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The Geotechnical Monitoring System (GTMS) based on Distributed Temperature and Strain Sensing has been used for more than 15 years to mitigate geohazards along pipeline-crossing regions as distinct as tropical mountain ranges and the far north. The gained experience can be extended to similar infrastructures such as highways, railways, power cables or waterways. The present work reviews the optical fiber technology, the challenges and outcomes of the monitoring. It also draws a general applicable methodology. Different cases are reviewed, demonstrating the variety of geohazards that can be detected at an early stage.

Fatigue crack initiation and short crack propagation was systematically investigated in a rolled α / β Ti-6Al-4V alloy through a combination of in situ optical microscopy observations during fully-reversed uniaxial fatigue experiments and post-mortem electron backscattering diffraction analyses. The effect of microstructural attributes (phase, crystal orientation, grain boundary) on fatigue crack formation and early growth was statistically quantified based on the analysis of a large dataset of grains. Crack initiation was mainly observed on prismatic slip systems which was related to the effect of the rolling texture. Crack propagation was found to be mostly transgranular and crystallographic on both basal and prismatic slip systems. An analysis of the effect of the β phase was proposed to explain the preferential slip systems for propagation in lamellar colonies. Crack deflection was quantified for a large set of grain boundaries. A combination of elastic, plastic and geometric compatibility criteria was identified to consistently predict the preferential slip systems for crack propagation across grain boundary. Finally, a discussion on the transition from microstructure-sensitive to microstructure-insensitive crack propagation was proposed.

Hydrogen-induced cracking behavior in high-strength steel mainly composed of martensite was analyzed by acoustic emission (AE) technique and finite element method (FEM) in slow strain-rate tensile (SSRT) tests and welding tests. The crack initiation was detected by the AE signals, and the time evolution of stress concentration and hydrogen diffusion were calculated by FEM. The effect of hardness and plastic strain on the hydrogen diffusion coefficient was explicitly introduced into the governing equation in FEM. The criterion and indicator parameter for the crack initiation were derived as a function of maximum principal stress and locally accumulated hydrogen concentration. The results showed that the cracking criterion derived by AE and FEM is useful for predicting the cold cracking behavior and determining the critical preheat temperature to prevent hydrogen-induced cracking. Keywords: Hydrogen embrittlement, high-strength steels, Welded joints, Acoustic emission, Finite element analysis

A new fatigue prediction method for wide range of welded structures has been developed by integrating several advanced computational techniques such as thermo-mechanical finite element method, crystal plasticity model and extended finite element method. The method consists of the following procedures: (i) computation of materials properties; (ii) analysis of temperature field, microstructure and residual stress generated during a welding process; (iii) stress distribution analysis under cyclic loading; (iv) fatigue crack initiation analysis by the Tanaka-Mura model; (v) fatigue crack propagation analysis. Using the proposed methodology, the fatigue life of butt joint was evaluated and compared with the experimental data.

A crystal plasticity finite element (CPFE) simulation framework has been proposed in this study for the prediction of combined detrimental effect of mean stress and defects on the fatigue behavior of aluminum alloy. Experimental data for mean-stress effect on fatigue life and crack growth behavior was obtained on metal inter gas (MIG) welded joints of Al-5083/Al-5.8%Mg alloy plates and has been detailed in authors’ previous work, referred later. The present study focuses on its prediction using computational framework only. A 2D representative model for material’s microstructure was used for the simulations, generated using an anisotropic tessellation algorithm using the EBSD measurements data. A total of 10 different microstructure models were generated for each loading condition using six-node plane strain type quadratic triangular (CPE6) elements of mesh size 6 μ m. Two different types of cases were investigated: one without defect and other with a semi-circular surface defect. The simulated loadings at different stress ranges and stress ratios (R-ratio) were similar to the experimental conditions for the better comparison of the results. Significant heterogeneity in the distribution of R-ratios and the far-field applied R-ratio was observed. When defect was not considered, a clear deviation in the predicted fatigue lives from the experimental data was observed at different R-ratios: the predicted fatigue lives were higher than the experimentally observed fatigue lives. This was probably because of not considering the detrimental effect of defects on fatigue lives. But, when the defects were considered, the predicted results for different R-ratios were consistent with the experimental fatigue lives. The proposed CPFE simulation framework not only predicted well the effect of defects and mean stress on the fatigue lives, but also the scatter induced in them due to the defects.

Many pipelines are built in regions affected by harsh environmental conditions where changes in soil texture between winter and summer increase the likelihood of hazards. Pipeline routes also cross mountains that are characterized by steep slopes and unstable soils as in the Andes and along the coastal range of Brazil. In other cases, these pipelines are laid in remote areas with significant seismic activity or exposure to permafrost. Depending on weather conditions and location, visual inspection is difficult or even impossible and therefore remote sensing solutions for pipes offer significant advantages over conventional inspection techniques. Optical fibers can help solve these challenges. Optical fiber based geotechnical and structural monitoring use distributed measurement of strain and temperature thanks to the sensitivity of Brillouin scattering to mechanical and thermal effects. The analysis of scattering combined with a time domain technique allows the measurement of strain and temperature profiles. Temperature measurement is carried out to monitor soil erosion or dune migration through event quantification and spatial location. Direct measurement of strain in the soil also improves the detection of environmental hazards. As an example, the technology can pinpoint the early signs of landslides. In some cases, actual pipe deformation must be monitored such as in the case of an active tectonic fault crossing. Pipe deformation monitoring operation is achieved by the measurement of distributed strain along fiber sensors attached to the structure. This paper comprehensively reviews over 15 years of continuous development of pipeline geohazard risk monitoring with optical fiber distributed sensors from technology qualification and validation to its implementation in real cases as well as its successful continuous operation. Case studies presented include pipeline monitoring in Arctic and Siberian environment as well as in the Andes which illustrate how the technology is used and demonstrate proof of early detection and location of geohazard events such as erosion, landslide, settlement and pipe deformation.

A framework for uncertainty quantification of fatigue life prediction in welded structures has been developed based on multi-scale finite element analysis (FEA) considering microstructure. The multi-scale FEA consists of the following procedures: (i) mechanical and thermal properties are estimated by using commercially available software and database; (ii) temperature field, residual stress and distortion generated during a welding process is calculated on the global model by thermo-mechanical FEA; (iii) macroscopic stress field under cyclic loading condition is calculated with a hardening constitutive model; (iv) the mesoscopic stress field is derived by crystal plasticity finite element analysis with sub-model technique and the cycles for a fatigue crack initiation is analyzed by strain energy accumulation on the slip plane; (v) the cycles for fatigue crack propagation is analyzed by extended finite element method and the total number of cycles to the failure is obtained. The possible uncertainties in the current model include physical variability (weld shape, residual stress, loading and microstructure), data uncertainty due to measurement error and modeling uncertainty in numerical approximations and finite element discretization. A sensitivity analysis was performed by changing the input parameters in the proposed simulation. Additionally, fatigue database of weld joint were aggregated from public databases, published papers and academic resources, and compared with simulation results to quantify the contribution of each source of uncertainty. The effects of residual stress, toe radius and microstructure on the fatigue life of welded joints were evaluated by the proposed methodology. It was shown that the fatigue life increased with the toe radius, and the scattering in high cycle region appeared due to considering microstructure. The features and limitations of our methods will be discussed.

This paper proposes a numerical framework to predict fatigue life on welded joints by integrating several computational techniques. The framework consists of five steps: i) materials properties estimation; ii) welding simulation using thermo-mechanical finite element method; iii) macroscopic stress field analysis under cyclic loading; iv) mesoscopic stress field analysis using crystal plasticity finite element method (CPFEM); v) analysis of fatigue crack growth. The total number of cycles to failure is eventually obtained by the sum of initiation life calculated by CPFEM and propagation life calculated by X-FEM. A fatigue life of butt joint is evaluated by the proposed method. The results demonstrated the possibility of evaluating the fatigue life and its scattering by the proposed framework.

Submillimeter crack is detected with a dedicated fiber-optic strain cable, a 1-m-spatial-resolution (w) distributed Brillouin sensor and an advanced signal processing technique. The signal processing approach consists in spectrum shape analysis and multiple peaks detection.

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

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