Distributed Brillouin Scattering Sensor for Discrimination of Wall-Thinning Defects in Steel Pipe under Internal Pressure

Fiber Optics Group, Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada.
Applied Optics (Impact Factor: 1.78). 04/2004; 43(7):1583-8. DOI: 10.1364/AO.43.001583
Source: PubMed


A distributed Brillouin scattering sensor has been employed to identify several inner wall cutouts in an end-capped steel pipe by measuring the axial and hoop strain distributions along the outer surface of the pipe. The locations of structural indentations that constitute 50-60% of the inner pipe wall are found and distinguished by use of their corresponding strain-pressure data. These results are quantified in terms of the fiber orientation, defect size and depth, and behavior relative to those of unperturbed pipe sections.

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Available from: Shahraam Afshar, May 29, 2014
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    • "Apart from a few field installations, such systems have been mostly used in experimental research to evaluate a specific parameter in comparison with more conventional sensors. Several studies have addressed measurement performance when the sensor is attached or embedded in a concrete beam under deflection [13] [14] [15], or to study preembedded defects in steel pipelines [16], composite pipes [17], and well casing [18]. Also, in a study with the same DBS as used in this study, validation of measured bending strain was evaluated in a number of long beams made of concrete, wood, and aluminum with different sensor attachment methods [19]. "
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    ABSTRACT: Distributed Brillouin sensing systems (DBSs) have growing applications in engineering and are attracting attention in the field of underground structures, including mining. The capability for continuous measurements of strain over large distances makes DBSs a promising monitoring approach for understanding deformation field evolution within a rock mass, particularly when the sensor is installed away from excavation damaged zone (EDZ). A purpose-built fiber optic sensing cable, a vital component of DBSs, was assessed in laboratory conditions. A test program was performed to observe DBSs response to various perturbations including strain and joint movements, including opening and shearing of joints. These tests included assessment of the strain-free cable response and the application of extensional and lateral displacement to various sensing cable lengths (strained lengths), from 1 m down to 1 cm. Furthermore, tests were done to evaluate the time-dependent behavior of the cable and to observe the effect of strain transfer using a soft host material (e.g. a soft grout) under lateral displacement. The noise level of the DBSs range was ±77 με, determined through repeated measurements on an unstrained cable. Stretching test results showed a clear linear correlation between applied strain and Brillouin frequency shift change for all strained lengths above half the spatial resolution of the DBSs. However, for strained lengths shorter than half the spatial resolution, no strain response was measurable and this is due to the applied internal signal processing of the DBSs to detect peak Brillouin gain spectrum and noise level. The stability with time of the measurements was excellent for test periods up to 15 h. Lateral displacement test results showed a less consistent response compared to tension tests for a given applied displacement. Although the Brillouin frequency shift change is correlated linearly with the applied displacement in tension, it shows a parabolic variation with lateral displacement. Moreover, the registered frequency response (correlated with strain) of the system decreased significantly when the sensing cable was embedded in a sand-filled tube compared with direct cable displacement.
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    • "The temperature based techniques cannot monitor the deformations of the pipelines. The strain based approaches have been adopted to monitor the local damages in the pipelines (Zou et al. 2004, Ravet et al. 2006, Glisic and Yao, 2012). However, the distributed fiber optic sensors are rarely used to monitor the global buckling of pipelines. "
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    ABSTRACT: A methodology based on distributed fiber optic sensors is proposed to detect the lateral buckling for subsea pipelines in this study. Uncontrolled buckling may lead to serious consequences for the structural integrity of a pipeline. A simple solution to this problem is to control the formation of lateral buckles among the pipeline. This firms the importance of monitoring the occurrence and evolution of pipeline buckling during the installation stage and long-term service cycle. This study reports the experimental investigations on a method for distributed detection of lateral buckling in subsea pipelines with Brillouin fiber optic sensor. The sensing scheme possesses the capability for monitoring the pipeline over the entire structure. The longitudinal strains are monitored by mounting the Brillouin optical time domain analysis (BOTDA) distributed sensors on the outer surface of the pipeline. Then the bending-induced strain is extracted to detect the occurrence and evolution of lateral buckling. Feasibility of the method was validated by using an experimental program on a small scale model pipe. The results demonstrate that the proposed approach is able to detect, in a distributed manner, the onset and progress of lateral buckling in pipelines. The methodology developed in this study provides a promising tool for assessing the structural integrity of subsea pipelines.
    SMART STRUCTURES AND SYSTEMS 02/2015; 2(15):245-258. DOI:10.12989/sss.2015.15.2.245 · 1.37 Impact Factor
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    • "Bao [6] proposed in-laboratory and in-field measurements concerning beam deflection under bending, investigating the accuracy of the readings. The experiments carried out by Bao [6], Kim et al [8] and more recently by Zou et al [9] clearly showed that the accuracy of the read strains is strongly affected by the spatial resolution of the sensors, which depends on the frequency of the waves; for this reason the local accuracy of readings could actually represent a great problem if strain exhibits strongly localized changes. In particular, this frequently happens for bending beams near the support zones and in the presence of slight modifications of the geometry for technological reasons or when localized damage occurs [10] [11]. "
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    ABSTRACT: In recent years the use of distributed optical fiber sensors for measurements of strain in beams, by means of the Brillouin scattering effect, has been proposed. Several works pointed out the practical difficulty of this kind of measurement, connected both to theoretical and to experimental problems, e.g. mechanical characterization of optical fibers, decaying of strains in the protective coatings, spatial resolution of the Brillouin scattering, brittleness of the glass core, elastic–plastic response of the polymeric jackets, end effects and the different responses of the fiber for dilatation and contraction. Dealing with each of the above problems still requires a great research effort. However, recent literature shows that distributed optical fiber measurement techniques are extremely useful for finding qualitative responses in terms of strains. Indeed, in spite of the above-mentioned uncertainties, the great advantage of the proposed distributed measurement of strains remains evident for the safety assessment of large structures, such as bridges, tunnels, dams and pipelines, over their whole lifetimes. In view of this, in the present paper the detection of defects or damage in bending beams—by using distributed optical fiber sensors in a method based on time domain stimulated Brillouin scattering—is proposed. In particular, laboratory tests were carried out to measure the strain profile along a steel beam. Two tests were performed: the first one involves an integral steel beam, while the second experiment is performed on a damaged beam. Comparison between these two tests allows the detection of the position and the establishing of bounds on the size of the defect. At the end, the quality and accuracy of the measurements are discussed and a sensitivity analysis of the strain readings taking into account the bonding conditions at the interface between the structure and the fiber is also carried out by means a parametric numerical simulation.
    Smart Materials and Structures 03/2006; 15(2):612. DOI:10.1088/0964-1726/15/2/045 · 2.50 Impact Factor
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