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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.

We present a comprehensive solution for in-line and realtime monitoring of long distance pipeline using distributed fiber optic sensors. The technique is based on Brillouin scattering and is capable of measuring strain and temperature over distances larger than 150 km with meter resolution using a single instrument. The solution includes ground movement, leakage and third party intrusion detection. The solution presentation is supported by experimental results and practical cases of implementation.Copyright © 2008 by ASME

Blockages in pipelines owing the formation of wax or hydrates have been widely reported, as for example by Kaczmarski et al [13]. The chemistry is well understood [7]. The prospect of using fibre optic sensing technology to monitor variations in operational parameters along the whole length of the pipeline has previously been considered. This might include bending strains perhaps as a consequence of VIV in free spans [12], acoustic emissions for detection of slugs, as well as temperature and pressure. Monitoring of the effects of hydrocarbon pipeline blockages such as may be caused by hydrates and waxes is receiving a higher level of consideration as the distributed sensing capability offered by the use of fibre optic technology matures. The extent of the hydrate or wax formation problem increases with pipeline length through the effects of cooling. The challenge is significantly greater when assuring flows in deep water and remote subsea locations. Commercially available strain and temperature sensing equipment such as discrete FBGs (Fibre Bragg Gratings) and fully distributed sensing techniques such as Raman DTS (distributed temperature sensor) and Brillouin OTDR (optical time domain reflectometry) typically offer sensing lengths of the order of 20-30km. Whilst this is in many instances a useful length, it is not sufficient to be able to monitor the whole of a pipeline which may be several hundreds of kilometres in length. To date two sensing technologies have come to the fore for this application. Each has its own merits and disadvantages. These are Fibre Bragg Gratings, and Optical Time Domain Reflectometry. Whilst the former is able to provide a high rate of response (perhaps several Hz to kHz) it is limited to discrete sensing locations (which each require a Bragg grating). This in itself might not be a significant limitation for measurements in fibres a few kilometres in length but is a potential issue with very long pipelines since the number of FBGs which can be interrogated is limited. Whilst new developments continue this issue is reducing since more gratings (currently 100s) can be accessed using time division multiplexing (TDM) perhaps coupled with wavelength division multiplexing (WDM), and FBGs can be written directly into the fibre. The authors have developed and demonstrated a method for extending the reach of a Brillouin OTDR interrogating system such that sensing sections of conventional length (approximately 25km) can be successfully interrogated from distances well in excess of 100km without having to compromise on the performance. With a single instrument, more than 250km of sensing fibre can be monitored to within 1.5 metre resolution. By this means, temperature and strain profiles may be measured for the entire pipeline length which will enable active flow assurance measures to be taken including identifying the presence, nature and extent of blockages as they form. Consequently, any corrective action taken by the pipeline operators will be on an informed basis (such as the injection of an optimised quantity of inhibitor), and will incur a significantly lower level of risk than is currently possible.

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.

We demonstrate that an optical fibre current sensor can measure current over 500 kA with an accuracy of 0.2%. This level of accuracy has never previously been achieved using a traditional non-optical sensor.

Performance and stability of a field fibre optics interferometric current sensor are presented, showing a ±0.5% accuracy over a broad temperature range and an excellent insensitivity to the sensing fibre positioning

This paper present a polarimetric fiber optics current sensor using a 22.5 degree Faraday rotator and a Faraday rotation mirror. The objective of this sensor is to be low-cost, high accuracy and easy to manufacture

The experimental validation of a numerical technique for temperature/strain profile reconstruction based on Brillouin optical-fibre time-domain analysis (BOTDA) sensors is presented. In this approach, we search directly for the Brillouin frequency shift profile along the fibre that matches the measured data. The algorithm is based on a harmonic expansion of the unknown profile, whose coefficients are determined by means of a multidimensional minimization. Experimental measurements have been carried out in order to reveal the influence of nonlocalities in Brillouin measurements, and to prove the capability of the proposed algorithm to compensate for these effects.