RISERS”

FIELD OF THE INVENTION

[0001 ] This is a specification of a patent for a system for monitoring the integrity of risers and marine structures using strain sensors installed by clamps, and a method of installation and pre-stress calibration of strain sensors for monitoring the integrity of risers and marine structures, consisting of a set of instrumented rods supported on clamps, adjustable to any diameter of pipe, where said rods contain strain sensors, equipped with means of pre-stress calibration suitable for operation at any depth.

[0002] The system of the present invention accurately performs the measurement of forces in magnitude and direction, and can be applied to recently installed submerged pipes or those installed for a longer time, making it possible to assess the risks of flaws in the structural integrity thereof, and which can also be installed and operated by persons or remotely operated vehicles (ROV).

GROUNDS OF THE INVENTION

[0003] In the oil industry, the transportation of the fluid produced by the well to the stationary production unit (SPU), and from this to the refineries, is done through rigid or flexible pipelines, known as collection, production and export lines, which are subjected to mechanical forces due to various factors, such as the weight of the structure, marine currents, tidal movements, waves and the relative movement of the SPUs.

[0004] These forces, which vary over time, induce structural fatigue in the lines; in addition to this, forces generated during the installation of pipelines also contribute to the fatigue of the material, and may, as a final consequence, cause the breaking of these lines, with a consequent leakage of oil and/or gas, produced or drained, which, regardless of volume, is a constant concern in the oil industry. This issue goes far beyond the considerable costs deriving from unscheduled stoppages to production and repairs, human costs (loss of life, injury) and environmental impacts that assume immeasurable proportions.

[0005] So, the monitoring of the stresses of these lines, especially of their vertical sections, known as "risers", has become essential to the evaluation and monitoring of fatigue, in order to enable the scheduling of repairs and/or replacement at an appropriate time, appreciably minimizing the risks of breakage, and reducing the cost of excessively early replacements.

BACKGROUND OF THE TECHNIQUE

[0006] The monitoring of the mechanical stresses on pipes (risers) can be performed by means of sensors, of strains or movement, which are positioned together with the said pipes, which may be of a diverse nature, such as, resistive or capacitive extensometers, piezoelectric, Bragg gratings, optical, acoustic, and other.

[0007] Currently, the standard adopted in monitoring system protection is the use of a robust mechanical device, able to resist the stresses imposed during the installation of the riser; however, this solution brings its own problems, and therefore it is desirable to propose means of assembling the monitoring system, following the installation of the structure, that are easier to operate regarding attachment to the riser.

[0008] Another concern of paramount importance is to maintain the zero-strain reference, which is to say, the load reference prior to the installation of the structure, to achieve absolute measurements, and, in this regard, the calibration and proper adjustment of the sensors is of fundamental importance for the measurements to be accurately and reliably performed.

[0009] To better estimate the fatigue of the material, it is also important to know the direction and type of forces acting on the pipeline, such as traction, bending, compression and torsion.

[0010] Despite the various techniques employed by the oil industry today, it is still a challenge to accurately measure the stresses suffered by the collection, production or outflow line, and to precisely determine the type of force, due to the type of configuration and/or layout of the sensors; the setting of the pre-stressing compensation, hereafter referred to as the offset, and the deviations related to the gaps between the sensor element and the piping structure.

[001 1 ] We already know from the current state of the art the development proposed through patent document US5868524, which concerns a fixing system and method for remotely connecting or disconnecting a submerged pipe to/from another submerged pipe or from a riser or similar, for use with a riser, whose end uses a connector that carries clamps that open to receive or release the pipe connection, where its end sections are radially increased and furnished with ring-shaped grooves that are seated when the sections are confined to the housing of the hollow metal sealing ring, and, with the clamps closed and holding the end sections of the connections, the locking collar is moved over the free end of the clamps, and the sealing ring is energized by the application of high pressure fluid, causing it to expand and seal the ends of the connector, restricting the lateral movement thereof, forcing the maintenance of the connection of the clamp, where the structure of the ring is self-bearing, in its expanded configuration, to retain the sealing and structural support when the pressure of the energizing fluid is released. The free ends of the clamps are equipped with hydraulically activated rods, which force the clamps to open to allow the separation of the ends of the connector as necessary, for example, to replace the worn pipe. The expanded ring and the flexible tube connector are returned to the surface and replaced by a new hose and a new unexpanded ring. The connection or reconnection to the pipe line, or release of the pipe, and the replacement and reconnection of the seal can be carried out by the ROV, without the return of the connector to the surface.

[0012] Although the development previously described provides a good connection, the fact that it uses a pressurized system tends to make the implementation of the proposed solution more complex and costly, as a result of this development.

[0013] We already know from the current state of the art the development proposed through patent document US7277162, which is a method that uses fiber optic technology to measure the vibration characteristics of long, thin structures subjected to dynamic disturbances imposed by water or wind-generated loads, which method is based on measurements of strain bending at selected locations along the length of long, thin structures, such as marine risers or large cables, using optical domain reflectometry and Bragg gratings, where the engineering interpretation of the flexural strain information determines the vibration characteristics, including frequency, amplitude and wavelength, and the measurements of maximum bending strain assess pending structural damage, being applicable to the measurement of the response of vortex-induced vibrations (VIV) in marine risers; said optical fiber-based method is also applicable to the measurement of the flexural characteristics of a flexible tube using plastic optical fibers, which can be interpreted to assess the structural integrity of the pipe and prevent locking during implantation in a ring of small diameter.

[0014] We also know from the state of the art the development proposed in patent document US7461561 , which concerns devices and methods for monitoring fatigue, structural response and operational limits of structural components, and, more specifically, monitoring fatigue, response and operation in steel catenary elevators using fiber optic sensors, which can be pre-installed in new rods or post- installed in existing submarine rods using a variety of methods.

0015 We also know from the state of the art the development proposed in patent document W02005/064300, which concerns an instrumented piping device for the transportation of pressurized fluid, for example, in the field of oil exploration and transportation of gas or hydrocarbons, comprising a tube where the fluid circulates, where said tube possesses means for measuring the principal strains in the pipe and means for measuring the temperature of the fluid in the pipe, where the aforementioned measuring means are solidly connected to the surface of the pipe and transferred to an electronic measuring system through at least one optical transference cable, and take the form of means for assembling at least two non parallel optical fibers having at least three sets of at least two optical measurers with Bragg gratings, fixed to at least three measuring points, connected to the transfer cable by means of optical fibers, where at least one of these sets has a temperature gauge.

0016 We also know from the state of the art the development proposed in patent document W02009/056853, which concerns apparatus for monitoring the physical parameters of a structure, comprising a clamp which, when in use, is positioned to embrace the structure to be monitored, and a stress sensor attached to the clamp, and positioned so as to detect the stress in the direction of the perimeter of the structure, and a method for monitoring a structure comprising the placement of a clamp to embrace the structure to be monitored, where the clamp has a stress sensor attached to it, collecting information from the strain sensor attached to the clamp for detecting strain in the direction of the perimeter of the structure.

[0017] One of the main inconveniences observed in the clamps that are attached to the pipes already installed stems from the fact that they do not have adequate means for allowing the adjustment of this attachment, which enables the clamp to slide in relation to its initial position of attachment to the pipe.

[0018] Notwithstanding the fact that the developments described in the above documents focus on strain measurements in structures, their means of measurement do not provide for the possibility of pre-stress adjustment, thus preventing the obtaining of precise information about the strains that have occurred.

[0019] We also know from the state of the art the development proposed in the patent document KR20120007278, which concerns a fiber optic sensor for measuring strain to minimize additional strains due to torsion, and to prevent damage to a sensing unit of a fiber optic sensor, comprising a Bragg grating sensor, a protective duct, fittings and an adjusting bolt, where said Bragg grating is formed in the fiber network, the protective duct covering the surface of the FBG sensor, and the adjusting screw for applying the initial stress on the optical fiber grating sensor.

[0020] Although the development described above foresees the possibility of adjusting the sensor's prestress, the use of an adjustable screw implies manual adjustment and, as such, is unable to offer fine-tuned control, and may not faithfully reflect the preexisting stress in the structure to be monitored.

[0021 ] The present invention aims to provide means of fixing where the sensors are installed, and means of pre-setting of the initial record of the riser (from the factory) to subsequently be able to receive the record of stresses suffered by the piping on installation and/or in operation, and also to enable the determination of the type of stress (traction, compression, bending or twisting) and its meaning. SUMMARY OF THE INVENTION

[0022] The present invention concerns a system for fixing and pre-setting the mechanical stress offset of the sensors, for measuring strains in pipelines and structures.

[0023] This system for monitoring the integrity of risers and marine structures through strain sensors installed by clamps comprises:

[0024] Clamps with a diameter adjustable to the diameter or cross section of the pipe or structure to be monitored;

[0025] Clamps possessing housings aligned with each other to receive the bases of the rods of the strain sensors;

[0026] Ends of the strain sensor rods equipped with plug-in fittings in the housings of the clamps to ensure the transmission of strains to the rods;

[0027] Connection of the rods of the strain sensors to the fittings of the housings of the clamps, to transmit the strains suffered by the pipe;

[0028] Means of fixing the clamps to the piping; and

[0029] Means of pre-setting calibration of the mechanical stress offset of the strain sensors.

[0030] The system can be adopted in newly installed structures, and in structures already in operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031 ] For better comprehension of the system for monitoring the integrity of risers and marine structures using strain sensors installed by clamps, hereby proposed, reference is made to the attached drawings, where:

[0032] Figure 1 illustrates the anterior perspective view of the clamp, with its claws in an open and unlocked state;

[0033] Figure 2 illustrates the posterior perspective view of the clamp, with its claws in the open and unlocked state;

[0034] Figure 3 illustrates the anterior perspective view of the clamp, with its claws in the closed and unlocked state;

[0035] Figure 4 illustrates the posterior perspective view of the clamp, with its claws in the closed and unlocked state; [0036] Figure 5 illustrates the anterior perspective view of the clamp, with its claws in the closed state and the locks positioned to be threaded;

[0037] Figure 6 illustrates the anterior perspective view of the clamp, with its claws in the closed state and the locks threaded;

[0038] Figure 7 illustrates the rear view of the clamp, with its claws in the closed state and the locks threaded (THIS DRAWING ONLY APPEARS IN THE AMENDED EXAMPLE);

[0039] Figure 8 illustrates the perspective view of the strain sensor housing;

[0040] Figure 9 illustrates the perspective view of the longitudinal cross-section of the strain sensor housing, illustrating the sensor support rod without pre-setting of the mechanical strain offset, and

[0041 ] Figure 10 illustrates the perspective view of the longitudinal cut of the strain sensor housing, illustrating the sensor support rod with presetting of the mechanical strain offset.

PREFERRED DESCRIPTION OF THE INVENTION

[0042] In accordance with the attached illustrations, the system for monitoring the integrity of risers and marine structures using strain sensors installed by clamps, hereby proposed, is formed of a metal structure (1 ), comprising two claws (2), in "C" form, externally flanked by frames (3), also in "C" form, where the front ends (3a) are arranged on a plane shifted outwards in relation to the rear of said frames (3), both incorporating supporting elements (3b), and having curved internal front edges (3c), so as to be able to act as a guiding element in the installation of the clamp in the piping to be monitored, said claws (2) being endowed with housings (2a), where the housings (4) of the strain sensors are installed, parallel to each other, and where the rear ends of said claws are fixed in a hinged manner to the central plate (5), which can be moved linearly, forwards and backwards, controlled by the rear spindle (6), which is equipped with a handle (7), which may be operated by the diver or by ROV, and whose displacement moves, also linearly, the lateral signs (8), fixed laterally to said central plate (5), which signal the opening and closing positions of said claws (2), which are also endowed with fixed spindles (9) fixed in a hinged manner to one end of said claws (2), and which, in the closed state, fit into their own cuttings (1 0), produced at the opposite ends of said claws (2), being also endowed with a handle (1 1 ), which can also be operated by the diver or ROV.

[0043] The housings (4) of the strain sensors possess a substantially cylindrical shape, having, on their inside, a supporting rod (4a) of the sensor, fixed, on one side, in a stationary manner, to the seat (4b), by a locking pin (not illustrated), in the element (4c), which, in turn, is internally threaded to the closing element (4d) of the said strain sensor housing, and also retained by the screw (not illustrated), and where the sensor support rod is fixed, on the other side, to the seat (4e), by a locking pin (not illustrated), in the element (4f), supporting the rod (4g) of the piston (4h), which is able to move linearly, by the action of hydraulic or pneumatic pressure, admitted through the nozzle (4i), for pre-setting of the mechanical strain offset of the strain sensor.

[0044] The method of installation and prestress calibration of strain sensors for monitoring the integrity of risers and marine structures comprises the steps of:

[0045] Installing the strain sensors in the housings of the clamps;

[0046] Connecting the ends of the clamp rods, for transmission of the stresses to the strain sensors;

[0047] Fixing the clamps to the structure to be monitored;

[0048] Calibrating the pre-setting of the mechanical stress offset of the strain sensors;

[0049] Transmitting the strain suffered by the structure to the strain sensors, and [0050] Determining the state of stress of the structure and its direction, by the form of sensitization of the strain sensors.

[0051 ] The method of installation and prestress calibration of strain sensors for monitoring the integrity of risers and marine structures may alternatively comprise, in the case of newly installed structures, the steps of:

[0052] Making markings on the structure to be monitored, before its installation, corresponding to the ends of the strain sensor, in the state without strain;

[0053] Installing the structure to be monitored;

[0054] Installing the strain sensors in the housings of the clamps;

[0055] Connecting the ends of the clamp rods for transmission of the stresses to the strain sensors; [0056] Fixing the clamps to the structure to be monitored;

[0057] Calibrating the presetting of the mechanical stress offset of the strain sensors, according to the variation observed between the markings produced on the structure to be monitored, following the installation of said structure;

[0058] Transmitting the strain suffered by the structure to the strain sensors, and [0059] Determining the state of stress of the structure and its direction, by the form of sensitization of the strain sensors.