This paper examines the efficacy of quasi-distributed acoustic sensors (q-DAS) in identifying damage within pipeline structures, placing a substantial emphasis on generating synthetic q-DAS measurements in active ultrasonic testing setting and bridging the gap between synthetic and real q-DAS measurements. Our research utilizes simulation software to model the ultrasonic guided wave propagation and its interaction with pipeline defects. The pipeline structural health monitoring setup is based on the pulse-echo method utilizing a torsional symmetric mode T(0,1) at 32kHz, with an aim to identify corrosion and weld irregularities over extensive pipeline lengths. We have prioritized the calibration of simulation models against experimental data, fine-tuning the simulation processes to reflect actual conditions with higher fidelity. The study specifically highlights the simulation’s accuracy in capturing the distinct signatures of critical pipeline features and the subsequent detection capabilities within an operational context. By focusing on the experimental validation, we have advanced the understanding and application of structural health monitoring for essential infrastructure, ensuring the simulations' predictive strength aligns closely with real-world sensor data and observed phenomena.
Distributed acoustic fiber optic sensors (DAS) enable spatially distributed monitoring of perturbations and contain rich multidimensional information that can be used in structural health monitoring. Machine learning based on physics-based simulations can make a breakthrough in traditional data analysis methods to improve their efficiency and performance, solving a series of problems such as huge data volume, low data processing speed, data signal-to-noise ratio, etc. Here, the relationship of DAS response and corrosion type are studied. First, we present a systematic theoretical study of the potential of direct coupling of quasi-distributed acoustic sensing (q-DAS) with guided ultrasound typically used for real-time pipeline health monitoring. To investigate properties of scattered acoustic waves and the performance of DAS and q-DAS in identifying defects, we use finite element analysis to simulate the response in a variety of pipeline structures including welds, clamps, defect types, and sensor installations representing various corrosion patterns expected in practice. A specific emphasis will be placed upon simulating and modeling pitting corrosion defects and contrasting with other types of corrosion observed in practice. We also aim to compare and analyze signal characteristics due to different kinds of corrosion types and structures, and to enhance machine learning algorithms for detection and size prediction of major pipeline structural changes and corrosion types. Ultimately, results of simulated DAS and q-DAS sensor networks are analyzed by a neural network-based machine learning algorithm for defect identification through supervised learning. To evaluate and improve effectiveness, we estimate model uncertainty and identify features of simulated results that contribute most to the model performance and efficacy.
The fiber-optic distributed acoustic sensing (DAS) technique has increasingly become more attractive for structural health monitoring (SHM) and non-destructive evaluation (NDE) purposes. When it comes to traditional acoustic NDE methods, the presence of weldings can present a significant challenge as it can heavily scatter waves resulting in complex data analysis and interpretation. The present work aims to develop an improved understanding and interpretation framework in cases where welds play an important role in the signal with an emphasis on the steel shell of a canister, typically used for Dry Cask Storage Systems (DCSSs) that house spent nuclear waste fuel rods. We also introduce a promising approach in the use of guided ultrasonic waves along with fiber optic sensors that seeks to overcome the challenges that emerge when using traditional acoustic sensing based NDE techniques in welded structures. The study is conducted in a simulation theoretical manner, using a canister model constructed from a representative stainless-steel plate, with different configurations of weldings typically present for DCSS structure. Progressively increasing complexity of the weld physical representation is considered to fully incorporate in physics-based analysis. Furthermore, the acoustic response of these models is obtained from the simulations as a response of an assumed DAS or quasi-distributed acoustic sensing Q-DAS system network. The features originated from the welds are extracted and analyzed, and additional features associated with structure integrity associated with corrosion defects, etc. will also be explored for NDE inspection as in a traditional acoustic NDE approach.
Fiber-optic distributed acoustic sensing (DAS) is becoming an increasingly important tool for real-time monitoring of energy and civil infrastructure structural health such as pipelines. We present a systematic theoretical study of the potential for DAS to be directly coupled with guided ultrasonic waves typically used in conventional acoustic non-destructive evaluation (NDE) methods for real-time pipeline health monitoring. We are referring to this innovative new NDE technique as ultrasonic guided wave and optical fiber sensor fusion. In the practical application of DAS coupled with guided ultrasonic waves, the structural design of (1) the specific guided waves excited, (2) the physical installation of the acoustic transducers and the fiber optic sensors, and (3) the functional performance specifications (gauge length, sensitivity, Etc.) of fiber optic DAS have an important influence on overall capabilities of the monitoring system. Meanwhile, physics-based analysis of acoustic waves is still a challenge due to the complex nature of the Lamb wave when it propagates, scatters, and disperses in the presence of structural defects. In this work, we simulate carbon steel pipes relevant for oil and gas pipeline applications with diameters of approximately 6-12” and wall thickness of 0.5” as the objects to be monitored. By establishing and implementing these capabilities, we seek to pursue an in-depth study on structural parameter optimization of DAS network, measurement range, and signal processing with an ultimate goal of increasing the sensitivity and efficacy of DAS to defect identification for various modes of corrosion expected in practice. To study the characteristics of scattered acoustic waves and performance of DAS for defect identification, we simulated the response of DAS for multiple pipe structures, defect types, and DAS sensor network configuration using finite element software Ansys, then the properties of signal response are extracted to construct defect-sensitive features. The raw data simulated, and the associated features extracted can ultimately be utilized as annotated training data to benchmark various designs for DAS applications, guided acoustic excitation sources, and learning model parameters to enhance early detection of potentially problematic defects.
We demonstrate a novel probabilistic Brillouin frequency shift (BFS) estimation framework for both Brillouin gain and phase spectrums of vector Brillouin optical time-domain analysis (BOTDA). The BFS profile is retrieved along the fiber distance by processing the measured gain and phase spectrums using a probabilistic deep neural network (PDNN). The PDNN enables the prediction of the BFS along with its confidence intervals. We compare the predictions obtained from the proposed PDNN with the conventional curve fitting and evaluate the BFS uncertainty and data processing time for both methods. The Brillouin phase spectrum generally provides a better measurement accuracy with reduced measurement time in comparison to the Brillouin gain spectrum-based measurement, for an equal signal-to-noise ratio and linewidth. The proposed method is demonstrated using a 25 km sensing fiber with 1 m spatial resolution. The PDNN based signal processing of the vector BOTDA system provides a pathway to enhance the BOTDA system performance.
The sensing range of Brillouin optical time-domain analysis (BOTDA) is typically restricted to tens of kilometers by the fiber attenuation, pump depletion, and unwanted nonlinear effects. It limits the use of BOTDA in applications such as oil and gas pipeline monitoring that requires a sensing range up to hundreds of kilometers. In this work, a Raman amplification technique and a differential pulse-width pair (DPP) technique are employed to achieve high spatial resolution and long distance measurement. The Raman amplification technique involves three Raman pump configurations such as forward/backward and bi-directional pump with respect to different Brillouin pump pulses. Variations in pump and probe power, Raman propagation direction and injection location are explored to allow full control over signal amplification in any particular section of the total sensing fiber length. The signal-to-noise ratio (SNR) for a certain location along the length of the fiber can be enhanced to provide more useful localized information. In addition, a novel fitting algorithm based on artificial neural networks (ANNs) for Brillouin scattering spectrum is proposed for the estimation of Brillouin frequency shift with high accuracy. It is experimentally demonstrated for a sensing range of 100 km with a spatial resolution of 1 m and ANN based novel fitting algorithm.
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