The present invention relates to a method for the installation of optical fibre sensors along pipelines used in fluid transportation, wherein pipelines also refer to the "riser" systems which convey the fluids produced in underwater wells to the surface.

Optical fibre sensors, already widely used in systems for monitoring civil infrastructures, are also becoming asserted in the field of hydrocarbon distribution, in particular for monitoring the state of pipelines used for the transportation of the same .

With respect to the traditional systems, monitoring by means of optical fibres allows a continuous observation, in terms of both space and time, long sections of transport lines, equal for example, to tens or hundreds of kilometres.

The monitoring systems of pipelines for fluid transportation currently known, using optical fibre sensors, are based on the properties of these fibres of undergoing alterations induced by vibrations, mechanical tensions, chemical agents or temperature variations, detecting various anomalous functioning situations such as, for example, fluid leakages, risks of blockage by obstruction, the approaching of persons or mechanical means, the tensional state of structures or ordinary maintenance activities such as in-line inspections .

The optical fibre sensors are currently installed close to the structure to be monitored.

If suitably positioned, this installation makes it possible to obtain reliable information with respect to interferences of third-party subjects or fluid leakages .

At times, for the positioning of optical fibre sensors, which are in the form of a coated cable, previously laid cable paths can be used, for example electric or telecommunications. Otherwise, a specific positioning of the sensor, parallel to the structure to be monitored, is necessary.

For detecting the tensional state of the structure, an installation close to the same is not sufficient. On the contrary, the optical fibre sensors must be rigidly connected to the pipe .

The detection of the tensional state, in fact, requires a precise correlation between the disturbances detected by the optical fibre sensor and those suffered by the pipe itself .

If the sensor is installed close to and not in contact with the pipe, it may happen that the stress detected by the sensor does not perfectly correspond to the state of stress suffered by the pipe. A non- homogeneous movement of the ground in the positioning points of the pipe and sensor, for example, can cause different types of stress.

A precise correlation can only be obtained with a rigid, continuous and guaranteed contact between the sensor and pipe .

At present, this installation mode is not feasible due to the difficulties encountered in obtaining a fixing of the optical fibre to the pipe which is such as to guarantee a continuous adhesion of the sensor to the pipe along the whole of its extension.

By using traditional fixing and installation means of cables, such as for example cable ties externally secured to the pipe through common fixing means, it is not in fact possible to obtain a perfectly adhering coupling between the fibre and pipe along the whole extension of the same. These fixing means are in fact at the most capable of carrying out a discontinuous coupling with a point adherence, where "discontinuous" means "with intervals higher than ten centimetres" .

Furthermore, the fixing of optical fibre sensors to the pipe by traditional cable fixing and installation means can be even more problematic in the presence of pipelines equipped with a protective coating, in particular in view of the necessity for maintaining intact the characteristics of the same.

Although the pipelines are usually made of a metallic or plastic material, they can in fact be provided with an external protective coating made with one or more layers of material suitable for preventing contact of the external surface of the pipe with external agents which could damage it.

The most widely-used coating materials, particularly associated with steel pipes, are those consisting of thermosetting resins, such as for example, epoxy or polyurethane resins, or polyolefins such as polyethylene or polypropylene .

Coatings made of these materials additionally have anticorrosive properties.

Analogously, when a weighting of the pipe is required, as for example for some sea sections, a further layer based on a cementitious conglomerate is applied onto the protective coating.

The difficulty of adhering the optical fibre sensor to the pipe, maintaining its integrity, makes it necessary to adopt complex installation measures which prevent continuous operating during the setting-up phase of the pipes. A specific preventive preparation phase of the pipelines is in fact required, with respect to the positioning or re-laying of the same, during which sensors are applied.

This preventive operation is not only too onerous in terms of both times and costs, to enable it to be effected on long sections of pipe, but it also creates a high risk, during the laying of the pipe to which the sensor has been applied, of damaging the optical fibres of the same .

The techniques currently known therefore at the most allow installation along short sections of pipe which must then be laid with extreme care .

In order not to significantly interfere with the positioning activity, and be able to cover most of the extension of the pipe, a rapid and simple installation is therefore required which can be effected contemporaneously with the installation and/or maintenance phase of the pipe, consequently during the positioning or before the re-laying or immersion of the same .

The techniques currently known, moreover, can only be applied for the installation of sensors on risers, but not on underwater pipes.

An objective of the present invention is therefore to overcome the drawbacks mentioned above and in particular to conceive a method for installing optical fibre sensors along pipelines used for the transportation of fluids which allows the application of optical fibre sensors in direct contact with the pipelines forming an adherent coupling between the fibre and pipe along the whole extension of the sensor, without altering the characteristics of the pipe or its protective coating.

A further objective of the present invention is to contrive a method for the installation of optical fibre sensors along pipelines used for fluid transportation which guarantees a stable and long-lasting fixing to the pipe .

Another objective of the present invention is to conceive a method for the installation of optical fibre sensors along pipelines used for fluid transportation which can also be applied to underwater pipes.

Yet another objective of the present invention is to provide a method for the installation of optical fibre sensors along pipelines used for fluid transportation which can be actuated in continuous and also contemporaneously with the installation and/or maintenance phase of the pipe.

These and other objectives according to the present invention are achieved by providing a method for the installation of optical fibre sensors along pipelines used for fluid transportation as specified in claim 1.

Further characteristics of the method for the installation of optical fibre sensors along pipelines used for fluid transportation are object of the dependent claims.

The characteristics and advantages of a method for the installation of optical fibre sensors along pipelines used for fluid transportation according to the present invention will appear more evident from the following illustrative and non-limiting description, referring to the enclosed schematic drawings in which: figure 1 is a schematic view of a portion of underground pipe to which optical fibre sensors have been fixed according to the installation method of the present invention;

- figure 2 is a sectional view of a portion of pipe in correspondence with which an optical fibre sensor is applied according to the installation method of the present invention;

- figure 3 is a perspective view of a portion of the optical fibre sensor used in the installation method of the present invention;

- figure 4 is a block scheme of the method for the installation of optical fibre sensors along pipelines used for fluid transportation according to the present invention.

With reference to the figures, these show a monitoring system of pipelines 13 for the transportation of fluids already set up and indicated as a whole with 10.

The monitoring system 10 comprises at least one optical fibre sensor 11, therefore having a longitudinal development, applied along the extension of a pipe 13 , directly in contact with the external surface of the same 13 or, if present, with one of its coating layers 12, for example of the anticorrosive type.

The at least one optical fibre sensor 11 can preferably be applied as shown in figure 1 along a directrix of the pipe 13, therefore parallel to the axis of the same 13, or according to a helicoidal development coaxial to the pipe 13 (not illustrated) .

According to a preferred embodiment, the monitoring system 10 comprises three optical fibre sensors 11 integrally applied with the pipe 13 and distributed on the external surface of the pipe 13 in different angular positions, preferably uniformly distributed, i.e. in angular positions at a distance of 120° between each other.

For laying requirements, it is possible however to distribute the sensors along the external surface also at different angular distances with respect to those of the preferred arrangement.

For the application of the sensor 11 in contact with the surface of the pipe 13, optical fibre sensors 11 are used, comprising at least one optical fibre 15a, 15b immersed in a filled supporting body 14, having a longitudinal development.

At least a portion of the outer surface of the supporting body 14 advantageously has a substantially flat conformation. In particular, the portion of flat surface extends for the whole longitudinal development of the supporting body 14.

The portion of flat outer surface of the sensor 11 is put in contact with the external surface of the pipe 13 or with one of its coating layers 12, thus creating a coupling interface with a continuous band between the sensor 11 and pipe 13. In this way it is possible to form a direct and stable coupling by adhesion between the sensor 11 and coating layer 12 of the pipe 13 using a specific adhesive 18 for the purpose.

At least the portion of flat outer surface of the sensor 11 in contact with the pipe 13 preferably has a surface processing, such as for example knurling, suitable for increasing the contact surface between the two elements 14, 13 and consequently improving the reciprocal adherence .

The at least one optical fibre 15a is preferably integral with the supporting body 14 so as to be subjected to the same tensional stress suffered by the supporting body 14 and therefore by the pipe 13 to which it is applied.

According to a preferred embodiment, the supporting body 14 has a substantially rectangular section and comprises a plurality of optical fibres 15a, 15b part of which are integral with the supporting body, and part of which are loose .

The loose optical fibres 15b are preferably housed in a hollow tube 16 immersed in the supporting body 14. In order to preserve the characteristics of the fibres with time, the hollow tube 16 can be under vacuum or filled with a gel or other material suitable for the purpose which however does not constrain the optical fibres 15b immersed in the same, maintaining them in a loose configuration.

In the preferred embodiment illustrated, the optical fibre sensor 11 used in the method according to the present invention comprises two pairs of optical fibres 15a, 15b, a first pair of optical fibres 15a integral with the supporting body 14 for detecting a variation in the tension, and a second pair of optical fibres 15b in a loose configuration for detecting a variation in the temperature, respectively.

Said optical fibres 15a, 15b are arranged symmetrically inside the supporting body 14. The hollow tube 16 inside the supporting body 14 can also house a plurality of additional loose optical fibres 15b for the production, for example, of anti- intrusion sensors, leakage sensors, or sensors for the transmission of signals in the field of telecommunications.

The supporting body 14 with a substantially rectangular section is optionally equipped, in correspondence with the larger sides of the rectangular section respectively, with a central indentation (not illustrated) which, along the development of the sensor 11, forms a groove parallel to said development.

This confers flexural resistance to the lower supporting body 1 , allowing a better adaptation of the same 14 to the curvature of the external surface of the pipe 13 in the case of small diameters.

In the presence of a coating layer 12 of the pipe 13, the supporting body 14 is preferably made of a polyolefin-based material, for example having a low density, and the adhesive 18 used for fixing to the coating layer 12 of the pipe is of the hot melt type also polyolefin-based. It is otherwise also possible to use epoxy, acrylic adhesives and so forth.

Furthermore, in the case of pipelines coated with an ultrasonic weldable material, such as for example, polyethylene, the fixing of the supporting body 14 to the coating layer 12 can be effected, as an alternative to adhesion, by ultrasonic welding.

Said industrial-type adhesives all ensure an optimum adhesion to both the external surface or possibly the coating layer 12 of the pipe 13, and also to the optical fibre sensor 11, guaranteeing an integral coupling between the two elements .

A rigid and integral system is thus created, consisting of the body 20 of the pipe 13 possibly with its coating 12 , the supporting body 14 of the sensor and optical fibres 15a, 15b inside the same 14.

Finally, the optical fibre sensor 11 fixed to the pipe 13 is preferably covered by means of a coating tape 19 suitable for eliminating the stress to which the sensor would be subjected by coming for example into direct contact with the ground or with the underwater environment .

Said coating tape 19 can be made for example of teflon ^® .

The method 100 for the installation of optical fibre sensors along pipelines used for the transportation of fluids according to the present invention therefore comprises the following phases .

At least one segment of adhesive 18 is applied (phase 110) to a surface externally coupled with the pipe 13 along the longitudinal development of the same 13. The externally coupled surface can be formed by the external surface itself of the pipe 13 or its coating layer 12. Said application can be effected parallelly to the axis of the pipe 13 or according to a helicoidal development coaxial to the same 13.

An optical fibre sensor 11 comprising a supporting body 14 in which at least one optical fibre 15a, 15b is inserted, is positioned (phase 120) along each segment of adhesive 18.

Three segments of adhesive are preferably applied, on each of which a respective sensor 11 is positioned in order to obtain an accurate evaluation of the stress exerted on the pipe .

By processing the measurements of the three sensors 11, it is possible to obtain the three-dimensional spatial definition of the compression, tensional and flexural stress. The arrangement of the three segments of adhesive is preferably angularly equidistanced , i.e. the three segments are applied at angular positions of 120° with respect to each other.

In particular, in order to measure the longitudinal compression, the supporting body 14 comprising the integral optical fibres 15a is pre-tensioned (phase 130) .

The supporting body 14 is preferably applied on the segment of adhesive 18 so that a portion of its substantially flat outer surface remains in contact with the adhesive 18.

In the presence of a coating layer 12 of the pipe 13, both the supporting body 14 and adhesive 18 are preferably polyolefin-based in order to guarantee an excellent coupling integral with the coating layer 12.

Once the optical fibre sensor 11 is firmly coupled by adhesion with the pipe 13, said sensor 11 is covered (phase 140) with a coating tape 19 positioned along the development of the same 11 to protect it from stress deriving from the ground or underwater environment in which the pipe has been laid.

In particular, these operations can be effected on both pipelines which have already been laid, and also pipelines 13 still to be laid. In particular, if applied to pipelines still to be laid, the phases of the installation method of optical fibre sensors according to the present invention can be effected contemporaneously with the installation and/or maintenance of the pipelines 13 and in particular before the burying or immersion phase.

In particular, in the case of underground pipes, the application of the sensors takes place after the laying of the pipe 13 in the excavated area and immediately before the re-laying of the same to avoid damage to the sensors 11 installed.

Should the application route of the sensors 11 require the crossing of elements of the pipe 13 to which this application is not possible, such as for example valves, flanged joints, dielectric joints and so forth, the sensors are fixed with different systems which allow these elements to be bypassed.

The signals detected relating to these positions are generally suitably filtered.

The characteristics of the method, object of the present invention, as also the relative advantages, are evident from the above description.

The adhesion not directly of the optical fibres but of a support having a longitudinal development, with which the fibres are integral or in any case containing the fibres, through a material which can be made integral with the pipe possibly coated and/or weighted, allows a rigid and integral system to be created consisting of the metal or plastic body of the pipe, possibly its coating, the supporting body of the sensor and optical fibre inside the same. In this way a direct correlation is obtained between the stress suffered by the optical fibre and the stress suffered by the pipe.

It is therefore possible to detect the stress to which the pipe or its sections is subjected, in order to monitor particularly important or critical areas such as for example landslide areas or areas with particular risks of a geological nature.

Thanks to the installation method according to the present invention, the application of optical fibre sensors is also effected without damaging the optical fibres or altering the characteristics of the coating layer, at the same time guaranteeing a stable and long- lasting fixture between the two elements .

The effectiveness offered by the method according to the present invention also allows a continuous actuation contemporaneously with the installation and/or maintenance of the pipe .

Finally, the method thus conceived can obviously undergo numerous modifications and variants, all included in the invention; furthermore, all the details can be substituted by technically equivalent elements .