Pipeline system Field of invention

The present invention relates to a pipeline system, in particular a pipeline system including at least a pipeline portion with a plurality of sensors.

Art background

In the field of offshore oil and/or gas production pipeline systems are normally used. In particular, at offshore

oilfields, subsea pipelines are used to transport the

multiphase mixture of oil, gas and water from producing wells to the processing facilities on the land. Several kilometres of pipeline run on the seabed for this purpose.

The pipeline is provided with a coating for isolating the pipeline from the contact with sea water, in order to prevent corrosion.

Along the pipeline a plurality of sensors are normally installed inside the coating of the pipeline, for remotely monitoring the conditions of the pipeline itself and promptly detect any damage or problem. For example, PH sensors may be provided for indirect measurement of corrosion or pressure sensors for monitoring any excessive pressure drop along the pipeline which may be due to a leak. Mass flow rate sensors may also be installed for detecting leaks. In any case, sensors have normally to be installed in contact with the pipeline, i.e. inside the pipeline coating, in order to properly function.

The sensors distributed along the pipeline needs power to do the provided measurements and communicate the results along the pipeline. The battery packages are placed outside the coating of the pipeline. This will assure that batteries could be changed, for example when exhausted, without removing any part of the coating. Battery packages cannot be mounted on the pipeline before reeling, due to the diameter on the reels used for storage of pipeline. The reels needs pipeline with uniform diameter and the presence of battery packages would violate these requirements. Therefore, but battery packages have to be mounted on the pipeline as the last job before the pipeline is installed. This job is normally done on the vessel which installs the pipeline in a subsea installation, thus making the installation process longer.

Another drawback is the fact that, even if these batteries can last for 20-25 years, they are nevertheless subject to run off of charge, needing the exhausted battery to be replaced with a new one. The maintenance operation for replacing the battery in a subsea environment may be a difficult operation, in any case involving time and costs to be performed.

In addition, an electrical connection has to exist between the batteries and the electronics/sensors which are present inside the coating. This means that, when installing the sensors on the pipeline, an electrical connection has to be provided for each sensor. The electrical connection has to pass through the coating, in order to connect it, during the later installation phase, with the battery package providing power. The connection between the electronic inside the coating on the pipeline and the battery package is a weak point in the assembly for each sensor node distributed along the pipeline, for example a point through which sea water can reach the pipeline.

A further drawback of the presence of the battery packages outside the pipeline is the fact that the distributed battery packages increases the diameter of the pipeline but only on some spots, i.e. the spots where a sensor is present, giving a lesser smooth pipeline which makes the piping installation process more complicated.

A possible solution for avoiding the use a battery package in a subsea device is described in DE 10 2008 056087, where the use of optical fibres guided on a pipeline for the purpose of measuring temperature and/or pressure is described. The optical fibres comprise individual sensors on the pipeline in a decentralized manner and can be supplied by an external underwater Bragg unit to which an accumulator is associated. Such accumulator receives energy from an inductive converter inductively couple to an electrical underwater cable. Such a solution is not optimal because an electrical connection must be established between any accumulator used and at least one inductive converter, which has to be proximal to the

electrical underwater cable.

Summary of the Invention It is an object of the invention to provide a pipeline system which overcomes at least part of the above and/or other drawbacks .

More in particular, it may be an object of the present invention to provide a pipeline including a plurality of sensor which can be mounted on the pipeline during reeling, with no need of further operation for assuring the sensor electrical powering, to be performed immediately before the pipeline installation.

It may be a further object of the present invention to provide a pipeline including a plurality of sensors and an external coating with a smooth surface along all its length, without any clumsy elements on the outside, in particular clumsy element constituted by battery packages for the sensor powering. A smooth surface makes the pipeline installation process easier, with respect to known pipelines.

It may be a further object of the present invention to provide a pipeline including a plurality of sensors, wherein maintenance times and costs are reduced, with respect to known pipelines.

It may be a further object of the present invention to provide a pipeline including a plurality of sensors which does not require a plurality of wires or other electrical connection passing through the coating layer, for connecting the sensors to a respective power sources, thus improving the pipeline reliability.

In order to achieve the objects defined above, a pipeline system and a sensor for pipeline measurements in a pipeline according to the independent claims are provided. The

dependent claims describe advantageous developments and modifications of the invention.

According to a first aspect of the present invention a pipeline system comprising:

a pipeline portion,

at least one sensor on the pipeline portion for

measuring a physical property of the pipeline portion or of a fluid inside the pipeline portion, and

an electromagnetic field source distributed along the pipeline portion and creating an electromagnetic field around the pipeline portion, ,

wherein the sensor includes an accumulator for storing an electric charge induced in the accumulator when the sensor is subject to the electromagnetic field created by the

electromagnetic field source, the accumulator being able to power the sensor by means of the stored electric charge.

The fluid inside the pipeline typically comprises a liquid, for example oil, or a gas, for example natural gas.

Advantageously, in the present invention the battery and the electrical connections between the battery and sensor of the prior art pipelines are replaced by a sensor including an accumulator capable of storing an electrical charge when immersed in an electromagnetic field created around the pipeline by an electromagnetic field source.

According to an exemplary embodiment of the present

invention, the electromagnetic field source consists of an electrical heating device for heating the pipeline portion. Pipelines are typically provided with Direct Electrical

Heating (DEH) . The oil and or gas products inside the

pipeline normally exit from a well at high temperature and pressure, but must be kept warm along the pipeline, in order to avoid the formation of plugs. This may become critical particularly during production shut-downs. Being a pipeline typical length in the order of several kilometres the

electrical current passing in the DEH system is normally high and the electromagnetic field generated is proportional to this current. Advantageously, according to the present invention, such strong electromagnetic field cannot also be used for providing an electrical charge to the sensors installed along the pipeline.

According to an exemplary embodiment of the present

invention, the accumulator powers the sensor by means of the stored electric charge when the electromagnetic field source is switched off.

Advantageously, this allows the sensors to transfer data without being disturbed by the strong electromagnetic field which is normally generated by a DEH system.

The present invention allows a pipeline system to be

externally smooth, the sensor and their powering means being completely internal to the cover layer which provide the external surface of the pipeline. This makes the handling of the pipeline particular easy and practical, particularly during installation. According to a second aspect of the present invention, a sensor for making measurements along a pipeline system including an accumulator for storing an electric charge when subject to an electromagnetic field created by an

electromagnetic field source included in the pipeline system.

The same advantages mentioned with reference to the first aspect of the present invention can be achieved also by the second aspect of the invention.

Brief Description of the Drawings The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 shows a schematic view of a pipeline system according to the present invention, Fig. 2 shows a schematic block view of a sensor for a

pipeline system according to the present invention.

Detailed Description Fig. 1 shows a pipeline system 100 according to the present invention .

The pipeline system 100 include a metallic pipeline portion 101 extending along a longitudinal axis X, which may be used in a subsea installation for connecting a well in an offshore oil and/or gas extraction field to an inshore processing facility, for example a refinery.

According to different embodiments of the present invention, the pipeline portion 101 may coincide with an entire subsea pipeline, extending on the seabed from a well to an inshore processing facility, or it may be only a part of it.

The pipeline system 100 further includes a coating 130 for protecting the pipeline portion 101 from the contact with the sea water, which generates corrosions. Processes and

materials used in the coating process are conventional and known in the art and for this reason not describes in further detail. The coating provides an external smooth cylindrical surface 131 to the pipeline portion 101. The pipeline system 100 further includes a plurality of sensors 110, in contact with the pipeline portion 101 and installed in such a way to be completely covered by the coating 130, i.e. the sensors are comprised between the pipeline portion 101 and the external surface 131 of the coating .

Sensors typically used along a pipeline installation are:

- electrical or electrochemical sensors for corrosion

detection,

- PH sensors for indirect corrosion detection,

- pressure sensors for monitoring pressure drops along the pipeline portion 101 and possibly detect leaks through excessive pressure drop detection,

- mass flow rate sensors, for monitoring the quantity of oil and/or gas transferred along the pipeline and detect leaks,

- temperature sensor, for controlling that oil and/or gas inside the pipeline are above a desired level, in order to avoid plug formation,

- strain gauges for measuring mechanical displacement of the pipeline during its lifetime,

- gravity sensors, for identifying the rotation of the pipeline, immediately after installation, and during the lifetime of the pipeline,

- other sensors.

With reference to Fig. 2, each sensor 110 includes a probe 111 for the measurement of a respective physical property, for example PH or pressure or temperature. The probe is directly connected to the pipeline portion 101 for the measurement of the respective physical property. Each sensor 110 also includes an electronic circuit 112 for receiving and transmitting the measured property to a control and

monitoring centre, which may be either offshore or inshore, and an accumulator 113 for storing an electrical charge which is subject to form on the accumulator 113 when the

accumulator 113 is immersed in an electromagnetic field.

According to the present invention, the accumulator 113 may be of any type, for example a capacitive accumulator having two conductor elements separated by a dielectric. When subject to an electromagnetic field, electrical charges of opposite sign are subject to form on the two conductor elements of the accumulator 113.

The pipeline system 100 includes also a Direct Electric

Heating (DEH) which comprises a metallic cable 120 (normally referred to as "piggyback" cable) connected to the metallic wall of the pipeline portion 101. The current, flowing in the cable 120 and in the pipeline wall, transfers heat to

pipeline and through the pipeline to the oil and/or gas products inside the pipeline, which can be therefore kept above a desired temperature, thus avoiding plug formation. The metallic cable 120 is also an electromagnetic field source creating an electromagnetic field in which the sensors 110 are immersed. In fact, the current circulating flowing in the cable 120 and in the pipeline wall creates an

electromagnetic field around the pipeline, to which the accumulator 113 is sensitive. Therefore, when the metallic cable 120 is switched on for heating the pipeline, thus preventing the formation of plugs along it, it also induces an electrical charge in the accumulator 113. The value of the current circulating in the metallic cable 120 is enough to assure both the functions of heating the pipeline portion 101 and of electrically charging the accumulator 113.

For a typical pipeline having a length in the order of 10 km a typical value of the current in the metallic cable 120 is from 800 to 2000 A. The charge in the accumulator 113 is such to assure typically a power of 2 to 3 W for each sensor 110, at a voltage comprised between 5 and 10 V.

The metallic cable 120 providing the electromagnetic field source for the charging of each accumulator 113 can be periodically switched off without prejudicing its function of heating the pipeline portion 101 and preventing plug

formation, thanks to the thermal inertia of the pipeline portion and to the coating 130, which prevents heating power to be lost towards the external environment. The time

intervals during which the metallic cable 120 is switched off are conveniently used by the plurality of sensors 110 transmitting the respective measured physical properties to the control and monitoring centre. The data transmission will not be disturbed by the electromagnetic field of the metallic cable 120. This also means that no screens have to be

provided between the electromagnetic field around the

pipeline and the sensors as they would be useless during transmissions and they would also negatively influence the charging of the accumulator 113. During data transmission, the sensors 110 are powered by the electric charge previously stored in the respective accumulators 113. The electric charge in the accumulators 113 is sufficient to assure an effective communications of the respective measured physical properties. Re-charging of the accumulators 113 will occur when the metallic cable 120 is again switched on.

Therefore, the sensor 110 can properly function without conventional batteries, using the energy stored in the accumulator 113, only for the period necessary to transmit measured data.