Method for detecting the presence of a flexible pipe butting or hucking and /

Abstract

Disclosed is a method for detecting the presence of a flexible pipe burial or arching and / or external feature, in particular, a method for detecting the presence of a pipe burial or arching and / or external feature of a flexible pipe relative to a flexible pipe. The method includes helically winding a temperature sensing element (204) around a layer of the flexible conduit; helically winding a heating element (206) around the layer of the flexible conduit; heating the heating element to a preset temperature; measuring temperatures at at least two locations along the flexible conduit; comparing the measured temperature responses at the at least two locations; and determining an exterior near the pipe at one of the at least two locations from a comparison of the measured responses.

Description

[0001] This application is a divisional application of the Chinese patent application with application number 201780076048.2 and name “Detection Device and Method” (based on the international patent application with international application date of October 3, 2017 and international application number PCT / GB2017 / 052960, which entered the Chinese national stage on June 6, 2019). Technical Field

[0002] The present invention relates to an apparatus and method. In particular, but not exclusively, the present invention relates to a method for detecting entrenchment or upheaval of a flexible pipeline (e.g. in the seabed) and / or the presence and position of external features relative to the flexible pipeline, and an apparatus for use in the method. Background Art

[0003] Traditionally, flexible pipes are used to transport production fluids (such as oil and / or gas and / or water) from one location to another. Flexible pipes are particularly suitable for connecting a seafloor location (which may be deep underwater) to a sea level location. The pipe may have an inner diameter of generally about 0.6 meters (e.g., a diameter may be in the range of from 0.05 meters to 0.6 meters). Flexible pipes are generally formed as an assembly of a flexible pipe body and one or more end fittings. The pipe body is generally formed as a combination of layered materials forming a pressure-bearing conduit. The pipe structure allows large deflections without causing bending stresses that damage the function of the pipe during its service life. The pipe body is generally constructed as a combined structure comprising a polymer and / or a metal and / or a composite layer. For example, the pipe body may include a polymer layer and a metal layer, or a polymer layer and a composite layer, or a polymer layer, a metal layer and a composite layer.

[0004] In many known flexible pipe designs, the pipe body includes one or more pressure armour layers. The main load on these layers is formed by radial forces. The pressure armour layer often has a specific cross-sectional profile to interlock so as to be able to hold and absorb the radial forces generated by the external or internal pressure on the pipe. Therefore, the cross-sectional profile of the winding wire that prevents the pipe from collapsing or rupturing due to pressure is sometimes referred to as a pressure-resistant profile. When the pressure armour layer is formed by the spirally wound wire forming the hoop component, the radial force from the external or internal pressure on the pipe causes the hoop component to expand or contract, thereby applying a tensile load to the wire.

[0005] In many known flexible pipe designs, the pipe body includes one or more tensile armour layers. The primary load on such layers is tension. In high pressure applications, such as in deep and ultra-deep water environments, the tensile armour layers are subject to high tensile loads from a combination of internal pressure end cap loads and the self-supporting weight of the flexible pipe. This may cause failure of the flexible pipe due to this condition over a long period of time.

[0006] Unbonded flexible pipes have been used in deepwater (less than 3,300 feet (1,005.84 meters)) and ultra-deepwater (greater than 3,300 feet) developments. It is the increasing demand for oil that has caused exploration to occur at increasingly greater depths where environmental factors are more extreme. For example, in such deepwater and ultra-deepwater environments, seafloor temperatures increase the risk of cooling the production fluid to a temperature that could cause the pipeline to become blocked. The increased depth also increases the pressure associated with the environment in which the flexible pipe must operate. For example, the flexible pipe may be required to operate at an external pressure in the range of 0.1 MPa to 30 MPa acting on the pipe. Similarly, the transport of oil, gas or water can well produce high pressures acting on the flexible pipe from the inside, such as using internal pressures in the range of 0 to 140 MPa from a bore fluid acting on the pipe. As a result, the demand for high levels of performance in each layer of the flexible pipe body has increased.

[0007] Flexible pipes may also be used in shallow water applications (eg, less than about 500 meters deep) or even in coastal (onshore) applications.

[0008] In some cases, the flexible pipeline may be entrenched where the flexible pipeline extends at least partially along the seafloor. In some cases, it is desirable for the pipeline to be entrenched in the seabed (e.g., to protect the pipeline), and therefore pipe arching is undesirable. However, in other cases, unplanned entrenchment of a portion of the pipeline (e.g., on an uneven seabed or due to liquefaction of the seabed caused by seismic activity) is undesirable because it may impede the ability to visually inspect the pipeline and / or subject the pipeline to localized stresses.

[0009] In some cases, it is important to be able to detect the presence and confirm the position of external features relative to a flexible pipeline (e.g., pipeline auxiliary equipment), for example to confirm that they have not been dislodged and dropped, or that the position relative to each other is as specified and within tolerances. Other examples of external features relative to the pipeline include marine growth, which may be undesirable.

[0010] The temperature of various sections of a pipeline can be accurately monitored using known temperature monitoring techniques, such as the use of optical fiber. However, if the operating temperature of the pipeline is such that there is only a very small thermal gradient between the bore of the pipeline (and the fluid therein) and the external environment, it is unlikely that any temperature changes indicative of a change in the condition of the pipeline or ancillary equipment on the pipeline will be detected. Summary of the invention

[0011] According to a first aspect of the present invention, there is provided a method for detecting the presence of a pipe trench or bulge and / or external features of a flexible pipe relative to the flexible pipe, the method comprising the steps of: spirally winding a temperature sensing element around a layer of the flexible pipe; spirally winding a heating element around the layer of the flexible pipe; heating the heating element to a predetermined temperature; measuring the temperature at at least two locations along the flexible pipe; comparing the measured temperature responses at the at least two locations; and determining the exterior of the pipe vicinity at one of the at least two locations based on the comparison of the measured responses.

[0012] According to a second aspect of the present invention, there is provided an apparatus for detecting the presence of buried trenches or bulges and / or external features of a flexible pipe relative to the flexible pipe, comprising: a temperature sensing element disposed at a position radially outside a layer of the flexible pipe; a heating element disposed at a position radially outside the layer of the flexible pipe; a controller for controlling the heating element to be heated to a predetermined temperature; measuring the temperature at at least two positions along the flexible pipe; comparing the measured temperature responses at at least two positions; and determining the exterior of the pipe near one of the at least two positions based on the comparison of the measured responses.

[0013] Certain embodiments of the present invention provide the advantage that buried trenches or bulges of a flexible pipe and / or the presence of external features relative to the flexible pipe may be detected with greater sensitivity than known arrangements.

[0014] Certain embodiments of the present invention provide the advantage that changes in the environment of a flexible pipe or ancillary equipment may be detected regardless of the operating temperature of the pipe.

[0015] Certain embodiments of the present invention provide the advantage that buried trenches or bulges of a flexible pipe and / or the presence of external features relative to the flexible pipe may be detected for insulating the pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0017] Figure 1 A flexible conduit body is shown;

[0018] Figure 2aA cross section of a flexible pipe body and a pipe trench having an apparatus for detecting the flexible pipe body is shown;

[0019] Figure 2b Shows Figure 2a A close up view of a portion of the pipe body and the device;

[0020] Figure 3 A cutaway perspective view of a flexible conduit body and device is shown;

[0021] Figure 4a Shows Figure 2a Simulated temperature map of the cross section shown in;

[0022] Figure 4b Shows Figure 4a a close up of a portion of a cross section of;

[0023] Figure 4c Shows Figure 4a a close up of a portion of a cross section of;

[0024] Figure 5 shows a portion of a flexible pipe body and a cross section with another apparatus for detecting buried pipe trenches of flexible pipe body; and

[0025] Figure 6 A controller is shown connected to the heating element and the temperature sensing element.

[0026] In the drawings, like reference numerals denote like components. DETAILED DESCRIPTION

[0027] Throughout the specification, reference will be made to flexible pipe.It will be understood that a flexible pipe is an assembly of a portion of a pipe body and one or more end fittings, in each of which a respective end of the pipe body terminates. Figure 1 1 shows how a pipe body 100 is formed from a combination of layered materials that form a pressure-containing conduit according to an embodiment. Figure 1 , it should be understood that the present invention is broadly applicable to coaxial pipe body structures including two or more layers made of a variety of possible materials. For example, the pipe body can be formed of polymer layers, metal layers, composite layers, or a combination of different materials. It should also be noted that the layer thicknesses are shown for illustrative purposes only. As used herein, the term "composite" is used to broadly refer to materials formed of two or more different materials, such as a material formed of a matrix material and reinforcing fibers.

[0028] like Figure 1As shown, the pipe body includes an optional innermost carcass layer 101. The carcass provides an interlocking structure that can be used as an innermost layer to completely or partially prevent the collapse of the internal pressure sheath 102 due to pipe decompression, external pressure and tensile protection pressure, and mechanical crushing loads. The carcass layer is typically a metal layer, which is formed, for example, of stainless steel. The carcass layer can also be formed of a composite material, a polymer or other material or a combination of materials. It should be understood that certain embodiments of the present invention are suitable for "smooth hole" operations (i.e., without a carcass layer) as well as such "rough hole" applications (with a carcass layer).

[0029] The internal pressure sheath 102 acts as a fluid retaining layer and comprises a polymer layer that ensures the integrity of the internal fluid. It should be understood that this layer itself may comprise a number of sub-layers. It should be understood that when the optional carcass layer is used, the internal pressure sheath is often referred to as a barrier layer by those skilled in the art. In operations without such a carcass (so-called smooth-bore operations), the internal pressure sheath may be referred to as a liner.

[0030] The optional pressure armor layer 103 is a structural layer that increases the resistance of the flexible pipe to internal and external pressure and mechanical crushing loads. This layer also structurally supports the internal pressure sheath and can be formed by an interlocking structure of wires wound at a lay angle close to 90°. The pressure armor layer is typically a metal layer, which is formed, for example, of carbon steel. The pressure armor layer can also be formed of composite materials, polymers or other materials or combinations of materials.

[0031] The flexible pipe body also includes an optional first tensile armor layer 105 and an optional second tensile armor layer 106. Each tensile armor layer is used to withstand tensile loads and internal pressure. The tensile armor layer is usually formed by a plurality of wires (in order to give strength to the layer), which are located above the inner layer and are spirally wound along the length of the pipe with a twist angle usually between about 10° and 55°. The tensile armor layers are usually reverse wound in pairs. The tensile armor layer is usually a metal layer, which is formed, for example, of carbon steel. The tensile armor layer can also be formed of a composite material, a polymer or other material or a combination of materials.

[0032] The flexible pipe body shown also includes an optional tape layer 104, which helps to contain underlying layers and to some extent prevent abrasion between adjacent layers. The tape layer may be a polymer or composite material or a combination of materials.

[0033] The flexible pipe body also typically includes an optional insulation layer 107 and an outer jacket layer 108, which includes a polymer layer for protecting the pipe from penetration by seawater and other external environments, corrosion, abrasion and mechanical damage.

[0034] Each flexible pipe includes at least one portion (sometimes referred to as a segment or section of the pipe body 100) and an end fitting located at at least one end of the flexible pipe. The end fitting provides a mechanical device that forms a transition between the flexible pipe body and the connector. For example, Figure 1 The various pipe layers shown terminate in end fittings, thereby transferring loads between the flexible pipe and the connector.

[0035] One aspect of the present invention is generally directed to a method for detecting pipe burrowing or cambering of a flexible pipe and / or detecting the presence of an external feature relative to the flexible pipe by comparing temperatures at at least two locations of a temperature sensing element that has been heated to a predetermined temperature by a heating element.

[0036] Figure 2a and 2b An apparatus 210 for detecting buried trenches of a flexible pipe 200 is shown, which includes a temperature sensing element 204 surrounding the layer of the flexible pipe 200 and a heating element 206 surrounding the layer of the flexible pipe. In this example, the temperature sensing element 204 and the heating element 206 are both located around the insulating layer 107. That is, the temperature sensing element 204 and the heating element 206 are located at a position between the insulating layer 107 and the outer jacket 108. The heating element 206 is adjacent to the temperature sensing element 204. The heating element and the temperature sensing element are disposed in the gap 202 between the insulating layer 107 and the outer jacket 108.

[0037] Although the layers 101 to 107 of the flexible pipe 200 are Figure 1 The corresponding different layers in are identical, but for clarity they are shown in Figure 2a and 2b It is shown as a single unit 240.

[0038] In this example, the temperature sensing element is a fiber optic element. In this example, the heating element is a resistive heating element, which has a power of substantially 50 watts per meter, but any suitable heating element with suitable power requirements can be used. This can be operated in a continuous or zoned manner.

[0039] Both the temperature sensing element and the heating element are thin elongated filaments that extend along the length of the tube.

[0040] Figure 3 A cutaway perspective view of a flexible conduit 200 and a device 210 is shown.

[0041] The temperature sensing element and the heating element each extend in a spiral along the length of the tube.

[0042] During manufacture of the flexible pipe, the device 210 is applied to the flexible pipe 200 by spirally wrapping the temperature sensing element 204 around the layers of the flexible pipe 200 and the heating element 206 around the layers of the flexible pipe 200. In this example, the temperature sensing element 204 and the heating element 206 are both spirally wrapped around the insulating layer 107. In this example, the temperature sensing element 204 and the heating element 206 are simultaneously spirally wrapped around the layers of the flexible pipe.

[0043] Once the temperature sensing element 204 and the heating element 206 are helically wrapped around the layer of flexible tubing, an outer jacket layer 108 is applied over the layer. Tension in the outer jacket layer 108 and / or the stiffness of the outer jacket layer may create a gap 202 between the outer jacket and the temperature sensing element 204 and the heating element 206.

[0044] The temperature sensing element and the heating element are positioned close to each other so that the heat generated by the heating element can be detected by the temperature sensing element. In this example, the temperature sensing element is 30 mm away from the heating element for a pipe with an outer diameter of 300 mm, but they can be placed at any distance suitable for working together. The temperature sensing element and the heating element can also be carried in a belt or sheath element as disclosed in EP2725186A1.

[0045] The device 210 further includes a controller C, such as Figure 6 As shown, it is connected to a heating element and a temperature sensing element. The controller is used to control the heating element 206 to be heated to a predetermined temperature, and the temperature at at least two positions along the flexible pipe is measured. The controller compares the measured temperature response and determines the exterior of the pipe near one of the at least two positions. That is, the controller determines whether the flexible pipe 200 has been buried in a trench and / or whether there are external features at one of the at least two positions from the comparison of the temperature responses measured at at least two positions. In this example, the controller uses Raman-based distributed temperature sensing to measure the temperature at at least two positions, but any suitable temperature measurement method can be used, such as Brillouin or fiber Bragg grating. In this example, the controller controls the heating of the heating element via an interface between a fiber optic interrogator and a resistive heating element power supply to adjust or regulate the heat according to the requirements of the deployment.

[0046] In this example, the controller determines whether the flexible pipe 200 has been trenched in a trench 302 on the seafloor 304 , as described below.

[0047] During use, the heating element is heated until it reaches a predetermined temperature. For this example, the heating element takes 20 minutes to heat to the predetermined temperature.

[0048] Figure 4a A simulated temperature graph of the flexible pipe 200 and the device 210 is shown once the heating element 206 has been heated to a predetermined temperature. In this example, the heating element 206 is heated to 50 degrees Celsius (° C.). In this example, the temperature of the fluid in the pipe bore 208 is 10° C., while the temperature of the seawater is 5° C.

[0049] In this example, the controller measures the temperature at locations A and B on the temperature sensing element 204, as shown in FIG. Figure 3 As shown, positions A and B are offset axially along the pipe.

[0050] Figure 4a FIG. 2 is a diagram of a temperature diagram of the temperature in the region of the heating element 206. The upper portion of the diagram (above the dashed line) shows a location 206 located away from the seabed. A The cross-sectional view has been taken with the heating element at position 206 close to the seabed 304 (below the dashed line) B That is, the temperature sensing elements at different longitudinal positions A and B are shown as 204, respectively. A and 204 B . Figure 4b and 4c The device 210 is shown at different positions A and B, respectively.

[0051] Over time, the heat generated by the heating element 206 dissipates from the heating element, such as Figure 4a 302. That is, the heat generated by the heating element 206 is dissipated into the flexible pipe layer surrounding the heating element and subsequently dissipated into the area surrounding the flexible pipe. The ocean and the trench 302 provide different levels of insulation to the flexible pipe 200, so that when buried in the trench, the heat generated by the heating element 206 is dissipated differently at different locations along the flexible pipe 200. That is, due to the insulating effect of the trench 302, the heat generated by the heating element 206 at location A where the flexible pipe 200 is exposed to the ocean will be dissipated from the flexible pipe 200 faster than at location B where the flexible pipe 200 is buried in the trench 302.

[0052] The temperatures measured by the controller at locations A and B, respectively, through temperature sensing elements 204A and 204B will be different due to the different levels of insulation. In this example, the temperature measured at location A will be lower than the temperature measured at location B.

[0053] Therefore, if the temperature difference or temperature ratio between one of the at least two locations and the other of the at least two locations is higher than a threshold, the controller determines that the flexible pipe has been buried and / or the external feature exists at the one of the at least two locations.

[0054] That is, in this example, if the temperature difference or temperature ratio between position A and position B is higher than a threshold value, it is determined that the flexible pipe has been buried.

[0055] The temperature difference threshold may be 3°C. Alternatively, the temperature difference threshold is another smaller or larger temperature difference, depending on the condition, location and environment of the pipeline in question. The temperature ratio threshold will depend entirely on the initial (normal operating) temperature of the pipeline in that location, but can be determined and set for a specific location.

[0056] In this example, the heating element 206 is turned off before measuring the temperature at locations A and B along the flexible pipe. In this way, the temperature difference / temperature ratio between the two locations will become more apparent over time because heat is dissipated from the heating element at different rates due to the different levels of insulation. That is, the transient cooling rate is monitored because the difference in heat dissipation rate is emphasized during this phase.

[0057] The method for detecting pipeline burial of a flexible pipe as described in the above embodiment includes the following steps: spirally winding a temperature sensing element around a layer of the flexible pipe, and spirally winding a heating element around a layer of the flexible pipe; heating the heating element to a predetermined temperature; measuring the temperature at at least two locations along the flexible pipe; comparing the measured temperature responses at the at least two locations; and determining from the comparison of the measured temperature responses whether the flexible pipe has been buried at the at least two locations and / or whether the external feature exists at one of the at least two locations.

[0058] Various modifications to the detailed arrangements described above are possible. For example, the heating element and temperature sensing element of the device may be located at any suitable location within the flexible pipe. The heating element and temperature sensing element may be located between any two layers of the flexible pipe, such as between the outer jacket layer 108 and the protective layer 106 (i.e., the insulating layer between the layers is optional).

[0059] Generally speaking, the more insulated the flexible pipe is, the more advantageous it is to have the heating element and the temperature sensing element close to the radially outer portion of the pipe, i.e. as close as possible to the feature / buried trench / arch that the device is trying to detect. Thus, the temperature sensing element and the heating element can be attached to the outside of the flexible pipe, i.e. radially outside of the outer jacket layer 108. In this way, the device can be retrofitted to existing flexible pipes.

[0060] Alternatively, the heating element and the temperature sensing element may be located within the layers of the flexible pipe. Figure 5As shown, the heating element and the temperature sensing element can be located in the gap 502 between the guard windings of the guard layer 106, which is located radially outside the body 540. That is, the temperature sensing element and the heating element can be wound between the guard windings of the guard layer. The gap 502 can be a small opening between the guard windings, or a small opening such as a Figure 5 As shown, it can be a larger gap due to the absence of an additional guard winding. An outer sheath can then be provided over the guard layer. Suitably, the temperature sensing element and the heating element can be embedded in a groove in the guard winding.

[0061] The heating element may be a heating layer of the pipe body rather than a filament-type heating element.

[0062] The apparatus and methods of all the described embodiments can be used to detect external features relative to a flexible pipe. The external features can be pipe auxiliary equipment. The external features relative to the flexible pipe can have a similar insulating effect on the heat dissipation from the heating element as the groove 302. Therefore, the presence of an external feature at a specific location can be detected in the same manner as detecting a buried trench of a flexible pipe. In addition, if it is known that an external feature exists but the location of the external feature is unknown, the location of the external feature can be determined by testing the presence of the external feature at multiple locations.

[0063] The apparatus and methods of all described embodiments can be used to detect arching of a flexible pipe. Arching of a flexible pipe will affect the heat dissipation from the heating element at the location of the pipe arching, i.e., once arching has occurred, the location of the pipe previously buried in the trench will be less thermally insulated. Therefore, the occurrence of pipe arching can be detected by using the same method as detecting buried pipes, however using different temperature thresholds.

[0064] In another embodiment, there may be no gap 202 because the heating element 206 and the temperature sensing element 204 are placed between the layers of the flexible tubing. If the outer sheath or indeed any radially outer layer over the device is compliant and flexible, it may be formed around the temperature sensing element and the heating element.

[0065] In another embodiment, the heating element and the temperature sensing element may be combined into a single body that is spirally wound together around the layer of flexible tubing. For example, the heating element and the temperature sensing element may both be contained within an elongated flexible tubular sheath that is wound around the layer of flexible tubing.

[0066] In another embodiment, the heating element may not be turned off before measuring the temperature. In this embodiment, the insulating effect of the buried trench and / or the presence of external features are significant enough to allow the heating element to measure heat while it is still generating heat.

[0067] The heating element may be heated to any predetermined temperature and for any duration. The temperature and duration requirements may be selected based on the specific arrangement of the flexible conduit, including the dimensions and constituent layers, and the environmental conditions of the particular application.

[0068] Rather than heating continuously along the heating element, the heating element provides heat at discrete locations along the heating element.

[0069] The temperature may be measured at any number of locations along the temperature sensing element.

[0070] The temperatures may be compared at any number of locations along the temperature sensing element.

[0071] The device may further include an additional temperature sensing element and an additional heating element. For example, the additional temperature sensing element and the additional heating element may be spirally wound out of phase with respect to the first temperature sensing element and the heating element, for example, when the first temperature sensing element and the heating element are located at the top of the cross-section of the flexible pipe, the additional temperature sensing element and the additional heating element may be located at the bottom of the same cross-section. The temperatures measured by the first temperature sensing element and the additional temperature sensing element at corresponding positions in a given cross-section may be compared to determine the presence of buried trenches or bulges and / or external features of the flexible pipe relative to the flexible pipe.

[0072] Rather than using a spirally wound arrangement of temperature sensing elements and heating elements, these temperature sensing elements and heating elements may be arranged in other shaped paths along the flexible pipe. For example, two or more temperature sensing elements may be arranged extending generally in a straight line along the pipe (e.g., at opposite sides of a tubular cross-section of the pipe). Other arrangements are envisioned that are capable of capturing temperature data at different regions of the pipe.

[0073] With the above arrangement, the presence of buried trenches or bulges and / or external features relative to the flexible pipe may be detected.

[0074] With the above arrangement, the additional heat generated by the heating element enhances the insulating effect caused by the buried trench, dome or external feature.

[0075] With the above arrangement, the presence of a buried trench or bulge and / or external feature of a flexible pipe relative to the flexible pipe can be detected independently of the temperature difference between the bore fluid of the flexible pipe and the external environment. For example, if the temperature difference between the bore fluid and the external environment is small, the insulating effect of the trench / external feature will be minimal.

[0076] It will be apparent to those skilled in the art that features described in relation to any of the above embodiments may be applied interchangeably between the different embodiments.The above embodiments are examples to illustrate various features of the present invention.

[0077] Throughout the description and claims of this specification, the words "comprise" and "contain" and their variations mean "including but not limited to", and they are not intended to (and do not exclude) other parts, additives, components, integral bodies or steps. Throughout the description and claims of this specification, unless the context requires otherwise, the singular encompasses the plural. In particular, where an indefinite article is used, this specification should be understood to contemplate the plural as well as the singular, unless the context requires otherwise.

[0078] 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 features disclosed in this specification (including any accompanying claims, abstract and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, except that combinations of at least some such features and / or steps are mutually exclusive. The invention is not limited to the details of any foregoing embodiments. The invention extends to any novel features or any novel combination of features disclosed in this specification (including any accompanying claims, abstract and drawings), or any novel features or any novel combination of steps of any method or process so disclosed.

[0079] The reader's attention is directed to all papers and documents filed in connection with the present application concurrently with or previous to the present specification, and the contents of all these papers and documents are incorporated herein by reference.

Claims

1. A method for detecting the presence of a pipeline trench or bulge and / or external features of a flexible pipeline relative to the flexible pipeline, the method comprising the following steps: helically wrapping a temperature sensing element (204) around the layer of flexible tubing (200); helically wrapping a heating element (206) around the layer of flexible tubing (200); heating the heating element (206) to a predetermined temperature; measuring the temperature at at least two locations along the flexible pipe (200); comparing the measured temperature responses at the at least two locations; as well as determining from a comparison of the measured responses whether the flexible pipe (200) has been trenched, arched, and / or has an external feature present at one of the at least two locations, It is characterized in that The method further includes the step of turning off the heating element (206) before measuring the temperature at the at least two locations along the temperature sensing element (204).

2. A method according to any one of the preceding claims, wherein: If the temperature difference or temperature ratio between one of the at least two locations and another of the at least two locations is higher than a threshold, it is determined that the flexible pipe (200) has been buried and / or an external feature exists at the one of the at least two locations.

3. A method according to any one of the preceding claims, wherein: The temperature sensing element (204) is an optical fiber element.

4. A method according to any one of the preceding claims, wherein: The external features are pipeline auxiliary equipment.

5. A method according to any one of the preceding claims, wherein: The temperature sensing element (204) and the heating element (206) are wound between the guard windings of the guard layer.

6. The method of claim 5, further comprising the step of applying an outer jacket layer (208) over the protective layer.

7. A method according to any one of the preceding claims, wherein: The temperature sensing element (204) and the heating element (206) are simultaneously helically wound around the layer of the flexible tubing.

8. A method according to any one of the preceding claims, wherein: The controller performs the following steps: Controlling the heating element (206) to heat to a predetermined temperature; measuring the temperature at at least two locations along the temperature sensing element (204); comparing the measured temperature responses at the at least two locations; as well as A comparison of the measured temperature responses at the at least two locations determines whether the flexible pipe (200) has been trenched and / or whether an external feature is present at one of the at least two locations.

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