Previously, a sensor was proposed for detection of internal corrosion in pipelines made of ferromagnetic materials. The original sensor prototype was composed of a beam made of non-magnetic material, a strong permanent magnet, and the Fiber Bragg Grating strain sensor. The operating principle of the sensor is based on the fact that the magnetic attraction force between the magnet and the pipe wall decreases as the thickness of the pipe wall decreases due to internal corrosion. The FBG sensor is attached to the beam and allows to monitor the strain generated by the magnetostatic force acting on the magnet. Hence, the change in the force can be related to the change in the thickness of the pipe wall and detected using an optical strain gauge. In this work we present results of numerical investigations for two different alternative sensor configurations that are aimed at improving the detection range of the sensor. In the first configuration, the magnet is encased in an enclosure made of ferromagnetic material. In the second configuration we consider a more complex magnetic circuit that includes a magnetic counterbalance placed on the opposite side of the first magnet. We compare the absolute and relative changes in the magnetostatic force in both configurations to the baseline case of the original prototype and formulate suggestions for the improved design.
Various types of ultrasound transducers have been developed for use in structural health monitoring, nondestructive testing, medical imaging and diagnostics applications. Recently, research efforts have been focused on development of optical ultrasonic transducers due to certain advantages that they possess over the traditional transducers, e.g. compact size, ability to be permanently integrated into structural components, safety in 1 volatile environments, and immunity to electromagnetic interference. Optical transducers generate ultrasound using a photoacoustic effect, where the absorbed light is turned into heat, which causes rapid expansion of the absorber material creating an elastic wave. In this work we develop a numerical model for analysis of a fiber-optic based transducer with the absorbing composite material made of polydimethylsiloxane (PDMS) with gold nanoparticles. Previous numerical and experimental studies have demonstrated effective generation of ultrasound by such transducers in mediums that have acoustic properties that are very well matched to those of PDMS (e.g. water and biological tissues). Here, we investigate the effects of laser pulse parameters and the absorbing layer thickness on the generation of acoustic pressure waves when coupled into carbon steel. We attempt to get insight into the formation of the temporal function of the pressure wave transferred from the absorber layer into steel. This study also aids in evaluating the feasibility of developing optoacoustic transducers for structural health monitoring applications. The obtained results are useful for development of designs for experimental transducers.
A corrosion sensor utilizing fiber optics and the magnetic attraction force is proposed. The sensor aims to detect the internal corrosion of pipelines that are made of ferromagnetic materials. Its components include a beam made of a non-magnetic material, a strong permanent magnet, and a Fiber Bragg Grating (FBG) sensor that is very sensitive to strain changes. The sensor is based on the assumption that the magnetic attraction force generated between a magnet and a ferromagnetic material decreases if the thickness of the ferromagnetic material is decreased. To generate this force between the sensor and the pipe, the beam is positioned in a way that the magnet is only few millimeters away from the pipe. The internal corrosion causes a reduction in the thickness of the interior pipe wall, which according to the assumption should reduce the attraction force. As a result, the strain measured by the optical fiber will be affected as it is directly related to the variations in force. We present an initial numerical investigation of the feasibility of the proposed working principle utilizing a Finite Element Analysis (FEA) simulation tool. Simulation results show that the attraction force first increases then saturates with the increase in wall thickness. The change in force becomes significant once the thickness reduces to a threshold value. We also investigate the effect of changing the magnet size, magnetic permeability of pipe material, separation distance between pipe and magnet, and the magnetic flux density of the magnet.
A fiber optic based corrosion sensor utilizing the magnetic interaction force is proposed. The sensor aims to detect corrosion in structures, which are made from ferromagnetic materials (e.g. pipelines made of carbon steel). It consists of a beam that is made from a non-corrosive material with embedded Fiber Bragg Grating (FBG) sensor and a permanent magnet. The beam is placed in a position such that the permanent magnet is within a few millimeters away from the ferromagnetic material to allow for the generation of the magnetostatic attraction force between the sensor and the pipe. The corrosion causes a reduction in material thickness, which increases the distance between the material and the magnet, thus the attraction force will decrease. This change in the force can be related directly to the change in the strain measured by the optical fiber as it causes a shift in the wavelength of the reflected light. We present initial analytical investigation of the feasibility of the proposed concept for practical application of monitoring the external corrosion process on the exposed pipelines. The estimated magnitude of strain change due to corrosion is within the measurement range of typical FBG strain sensors.
In the oil and gas industry, pipeline integrity is a serious concern due to the consequences of pipeline failure. External corrosion was identified as one of the main causes of pipeline failures worldwide. A solution that addresses the issue of detecting and quantifying corrosivity of environment for application to existing exposed pipelines has been developed. The proposed sensor consists of an electric circuit and a sensing array connected to the circuit. The sensing array is an assembly of strips made of a metal identical to that of the pipe, having the same length and width, but different thicknesses. The sensing array is exposed to the same environment as the pipe. As corrosion propagates in the metal strips of the array, it corrodes the metal until it finally breaks the metal strip apart resulting in a discontinuity in the circuit. The sensor circuit is energized using electromagnetic field, and its function is to indicate which strips in the array are fully corroded. Visual indication is provided to the operator via LEDs. The proposed sensor can be installed on existing pipelines without altering the pipe structure or disturbing the production process. It is passive and has low maintenance requirements. Circuit design was validated through lab experiments. Results obtained from experiments were consistent with simulation results.
Pipeline Inspection Gauges (PIGs) are used for internal corrosion inspection of oil pipelines every 3-5 years. However, between inspection intervals, rapid corrosion may occur, potentially resulting in major accidents. The motivation behind this research project was to develop a safe distributed corrosion sensor placed inside oil pipelines continuously monitoring corrosion. The intrinsically safe nature of light provided motivation for researching fiber optic sensors as a solution. The sensing fiber's cladding features polymer plastic that is chemically sensitive to hydrocarbons within crude oil mixtures. A layer of metal, used in the oil pipeline's construction, is deposited on the polymer cladding, which upon corrosion, exposes the cladding to surrounding hydrocarbons. The hydrocarbon's interaction with the cladding locally increases the cladding's refractive index in the radial direction. Light intensity of a traveling pulse is reduced due to local reduction in the modal capacity which is interrogated by Optical Time Domain Reflectometery. Backscattered light is captured in real-time while using time delay to resolve location, allowing real-time spatial monitoring of environmental internal corrosion within pipelines spanning large distances. Step index theoretical solutions were used to calculate the power loss due changes in the intensity profile. The power loss is translated into an attenuation coefficient characterizing the expected OTDR trace which was verified against similar experimental results from the literature. A laboratory scale experiment is being developed to assess the validity of the model and the practicality of the solution.
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