WO2020003023A1

WO2020003023A1 - A method for monitoring a continuous pipeline, monitoring device and assembly comprising said device

Info

Publication number: WO2020003023A1
Application number: PCT/IB2019/054382
Authority: WO
Inventors: Daniele RIPARI; Gilberto LATINI
Original assignee: Saipem S.P.A.
Priority date: 2018-06-27
Filing date: 2019-05-27
Publication date: 2020-01-02
Also published as: CL2020003362A1; IT201800006717A1; EP3814675A1

Abstract

A method for monitoring a continuous pipeline (1) comprises the following steps of providing a continuous pipeline (1), supplying a flow of fluid flowing inside said continuous pipeline (1), said fluid having a fluid temperature (Tf) substantially in thermal equilibrium with said ambient temperature (T1), providing a monitoring device (6) which defines a longitudinal monitoring direction (Y-Y) coinciding with or parallel to the longitudinal development direction of said monitoring device (6), wherein said monitoring device (6) extends over a second predefined longitudinal distance (x6) along said longitudinal direction (X-X) of the monitoring device (6), said monitoring device (6) comprising at least one heating element (7) and at least one optical fiber sensor (8), and wherein the method comprises the steps of locally heating, by means of said at least one heating element (6), the optical fiber sensor (8), bringing it to a monitoring temperature (T6) which is higher than the ambient temperature (T1), arranging said monitoring device (6) alongside said continuous pipeline (1), so that the outer wall (2) of said pipeline section (5) locally flanks said monitoring device (6).

Description

Method for monitoring a continuous pipeline, monitoring device and assembly comprising said device

DESCRIPTION

[0001]. Field of the invention

[0002]. The present invention relates to a method for monitoring a continuous pipeline.

[0003]. The present invention also relates to a monitoring device a continuous pipeline, as well as an assembly comprising said monitoring device.

[0004]. Background art

[0005]. The employment of acoustic probes to detect leaks of a product carried in a buried continuous pipeline, such as, for example, a piping for the transport of hydrocarbons, is generally known. For example, acoustic sensors are provided adapted to detect the frequency emitted by the leak.

[0006]. Flowever, acoustic probes of this type are prone to an intrinsic delay in identifying the leak and require the interruption of transport during the subsequent step of inspecting the continuous pipeline to localize the leak.

[0007]. Leak detection methods are also known, which are based on mathematical models capable of detecting a leak of the load by measuring the flow flowing through the continuous pipeline. These methods show limits on the long distance, where a greater precision of the flowmeter measurement is required.

[0008]. Distributed optical fiber temperature sensors are known, which detect a temperature variation along a predefined path. Furthermore, monitoring the temperature close to a continuous pipeline by means of optical fiber sensors placed close to the continuous pipeline is known. The optical fiber is interrogated optically and when a thermal gradient is detected, it indicates a leak. For example, when the pipeline carries a hot product, the leak is localized by detecting the heating of the optical fiber.

[0009]. Among the intrinsic advantages of the employment of the optical fiber there are the very limited dispersions, which potentially allow a long distance monitoring, in the order of tens of kilometers, without thereby resulting in a reduced sensitivity and accuracy of the detection signal. For example, document US-2017-0276267 shows an optical fiber sensor placed in a groove formed on the outer surface of a metal piping.

[0010]. The evaluation of the position of the leak along the pipeline may be carried out by jointly employing two types of optical fiber sensors. A solution of this type is shown, for example, in document US-7564540 which envisages a first continuous distributed sensor combined with a second temporary localized sensor to allow the punctual comparison of the signals from both said sensors so as to localize the leak. Flowever, this type of solution intrinsically increases the number of components subject to failures, increasing the risk of false positives and therefore returning information which is not always reliable.

[0011]. Furthermore, the previous solutions described above do not allow to detect a leak in a continuous pipeline which carries a fluid in thermal equilibrium with the surrounding environment.

[0012]. The need is therefore felt to provide a solution to the drawbacks complained with reference to the known solutions, and to propose an improved solution for monitoring a continuous pipeline, even in the case in which, locally, the fluid transported inside the pipeline is in thermal equilibrium with the surrounding environment.

[0013]. Solution

[0014]. It is an object of the present invention to meet the aforementioned needs with reference to the background art.

[0015]. This and other objects are achieved by a method according to claim 1 , as well as by a device according to claim 8, as well as by an assembly according to claim 10.

[0016]. Some advantageous embodiments are the subject of the dependent claims.

[0017]. By virtue of the proposed solutions, it is possible to detect a leak in a pipeline which carries fluid which is locally in thermal equilibrium with the environment in which the pipeline is placed.

[0018]. Drawings

[0019]. Further features and advantages of the method, device and assembly will become apparent from the following description of preferred embodiments thereof, given by way of indication and not by way of limitation, with reference to the accompanying drawings, in which:

[0020]. - Figure 1 shows an axonometric view which diagrammatically shows a monitoring device, according to an embodiment, and a continuous pipeline placed on the bed of a water body;

[0021]. - Figure 2 shows a diagrammatic cross section which diagrammatically shows a monitoring device, according to an embodiment, and a continuous pipeline;

[0022]. - Figure 3 shows a diagrammatic sectional view of a monitoring device according to an embodiment;

[0023]. - Figure 4 shows an axonometric view of the monitoring device in Figure 3, with partially transparent parts for clarity purposes;

[0024]. - Figure 5 shows a diagrammatic sectional view of a monitoring device according to an embodiment;

[0025]. - Figure 6 shows an axonometric view of the monitoring device in Figure 5, with partially transparent parts for clarity purposes.

[0026]. Description of some preferred embodiments

[0027]. In accordance with a general embodiment, a method for monitoring a continuous pipeline 1 is provided.

[0028]. The method is adapted to detect at least one leak of fluid 9 in said continuous pipeline 1 . For example, said leak of fluid 9 may be caused by a breakage of a portion of the continuous pipeline 1 . For example, said leak of fluid 9 may be caused by the formation of accidental cracks or punctures in the continuous pipeline.

[0029]. In accordance with a possible operating mode the method is adapted to localize at least one leak of fluid 9 in said continuous pipeline 1 . Preferably, said continuous pipeline 1 comprises a plurality of pipeline sections or piping sections connected in series to form said continuous pipeline 1 . For example, a single pipeline section of said continuous pipeline 1 extends longitudinally for about 12 meters.

[0030]. The method comprises the step of providing a continuous pipeline 1 having a longitudinal direction X-X, coinciding with or parallel to the longitudinal development direction of said continuous pipeline 1 .

[0031]. Said continuous pipeline 1 is placed in an environment having a predefined ambient temperature T 1 .

[0032]. Said continuous pipeline 1 comprises at least one outer wall 2, defining the radial volume of said continuous pipeline 1 .

[0033]. Said continuous pipeline 1 further comprises a first cross section 3 and a second cross section 4, spaced apart along said continuous pipeline by a first predefined distance x1 , so as to define a pipeline section 5.

[0034]. The method comprises the step of supplying a flow of fluid inside said continuous pipeline 1.

[0035]. Said fluid flowing inside said continuous pipeline having a fluid temperature Tf substantially in thermal equilibrium with said ambient temperature T1 .

[0036]. For example, said ambient temperature T 1 is between 10°C and 20°C.

[0037]. The method comprises the step of providing a monitoring device 6. Preferably, said monitoring device 6 defines a longitudinal monitoring direction Y-Y, coinciding with or parallel to the longitudinal development direction of said monitoring device 6.

[0038]. Preferably, said monitoring device 6 extends over a second predefined longitudinal distance x6 along said longitudinal direction of the monitoring device Y-Y.

[0039]. Said monitoring device 6 comprises at least one heating element 7 and at least one optical fiber sensor 8.

[0040]. In accordance with a preferred embodiment, said at least one heating element forms an umbilical cable. For example, said umbilical cable comprises a bundle of heating elements 7. Preferably, said bundle of heating elements 7 comprises electrically powered heating elements, for example, it comprises a first wire-shaped element 71 which forms the positive pole and a second wire-shaped element 72 which forms the negative pole. In accordance with an embodiment, said bundle of heating elements comprises a wrapping sheath 18 adapted to wrap said heating elements forming said bundle of heating elements. For example, the diameter of said at least one heating element 7 is substantially equal to 2.5 millimeters.

[0041]. The method comprises the step of locally heating, by means of said at least one heating element 7, the optical fiber sensor 8, bringing it to a monitoring temperature T6 higher than the ambient temperature T1 . Thereby, the monitoring temperature T6 is higher than the fluid temperature Tf. For example, the monitoring temperature T6 is between 12°C and 30°C, when the ambient temperature T 1 is between 10°C and 20°C.

[0042]. The method comprises the step of arranging said monitoring device 6 alongside said continuous pipeline 1 , so that the outer wall 2 of said pipeline section 5 locally flanks said monitoring device 6. The arranging step may be carried out either before the continuous pipeline 1 is launched, or during the launch of the continuous pipeline 1 , or when the continuous pipeline 1 has already been placed.

[0043]. In accordance with a possible operating mode, the method comprises the step of detecting a deacrease of the monitoring temperature T6 caused by a leak of fluid 9, which, hitting said optical fiber sensor 9, alters the thermal equilibrium thereof. Thereby, it is possible to detect a leak of fluid 9 in said pipeline section 5.

[0044]. In accordance with a possible operating mode, the method comprises the further step of activating an alarm to signal a leak of fluid 9. Preferably, the step of activating an alarm is carried out if the monitoring device detects a deacrease of the monitoring temperature T6.

[0045]. In accordance with a possible operating mode, the detection of said leak of fluid 9 through said outer wall 2 occurs by detecting the deacrease of said monitoring temperature T6 caused by the leak of fluid 9 being said fluid temperature Tf in thermal equilibrium with the ambient temperature T 1 .

[0046]. In accordance with a possible operating mode, the monitoring device 6 detects a thermal gradient in a predetermined time interval, so that, if the detected thermal gradient exceeds a predefined threshold gradient value, then the method comprises the further step of activating an alarm.

[0047]. In accordance with a possible operating mode, the method comprises the step of detecting a leak of fluid 9 from said pipeline section 5 through said outer wall 2 by detecting the deacrease of said monitoring temperature T6 caused by the leak of fluid 9 being said fluid temperature Tf lower than the monitoring temperature T6.

[0048]. By virtue of such method, it is possible to detect a leak of fluid from a continuous pipeline when the fluid flowing inside the continuous pipeline is in thermal equilibrium with the environment in which the continuous pipeline 1 is placed.

[0049]. The thermal gradient detected by the monitoring device 6 is indicative of a leak of fluid 9 which determines the deacrease of temperature detected by the monitoring device 6.

[0050]. In accordance with a possible operating mode, the heating step is carried out by raising the monitoring temperature T6 by at least 2°C with respect to the ambient temperature T 1 .

[0051]. In accordance with a possible operating mode, the heating step is carried out by raising the monitoring temperature T6 by at least 3°C with respect to the ambient temperature T 1 .

[0052]. In accordance with a possible operating mode, the heating step raises the monitoring temperature T6 by at least 5°C with respect to the ambient temperature T 1.

[0053]. In accordance with a possible operating mode, the detection step is carried out by detecting the local temperature difference between the fluid temperature Tf and the monitoring temperature T6.

[0054]. Preferably, the second predefined longitudinal distance x6 of the monitoring device 6 is at least equal to the first longitudinal distance x1 defining the pipeline section 5.

[0055]. In accordance with an embodiment, said optical fiber sensor 8 comprises at least one optical fiber and at least one optical temperature transducer, adapted to transmit an optical signal to said at least one optical fiber in response to a detected variation in temperature.

[0056]. In accordance with an embodiment, said optical fiber sensor 8 comprises at least one optical fiber bundle.

[0057]. In accordance with an embodiment, said at least one optical temperature transducer comprises a plurality of active portions, adapted to transmit an optical signal to said at least one optical fiber in response to a detected variation in temperature.

[0058]. In accordance with an embodiment, said plurality of active portions are distributed, preferably in a uniform manner, along the longitudinal monitoring direction Y-Y of the monitoring device 6.

[0059]. In accordance with a possible operating mode, the method comprises the step of submerging at least said pipeline section in a water body 10. Preferably, the temperature of said water body 10 is locally equal to the ambient temperature T 1 close to the pipeline section 5.

[0060]. In accordance with a possible operating mode, the method comprises the step of submerging said continuous pipeline 1 in a water body 10. Preferably, the temperature of said water body 10 being locally equal to the ambient temperature T 1 close to the continuous pipeline 1 .

[0061]. In accordance with a possible operating mode, the method comprises the step of burying at least said pipeline section 5, for example, in a trench 17.

[0062]. In accordance with a possible operating mode, the method comprises the step of burying at least said pipeline section 5 in the bed 1 1 of said water body 10.

[0063]. In accordance with a possible operating mode, the method comprises the further step of supplying said at least one heating element 7 with electric power.

[0064]. Preferably, said at least one heating element 7 is a wire-shaped element.

[0065]. In accordance with an embodiment, said monitoring device 6 extends over a monitoring length x6 along said longitudinal monitoring direction Y-Y. In accordance with an embodiment, said at least one optical fiber of said optical fiber sensor 8 extends over a length equal to said monitoring length x6. In accordance with an embodiment, said monitoring device 6 comprises a plurality of heating elements 7, each heating element 7 of said plurality of heating elements 7 extending over a fraction of said monitoring length x6, so that said plurality of heating elements 7 of said monitoring device 6 are connected in series by means of joining devices 12.

[0066]. In accordance with an embodiment, each heating element 7 of said plurality of heating elements 7 extends for a fraction of said monitoring length x6, said fraction of said monitoring length x6 being substantially equal to 1 kilometer. In accordance with an embodiment, said monitoring length x6 is at least 5 kilometers long. In accordance with an embodiment, said monitoring length x6 is at least 20 kilometers long. For example, in accordance with an embodiment, said monitoring length x6 is at least 30 kilometers long.

[0067]. In accordance with an embodiment, at least some joining devices 12, and, preferably, each joining device 12 comprises at least one data processing unit 13. Thereby, said monitoring device 6 comprises a plurality of data processing units 13. Preferably, a controller is provided, operatively connected to each of said data processing units 13.

[0068]. In accordance with an embodiment, said at least one data processing unit 13 is adapted to control the temperature of a heating element 7 adjacent thereto or flowing into it to keep the monitoring temperature T6 at a predefined value or around a predefined value.

[0069]. In accordance with an embodiment, the at least one data processing unit 13 of each joining device 12 is adapted to determine the monitoring temperature desired.

[0070]. In accordance with a possible operating mode, the method comprises the step of assembling said at least one heating element 7, and preferably said plurality of heating elements 7 connected in series, said optical fiber sensor 8 and said joining devices 12 each comprising at least one data processing unit 13 in a single wire-shaped or elongated body, for example, a cable, having an outer monitoring surface 14. For example, said outer monitoring surface 14 is a thin skin. For example, said outer monitoring surface 14 is a portion of a wrapping sheath 18, adapted to wrap the optical fiber sensor 8 and/or said at least one heating element 7. Preferably, said wrapping sheath 18 is made of a polymeric material, for example polyethylene. In accordance with an embodiment, said wrapping sheath 18 comprises said outer monitoring surface 14. [0071]. In accordance with a possible operating mode, the assembling step comprises the step of burying said optical fiber sensor 8 and said at least one heating element 7 in an at least one conductive means 15, 16, adapted to transmit heat by conduction and/or by convection between said at least one heating element 7 and said at least one optical fiber sensor 8. For example, said conductive means 15, 16 comprises a conductive gel adapted to minimize the friction between the components of the optical fiber sensor. For example, said conductive means comprises an anti pollution gel adapted to break down hydrogen ions.

[0072]. In accordance with a possible operating mode, the arranging step comprises the further step of wrapping said monitoring device 6 around said outer wall 2 of said continuous pipeline 1 . For example, said monitoring device 6 extends as a spiral or helix around said outer wall 2 of the continuous pipeline 1 .

[0073]. In accordance with a possible operating mode, the arranging step comprises the further step of flanking said monitoring device 6 alongside said outer wall 2 of said continuous pipeline 1 . Thereby, the longitudinal direction X-X of the continuous pipeline 1 is substantially parallel to the longitudinal monitoring direction Y-Y.

[0074]. In accordance with a possible operating mode, the arranging step comprises the step of placing said monitoring device 6 and said continuous pipeline 1 in a trench 17, for example a trench 17 dug into the bed of a water body 10. Preferably, the step of placing said monitoring device 6 and said continuous pipeline 1 in a trench 17 is carried out by flanking said monitoring device 6 to said continuous pipeline 1. In accordance with a possible operating mode, the step of placing said monitoring device 6 and said continuous pipeline 1 in a trench 17 is carried out by burying in a trench 17 at least one portion of continuous pipeline 1 and said monitoring device 6. In accordance with a possible operating mode, the step of placing said monitoring device 6 and said continuous pipeline 1 in a trench 17 is carried out by burying in a trench 17 at least one portion of continuous pipeline 1 together with said monitoring device 6 alongside said continuous pipeline 1.

[0075]. In accordance with an embodiment, the method comprises the further step of burying said continuous pipeline 1 and said monitoring device 6 in a trench 17.

[0076]. In accordance with a possible operating mode, the arranging step comprises the further step of placing said monitoring device underneath said continuous pipeline 1 , for example when said continuous pipeline 1 is arranged in a trench 17.

[0077]. In accordance with a possible operating mode, the arranging step envisages placing said outer wall 2 of the continuous pipeline 1 in contact with said monitoring device 6. Thereby, the arranging step envisages placing said outer wall 2 of the continuous pipeline 1 in contact with the outer monitoring wall 14 of the monitoring device 6.

[0078]. In accordance with a possible operating mode, the arranging step envisages placing said outer wall 2 of the continuous pipeline 1 at a predefined transversal distance from said monitoring device 6.

[0079]. In accordance with an operating mode, the method comprises the further step of localizing the leak of fluid 9 in a pipeline section 5 based on the position of the data processing unit 13, which receives information on the deacrease of temperature detected by the optical fiber sensor 8. Preferably, the method comprises the step of distributing along the longitudinal extension of the monitoring device 6 a certain number of data processing units 13, so as to localize the leak of fluid 9 close to the data processing unit 13 which detects the thermal gradient.

[0080]. In accordance with an operating mode, the method comprises the further step of detecting the ambient temperature T1 , preferably by means of a detection device operatively connected to at least one data processing unit 13.

[0081]. In accordance with an operating mode, the method comprises the further step of detecting the fluid temperature Tf, preferably by means of a detection device operatively connected to at least one data processing unit 13. In accordance with a possible operating mode, when the ambient temperature T1 varies locally, the detection device detects the variation in ambient temperature T1 and transmits a signal to said data processing unit 13 to regulate the monitoring temperature T6 accordingly.

[0082]. In accordance with a preferred operating mode, the method comprises the step of regulating the monitoring temperature T6 in response to the environmental conditions of some portions of the continuous pipeline 1 . In accordance with a possible operating mode, when the fluid temperature Tf varies locally, the detection device detects the variation in fluid temperature Tf and transmits a signal to said data processing unit 13 to regulate the monitoring temperature T6 accordingly.

[0083]. By virtue of such a method, it is possible to automatically adjust, when needed, the temperature of some portions of said monitoring device 6 so as to ensure a certain thermal difference between the fluid temperature Tf and the monitoring temperature T6.

[0084]. By virtue of such a method, it is possible to automatically adjust the temperature of some portions of said monitoring device 6, for example, by raising it when the ambient temperature T1 increases, for example, at a pipeline section exposed to direct sunlight or to other thermal perturbations, to ensure a certain thermal difference between the fluid temperature Tf and the monitoring temperature T6.

[0085]. By virtue of such a method, it is possible to automatically adjust the temperature of some portions of said monitoring device 6, for example, by lowering it when the ambient temperature decreases T1 , for example, at night time, to ensure a certain thermal difference between the fluid temperature Tf and the monitoring temperature T6. [0086]. In accordance with a general embodiment, a device for monitoring 6 a continuous pipeline 1 is provided.

[0087]. Said monitoring device 6 is particularly adapted, but not uniquely designed, to carry out the steps of the method described above.

[0088]. Preferably, said monitoring device 6 comprises any one of the features according to any one of the previously described embodiments as well as according to any one of the modes of operation described above.

[0089]. Preferably, said monitoring device 6 defines a longitudinal monitoring direction Y-Y, coinciding with or parallel to the longitudinal development direction of said monitoring device 6.

[0090]. Said monitoring device 6 is arranged locally alongside said continuous pipeline 1 , and preferably locally alongside said outer wall 2 of the continuous pipeline 1.

[0091]. Said monitoring device 6 comprises at least one heating element 7 and at least one optical fiber sensor 8.

[0092]. Said heating element 7 is adapted to raise the temperature of the said optical fiber sensor 8 locally.

[0093]. Advantageously, said monitoring device 6 is adapted to detect a deacrease of the monitoring temperature T6 caused by a leak of fluid 9, which, hitting said optical fiber sensor 9, alters the thermal equilibrium thereof. Thereby, said monitoring device 6 is adapted to detect a leak of fluid 9 from said continuous pipeline 1 by detecting a deacrease of the temperature of the optical fiber sensor 8.

[0094]. In accordance with an embodiment, said at least one heating element 7 is a wire shaped element.

[0095]. In accordance with an embodiment, said monitoring device 6 extends over a monitoring length x6 along said longitudinal monitoring direction Y-Y.

[0096]. In accordance with an embodiment, said at least one optical fiber of said optical fiber sensor 8 extends over a length equal to said monitoring length x6.

[0097]. In accordance with an embodiment, said monitoring device 6 comprises a plurality of heating elements 7, each heating element 7 of said plurality of heating elements 7 extending over a fraction of said monitoring length L6, so that said plurality of heating elements 7 of said monitoring device 6 are connected in series by means of joining devices 12.

[0098]. In accordance with an embodiment, each joining device 12 comprises at least one data processing unit 13.

[0099]. In accordance with an embodiment, said at least one data processing unit 13 is adapted to control the temperature of a heating element 7 adjacent thereto to keep the monitoring temperature T6 at a predefined value. [00100]. In accordance with an embodiment, said at least one data processing unit 13 of each joining device 12 is adapted to determine the monitoring temperature desired.

[00101]. In accordance with a general embodiment, an assembly 20 is provided.

[00102]. Said assembly 20 comprises at least one monitoring device 6, according to any one of the embodiments described above.

[00103]. In accordance with an embodiment, said assembly 20 comprises at least one pair of monitoring devices 6.

[00104]. Said assembly 20 further comprises at least one portion of said continuous pipeline 1 .

[00105]. In accordance with an embodiment, said assembly 20 comprises said monitoring device 6 and said pipeline section 5.

[00106]. In accordance with an embodiment, said assembly 20 comprises said monitoring device 6 and said continuous pipeline 1 .

[00107]. By virtue of the features described above, provided jointly or separately from one another in particular embodiments, it is possible to meet the aforementioned needs obtaining the aforementioned advantages, and in particular:

[00108]. - it is possible to detect leaks also in a continuous pipeline carrying a fluid in thermal equilibrium with the surrounding environment, for example, the submerged environment;

[00109]. - it is possible to regulate the monitoring temperature as a function of the fluid temperature and/or of the ambient temperature;

[00110]. - by virtue of the employment of the optical fiber sensor, the background noise and the disturbances are minimized, allowing to carry out monitoring operations over a long distance, longer than one kilometer;

[00111]. - by virtue of the employment of the optical fiber sensor, the background noise and the disturbances are minimized, allowing more accurate measurements in terms of detected thermal gradient;

[00112]. - an improved versatility is allowed as compared to known solutions.

[00113]. In order to meet contingent and specific needs, those skilled in the art can make several changes and adaptions to the embodiments described above and replace elements with others which are functionally equivalent, without however departing from the scope of the following claims. LIST OF REFERENCES

1 . continuous pipeline

2. outer wall of the continuous pipeline

3. first cross section of the continuous pipeline

4. second cross section of the continuous pipeline

5. pipeline section

6. monitoring device

7. heating element

8. optical fiber sensor

9. leak of fluid

10. water body

1 1 . bed

12. joining device

13. data processing unit

14. outer surface of the monitoring device

15,16. conductive spacer means

17. trench

18. wrapping sheath

20. assembly

71 . positive pole

72. negative pole

T 1 . ambient temperature

T6. monitoring temperature

Tf. fluid temperature

X-X. longitudinal direction of the continuous pipeline x1 . first longitudinal distance

UΎ. longitudinal direction of the monitoring device x6. monitoring distance

Claims

1. A method of monitoring a continuous pipeline (1 ) comprises the following steps:

- providing a continuous pipeline (1 ) having a longitudinal direction (X-X), coinciding with or parallel to the longitudinal development direction of said continuous pipeline (1 ); said continuous pipeline

(1 ) comprising at least one outer wall (2), defining the radial volume of said continuous pipeline (1 ); said continuous pipeline (1 ) comprising a first cross section (3) and a second cross section (4), spaced apart along said continuous pipeline by a first predefined distance (x1 ), so as to define a pipeline section (5); said continuous pipeline (1 ) being placed in an environment having a predefined ambient temperature (T1 );

- supplying a flow of fluid, flowing inside said continuous pipeline (1 );

said fluid having a fluid temperature (Tf) substantially in thermal equilibrium with said ambient temperature (T1 );

- providing a monitoring device (6); said monitoring device (6) comprising at least one heating element (7) and at least one optical fiber sensor (8);

- heating locally the optical fiber sensor (8) by means of said at least one heating element (6), bringing it to a monitoring temperature (T6) higher than the ambient temperature (T 1 );

- arranging said monitoring device (6) alongside said continuous pipeline (1 ), so that the outer wall

(2) of said pipeline section (5) locally flanks said monitoring device (6);

- detecting a descrease of the monitoring temperature (T6) caused by a leak of fluid (9), which, hitting said optical fiber sensor (9), alters the thermal equilibrium thereof.

2. A method according to claim 1 , wherein the heating step is carried out by raising the monitoring temperature (T6) by at least 2°C with respect to the ambient temperature (T1 ), and preferably by raising the monitoring temperature (T6) by at least 3°C with respect to the ambient temperature (T1 ).

3. A method according to claim 1 or 2, wherein the detection step is carried out by detecting the local temperature difference between the fluid temperature (Tf) and the monitoring temperature (T6); and/or wherein

- the method comprises the further step of localizing the leak of fluid (9) in a pipeline section (5) based on the position of the data processing unit (13), which receives information on the deacrease of temperature of the optical fiber sensor (8); and/or wherein

- the method comprises the further step of supplying said at least one heating element (7) with electric power.

4. A method according to any one of the preceding claims, comprising the further step of detecting the ambient temperature (T1 ), preferably by means of a detection device operatively connected to at least one data processing unit (13); and/or wherein - the method comprises the further step of detecting the fluid temperature (Tf), preferably by means of a detection device operatively connected to at least one data processing unit (13); and/or wherein

- when the ambient temperature (T1 ) varies locally, the detection device detects the variation in ambient temperature (T1 ) and transmits a signal to said data processing unit (13) to regulate the monitoring temperature (T6) accordingly; and/or wherein

- the method comprises the step of regulating the monitoring temperature (T6) in response to the environmental conditions of some portions of the continuous pipeline (1 ); and/or wherein

- when the fluid temperature (Tf) varies locally, the detection device detects the variation in fluid temperature (Tf) and transmits a signal to said data processing unit (13) to regulate the monitoring temperature (T6) accordingly.

5. A method according to any one of the preceding claims, comprising the step of submerging at least said pipeline section (5) in a water body (10); and/or wherein

- the temperature of said water mass being locally equal to the ambient temperature (T1 ) close to the pipeline section (5); and/or wherein

- submerging said continuous pipeline (1 ) in a water body (10); and/or wherein

- the temperature of said water body (10) being locally equal to the ambient temperature (T1 ) close to the continuous pipeline (1 ); and/or wherein

- burying at least said pipeline section (5), for example, in a trench; and/or wherein

- burying at least said pipeline section (5) in the bed (1 1 ) of said water body (10).

6. A method according to any one of the preceding claims, comprising the step of assembling said at least one heating element (7), preferably said plurality of heating elements connected in series, said optical fiber sensor (8) and said joining devices (12) each comprising at least one data processing unit (13) in a single wire-shaped body, e.g. a cable, having an outer monitoring surface (14); and/or wherein

- the assembling step comprises the step of burying said optical fiber sensor (8) and said at least one heating element (7) in a conductive spacer means (15) adapted to transmit heat by conduction between said at least one heating element (7) and said at least one optical fiber sensor (8), wherein, for example, said conductive spacer means (15) is conductive gel.

7. A method according to any one of the preceding claims, wherein the arranging step comprises the further step of wrapping said monitoring device (6) around said outer wall (2) of said continuous pipeline (1 );

or

wherein the arranging step comprises the further step of flanking said monitoring device (6) alongside said outer wall (2) of said continuous pipeline (1 ); and/or wherein - the arranging step comprises the step of placing said monitoring device (6) and said continuous pipeline (1 ) in a trench (17), for example a trench (17) dug into the bed of a water body (10); and/or wherein

- the method comprises the further step of burying said continuous pipeline (1 ) and said monitoring device (6) in said trench (17); and/or wherein

- the arranging step comprises the further step of placing said monitoring device underneath said continuous pipeline (1 ); and/or wherein

- the arranging step envisages placing said outer wall (2) of the continuous pipeline (1 ) in contact with said monitoring device (6); and/or wherein

- the arranging step envisages placing said outer wall (2) of the continuous pipeline (1 ) in contact with the outer monitoring wall (14) of the monitoring device (6); and/or wherein

- the arranging step envisages placing said outer wall (2) of the continuous pipeline (1 ) at a predefined transversal distance with said monitoring device (6).

8. A monitoring device (6) of a continuous pipeline (1 ), said continuous pipeline (1 ) having a longitudinal direction (X-X), coinciding with or parallel to the longitudinal development direction of said continuous pipeline (1 );

- said monitoring device (6) being arranged locally alongside said continuous pipeline (1 );

- said monitoring device (6) comprising at least one heating element (7) and at least one optical fiber sensor (8),

- said heating element (7) being adapted to raise the temperature of the said optical fiber sensor (8) locally;

- said monitoring device (6) is adapted to detect a deacrease of the monitoring temperature (T6) caused by a leak of fluid (9), which, hitting said optical fiber sensor (9), alters the thermal equilibrium thereof.

9. A monitoring device (6) according to claim 8, wherein said optical fiber sensor (8) comprises at least one optical fiber and at least one optical temperature transducer, adapted to transmit an optical signal to said at least one optical fiber in response to a detected variation in temperature; and/or wherein

- said optical fiber sensor (8) comprises at least one bundle of optical fibers; and/or wherein

- said at least one optical temperature transducer comprises a plurality of active portions, adapted to transmit an optical signal to said at least one optical fiber in response to a detected variation in temperature; and/or wherein

- said plurality of active portions are distributed, preferably in a uniform manner, along the longitudinal monitoring direction (Y-Y) of the monitoring device (6); and/or wherein

- said at least one heating element (7) is a wire-shaped element; and/or wherein - said monitoring device (6) extending for a monitoring length (L6) along said longitudinal monitoring direction (Y-Y),

said at least one optical fiber of said optical fiber sensor (8) extending over a length equal to said monitoring length (L6),

said monitoring device (6) comprising a plurality of heating elements (7),

each heating element (7) of said plurality of heating elements (7) extending over a fraction of said monitoring length (L6), so that said plurality of heating elements (7) and said monitoring device (6) are connected in series by means of joining devices (12); and/or wherein

- each joining device (12) comprises at least one data processing unit (13); and/or wherein

- said at least one data processing unit (13) being adapted to control the temperature of a heating element (7) adjacent thereto to keep the monitoring temperature (T6) at a predefined value; and/or wherein

- the at least one data processing unit (13) of each joining device (12) being adapted to determine the desired monitoring temperature.

10. An assembly (20) comprising at least one monitoring device (6) according to any one of the claims 8 or 9, and at least one portion of a continuous pipeline (1 ).