Daniele Inaudi

Fiber Optic Sensing for Innovative Oil and Gas Production and Transport Systems

Fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of elongated structures such as pipelines, flow lines, oil wells and coiled tubing. Distributed sensing systems based on Brillouin and Raman scattering are used for example to detect pipeline leakages, verify pipeline operational parameters, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hot-spots in high-power cables. Point sensors based on Interferometric and FBG setups are also effective tools to assess the static and dynamic response of structures such as offshore platforms and risers.This contribution presents different applications of distributed and point sensors to innovative oil and gas structures such as composite coiled tubing, high-pressure composite gas pipeline and deepwater risers.

Ten-year monitoring of high-rise building columns using long-gauge fiber optic sensors

A large-scale lifetime building monitoring program was implemented in Singapore in 2001. The monitoring aims of this unique program were to increase safety, verify performance, control quality, increase knowledge, optimize maintenance costs, and evaluate the condition of the structures after a hazardous event. The first instrumented building, which has now been monitored for more than ten years, is presented in this paper. The long-gauge fiber optic strain sensors were embedded in fresh concrete of ground-level columns, thus the monitoring started at the birth of both the construction material and the structure. Measurement sessions were performed during construction, upon completion of each new story and the roof, and after the construction, i.e., in-service. Based on results it was possible to follow and evaluate long-term behavior of the building through every stage of its life. The results of monitoring were analyzed at a local (column) and global (building) level. Over-dimensioning of one column was identified. Differential settlement of foundations was detected, localized, and its magnitude estimated. Post-tremor analysis was performed. Real long-term behavior of concrete columns was assessed. Finally, the long-term performance of the monitoring system was evaluated. The researched monitoring method, monitoring system, rich results gathered over approximately ten years, data analysis algorithms, and the conclusions on the structural behavior and health condition of the building based on monitoring are presented in this paper.

Long-gauge fibre optic sensors: performance comparison and applications

Long-gauge deformation sensors have opened new possibilities for the health monitoring of civil engineering structures. They are particularly suitable for applications in structures built of inhomogeneous materials, such as concrete, and with complex strain fields, such as bridges, buildings, dams, whenever the global structural behaviour assessment is of interest. Different technologies and measurement principles have been developed for measuring average strains over measurement bases that can reach tens of meters with resolutions in the micrometer range. In this work, the performances of seven commercially available alternative solutions, based on fibre Bragg-grating, Fabry-Perot interferometry, stimulated Brillouin scattering, low-coherence interferometry and traditional vibrating-wire technology, were tested and directly compared both in laboratory and in field conditions. The results are presented and discussed, aiming at the assessment of the main characteristics of each technology, and taking into account the principal requirements of in-field civil engineering applications. The efficiency of a monitoring method based on long-gauge sensors is illustrated through an application at the Ricciolo Viaduct in Switzerland.

Dynamic demodulation of long-gauge interferometric strain sensors

Long-guage interferometric SOFO sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & gas and other structures. The sensors are based on an all-fiber Mechelson interferometer with one arm mechanically coupled to the structure and one used as reference. The original demodulation system is based on low-coherence interferometry. The path-matching readout unit features excellent long-term stability and preceision, but is not suitable for dynamic measurements because the scanning mirror requires about 7 seconds to acquire a complete interferogram. In order to allow the use of the same sensors for the measurement of dynamic events, a new demodulator was developed. It is based on the coherent demodulation of a coherence-colloapsed laser source and is able to demodulate 8 SOFO sensors at frequencies of up to 1 kHz with resolutions of 0.01 microns. This system is particularly adapted for the analysis of dynamic structural deformations produced by traffic, wind, seismic and impacts. The use of long-gauge sensors allows a direct measurement of the dynamic strains and the calculation of modal strains and curvatures. This paper presents the optical setup of the SOFO dynamic demodulation system and discusses its performances through the presentation of laboratory and field tests.

Distributed Fiber-Optic Sensing and Integrity Monitoring

Structural health monitoring is a process meant to provide accurate and real-time information concerning structural condition and performance. Needs for structural health monitoring in the past two decades increased rapidly, and these needs stimulated the development of various sensing technologies. Distributed optical-fiber sensing technology has opened new possibilities in structural monitoring. A distributed deformation sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors a one-dimensional strain field and can be installed over the entire length of the monitored structural members (suspension cables, bridge girders, tunnel vaults, dam basis, etc.). Therefore, the sensor provides for integrity monitoring, that is, direct detection, characterization (including recognition, localization, and quantification or rating), and report of local strain changes generated by damage. An integrity monitoring principle for long bridges and tunnels is developed. Various distributed sensing techniques are summarized, and their potential for the use in integrity monitoring is compared. Finally, the first large-scale, actual on-site application is briefly presented.

Geo-structural monitoring with long-gage interferometric Sensors

The monitoring of geotechnical structures like piles, anchors and tunnels requires the measurement of deformations over bases of a few meters to a few tens of meters. The SOFO monitoring system, based on the use of long-gage low-coherence interferometric sensors therefore presents interesting application opportunities in this domain. The SOFO system was installed in a number of piles to monitor their short an long term deformations, to evaluate the lateral friction and to assess their ultimate bearing capacity. The sensors were also installed inside anchor cables to measure the deformations of the rock, in the free and in the anchored parts. Additional sensors were installed directly on single cable strands. This paper presents the sensor installation and the results from selected applications in the monitoring of piles and anchors.

Health monitoring of full composite CNG tanks using long-gauge fiber optic sensors

The Compressed Natural Gas (CNG) used as a carburant in automotive industry offers low cost and notably less pollution. Full composite tank used to store the CNG onboard features low weight and extended lifespan. However, the safety issues and maintenance fees remain a challenge for its use in ordinary cars. The structural health monitoring of tanks with accent to damage detection can significantly increase the safety and decrease the maintenance fees. Structural health monitoring and damage detection of composite tanks impose important challenges to the monitoring strategy and monitoring system to be used. The issues of non-intrusive installation of sensors, their topologies and network, and particularly analysis and interpretation of resulting data are very complex. The long-gage interferometric sensors of SOFO type, for direct embedding in the full composite tank during production are developed. The sensor consists of single mode optical fiber embedded into the very thin composite tape. Such packaging offers to optical fiber excellent protection during handling and embedding and makes sensor non-intrusive to the tank material. Appropriate topologies of the sensors are combined in single sensor network used to monitor strain state and damage. The results of monitoring are analyzed at several levels, and the damage is detected using algorithms combining the global deformation and changes in both the tank stiffness and sensors cross-correlation. The monitoring strategy, sensors used in full composite tank monitoring, installation issues and the results of the structural health monitoring performed in laboratory are presented in details in this paper.

Bridge Spatial Displacement Monitoring with Fiber Optic Deformations Sensors

Our laboratory fitted an highway bridge near Geneva (Switzerland) with more than 100 low-coherence fiber optic deformation sensors. The Versoix Bridge is a classical concrete bridge consisting in two parallel prestressed concrete beams supporting a 30 cm concrete deck and two overhangs. To enlarge the bridge, the beams were widened and the overhang extended. In order to increase the knowledge on the behaviour between the old and the new concrete, low-coherence fiber optic sensors was chosen in order to measure the displacements of the fresh concrete during the setting phase and to monitor its long term deformations. The aim is to retrieve the spatial displacements of the bridge in an earth-bound coordinate system by monitoring its internal deformations. The curvature of the bridge is measured locally at multiple locations along the bridge span by installing sensors at different distances from the neutral axis. By taking the double integral of the curvature and respecting the boundary conditions, it is than possible to retrieve the deformation of the bridge. The choice of the optimal emplacement of the sensors and the mathematical model required to interpreter the results are also presented.

An improved fiber optic strain sensor for gas tank monitoring with rf subcarrier phase and I&Q demodulation techniques

With increased interest in the use of compressed gas as a vehicle fuel, attention has been focussed on the safety issues surrounding the tanks used to store the fuel. Currently it is necessary to remove the tanks from the vehicle in order to inspect them, which entails a considerable cost in manpower and takes the vehicle being out of service. We have been developing a sensor scheme that can provide in situ monitoring of the tanks condition. This entails bonding optical fibre sensors to the tank and using them to measure the strains experienced by the tank during pressurisation. If the tank is significantly damaged, then the tank will expand in a distorted manner. We therefore measure the strain characteristics of a healthy tank and use them as a reference for future measurements. The method of strain measurement is the well established rf subcarrier phase detection technique, however in this application the changes in optical power caused by microbending of the fibres during pressurisation produces inaccuracies. In order to overcome this problem we use both in-phase and quadrature mixing and then take the ratio of the outputs to obtain a value of arctangent that is independent of amplitude.

EXPO '02, Piazza Pinocchio: monitoring visitor live loads

Once every generation, Switzerland treats itself to a National Exhibition commissioned by the Swiss Confederation. Expo 02 was spread out in five Arteplage over a whole region: the land of the three lakes, on the shores of the lakes of Biel, Murten and Neuchatel, which are located in the northwest of Switzerland. Each Arteplage relates to a theme, which is reflected in its architectures and exhibitions. The Arteplage of Neuchatel was related to Nature and Artificiality; A big steel-wood whale eating a village represents the fairy tale named Pinocchio from the Italian writer Collodi. The Piazza Pinocchio was built together with other exposition buildings on one large artificial peninsula. The belly of the whale holds the exposition dedicated to robotic and artificial intelligence, while the rest of the village was developed on two floors with steel piles/beams and wood walls and floors. A fiber optic sensor system was commissioned to monitor the visitors loads over the whole Piazza Pinocchio. The main requirements were: real-time computer-screen figure-form results of the live loads during 18 hours a day, automatic thermal-induced strain compensation, real-time warnings and pre-warnings for each single pile, automatic phone call advises when reaching warning thresholds and remote monitoring for complete management of the monitoring sytem. The SOFO system based on low coherence fiber optic deformation sensors was selected to carry out the requirements. The aim of this paper is to present an overview of the project, the installation solution, the results, and data analysis of the installed monitoring system.