Method for controlling a flexible cable and associated control device

Description

Technical field of the invention

[0001] The present invention relates to a method for non-destructive testing of a flexible line and an associated non-destructive testing device.

[0002] It concerns the technical field of non-destructive testing of subsea oil and gas installations, and more specifically that of non-destructive testing of the annular space of subsea flexible lines. State of the art

[0003] A flexible line, used in the field of subsea oil and gas installations, can be in the form of: of an unbonded flexible pipe intended for the transport of hydrocarbons across a body of water, such as an ocean, a sea, a lake or a river, and for example made according to the standards documents API 17 J (Specification for Unbonded Flexible Pipe) and API RP 17 B (Recommended Practice for Flexible Pipe) established by the American Petroleum Institute, or of an umbilical reinforced by armor intended for the transport of energy, data, or injection product, across a body of water, such as an ocean, a sea, a lake or a river, and for example made according to the standards documents API 17 E (Specification for Umbilicals), or of a combination of the two.

[0004] Such a flexible line is generally formed from a set of coaxial and superimposed cylindrical layers. A flexible line comprises at least one layer of armor arranged inside an annular space and an outer sheath surrounding said annular space. The flexible line is considered to be "unbonded" within the meaning of the present invention since at least one of the layers of said flexible line is capable of moving longitudinally relative to the adjacent layers during bending of the flexible line. In particular, an unbonded flexible line is a flexible line generally devoid of binding materials connecting layers forming the flexible line.

[0005] The flexible line is generally arranged across a body of water, between a bottom assembly, intended to collect the fluid extracted from the bottom of the body of water and a floating or fixed surface assembly, intended to collect and distribute the fluid, or can also extend between two bottom installations, or can still extend between two surface installations. The surface assembly can be a semi-submersible platform, an FPSO or another floating assembly.

[0006] Flexible lines intended for great depths are subjected to very high tensions, commonly several tens of tons, particularly during their commissioning and / or during their installation at sea. In particular, in the case where the surface assembly is floating and mobile depending on sea conditions, the rising flexible lines (risers in English) connecting the seabed to the surface assembly can sometimes be subjected to millions of bending variation cycles. This results in risks of degradation and rupture of the external sheath, which then no longer ensures its function of protecting the flexible line. This results in a risk of flooding of the annular space, in particular flooding of the layer(s) of tensile armor present in said annular space.These armor layers are in some cases sensitive to corrosion, in particular that induced by the permeation of acid compounds present in the transported fluid and / or by the presence of water in the annular space following degradation of the external sheath. However, to guarantee the resistance to tension and fatigue throughout the service life of the flexible line, it is necessary to ensure the integrity of the tensile armor layers, generally made from helical windings of metal wires.

[0007] To detect possible damage or ruptures of the outer sheath leading to flooding of the annular space, various tests are implemented, such as the annular test. The annular test consists of measuring the current volume of gas in the annular space of the flexible line, for example by creating a vacuum in the annular space. The measured current volume of gas is compared to the initial volume of the annular space to deduce whether water has partially or completely invaded the annular space. However, such a volume measurement is often not very accurate and therefore does not allow a determination of the presence and height of possible flooded areas threatening the integrity of the flexible line.

[0008] GB-B-2 446 670 describes a method for underwater inspection of the integrity of the annular space of a flexible line based on the technique of ultrasonic echography. According to this method, an ultrasonic probe emits an incident ultrasonic wave which penetrates the flexible line. In return, the probe receives the ultrasonic waves reflected at the discontinuities, i.e. at the interfaces, encountered in the flexible line. The amplitudes of the reflected ultrasonic waves make it possible, in particular, to determine whether the portion of the flexible line inspected is flooded. Such a method is based on a property of ultrasonic waves according to which ultrasonic waves propagate little in a gas as opposed to a liquid medium such as water. Thus, an interface comprising a gas generates reflected ultrasonic waves of greater amplitude than an interface comprising a liquid.

[0009] However, the ultrasonic method reaches its limits when the flexible line is subjected to both internal and external pressure, which is particularly the case when said flexible line is immersed in a body of water. Indeed, in a flexible line configuration in which the outer sheath and the armor layer are adjacent, the annular space is filled with gas, and from a certain pressure level, generally above about ten bars, said outer sheath and said armor layer are compressed against each other so that the interface between said outer sheath and the armor layer no longer contains gas. This is called intimate contact between the two layers.In such a case, the incident ultrasonic wave propagates mainly through the interface, and the reflected waves are of very low amplitude, like an annular space that would be filled with liquid, so that it is impossible to determine the presence of gas. Thus, when the contact pressure between the outer sheath and the armor elements is greater than a few tens of bars, the inspection method presented in patent GB-B-2 446 670 does not make it possible to distinguish between a flooded annular space and a dry annular space. In another flexible line configuration in which one or more intermediate sheaths are arranged between the outer sheath and the armor layer, the different interfaces between the outer sheath and the intermediate sheaths may contain gas, so that the ultrasonic waves are directly reflected at these interfaces before they can even reach the annular space.Here too, the inspection method presented in patent GB-B-2 446 670 does not allow a distinction to be made between a flooded annular space and a dry annular space.

[0010] Furthermore, an ultrasonic testing method requires mechanical scanning of a plurality of successive regions to be tested of the outer sheath and repetition, for each region to be tested of the outer sheath, of the steps of sending, receiving, analyzing and determining the medium at the interface between the region to be tested of the outer sheath and the annular space opposite the region to be tested of the outer sheath. Thus, it is generally necessary to mount the ultrasonic probe on a motorized rotating platform whose weight and implementation complexity are not negligible.

[0011] JP2011027216 describes a linked hydrocarbon transport pipeline, equipped with a leak detection system embedded in the pipeline.

[0012] The invention thus aims to provide a method for monitoring the integrity of a flexible line, in particular the annular space of the flexible line, which is non-intrusive, simple to implement and reliable regardless of the external pressure applied to the flexible line. Disclosure of the invention

[0013] The solution proposed by the invention, according to claim 1, is a method for non-destructive testing of a flexible line comprising at least one layer of armor arranged inside an annular space and an external sheath surrounding said annular space, said annular space comprising a fluid. The non-destructive testing method is remarkable in that it comprises the following steps: a) arranging in the vicinity of the external sheath at least one pair of electrodes, b) supplying said pair of electrodes, or a first pair of electrodes of said pairs of electrodes, with alternating voltage of determined frequency, or with alternating current of determined frequency, so as to generate an electromagnetic field extending through at least a portion of the annular space, c) measuring, at said pair of electrodes, or a second pair of electrodes of said pairs of electrodes, an electrical signal linked to the electromagnetic characteristics of said at least a portion of the annular space subjected to said generated electromagnetic field, d) processing said electrical signal so as to determine the nature of the fluid contained in the annular space.

[0014] In step a), at least one pair of electrodes is arranged outside said flexible line, in the vicinity of the external sheath. Alternatively, in step b), the power supply to said pair of electrodes is in pulsed voltage, or in pulsed current. Advantageously, the assembly formed of armor and fluid is subjected to the electromagnetic field.

[0015] In step d), said electrical signal is compared with reference values ​​so as to determine whether the fluid contained in the annular space is a gas or a liquid.

[0016] Thus, the non-destructive testing method that is the subject of the invention makes it possible to control the nature of the fluid contained in the annular space of a flexible line, via an electromagnetic field that makes it possible to pass through one or more sheaths regardless of the type of contact, intimate or not, between the external sheath, the armor layer, and possibly the intermediate sheaths. Similarly, this method has the advantage of requiring only a single measurement and therefore makes it possible to avoid the need for a scanning step.

[0017] The interaction of the electromagnetic field with the flexible line depends in particular on the geometry and electromagnetic properties of the various components present in the flexible line. The main electromagnetic properties are electrical conductivity, dielectric permittivity and magnetic properties, in particular magnetic permeability.

[0018] The outer sheath of the flexible line is generally made of electrically insulating (virtually zero electrical conductivity) and non-magnetic (magnetic permeability identical to that of a vacuum) polymeric materials. As a result, the electromagnetic field can easily pass through the outer sheath without undergoing strong attenuation, and reach the annular space.

[0019] The fluid present in the annular space has, due to its electromagnetic properties, an influence on the electromagnetic field and it is this influence that the present method aims to exploit in order to indirectly determine the nature of the fluid via electrical measurements.

[0020] Furthermore, non-destructive testing can be carried out on a standard flexible line without it being necessary to structurally modify the flexible line, all the elements of the non-destructive testing device being arranged outside the pipe, even if some of said elements of said non-destructive testing device are capable of interacting electromagnetically with elements internal to the flexible line.

[0021] In this application, the term "alternating voltage" means a voltage that varies periodically as a function of time, the "determined frequency" being the frequency of this periodic function. The term "alternating voltage" is not limited to sinusoidal voltages and also encompasses non-sinusoidal periodic voltages, for example periodic voltages of the triangular or square wave type. Similarly, in this application, the term "alternating current" means a current that varies periodically as a function of time.

[0022] Advantageously, during step b), the power supply is made with a sinusoidal alternating voltage of determined frequency, or with a sinusoidal alternating current of determined frequency.

[0023] According to another advantageous characteristic of the invention making it possible to obtain a simple method of implementation by means of a compact device, during step a), a single pair of electrodes is arranged in the vicinity of the external sheath.

[0024] According to yet another advantageous characteristic of the invention making it possible to improve the sensitivity of the measurement, the single layer of armor, or when the flexible line comprises several layers of armor, the layer of armor closest to the outer sheath, comprises at least a first group of armor and a second group of armor distinct from each other and in that step a) comprises the following steps: a1) arranging a first electrode of the single pair of electrodes opposite the first group of armors, a2) arranging a second electrode of the single pair of electrodes opposite the second group of armors.

[0025] Advantageously, the first electrode is placed exclusively opposite the first group of armors without being placed opposite the second group of armors. The second electrode is placed exclusively opposite the second group of armors, without being placed opposite the first group of armors.

[0026] According to yet another advantageous characteristic of the invention making it possible to decouple the taking of measurements and the supply of alternating voltage or alternating current so as to improve the precision of the measurement, during step a), two pairs of electrodes are arranged in the vicinity of the external sheath, namely on the one hand a first pair of electrodes and on the other hand a second pair of electrodes.

[0027] According to yet another advantageous characteristic of the invention making it possible to improve the sensitivity of the measurement, the single layer of armor, or when the flexible line comprises several layers of armor, the layer of armor closest to the outer sheath, comprises at least a first group of armor and a second group of armor distinct from each other and in that step a) comprises the following steps: a3) arranging a first electrode of the first pair of electrodes opposite the first group of armors, a4) arranging a second electrode of the first pair of electrodes opposite the second group of armors.

[0028] Advantageously, the first electrode of the first pair of electrodes is placed exclusively opposite the first group of armors without being placed opposite the second group of armors. The second electrode of the first pair of electrodes is placed exclusively opposite the second group of armors, without being placed opposite the first group of armors.

[0029] According to yet another advantageous characteristic of the invention making it possible to improve the sensitivity of the measurement, step a) comprises the following steps: a5) arranging a first electrode of the second pair of electrodes opposite the first group of armors, a6) arranging a second electrode of the second pair of electrodes opposite the second group of armors.

[0030] Advantageously, the first electrode of the second pair of electrodes is placed exclusively opposite the first group of armors without being placed opposite the second group of armors. The second electrode of the second pair of electrodes is placed exclusively opposite the second group of armors, without being placed opposite the first group of armors.

[0031] According to yet another advantageous characteristic of the invention making it possible to improve the sensitivity of the measurement, the single layer of armor, or when the flexible line comprises several layers of armor, the layer of armor closest to the outer sheath, comprises at least a third group of armor and a fourth group of armor distinct from each other and distinct from the first group of armor and the second group of armor, said third group of armor and said fourth group of armor being arranged between said first group of armor and said second group of armor, and step a) comprises the following steps: a7) arranging a first electrode of the second pair of electrodes opposite the third group of armors, a8) arranging a second electrode of the second pair of electrodes opposite the fourth group of armors.

[0032] Advantageously, the first electrode of the second pair of electrodes is placed exclusively opposite the third group of armors without being placed opposite the first group of armors, the second group of armors or the fourth group of armors. The second electrode of the second pair of electrodes is placed exclusively opposite the fourth group of armors, without being placed opposite the first group of armors, the second group of armors or the third group of armors.

[0033] According to yet another advantageous characteristic of the invention making it possible to improve the sensitivity of the measurement, step a) comprises the following step: a9) arranging the electrodes of the at least one pair of electrodes in contact with the external sheath.

[0034] According to yet another advantageous characteristic of the invention making it possible to ensure good penetration of the electromagnetic field through the external sheath and any intermediate sheaths, as well as good interaction of the electromagnetic field with the fluid contained in the annular space, step b) comprises the following step: b1) supplying with alternating voltage, or alternating current, of a determined frequency between 10 Hz and 10 MHz, advantageously between 100 kHz and 3 MHz, preferably between 200 kHz and 800 kHz or between 100 Hz and 200 kHz.

[0035] According to yet another advantageous characteristic of the invention making it possible to obtain an electrical signal that is easily exploitable and measurable with commercially available measuring instruments, in the case where, during step a), a single pair of electrodes is arranged in the vicinity of the outer sheath, the electrical signal measured during step c) is the complex impedance at the terminals of said single pair of electrodes. The impedance is said to be complex because it has a modulus and a phase, and it can be represented in a complex plane. In this embodiment, the measured electrical signal is a complex signal, because it has a modulus and a phase, and can be represented in a complex plane.

[0036] In the case where during step a) two pairs of electrodes are arranged in the vicinity of the outer sheath, namely on the one hand a first pair of electrodes and on the other hand a second pair of electrodes, according to yet another advantageous characteristic of the invention making it possible to obtain an electrical signal that is easily exploitable and measurable with commercially available measuring instruments, the electrical signal measured during step c) is a complex signal having a modulus and a phase. According to a first variant of this embodiment of the invention, the modulus of said complex signal is equal to the amplitude of the alternating voltage measured at the terminals of the second pair of electrodes, and the phase of said complex signal is equal to the phase shift measured between on the one hand the alternating voltage at the terminals of the second pair of electrodes and on the other hand the alternating voltage or current supplying the first pair of electrodes.According to a second variant of this embodiment of the invention, the modulus of said complex signal is equal to the ratio between, on the one hand, the amplitude of the alternating voltage measured at the terminals of the second pair of electrodes and, on the other hand, the amplitude of the alternating voltage supplying the first pair of electrodes, and the phase of said complex signal is equal to the phase shift measured between, on the one hand, the alternating voltage at the terminals of the second pair of electrodes and, on the other hand, the alternating voltage supplying the first pair of electrodes. This complex signal is the complex transmittance of the quadrupole whose two input terminals are connected to the first pair of electrodes and whose two output terminals are connected to the second pair of electrodes.According to a third variant of this embodiment of the invention, the modulus of said complex signal is equal to the ratio between, on the one hand, the amplitude of the alternating voltage measured at the terminals of the second pair of electrodes and, on the other hand, the amplitude of the alternating current supplying the first pair of electrodes, and the phase of said complex signal is equal to the phase shift measured between, on the one hand, the alternating voltage at the terminals of the second pair of electrodes and, on the other hand, the alternating current supplying the first pair of electrodes.

[0037] In the present application, the amplitude of an alternating voltage is defined by comparing the instantaneous values ​​of voltage during a period with the average value of the voltage during this period, the amplitude being equal to the maximum of the absolute values ​​of the differences between on the one hand the instantaneous values ​​and on the other hand the average value. In the case of a sinusoidal alternating voltage, the amplitude thus defined is equal to the effective voltage multiplied by the square root of two. Similarly, in the present application, the amplitude of an alternating current is defined by comparing the instantaneous values ​​of the current during a period with the average value of the current during this period, the amplitude being equal to the maximum of the absolute values ​​of the differences between on the one hand the instantaneous values ​​and on the other hand the average value.

[0038] According to yet another advantageous characteristic of the invention making it possible to simply exploit a complex signal, step d) comprises the following step: d1) comparing the modulus and / or the phase of the measured electrical signal with reference values ​​so as to determine the nature of the fluid contained in the annular space (13).

[0039] According to yet another advantageous characteristic of the invention making it possible to guarantee the precision of the measurement, during steps b) and c) the distance separating the electrodes of the or each of the pairs of electrodes is kept fixed.

[0040] According to yet another advantageous characteristic of the invention making it possible to ensure that a sufficient number of armors is arranged between the electrodes, during steps b) and c) the distance separating the electrodes from the or each of the pairs of electrodes is maintained between 100 mm and 500 mm, preferably between 200 mm and 500 mm.

[0041] According to yet another advantageous characteristic of the invention, the group of steps b), c) and d) is executed several times, simultaneously or sequentially, with a different determined frequency for each execution.

[0042] Another aspect of the description relates to a device for non-destructive testing of a flexible line comprising at least one layer of armor arranged inside an annular space and an external sheath surrounding said annular space, said annular space comprising a fluid. The testing device is remarkable in that it comprises: an electromagnetic field generator configured to generate an electromagnetic field extending through at least a portion of the annular space, said electromagnetic field generator comprising: at least one pair of electrodes intended to be arranged in the vicinity of the outer sheath, a voltage or current generator, configured to supply alternating voltage of determined frequency, respectively alternating current of determined frequency, to the single pair of electrodes or a first pair of electrodes of said pairs of electrodes so as to generate an electromagnetic field extending through at least a portion of the annular space a measuring instrument configured to measure, at said pair of electrodes, or a second pair of electrodes of said pairs of electrodes,an electrical signal linked to the electromagnetic characteristics of said at least one part of the annular space subjected to said generated electromagnetic field, a comparator configured to compare said electrical signal with reference values ​​so as to determine the nature of the fluid contained in the annular space.

[0043] Advantageously, the at least one pair of electrodes is arranged outside said flexible line, in the vicinity of the external sheath.

[0044] Alternatively, the power supply to the single pair of electrodes or the first pair of electrodes is in pulsed voltage, or in pulsed current. Advantageously, the assembly formed of armor and the fluid is subjected to the electromagnetic field.

[0045] Thus, the non-destructive testing device described makes it possible to control the nature of the fluid contained in the annular space of a flexible line, via an electromagnetic field capable of passing through one or more sheaths regardless of the type of contact, intimate or not, between the external sheath, the armor layer, and possibly the intermediate sheaths. Likewise, this device has the advantage of being effective from the first measurement and therefore makes it possible to avoid the need to install a mechanical scanning means such as a turntable.

[0046] According to yet another advantageous characteristic allowing the generation of an optimal electromagnetic field, the electrodes of the pair or pairs of electrodes comprise a conductive body made of metal, preferably copper.

[0047] According to yet another advantageous characteristic allowing the generation of an optimal electromagnetic field, the conductive body of the electrodes of the pair or pairs of electrodes have a parallelepiped shape with a rectangular base whose length and width are between 20 mm and 250 mm, preferably with a square base with sides equal to 70 mm.

[0048] According to yet another advantageous characteristic, allowing the impedance at the terminals of a pair of electrodes to be measured simply, the measuring instrument is a vector network analyzer. Description of figures

[0049] Other features and advantages of the invention will emerge from reading the description given below of particular embodiments of the invention, given for informational but non-limiting purposes, with reference to the appended drawings in which: there Figure 1is a schematic view of the non-destructive testing device intended for implementing the method according to the invention arranged opposite a flexible line extending from a bottom assembly to a surface assembly across a body of water; Figure 2 is a schematic perspective view of an example of a flexible line that the invention proposes to control; the Figure 3 is a schematic view of a first example embodiment of the non-destructive testing device intended for implementing the method according to the invention; Figure 4 is a schematic view of a first variant of a second exemplary embodiment of the non-destructive testing device intended for implementing the method according to the invention; Figure 5 is a schematic view of a second variant of the second embodiment of the non-destructive testing device intended for implementing the method according to the invention; Figure 6is a schematic perspective view of the second variant shown in Figure 5 ; there Figure 7 schematically represents: in broken line the curve of the reference values ​​of the modulus (M) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas, and in solid line the curve of the modulus (M) of the complex signals measured as a function of the determined frequency (F), when the annular space of the flexible line contains a liquid, and the frequency shift (D) between the two curves; the Figure 8schematically represents: in broken line the curve of the reference values ​​of the phase (P) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas, and in solid line the curve of the phase (P) of the complex signals measured as a function of the determined frequency (F), when the annular space of the flexible line contains a liquid, and the frequency shift (D) between the two curves; the Figure 9schematically represents: in broken line the curve of the reference values ​​of the real part (Re) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas, and in solid line the curve of the real part (Re) of the complex signals measured as a function of the determined frequency (F), when the annular space of the flexible line contains a liquid, and the frequency shift (D) between the two curves; the Figure 10schematically represents: in broken line the curve of the reference values ​​of the imaginary part (Im) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas, and in solid line the curve of the imaginary part (Im) of the complex signals measured as a function of the determined frequency (F), when the annular space of the flexible line contains a liquid, and the frequency shift (D) between the two curves.

[0050] For simplification, the different elements of the flexible line are shown flat on the Figure 3 to 5 , although in reality they are usually arranged in an arc. Detailed description of the invention

[0051] The solution proposed by the invention is a method for non-destructive testing of a flexible line (10) and the device (100) allowing the implementation of this method.

[0052] For the purposes of the invention, the term "flexible line" means any flexible line used in the field of subsea oil and / or gas installations for the transport of fluids, energy or even information. A subsea oil and / or gas installation generally comprises one or more surface assemblies (2) and one or more bottom assemblies (3).

[0053] Referring to the figure 1, a surface assembly (2) is arranged on the surface of a body of water (4). The body of water (4) is for example an ocean, a sea, a lake or a river. The surface assembly (2) can be fixed or floating. When it is fixed, the surface assembly (2) rests on a lattice or gravity type structure fixed to the bottom of the body of water. When it is floating, the surface assembly (2) is advantageously formed by a surface naval support which can be for example a floating production, storage and offloading unit called FPSO (Floating Production, Storage and Offloading) or a floating unit dedicated to liquefied natural gas called FLNG (Floating Liquified Natural Gas), a semi-submersible platform, which can be for example a TLP (Tension Leg Platform), an offloading buoy, a floating vertical column or a ship.

[0054] A bottom assembly (3) is arranged on the bottom of the body of water (4) and is in the form of one or a set of subsea production devices such as a well, wellhead, Christmas tree or X-tree, manifold, subsea processing unit (also abbreviated as SPU), subsea storage unit (also abbreviated as SSU), etc.

[0055] The oil and / or gas installation also comprises a network of flexible (1) and / or rigid lines enabling the surface assembly(s) (2) and the bottom assembly(s) (3) to be connected to each other. These flexible (1) or rigid lines are at least partially submerged in the body of water (4). The depth of the body of water (4) at the installation is, for example, between 50 m and 3000 m, or even 4000 m.

[0056] The flexible line (10) can be presented in the form: of a flexible pipe, as shown in the figure 2, of the unbonded type intended for the transport of hydrocarbons across the body of water (4), and for example produced according to the normative documents API 17 J (Specification for Unbonded Flexible Pipe) and API RP 17 B (Recommended Practice for Flexible Pipe) established by the American Petroleum Institute, or an umbilical reinforced with armor intended for the transport of electrical or hydraulic energy, data, or injection products, across the body of water (4), and for example produced according to the normative documents API 17 E (Specification for Umbilicals), or a combination of the two.

[0057] The flexible line (10) comprises at least one layer of armor (14, 23). Each layer of armor (14, 23) is in the form of a juxtaposition of several armors (15), generally between 30 and 100 armors (15). The armors (15), generally called tensile armors, have the function of absorbing the tensile forces exerted on the flexible line (10). The tensile breaking limit of the armors (15) is advantageously greater than 1000 MPa. Two adjoining armors (15) may be separated by a gap (16) with a width of between 5 mm and 0.001 mm. The armors (15) are wound helically so as to form a tube. The absolute value of the helix angle of the helicoid formed by an armor (15) is less than 60°, and is typically between 25° and 55°. An armor (15) is in the form of wire of rectangular, square, circular, oval, bean-shaped, T-shaped, or any other shape suitable to a person skilled in the art.

[0058] In some configurations, the flexible line (10) may comprise a pair of armor layers (14, 23). The two armor layers (14, 23) are crossed, i.e., they have substantially opposite helix angles, so as to balance the structure of the flexible line (10) in torsion, i.e., so as to limit its tendency to rotate under the effect of traction. The two armor layers (14, 23) are arranged coaxially, a first armor layer (14) being the armor layer closest to the outer sheath, and the second armor layer (23) being located inside the first armor layer (14).

[0059] The armors (15) may be made of metal, advantageously carbon steel or low-alloy steel or stainless steel. The metal armors are generally obtained by drawing, rolling, and heat treatment of metal wires. The metal armors (15) have an electrical conductivity generally between 3x10 6< S / m and 10x10 6< S / m, preferably between 5.5x10 6< S / m and 6.5x10 6< S / m. When they are made of carbon steel or low-alloy steel, the metal armors (15) are magnetic and have a relative magnetic permeability generally greater than or equal to 100. However, the present invention can also be applied to the case where the metal armors (15) are non-magnetic or weakly magnetic, for example if they are made of titanium, aluminum or certain grades of austenitic stainless steel.

[0060] The armors (15) can be made of composite materials, composed of a matrix and reinforcing fibers. The matrix is ​​formed from a thermosetting resin, for example an epoxy resin, or a thermoplastic resin, for example a resin based on polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF) or polyphenylene sulfide (PPS). The matrix is ​​generally non-magnetic and electrically insulating (virtually zero electrical conductivity). The reinforcing fibers are generally oriented parallel to the axis of the armor and can be made of carbon, glass or aramid. Glass, carbon and aramid are non-magnetic. Glass and aramid are electrical insulators while carbon is conductive. The armors (15) made of carbon fiber composite material have an electrical conductivity generally between 10x10 3< S / m and 50x10 3< S / m.The armors (15) generally have a width that can vary from 10 mm to 30 mm and a thickness that can vary from 0.5 mm to 10 mm.

[0061] The at least one layer of armor (14, 23) is arranged inside an annular space (13). For the purposes of the invention, the term "annular space" means a space delimited by two fictitious cylinders (24, 25) of different radii arranged coaxially. The thickness of the annular space (13), corresponding to the difference in the radii of the two fictitious cylinders, is generally between 5 mm and 60 mm, or even more. The annular space (13) comprises a fluid. This fluid is generally a gas when the flexible line (10) is intact and a liquid when the flexible sheath has suffered degradation.

[0062] At the single armor layer (14), or when the flexible line (10) comprises several armor layers (14, 23) of the armor layer (14) closest to the outer sheath (11), the latter being described in more detail in the remainder of the description, and for the purposes of the non-destructive testing method, it is possible to identify several armor groups (17, 18, 19, 20) comprising from 2 to 6 armors (15), or even more. Thus, the armor layer (14) closest to the outer sheath (11) may comprise at least a first armor group (17) and a second armor group (18) distinct from each other. The armor layer (14) closest to the outer sheath (11) may also comprise at least a third armor group (19) and a fourth armor group (20) distinct from each other and distinct from the first armor group (17) and the second armor group (18).The third group of armors (19) and the fourth group of armors (20) are preferentially arranged between the first group of armors (17) and the second group of armors (18).

[0063] The flexible line (10) comprises at least one outer sheath (11). The outer sheath (11) is arranged so as to surround said annular space (13). For the purposes of the present invention, the term "surround" means that the annular space (13) is inscribed in a cylinder formed by the outer sheath (11), the latter being able to be, or not, adjacent to said annular space (13). Indeed, in certain embodiments, the flexible line (10) may comprise one or more intermediate sheaths interposed between the outer sheath (11) and the annular space (13). The outer sheath (11) is in the form of a flexible tube of circular, possibly oval, cross-section. The outer sheath (11) is made of polymer, for example polyamide, polyethylene or elastomeric thermoplastic polymer. The outer sheath (11) generally has a thickness which may vary from 2 mm to 20 mm. The outer sheath (11) is generally obtained by extrusion.The outer sheath (11) is non-magnetic and electrically insulating (virtually zero electrical conductivity).

[0064] In practice, and as shown schematically in the figure 2 , when the flexible line (10) is a flexible conduit, it may comprise from the inside to the outside: an internal carcass (21), an internal sheath (12), also called a pressure sheath, a pressure vault (22), one or more layers of armor (14, 23), one or more intermediate sheaths (not shown), and the external sheath (11).

[0065] The internal carcass (21) is formed from a profiled stainless steel strip wound with a short pitch to form turns stapled together. The main function of the internal carcass (21) is to absorb radial crushing forces, for example those linked to hydrostatic pressure or those exerted by external equipment, in particular during the installation of the flexible pipe at sea. A flexible pipe comprising an internal carcass (21) is said to have a “rough bore” due to the geometry of said internal carcass.

[0066] However, the present invention could also be applied to a flexible pipe not comprising an internal carcass, such a pipe being called "smooth bore", because its first layer starting from the inside is the internal sheath (12), the latter having the shape of a tube having a smooth internal wall.

[0067] The inner sheath (12) is in the form of a flexible tube of circular, possibly oval, cross-section. The function of the inner sheath (12) is to confine the hydrocarbon circulating inside the flexible pipe, the inner carcass (21) not being watertight. The polymer material forming the inner sheath (12) is chosen in particular according to the chemical composition, the temperature and the pressure of the hydrocarbon that the flexible pipe must transport. The polymers most used to produce the inner sheath (12) are polyamides, cross-linked polyethylene and fluorinated polymers based on vinylidene fluoride, and in particular those based on polyvinylidene fluoride (PVDF). The inner sheath (12) generally has a thickness that can vary from 2 mm to 20 mm. The inner sheath (12) is generally obtained by extrusion. The outer sheath (11) and the inner sheath (12) are generally arranged coaxially.For the purposes of the invention, the term "coaxially" means that two tubular elements are coaxial except for manufacturing defects, i.e. these two tubular elements are deemed to be coaxial even if there is a gap between their axes of less than 10 mm. The outer sheath (11) and the inner sheath (12) then delimit the annular space (13) between them.

[0068] The pressure vault (22) is made up of one or more metal wires having a Z-, T-, C-, X-, or K-shaped cross-section, said wire(s) being wound helically with a short pitch, i.e. with a helix angle close to 90°, and stapled together. The main function of the pressure vault (22) is to absorb the radial forces linked to the pressure of the hydrocarbon flowing in the pipe, the internal sheath (12) not being capable of supporting high pressure on its own and therefore having to be supported by said pressure vault (22).

[0069] The device (100) for non-destructive testing of the flexible line (10) is intended to be at least partially immersed in the body of water (4) to carry out the testing of said flexible line (10).

[0070] As schematized on the figures 3 to 5 , the device (100) for non-destructive testing of the flexible line (10) comprises an electromagnetic field generator configured to generate an electromagnetic field extending through at least a portion of the annular space (13). Thus, an assembly formed of armor (15) and the fluid is subjected to said electromagnetic field.

[0071] The electromagnetic field generator may comprise at least one pair of electrodes (101, 102, 103, 104). Thus, the electromagnetic field generator may comprise a single pair of electrodes (101, 102), or two pairs of electrodes (101, 102, 103, 104) or more than two pairs of electrodes. The electrodes (101, 102, 103, 104) are intended to be arranged in the vicinity of the outer sheath (11) of the flexible line (10). "Vicency" means that the distance separating the electrodes (101, 102, 103, 104) from the outer sheath (11) is at least less than the radius of the flexible line (10). Advantageously, the distance separating the electrodes (101, 102, 103, 104) from the outer sheath (11) is less than 100 mm, preferably less than 20 mm. According to a preferred embodiment, the electrodes (101, 102, 103, 104) are intended to be arranged in contact with the outer sheath (11).For the purposes of the invention, the term "in contact" means that there is at least one point of contact between the electrodes (101, 102, 103, 104) and the outer sheath (11). The electrodes (101, 102, 103, 104) are thus intended to be immersed in the body of water (4) to carry out the control of the flexible line (10).

[0072] Each electrode (101, 102, 103, 104) may comprise a conductive body. Advantageously, the conductive body of one, several, or all of the electrodes (101, 102, 103, 104) may be made of metal, preferably copper, silver, or gold. The conductive body of each of the electrodes (101, 102, 103, 104) may have a circular, hexagonal, rectangular, square, diamond shape, or any other shape suitable to a person skilled in the art and preferably dimensions between 20 mm and 250 mm. The conductive body of the electrodes (101, 102, 103, 104) advantageously has a parallelepiped shape with a rectangular base whose length and width are between 20 mm and 250 mm, preferably with a square base with sides equal to 70 mm. The conductive body of each electrode (101, 102, 103, 104) has a thickness generally between 0.1 mm and 5 mm.The conductive body of each electrode (101, 102, 103, 104) may comprise a front face intended to face the flexible line (10) to be controlled. Each electrode (101, 102, 103, 104) may comprise a corrosion protection coating arranged on the front face of the conductive body of said electrode (101, 102, 103, 104). This corrosion protection coating may be made with an electrically insulating and non-magnetic material such as for example a polymer material. This corrosion protection coating may have a thickness of between 1 mm and 5 mm. Alternatively, or in addition to the corrosion protection coating, each electrode (101, 102, 103, 104) may comprise an elastomeric coating configured to expel water between said electrode and the outer sheath (11) of the flexible line (10) when said electrode comes into contact with said outer sheath.The elastomeric coating may have a thickness of between 1 mm and 5 mm. The conductive body of each electrode (101, 102, 103, 104) may also comprise a rear face opposite the front face. The conductive body of each electrode (101, 102, 103, 104) may finally comprise one or more lateral faces joining the front face to the rear face. Advantageously, the electrodes (101, 102, 103, 104) of the or each of the pairs of electrodes are separated by a fixed distance, in particular during the measurement. In particular, the distance separating the electrodes (101, 102, 103, 104) of the or each of the pairs of electrodes may be between 200 mm and 500 mm. The electrodes (101, 102, 103, 104) can be mounted on a remotely operated vehicle (ROV) so as to be able to easily operate the device (100) for non-destructive testing of the flexible line (10) within the body of water.The electrodes can also be mounted on a clamp, in particular inside the pads of said clamp, or on any means of attachment and / or movement on a flexible line (10) known to those skilled in the art.

[0073] Each electrode (101, 102, 103, 104) may comprise a means of electrical insulation with the surrounding environment, in particular the water of the body of water (4), so as to avoid the creation of a looping of the electromagnetic field between said electrodes (101, 102, 103, 104), by the rear face of their conductive bodies, through the water of the body of water. In particular, the electrical insulation means may be in the form of an electrically insulating coating arranged on the rear face and the side face(s) of the conductive body of the electrode (101, 102, 103, 104). The term "electrically insulating" means that the material used has a resistivity greater than 10 9 < Ω.m. This electrically insulating coating may be made of resin or syntactic foam. The coating generally has a thickness of between 10 mm and 30 mm, or even more.The insulating means may also be in the form of a bell surrounding the rear face and the face portion(s) of the electrode (101, 102, 103, 104). The bell may be made of resin or syntactic foam. The bell generally has a thickness of between 20 mm and 30 mm, or even more.

[0074] The electromagnetic field generator may also comprise a voltage generator (105) or alternatively a current generator. The voltage generator (105), or current generator (105), is configured to provide a variable voltage or a variable current. The variable voltage or variable current is in particular of the alternating, sinusoidal, square, triangular or pulsed type.

[0075] When the electromagnetic field generator comprises a single pair of electrodes (101, 102), the voltage generator (105) is configured to supply said pair of electrodes (101, 102) with alternating voltage of a determined frequency so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field. Alternatively, the current generator (105) is configured to supply said pair of electrodes (101, 102) with alternating current of a determined frequency so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field.Alternatively, the voltage generator (105) is configured to supply pulsed voltage to said pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field. Alternatively, the current generator (105) is configured to supply pulsed current to said pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field.

[0076] When the electromagnetic field generator comprises several pairs of electrodes (101, 102, 103, 104), the voltage generator (105) is configured to supply alternating voltage of determined frequency to the first pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field. Alternatively, the current generator (105) is configured to supply alternating current of determined frequency to the first pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field.Alternatively, the voltage generator (105) is configured to supply pulsed voltage to the first pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field. Alternatively, the current generator (105) is configured to supply pulsed current to the first pair of electrodes (101, 102) so as to generate an electromagnetic field extending through at least a portion of the annular space (13) of said flexible line (10). Thus, an assembly formed of armors (15) and the fluid is subjected to said electromagnetic field.

[0077] For this purpose, the voltage generator (105), or alternatively the current generator, may comprise means for electrical connection to the electrodes (101, 102, 103, 104) to be supplied with voltage, or alternatively with current, or with pulsed voltage, or with pulsed current. Each connection means may be in the form of an electrical cable, one of the ends of which is welded to the electrode (101, 102, 103, 104), or else equipped with an electrical connector cooperating with a corresponding electrical connector arranged on the electrode (101, 102, 103, 104). As such, the voltage generator (105), or alternatively the current generator, can be immersed and arranged in a sealed box near the pair or pairs of electrodes (101, 102, 103, 104) or be largely offset towards the surface assembly (2) or a boat, only the connection means extending from said surface assembly (2) or said boat towards the electrodes (101, 102, 103, 104) being at least partially immersed.The voltage generator (105) is configured to supply alternating voltage, or alternating current, of a determined frequency between 10 Hz and 10 MHz, advantageously between 100 kHz and 3 MHz, preferably between 200 kHz and 800 kHz. The voltage generator (105) is configured to deliver an alternating voltage of amplitude between 1 mV and 10 V, preferably between 100 mV and 1 V.

[0078] The device (100) for non-destructive testing of a flexible line (10) also comprises a measuring instrument (106).

[0079] When the electromagnetic field generator comprises a single pair of electrodes (101, 102), the measuring instrument is configured to measure, at the level of said pair of electrodes (101, 102), an electrical signal linked to the electromagnetic characteristics of said at least one part of the annular space (13) subjected to said generated electromagnetic field.

[0080] When the electromagnetic field generator comprises several pairs of electrodes (101, 102, 103, 104), the measuring instrument is configured to measure, at a second pair of electrodes (103, 104), the electromagnetic characteristics of said at least one part of the annular space (13) subjected to said generated electromagnetic field.

[0081] For this purpose, the measuring instrument (106) may comprise means for electrical connection to the electrodes (101, 102, 103, 104) on which the measurement is to be carried out. In particular, the measured electrical signal may be a complex signal, the modulus of said complex signal being equal to the amplitude of the voltage measured across the terminals of the second pair of electrodes (103, 104), and the phase of said complex signal being equal to the phase shift measured between, on the one hand, the voltage across the terminals of the second pair of electrodes (103, 104) and, on the other hand, the voltage or current supplying the first pair of electrodes (101, 102). Each connection means may be in the form of an electrical cable, one end of which is welded to the electrode (101, 102, 103, 104), or else equipped with an electrical connector cooperating with a corresponding electrical connector arranged on the electrode (101, 102, 103, 104).In this respect, the measuring instrument (106) can be immersed and arranged in a watertight box near the pair or pairs of electrodes (101, 102, 103, 104) or be largely offset towards the surface assembly (2) or a boat, only the connection means extending from said surface assembly (2) or from said boat towards the electrodes (101, 102, 103, 104) being at least partially immersed.

[0082] The electrical signal linked to the electromagnetic characteristics may be the voltage and / or the intensity and / or an impedance and / or any other electrical quantity suitable to a person skilled in the art. The measuring instrument (106) may comprise a voltmeter and / or an ammeter. In particular, the measuring instrument (106) may be an impedance meter, a combination of a voltmeter and an ammeter, which, by the voltage to intensity ratio, makes it possible to determine the impedance of an electrical circuit. The measuring instrument (106) is advantageously a vector network analyzer.

[0083] The device (100) for non-destructive testing of the flexible line (10) further comprises an analyzer configured to process the electrical signal linked to the measured electromagnetic characteristics so as to determine the nature of the fluid contained in the annular space (13) of said flexible line (10). This analyzer may take the form of a comparator (107) configured to compare the electrical signal linked to the measured electromagnetic characteristics with reference values ​​so as to determine the nature of the fluid contained in the annular space (13) of said flexible line (10). The comparator (107) may be in the form of a microprocessor executing a piece of computer program stored in a memory (108) and configured to determine, from the measurement of the input electrical signal and reference values ​​stored in said memory (108), the nature of the fluid contained in the annular space (13).The term "nature of the fluid" means that the fluid is a gas or a liquid. When the annular space (13) contains at least one liquid phase, the comparator (107) may also be configured to compare the measured electrical signal with reference values ​​so as to determine the nature of the liquid phase(s) contained in the annular space (13). The term "nature of the liquid phase(s)" means that the liquid is water and / or salt water and / or oil and / or any other liquid likely to have flooded the annular space (13). The comparator (107) is connected to the measuring instrument (106) by means of an electronic circuit and / or electrical or optical data cables and / or wireless communication devices and / or via any other connection means suitable to a person skilled in the art.

[0084] The device (100) for non-destructive testing of the flexible line (10) may also comprise one or more information means (109) connected to the comparator and configured to warn an operator of the nature of the fluid or of the liquid phase(s). This information means (109) may comprise a sounding member configured to emit a specific sound when the annular space contains at least one liquid phase or conversely only a gaseous phase. The sounding member may also be configured to emit a first sound when the annular space (13) contains at least one liquid phase and a second sound, different from said first sound, when said annular space (13) contains only a gaseous phase, or a different sound per type of liquid phase. In particular, the sounding member may comprise one or more loudspeakers.This information means (109) may, alternatively or in combination, comprise a light member configured to emit a light signal when the annular space contains at least one liquid phase or conversely only a gaseous phase. The light member may also be configured to emit a first light signal when the annular space (13) contains at least one liquid phase and a second light signal, different from the first light signal, when said annular space (13) contains only a gaseous phase, or even a different light signal per type of liquid phase. In particular, the light member may comprise one or more light-emitting diode (LED) type indicators. This information means (109) may, alternatively or in combination, comprise a display screen for displaying messages relating to the nature of the liquid contained in the annular space of the flexible line.The information means (109) are generally arranged on the surface assembly (2) or a boat. The information means (109) are connected to the comparator (107) by means of an electronic circuit and / or electrical or optical data cables and / or wireless communication means and / or or via any other connection means suitable to those skilled in the art.

[0085] The method for non-destructive testing of the flexible line (10) according to the invention is remarkable in that it comprises the following steps: a) arranging in the vicinity of the outer sheath (11) at least one pair of electrodes (101, 102, 103, 104), b) supplying said pair of electrodes (101, 102), or a first pair of electrodes (101, 102) of said pairs of electrodes (101, 102, 103, 104), with alternating voltage of determined frequency, or with alternating current of determined frequency, or with pulsed voltage, or with pulsed current, so as to generate an electromagnetic field extending through at least a portion of the annular space (13), and thus, subjecting an assembly formed of armor (15) and the fluid to said electromagnetic field, c) measuring, at said pair of electrodes (101, 102), or a second pair of electrodes (103, 104) of said pairs of electrodes (101, 102, 103, 104), an electrical signal linked to the electromagnetic characteristics of said at least one part of the annular space (13) subjected to said generated electromagnetic field,d) processing said electrical signal so as to determine the nature of the fluid contained in the annular space (13).

[0086] Generally, the signal processing consists of comparing said electrical signal with reference values ​​so as to determine the nature of the fluid contained in the annular space (13). Preferably, when the measured electrical signal is a complex signal, the signal processing consists of comparing the modulus and / or the phase of said complex with reference values ​​so as to determine the nature of the fluid contained in the annular space (13).

[0087] Under the effect of the electromagnetic field, the assembly formed by the juxtaposition of two conductive armors (15) separated by a gap (16) comprising a dielectric fluid that is significantly less conductive than the armors (15) will behave like a capacitor whose electrical capacity depends in particular on the dielectric permittivity of the fluid. Thus, the part located between the electrodes (101, 102, 103, 104) can then be compared to a network of capacitors in series. Knowing the actual average dimension of the gaps (16), it is possible to calculate theoretically, knowing the electrical conductivity of the armors (15) and of the fluid, the theoretical value of the electrical capacity as a function of the nature of the fluid. These calculated theoretical values ​​can then be stored as reference values ​​in the memory (108) of the device (100).Thus, by comparing the theoretical value of the electrical capacitance with the measurement of the total electrical capacitance between the electrodes (101, 102, 103, 104) at which the measurement is made, it is possible to determine which theoretical value the measured value is closest to and thus determine the nature of the fluid contained in the annular space (13) of the flexible line (10).

[0088] Referring to the figure 3, and according to a first exemplary embodiment, during step a), a single pair of electrodes (101, 102) is arranged in the vicinity of the outer sheath (11). In an embodiment with a single pair of electrodes (101, 102), it is firstly possible to arrange the two electrodes (101, 102) of the pair in an aligned manner along the same group of armors. However, the difference in measurable electrical capacity between different configurations of fluid contained in the annular space (13) is small, generally of the order of 1 / 10 e<, and it is thus difficult to effectively determine the nature of the fluid contained in said annular space (13) given the risks of interference with the measurement in real conditions, in particular due to imperfect positioning of said electrodes (101, 102) relative to the external sheath (11) and / or the armor (15).Therefore, in order to obtain more precise measurements and improved exploitation of the results, it is preferable that step a) includes the following steps: . a1) arranging a first electrode (101) of the single pair of electrodes (101, 102) opposite the first group of armors (17), a2) arranging a second electrode (102) of the single pair of electrodes (101, 102) opposite the second group of armors (18).

[0089] In a configuration with a single pair of electrodes (101, 102), the measurement carried out in step c) is then carried out at the same pair of electrodes (101, 102) at the terminals of which the current is delivered in step b).

[0090] By referring to the figures 4 And 5, and according to a second exemplary embodiment of step a), the latter may comprise step a3) consisting of arranging in the vicinity of the external sheath (11) two pairs of electrodes (101, 102, 103, 104). In a manner similar to the first exemplary embodiment of step a), it is preferable to avoid a configuration in which the electrodes (101, 102, 103, 104) are aligned along the same group of armors. Thus, in order to obtain more precise measurements and improved exploitation of the results, it is preferable for step a) to comprise the following steps: a3) arranging a first electrode (101) of the first pair of electrodes (101, 102) opposite the first group of armors (17), a4) arranging a second electrode (102) of the first pair of electrodes (101, 102) opposite the second group of armors (18).

[0091] As shown in the figure 4, in a first variant of the second example of embodiment of step a), the latter may comprise the following steps: a5) arranging a first electrode (103) of the second pair of electrodes (103, 104) opposite the first group of armors (17), a6) arranging a second electrode (104) of the second pair of electrodes (103, 104) opposite the second group of armors (18).

[0092] As shown in the figures 5 And 6 , in a second variant of the second example of embodiment of step a), the latter may comprise the following steps: a7) arranging a first electrode (103) of the second pair of electrodes (103, 104) opposite the third group of armors (19), a8) arranging a second electrode (104) of the second pair of electrodes (103, 104) opposite the fourth group of armors (20).

[0093] In a configuration with two pairs of electrodes (101, 102, 103, 104) the measurement carried out in step c) is then carried out at a second pair of electrodes (103, 104) different from the first pair of electrodes (101, 102) supplied with alternating voltage, or alternating current, or pulsed voltage, or pulsed current.

[0094] Other variants with more than two pairs of electrodes could also be imagined by those skilled in the art without distorting the very essence of the invention.

[0095] In practice, whatever the example or the variant embodiment chosen for the number of pairs of electrodes (101, 102, 103, 104), and as mentioned previously, each group of armors (17, 18, 19, 20) can comprise between 2 and 6 armors, possibly more. In order to obtain optimal measurements and exploitation of the results, it is preferable that the sum of the widths of the armors (15) of the armor group (17, 18, 19, 20) is at least equal to the width of the electrode (101, 102, 103, 104) which is arranged opposite.

[0096] In practice, and whatever the example or variant embodiment chosen for the number of pairs of electrodes (101, 102, 103, 104), to obtain a usable measurement, it is sufficient that the electrodes (101, 102, 103, 104) are arranged in the vicinity of the external sheath (11) of the flexible line (10), that is to say at a distance at least less than the radius of said flexible line (10). However, the accuracy of the measurement and the exploitation of the results improve the closer the electrodes (101, 102, 103, 104) are to the external sheath (11). Advantageously, the distance separating the electrodes (101, 102, 103, 104) from the outer sheath (11) is less than 100 mm, preferably less than 20 mm. In an optimal arrangement mode, step a) may comprise step a9) consisting of arranging the electrodes (101, 102, 103, 104) of the at least one pair of electrodes (101, 102, 103, 104) in contact with the outer sheath (11).

[0097] Still with a view to optimizing the method, step b) may comprise step b1) consisting of supplying with alternating voltage, or alternating current, of a determined frequency between 10 Hz and 10 MHz, advantageously between 100 kHz and 3 MHz, preferably between 200 kHz and 800 kHz. The selection of these frequency ranges makes it possible to ensure better penetration of the electromagnetic field through the outer sheath (11) and the annular space (13). Furthermore, the selection of this frequency range makes it possible to clearly distinguish between them the first case where the fluid is air (dry annular space), the second case where the fluid is fresh water having slowly diffused through the inner sheath (annular flooded by diffusion from the inside of the pipe), and the third case where the fluid is salt water (annular flooded by sea water probably due to a loss of sealing of the outer sheath).The distinction between air and fresh water is based primarily on the difference in the dielectric permittivities of air and water, a difference that is linked in particular to the significant polarity of water molecules. The distinction between fresh water and salt water is based primarily on the difference in electrical conductivity. The selection of the aforementioned frequency range makes it possible to best exploit these differences in electromagnetic properties in a simple and reliable manner.

[0098] Step b) may also comprise one or more additional steps, carried out simultaneously or sequentially, and consisting of supplying alternating voltage, or alternating current, of a determined frequency distinct from the other determined frequencies of step b) or of said additional steps. This is then referred to as a frequency sweep. In practice, when performing a frequency sweep, the group of steps b), c) and d) is carried out several times, simultaneously or sequentially, with a different determined frequency for each execution. The fact of making several different measurements by varying the determined frequency of the alternating voltage or alternating current supply makes it possible to improve the determination of the fluid contained in the annular space (13).

[0099] As mentioned above, and taking into account the behavior of the assembly formed by the armors (15) and the fluid contained in the annular space (13), when said assembly is subjected to an electromagnetic field, the signal linked to the electromagnetic characteristics of the annular space that it may be interesting to measure is the electrical capacitance between armor wires. However, it may prove complex to carry out a direct measurement. Thus, it may be judicious to go through the measurement of other electrical signals making it possible to then obtain by calculation the value of the electrical capacitance via standard physical models and theories.In another way it is also possible, knowing the theoretical electrical capacity, to deduce other theoretical electrical characteristics such as the theoretical voltage, the theoretical intensity, the theoretical impedance or the theoretical transmittance, and to take these theoretical values ​​as reference values ​​in order to compare them directly to the measured electrical signal, namely the measured voltage, the measured intensity, the measured impedance or the measured transmittance. Alternatively or additionally, the reference values ​​can also be obtained by measurements carried out in the laboratory on flexible line samples (10). Examples of curves of reference values ​​obtained in the laboratory are shown in the . figures 7 to 10. Thus, step c) may comprise a step of measuring the voltage across the single pair of electrodes (101, 102) or the second pair of electrodes (103, 104) and / or a step of measuring the current flowing through the electrodes of said single pair of electrodes (101, 102) or said second pair of electrodes (103, 104). Alternatively or in combination, step c) may also comprise step c1) of measuring the impedance across the single pair of electrodes (101, 102), or the transmittance between the first pair of electrodes (101, 102) and the second pair of electrodes (103, 104). Impedance and transmittance are complex signals.In the case where the impedance is measured, step d) may comprise step d1) consisting of comparing the impedance measured at the terminals of the single pair of electrodes (101, 102) with a reference impedance at the terminals of the single pair of electrodes (101, 102) so as to determine the nature of the fluid contained in the annular space (13) of the flexible line (10). In the case where the transmittance is measured, step d) may comprise step d1) consisting of comparing the transmittance between the first pair of electrodes (101, 102) and the second pair of electrodes (103, 104), with a reference transmittance between the first pair of electrodes (101, 102) and the second pair of electrodes (103, 104), so as to determine the nature of the fluid contained in the annular space (13) of the flexible line (10).In practice, the comparator compares the modulus and / or the phase and / or the imaginary part and / or the real part of the measured electrical signal with reference values ​​in order to determine the nature of the fluid contained in the annular space (13).

[0100] When a frequency sweep is carried out at step b), and when the electrical signal measured for each determined frequency is a complex signal of the complex impedance type or of the complex transmittance type, the measured complex signals can be represented and processed in different ways illustrated by the figures 7 to 10 .

[0101] In reference to the figure 7, the solid line curve (31) represents the modulus (M) of the complex signals measured as a function of the frequency (F), in the case where the annular space (13) of the flexible line is completely flooded with water. The broken line curve (32) represents the reference values ​​of the modulus (M) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas. The curve (32) of the reference values ​​of the modulus (M) is in particular determined during a calibration of the control device which is carried out on a section of flexible line whose annular space is dry and filled only with gas, typically filled with air.Comparison of the curve (31) of the modulus (M) of the complex signals measured during a check of a flexible line whose annular space is filled with a fluid of unknown nature, with the curve (32) of the reference values ​​of the modulus (M) corresponding to an annular space filled with gas, makes it possible to determine the nature of the fluid present in this annular space, and in particular it makes it possible to determine whether this fluid is a gas or fresh water or sea water.

[0102] In reference to the figure 8, the solid line curve (41) represents the phase (P) of the complex signals measured as a function of the frequency (F), in the case where the annular space (13) of the flexible line is completely flooded with water. The broken line curve (42) represents the reference values ​​of the phase (P) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas. The curve (42) of the reference values ​​of the phase (P) is in particular determined during a calibration of the control device which is carried out on a section of flexible line whose annular space is dry and filled only with gas, typically filled with air.Comparison of the curve (41) of the phase (P) of the complex signals measured during a check of a flexible line whose annular space is filled with a fluid of unknown nature, with the curve (42) of the reference values ​​of the phase (P) corresponding to an annular space filled with gas, makes it possible to determine the nature of the fluid present in this annular space, and in particular it makes it possible to determine whether this fluid is a gas or fresh water or sea water.

[0103] The curves representing the modulus (M) and the phase (P) of the complex signals as a function of the frequency (F) are advantageously used together during step d) of comparison with reference values.

[0104] In reference to the figure 9, the solid line curve (51) represents the real part (Re) of the complex signals measured as a function of the frequency (F), in the case where the annular space (13) of the flexible line is completely flooded with water. The broken line curve (52) represents the reference values ​​of the real part (Re) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas. The curve (52) of the reference values ​​of the real part (Re) is in particular determined during a calibration of the control device which is carried out on a section of flexible line whose annular space is dry and filled only with gas, typically filled with air.Comparing the curve (51) of the real part (Re) of the complex signals measured during a check of a flexible line whose annular space is filled with a fluid of unknown nature, with the curve (52) of the reference values ​​of the real part (Re) corresponding to an annular space filled with gas, makes it possible to determine the nature of the fluid present in this annular space, and it makes it possible in particular to determine whether this fluid is a gas or fresh water or sea water.

[0105] In reference to the figure 10, the solid line curve (61) represents the imaginary part (Im) of the complex signals measured as a function of the frequency (F), in the case where the annular space (13) of the flexible line is completely flooded with water. The broken line curve (62) represents the reference values ​​of the imaginary part (Im) of the complex signal as a function of the determined frequency (F), corresponding to the case where the annular space of the flexible line contains a gas. The curve (62) of the reference values ​​of the imaginary part (Im) is in particular determined during a calibration of the control device which is carried out on a section of flexible line whose annular space is dry and filled only with gas, typically filled with air.Comparing the curve (61) of the imaginary part (Im) of the complex signals measured during a check of a flexible line whose annular space is filled with a fluid of unknown nature, with the curve (62) of the reference values ​​of the imaginary part (Im) corresponding to an annular space filled with gas, makes it possible to determine the nature of the fluid present in this annular space, and it makes it possible in particular to determine whether this fluid is a gas or fresh water or sea water.

[0106] The curves representing the real part (Re) and the imaginary part (Im) of the complex signals as a function of the frequency (F) are advantageously used together during step d) of comparison with reference values.

[0107] Furthermore, the curves representing the modulus (M) and / or the phase (P) and / or the real part (Re) and / or the imaginary part (Im) of the complex signals measured as a function of the frequency (F), generally have at least one resonance peak, in particular when the frequency sweep covers determined frequencies varying between 10 Hz and 10 MHz, advantageously between 1 kHz and 5 MHz, preferably between 100 kHz and 3 MHz. This electrical resonance phenomenon is notably linked to the inductances of the electrical cables connecting the electrodes to the impedance or transmittance measuring device. Indeed, a pair of electrodes is generally comparable to a capacitance (capacitor) and when it is connected in parallel to an inductance (here that of the cable) we obtain a resonant circuit whose resonant frequency is inversely proportional to the square root of the product of the capacitance by the inductance.Furthermore, it has been discovered that the resonant frequency of a resonance peak varies depending on the nature of the fluid contained in the annular space of the flexible line, the resonant frequency in the presence of a water-filled annulus being significantly lower than that in the presence of a gas-filled annulus. This phenomenon is consistent with the fact that water has a significantly higher electrical permittivity than gases, particularly air, so that the capacitance across a pair of electrodes increases significantly when the annulus is flooded, which has the effect of lowering the resonant frequency.

[0108] Flooding of the annulus of a flexible line can therefore be detected by comparing the resonant frequency of a resonance peak with a reference value determined during calibration on a flexible line with a gas-filled annulus. With reference to figures 7 to 10, the resonance frequency of a resonance peak (33, 43, 53, 63) is measured on at least one of the curves representing the modulus (M) and / or the phase (P) and / or the real part (Re) and / or the imaginary part (Im) of the complex signals measured as a function of the frequency (F). Then, this measured resonance frequency is compared with a reference value which is the resonance frequency of the resonance peak (34, 44, 54, 64) determined on at least one of the reference curves (32, 42, 52, 62), which makes it possible to determine the frequency shift (D) which is equal to the difference between, on the one hand, the reference resonance frequency and, on the other hand, the measured resonance frequency. In practice, when the annular space contains a gas, the frequency shift (D) is small, i.e. generally less than 1 kHz.On the contrary, when the annular space contains a liquid, notably water, the frequency shift (D) is significant, i.e. generally greater than 5 kHz.

[0109] Also, and in order to obtain optimal measurements and exploitation of the results, it may be preferable to carry out a measurement statically. Thus, during steps b) and c) it is preferable to keep the distance separating the electrodes (101, 102, 103, 104) from the or each of the pairs of electrodes (101, 102, 103, 104) constant. This distance is advantageously between 200 mm and 500 mm. This then makes it possible to ensure that there is a sufficient number of armors (15) arranged between the electrodes (101, 102, 103, 104) from the or each of the pairs of electrodes (101, 102, 103, 104) so ​​that the measurement is optimal, generally between 8 and 20 armors.

Claims

1. A method for the nondestructive inspection of a flexible line (10) at least partially immersed in a body of water, the flexible line (10) comprising at least one armor layer (15) arranged inside an annular space (13) and an external sheath (11) surrounding said annular space (13), said annular space (13) comprising a fluid, characterized in that the method is a nondestructive control method of a flexible line comprising the following steps: a) arranging, outside said flexible line (10), at least one pair of electrodes (101, 102, 103, 104) in the vicinity of the external sheath (11), the electrodes (101, 102, 103, 104) being immerged in the body of water, b) supplying alternating voltage of determined frequency, or alternating current of determined frequency, or pulsed voltage, or pulsed current, to said pair of electrodes (101, 102), or a first pair of electrodes (101, 102) of said pairs of electrodes (101, 102, 103, 104), so as to generate an electromagnetic field extending through at least part of the annular space (13), and to subject an assembly formed by armors (15) and the fluid to said electromagnetic field, c) measuring, at said pair of electrodes (101, 102), or at a second pair of electrodes (103, 104) of said pairs of electrodes (101, 102, 103, 104), an electrical signal related to the electromagnetic characteristics of said at least one part of the annular space (13) subject to said generated electromagnetic field, d) comparing said electrical signal with the reference values so as to determine whether the fluid contained in the annular space (13) is a gas or a liquid, in particular so as to determine whether the fluid is a gas or freshwater or seawater.

2. The method for the nondestructive inspection of a flexible line (10) according to claim 1, characterized in that during step a), a single pair of electrodes (101, 102) is arranged near the external sheath (11).

3. The method for the nondestructive inspection of a flexible line (10) according to claim 2, characterized in that the sole armor layer (14), or when the flexible line (10) comprises several armor layers (14, 23), the armor layer (14) closest to the external sheath (11), comprises at least a first group of armors (17) and a second group of armors (18) separate from one another, and in that step a) comprises the following steps: a1) arranging a first electrode (101) from the sole pair of electrodes (101, 102) opposite the first group of armors (17), a2) arranging a second electrode (102) from the sole pair of electrodes (101, 102) opposite the second group of armors (18).

4. The method for the nondestructive inspection of a flexible line (10) according to claim 1, characterized in that during step a), two electrode pairs (101, 102, 103, 104) are arranged in the vicinity of the external sheath (11), namely on the one hand a first pair of electrodes (101, 102) and on the other hand a second pair of electrodes (103, 104).

5. The method for the nondestructive inspection of a flexible line (10) according to claim 4, characterized in that the sole armor layer (14), or when the flexible line (10) comprises several armor layers (14, 23), the armor layer (14) closest to the external sheath (11), comprises at least a first group of armors (17) and a second group of armors (18) separate from one another, and in that step a) comprises the following steps: a3) arranging a first electrode (101) from the first pair of electrodes (101, 102) opposite the first group of armors (17), a4) arranging a second electrode (102) from the first pair of electrodes (101, 102) opposite the second group of armors (18).

6. The method for the nondestructive inspection of a flexible line (10) according to claim 5, characterized in that step a) comprises the following steps: a5) arranging a first electrode (103) from the second pair of electrodes (103, 104) opposite the first group of armors (17), a6) arranging a second electrode (104) from the second pair of electrodes (103, 104) opposite the second group of armors (18).

7. The method for the nondestructive inspection of a flexible line (10) according to claim 5, characterized in that the sole armor layer (14), or when the flexible line (10) comprises several armor layers (14, 23), the armor layer (14) closest to the external sheath (11), comprises at least a third group of armors (19) and a fourth group of armors (20) separate from one another and separate from the first group of armors (17) and the second group of armors (18), said third group of armors (19) and said fourth group of armors (20) being arranged between said first group of armors (17) and said second group of armors (18), and in that step a) comprises the following steps: a7) arranging a first electrode (103) from the second pair of electrodes (103, 104) opposite the third group of armors (19), a8) arranging a second electrode (104) from the second pair of electrodes (103, 104) opposite the fourth group of armors (20).

8. The method for the nondestructive inspection of a flexible line (10) according to any one of the preceding claims, characterized in that step a) comprises the following step: a9) arranging the electrodes of at least one pair of electrodes (101, 102, 103, 104) in contact with the external sheath (11).

9. The method for the nondestructive inspection of a flexible line (10) according to any one of the preceding claims, characterized in that step b) comprises the following step: b1) supplying alternating voltage, or alternating current, with a determined frequency between 10 Hz and 10 MHz, advantageously between 100 kHz and 3 MHz, preferably between 200 kHz and 800 kHz.

10. The method for the nondestructive inspection of a flexible line (10) according to any one of claims 2 to 3, characterized in that the electrical signal measured during step c) is the complex impedance across the terminals of said sole electrode pair (101, 102).

11. The method for the nondestructive inspection of a flexible line (10) according to any one of claims 5 to 7, characterized in that the electrical signal measured during step c) is a complex signal, the modulus of said complex signal is equal to the amplitude of the voltage measured across the terminals of the second pair of electrodes (103, 104), and the phase of said complex signal being equal to the phase shift measured between the voltage across the terminals of the second pair of electrodes (103, 104) on the one hand, and the voltage or the current supplying the first pair of electrodes (101, 102) on the other hand.

12. The method for the nondestructive inspection of a flexible line according to any one of claims 10 to 11, characterized in that step d) comprises the following step: d1) comparing the modulus and / or the phase of the measured electrical signal with reference values so as to determine the nature of the fluid contained in the annular space (13).

13. The method for the nondestructive inspection of a flexible line (10) according to any one of the preceding claims, characterized in that during steps b) and c), the distance separating the electrodes of the or each of the pairs of electrodes (101, 102, 103, 104) is kept fixed.

14. The method for the nondestructive inspection of a flexible line (10) according to claim 13, characterized in that the distance separating the electrodes of the or each of the pairs of electrodes (101, 102, 103, 104) is between 100 mm and 500 mm, preferably between 200 mm and 500 mm.

15. The method for the nondestructive inspection of a flexible line (10) according to any one of the preceding claims, characterized in that the group of steps b), c) and d) is carried out several times, simultaneously or sequentially, with a different determined frequency for each execution.