Instrumented strakes and fairings for subsea riser and pipeline monitoring

Abstract

A vortex induced vibration suppression system for use on a subsea riser system having either a stake or fairing component includes at least one fiber optic sensor mounted on the component. The fiber optic sensor associated with the riser includes at least one sensor for producing a sensor signal. The system may include a plurality of sensors and the plurality of signals produced thereby are combined at a multiplexer for generating a single, composite sensor signal. The signal may be monitored in real time or near real time for observing and monitoring the reaction of the subsea riser to conditions inducing vibration.

Claims

1. A vortex induced vibration suppression device for use in combination with a subsea riser system, the suppression device for the riser system comprising: a. A riser; b. An element mounted external of and secured to the riser; c. At least one sensor mounted in the vicinity of the element, the sensor including an output cable for transmission of a sensor signal produced by the sensor, the sensor being adapted for compensating for ambient temperature conditions at the point of the location of the sensor; d. A processor for receiving the sensor signal, for producing a processed signal; and e. Said at least one fiber optic sensor having a Bragg grating with a reflectivity of greater than 4%.

2. The suppression device of claim 1, wherein the fiber optic sensor is an electrical based sensor.

3. The suppression device of claim 1, wherein the fiber optic sensor has an accelerometer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of the monitoring system of the subject invention.

(2) FIG. 2 is a drawing showing mounting of the sensors on a typical strake in a pre-assembly configuration and a post-assembly configuration.

(3) FIG. 3 is a diagrammatic view or a portion of a typical riser having fiber optic sensors in accordance with the subject invention.

DETAILED DESCRIPTION

(4) A system block diagram is shown in FIG. 1. Each riser strake S1-Sn on a riser column includes a fiber optic sensor array, F1-Fn, respectively. Each sensor in the each sensor array produces a sensor output signal on the dedicated fiberoptic cable C1-Cn. The individual sensor signals from each sensor in a sensor array are carried to the surface and combined at a junction system or multiplexer 10. The combined signal is then introduced into a processor 12. As shown, there is a one-to-one relationship between each sensor array and dedicated fiber optic cable for delivering the sensor readings to the surface junction system. The plurality of fiber optic sensor signals are multiplexed along a single fiber optic strand using wavelength division multiplexing and time division multiplexing methods well known to those who are skilled in the art.

(5) The processed signals are then introduced into the processor 12, for archiving in a database 14 or other device, and may be transmitted to a remote location, for management functions, as well. Any developed algorithms may be used to analyze and manage the data produced by sensor system of the subject invention. The analysis by the subject system is more reliable than prior art systems because the data being analyzed is real-time live data, rather than modeling data. This permits accurate assessment of the riser both on a long term basis, as well as during short intervals. For example, long term data may show deterioration over a period of time, whereas short term data may show riser response to storm conditions. This permits the operator to make critical decisions based on real, live data, rather than applying modeling techniques.

(6) In the preferred embodiment, the sensors are oriented to measure the strain on the riser in both the axial direction and the hoop direction. The quantity of axial measurements on each strake is generally four, but this may be altered based on application and preference. The sensors also measure strain in both tension and compression. Temperature compensation for the sensing devices is provided, for correcting the measurements based on the ambient external temperature at the point of each strake or fairing.

(7) Pressure measurements within the riser may be derived from hoop strain measurements, permitting riser pressure to be monitored without penetrating the riser, in a non-invasive system.

(8) In the preferred embodiment each fiber optic sensor has a Bragg grating with a reflectivity value of greater than 0.4%. However, this can be altered based on preference and application.

(9) Also, it should be understood that each fiber optic sensor could include an electric sensor and/or and accelerometer.

(10) The bandwidth of the fiber optic sensor system for a riser system is typically plus or minus 50 nm around a center wavelength of both 1550 nm and 1310 nm. The optical power of the fiber optic sensor system is greater than 10 dβ.

(11) FIG. 2 is a drawing showing the mounting system for placing sensors on at a typical strake 24. In one embodiment each sensor in the sensor array may be mounted on the riser system before the riser is deployed, as each riser component is assembled. In an alternative embodiment each sensor in the sensor array may be installed after the riser in place.

(12) In the first embodiment a typical riser pipe 20, as shown in cross-section, will have a plurality of fiber optic sensors Sm mounted directly on the exterior wall of the riser pipe and secured thereto with a suitable adhesive. In order to protect the fragile sensor Sm, the sensor is sheathed in a polyurethane envelope 22. A poly jacket 24 then wraps the pipe region where the sensors are located. The strake 24 is then mounted on the exterior of the assembly. This configuration is generally used in new, pre-deployment operation.

(13) In the alternative embodiment, a plurality of sensors Sr will be mounted on the interior surface of the jacket 22 before it is mounted on the riser 20. The jacket and sensor array is then mounted on the riser. The strake is then mounted on the exterior of the assembly in the area of the sensor array.

(14) FIG. 3 shows a typical riser system incorporating fiber optic sensor system of the subject invention. The riser 20 extends from the rig floor 30 to the sea floor 32. A plurality of strakes 24 will be mounted at selected positions on the riser pipe in typical manner. Sensors Sm and/or SR will mounted on the riser assembly as described, on selected strakes. A fiber optic cable C1-Cn will be associated with a respective sensor for carrying the signal produced at the sensor back to the rig floor 20. The cables C1-Cn are then combined for managing the signals as described.

(15) While certain features and embodiments of the invention have been shown and described in detail herein, it should be understood that the invention encompasses all modifications and enhancements within the scope and spirit of the following claims.