We demonstrate that BOTDA is the equipment of choice for Distributed Temperature Sensing (DTS) when challenging components such as Wet Mate Connectors (WMC) and Fiber Optic Rotary Joints (FORJ) are inserted in the sensing line. The parameter of Temperature Measurement Dead Zone (TMDZ) is introduced to support the discussion and quantify possible impairments. A laboratory qualification test with real FORJ and WMC is conducted confirming the theoretical expectations. The system is then implemented offshore demonstrating that FORJ and WMC do not affect the sensing operation in field environment.
A novel scheme is proposed to extend the sensing range of Brillouin optical time-domain analyzers (BOTDA).
Specially-designed erbium doped fiber amplifier (EDFA) repeaters are located every 65km fiber along the sensing cable
to achieve a total sensing length of 325km, corresponding to a 650km loop. At the end of the sensing fibre, we
experimentally demonstrated a measurement repeatability of 2°C (2σ) using a three meters spatial resolution.
Asset integrity monitoring based on distributed fiber optic monitoring using BOTDA is playing an increasingly
important role in today’s oil and gas and energy industries. Existing applications, part of operator’s asset integrity
management plans are as diverse as fatigue monitoring of subsea umbilicals, thermal optimization of direct electrical
heated subsea flowlines, pipeline leak and ground movement detection and 3D pipeline deformation monitoring or
thermal management of offshore wind farm electrical export cable. The monitoring solutions developed and qualified by OMNISENS over the last decade are now installed world wild, providing 24/7 event detection and localization for its
valuable customers.
This paper describes the outcome of two groups which are involved in the specification of guidelines for fibre optic
sensors performance and testing. The "Guideline for use of fibre optic sensors" from the COST-299 guideline group, and
the "Optical Strain Sensor based on Fibre Bragg Grating" from the GESA guideline group of the VDI - "The Association
of German Engineers". Through appropriate specifications and definitions, both guidelines aim at enabling better
understanding of fibre optic sensors characteristics and performances. A concise view into the structure of the guidelines
is presented, emphasizing important aspects. The English version of the two guidelines will be available in autumn 2009.
An increasing number of pipelines are constructed in remote regions affected by harsh environmental conditions where
pipeline routes often cross mountain areas which are characterized by unstable grounds and where soil texture changes
between winter and summer increase the probability of hazards. Third party intentional interference or accidental
intrusions are a major cause of pipeline failures leading to large leaks or even explosions. Due to the long distances to be
monitored and the linear nature of pipelines, distributed fiber optic sensing techniques offer significant advantages and
the capability to detect and localize pipeline disturbance with great precision. Furthermore pipeline owner/operators lay
fiber optic cable parallel to transmission pipelines for telecommunication purposes and at minimum additional cost
monitoring capabilities can be added to the communication system.
The Brillouin-based Omnisens DITEST monitoring system has been used in several long distance pipeline projects. The
technique is capable of measuring strain and temperature over 100's kilometers with meter spatial resolution. Dedicated
fiber optic cables have been developed for continuous strain and temperature monitoring and their deployment along the
pipeline has enabled permanent and continuous pipeline ground movement, intrusion and leak detection. This paper
presents a description of the fiber optic Brillouin-based DITEST sensing technique, its measurement performance and
limits, while addressing future perspectives for pipeline monitoring. The description is supported by case studies and
illustrated by field data.
Sub-millimeter crack is detected with a dedicated fiber optic strain cable, a 1 m spatial resolution (w) distributed
Brillouin sensor (DBS) and an advanced signal processing technique.
As fiber optic distributed scattering sensing systems are providing innovative solutions for the monitoring of large
structures, the comparison of the different techniques and solutions is difficult because of the lack of standardized
specifications and the difficulty associated to the characterization of such systems. The article presents a tentative
definition of performance specifications and qualification procedures applicable to fiber optic distributed sensing
systems aiming at providing clear guidelines for their design, specifications, qualification, application and selection.
The monitoring of temperature profiles over long distance by means of optical fibers represents a highly efficient way to perform leakage detection along pipelines, in dams, dykes, or tanks... Different techniques have been developed taking advantages of the fiber geometry and of optical time domain analysis for the localization of the information. Among fiber optics distributed temperature sensing techniques, Brillouin-based systems have demonstrated to have the best potential for applications over distances up to several tens of kilometers. The key features and performances are reviewed in the present article and a 55km pipeline equipped with a fiber optics leakage detection system is presented as a case study.
Supraconductive installations are now commonly used in large facilities, such as power plants and particle accelerators. This requires a permanent temperature control at very low temperature, but cryogenic temperature measurements in the 1-77K range requires expensive calibrated temperature probes. We report here the possibility to use stimulated Brillouin scattering in optical fibers for temperature sensing down to 1K. Such a technique offers the additional advantage to make possible distributed measurement, so that very large structures and systems can be controlled using a single fiber and a single analyzing instrument. In addition only one by-pass for the fiber is required as input to the cryogenic vessel, that is definitely a key advantage for the design and the energy loss. Brillouin scattering in optical fibers has never been investigated so far at temperature below 77K (nitrogen boiling point). This absence of interest probably results from the constant decrease of scattering efficiency that was observed while cooling the fiber down to 77K. Our measurements show the unexpected feature that scattering efficiency is significantly raised below 50K and is even much better than observed at room temperature. The relevance and the feasibility of the technique is demonstrated in real scale on the supraconductive magnets for the future world largest particle accelerator, namely the large hadron collider (LHC) at CERN Laboratory in Geneva.
Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is plus or minus 1 degree Celsius for temperature and plus or minus 20 (mu) (epsilon) for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.
Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is +/- 1 degree C for temperature and +/- 20 (mu) e for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.
A simple system for optical and microwave signals analysis based on the optical sampling technique is presented. It is novel in requiring only low-frequency detection and electronic components. This is made possible by the use of a commercially available L1NbO3 intensity modulator for processing the light wave. The ultimate performance of the system is discussed, and comparisons with standard detection systems are also made.
Brillouin gain spectrum measurement along an optical fiber has recently gained a lot of interests owing to its potentiality for strain monitoring in installed cables [1] and distributed temperature sensing [2]. This measurement requires two lightwaves propagating in opposite directions through the fiber, since Stimulated Brillouin Scattering (SBS) amplification is possible only in the backward direction.
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