin depth and, consequently, a higher resistance.

[0116] The impedance between the electrically conductive members that is determined from the measured voltage and applied current in the method 400 or by the impedance monitor 350, will not be the same as the characteristic impedance Zo of the electrically conductive members. Rather, this impedance, hereafter the measured impedance, Zm, can be modelled as if the electrically conductive members with characteristic impedance, Zo, are terminated at length, , with a load having a load impedance, ZL. Based on known transmission line relationships, the measured impedance is therefore where y is a propagation constant given by and fl is the voltage reflection coefficient given by

[0117] In a pipe body section 302, 304, if there are no defects in a pipe body section the load impedance, ZL, will be very high, if not infinite, because there will be an open circuit between the pair 324, 328 of electrically conductive members in the pipe body section 302, 304. Additionally, the length, will be the same as the length of the electrically conductive members. If there is a defect in the pipe body section, fluid entering the pipe body section 302, 304 will create a short circuit between the pair of electrically conductive members thereby reducing the load impedance, ZL. AS such, a defect in a pipe body section 302, 304 can be determined by reduction in measured impedance. In this case that there is a defect in the pipe body section 302, 304, the length, , will be the distance along the electrically conductive member from the end of the electrically conductive members that are connected to the set of leads to the point where the fluid has closed the circuit between the pair of electrically conductive members. The length, therefore, indicates the position of the defect along the electrically conductive members in the pipe body section 304, 306. As such, the length can be used to determine the distance of the breach or defect along the pipe body section 304, 306.

[0118] The measured impedance, Zm, depends on the frequency of the applied current. By measuring the impedance at a plurality a frequencies the position of a defect along the pipe body section 304, 306 may be determined. In the method 400, evaluating 412 the distance of the defect along the pipe body section 304, 306 may be done by performing a fit of measured impedance, Z / n, as a function of frequency using the above relationship of the measured impedance, Z / „. The value of the length, , may be determined from the fit. A fit may be performed to both the amplitude and phase of the measured impedance, Z / „. The fit for the amplitude and phase of the measured impedance, Z / n, may be performed simultaneously.

[0119] The resistance per unit length of the electrically conductive members may be known. The capacitance and inductance per unit length of the electrically conductive members may also be known or estimated. As such, fitting the measured impedance may be simplified. Otherwise, resistance, capacitance and / or inductance per unit length may be determined from the fit.

[0120] The method 400 shown in the embodiment shown in Figure 5 may comprise providing the pipeline apparatus 300 of the embodiment in Figure 3. As such, the processor 366 may be configured to perform the method 400 steps of determining if the impedance is indicative of a defect in the pipe body section 304, 306 and evaluating the distance of the defect along the pipe body section 304, 306 from a variation in the determined impedances across the plurality of frequencies. The processor 366 may comprise a memory (not shown) and computer readable instructions stored in the memory which, when executed, cause the processor to perform the method steps.

[0121] Various modifications to the detailed arrangements as described above are possible.

[0122] Whilst the above-described method 400 of Figure 5 and the impedance monitor 350 in the apparatus of Figure 3 advantageously measure impedance using four terminal sensing, the skilled person will appreciate that the impedance of the pairs of electrically conductive members in the first and second pipe body sections 304, 306 is not limited to using four terminal sensing. Rather, the impedance between the first and second pairs 324, 328 of electrically conductive members via the first and second leads 332, 334 in any suitable manner. In certain embodiments, the impedance monitor 350 and the sets of leads 332, 334 may be replaced by an alternative monitor and leads configured to measure the impedance in a different manner. The remaining steps of the method 400 and features of the apparatus 300 may remain the same as described above in reference to Figures 3 and 5.

[0123] In such embodiments, the method of monitoring the pipe may comprising, providing a pipeline apparatus. The pipeline apparatus comprises a first and second pipe body section, a first pair of electrically conductive members extending at least partially along the length of the first pipe body section, a second pair of electrically conductive members extending at least partially along the length of the second pipe body section and a first set of leads for a measurement of impedance between the first pair of electrically conductive members and a second set of leads for a measurement of impedance between the second pair of electrically conductive members. The method may comprise connecting an impedance monitor to the first pair of electrically conductive members and measuring the impedance between the first pair of electrically conductive members. The method may comprise connecting the impedance monitor to the second pair of electrically conductive members and measuring the impedance between the second pair of electrically conductive members. As such, the impedances of the first and second pairs of electrically conductive members may be measured independently.

[0124] 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.

[0125] 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.

[0126] 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.

Claims

27CLAIMS1. A pipeline apparatus comprising: a flexible pipe comprising: a first pipe body section, a second pipe body section and an end fitting connected to a first end of the first pipe body section; wherein the second pipe body section is coupled to a second end of the first pipe body section; a first pair of electrically conductive members extending at least partially along the length of the first pipe body section, wherein the first pair of electrically conductive members are electrically isolated from one another; and a second pair of electrically conductive members extending at least partially along the length of the second pipe body section, wherein the second pair of electrically conductive members are electrically isolated from one another and from the first pair of electrically conductive members; and a first set of leads for a measurement of impedance of the first pair of electrically conductive members and a second set of leads for a measurement of impedance of the second pair of electrically conductive members, wherein the first and the second sets of leads are connected to the first and second pairs of electrically conductive members, respectively, such that the impedance of the first pair of electrically conductive members and the impedance of the second pair of electrically conductive members are independently measurable via the first and second sets of leads.

2. A pipeline apparatus according to claim 1, comprising a cable extending from the end fitting to the second pipe body section, the cable comprising the first and second sets of leads and being configured to deliver the first set of leads to the first pair of electrically conductive members and to deliver the second set of leads to second first pair of electrically conductive members.

3. A pipeline apparatus according to any one of the preceding claims, comprising an impedance monitor, the impedance monitor arranged to measure the impedance between the first pair of electrically conductive members via the first set of leads and to measure the impedance between the second pair of electrically conductive members vis the second set of leads.

4. A pipeline apparatus according to claim 3 wherein the first and second sets of leads extend through the end fitting to the impedance monitor.

5. A pipeline apparatus according to claim 3 or 4, comprising a processor configured to determine if the impedance between each pair of electrically conductive members is indicative of a defect in the pipe body section.

6. A pipeline apparatus according any one of the preceding claims, wherein each of the first and second sets of leads each comprise a pair of current force leads and a pair of voltage sense leads, one of the current force leads and one of the force sense leads being connected to each of the respective pair of electrically conductive members.

7. A pipeline apparatus according to claim 6, when dependent on claim 3, wherein the impedance monitor comprises a current source configured to apply an alternating current to the pairs of current force leads and an voltage monitor configured to measure a voltage between the pairs of voltage sense leads such that impedance monitor is configured to measure impedance by four terminal sensing.

8. A pipeline apparatus according to any one of the preceding claims, wherein the first and second pipe body sections each comprise a polymer fluid barrier surrounding at least one pair of tensile armour layers, wherein each tensile armour layer comprises a plurality of helical armouring elements.

9. A pipeline apparatus according to claim 8, wherein one of the tensile armour layers in the first pipe body section comprises the first pair of electrically conductive members and one of the tensile armour layers in the second pipe body section comprises the second pair of electrically conductive members.

10. A method for monitoring a flexible pipe, the method comprising:providing the apparatus of any one of claims 1 to 9, connecting an impedance monitor to the first pair of electrically conductive members and measuring the impedance of the first pair of electrically conductive members; and connecting the impedance monitor to the second pair of electrically conductive members and measuring the impedance of the second pair of electrically conductive members.

11. The method of claim 10, comprising sequentially connecting the impedance monitor to the first and second pairs of electrically conductive members.

12. A pipeline apparatus comprising: a flexible pipe comprising: a pipe body section; a pair of electrically conductive members extending at least partially along the length of the pipe body section, wherein the pair of electrically conductive members are electrically isolated from one another; and a pair of current force leads and a pair of voltage sense leads connected to the pair of electrically conductive members such that one of the current force leads and one of the force sense leads is connected to each electrically conductive member; and an impedance monitor connectable to the current force leads and the voltage sense leads, the impedance monitor comprising a current source to provide an alternating current to the current force leads and a voltage monitor arranged to monitor the voltage between the voltage sense leads such that the impedance monitor is configured to measure the impedance of the pair of electrically conductive members by four terminal sensing.

13. A pipeline apparatus according to claim 12, wherein the impedance monitor comprises an energy limiter, the energy limiter comprising:a first circuit connectable between the pair of current force leads and the current source, at least one Zener diode arranged in parallel with the current source and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members; and a second circuit connectable between the pair of voltage sense leads and the voltage monitor, at least one Zener diode arranged in parallel with the voltage monitor and a resistor arranged in series with each electrically conductive member in the pair of electrically conductive members.

14. A pipeline apparatus according to any claim 13, wherein the resistors in the first circuit each have a resistance of between 5 and 20 ohms.

15. A pipeline apparatus according to any claim 13 or 14, wherein the resistors in the second circuit each have a resistance of between 75 and 200 ohms.

16. A pipeline apparatus according to any one of claims 13 to 15, wherein in each of the first and second circuits the at least one Zener diode comprises a pair of Zener diodes arranged in series with each other and facing in opposite directions.

17. A pipeline apparatus according to any one of claims 13 to 16, comprising a processor configured to determine if the impedance measured between the pair of electrically conductive members is indicative of a defect in the pipe body section.

18. A pipeline apparatus according to any one of claims 13 to 17, wherein the current source is configured to provide an alternating current at a plurality of frequencies between 10 Hz and 100 kHz.

19. A pipeline apparatus according to any one of claims 11 to 16, wherein the pipe body section comprises a polymer fluid barrier surrounding at least one pair of tensile armour layers, wherein each tensile armour layer comprises a plurality of helical armouring31 elements, and optionally wherein one of the tensile armour layers in the pipe body section comprises the pair of electrically conductive members.

20. A method for detecting defects within a flexible pipe, the method comprising: coupling an impedance monitor to a pair of current force leads and a pair of voltage sense leads of a pipe body section of a flexible pipe, wherein the pair of current force leads and the pair of voltage sense leads are connected to a pair of electrically conductive members extending at least partially along the length of the pipe body section, wherein the pair of electrically conductive members are electrically isolated from one another; generating an test current at the impedance monitor and applying the test current to the current force leads; measuring at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current; determining the impedance of the electrically conductive members based on the measured voltage and the test current; and determining if the impedance is indicative of a defect in the pipe body section.

21. A method according to claim 20, comprising: applying the test current to the current force leads at a plurality of frequencies; measuring at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current at each of the plurality of frequencies; determining the impedance of the electrically conductive members based on the measured voltage and the test current at each of the plurality of frequencies; and if the impedance indicates a defect in the pipe, evaluate the distance of the defect along the pipe body section from a variation in the determined impedances across the plurality of frequencies.3222. A method according to claim 21 , wherein evaluating the distance to a defect along the pipe comprises performing a fit to the determined impedances as a function of frequency.

23. A method according to claim 21 or 22, wherein the plurality of frequencies comprises at least 10 different frequencies between 10 Hz and 100 kHz.

24. A method according to any one of claims 20 to 23 comprising: sequentially coupling the impedance monitor to a pair of current force leads and a pair of voltage sense leads of a plurality pipe body sections, wherein each pair of current force leads and each pair of voltage sense leads are connected to a pair of electrically conductive members extending at least partially along the length of the pipe body section; and for each of the plurality of pipe body sections: generate an test current at the impedance monitor and applying the test current to the current force leads; measure at the impedance monitor the voltage between the pair of voltage sense leads in response to the test current; determine the impedance of the pair of electrically conductive members based on the measured voltage and the test current; and determine if the impedance is indicative of a defect in the pipe body section.

25. A method according to any one of claims 20 to 24, comprising providing the apparatus of any one of claims 12 to 19.

Images