Fei Lu

Bio: Fei Lu is an academic researcher from Oak Ridge Institute for Science and Education. The author has contributed to research in topics: Optical fiber & Fiber optic sensor. The author has an hindex of 4, co-authored 11 publications receiving 68 citations. Previous affiliations of Fei Lu include Leidos & United States Department of Energy.

Corrosion Sensors for Structural Health Monitoring of Oil and Natural Gas Infrastructure: A Review

Abstract: Corrosion has been a great concern in the oil and natural gas industry costing billions of dollars annually in the U.S. The ability to monitor corrosion online before structural integrity is compromised can have a significant impact on preventing catastrophic events resulting from corrosion. This article critically reviews conventional corrosion sensors and emerging sensor technologies in terms of sensing principles, sensor designs, advantages, and limitations. Conventional corrosion sensors encompass corrosion coupons, electrical resistance probes, electrochemical sensors, ultrasonic testing sensors, magnetic flux leakage sensors, electromagnetic sensors, and in-line inspection tools. Emerging sensor technologies highlight optical fiber sensors (point, quasi-distributed, distributed) and passive wireless sensors such as passive radio-frequency identification sensors and surface acoustic wave sensors. Emerging sensors show great potential in continuous real-time in-situ monitoring of oil and natural gas infrastructure. Distributed chemical sensing is emphasized based on recent studies as a promising method to detect early corrosion onset and monitor corrosive environments for corrosion mitigation management. Additionally, challenges are discussed including durability and stability in extreme and harsh conditions such as high temperature high pressure in subsurface wellbores.

Distributed fiber optic pH sensors using sol-gel silica based sensitive materials

Abstract: Fiber optic pH sensors using either silica (SiO2) or gold nanoparticle incorporated silica (Au-SiO2) as the sensitive layers for pH monitoring are presented. A facile sol-gel dip-coating process was utilized to immobilize the SiO2 based sensitive layers on the coreless fiber. In the high pH range of ∼8−12 simulating the wellbore cement conditions, the transmission spectra at room temperature demonstrated notable sensitivity using the SiO2 based coating. The sensitivity was enhanced via either increasing the coating thickness or incorporation of Au nanoparticles. The sensitivity was 19.9 T%/pH for the 1.6 μm thick SiO2 coating and 13.4 T%/pH for the 600 nm thick Au-SiO2 coating, respectively. And these two sensors revealed good reversibility, and the response times were in the order of 10 s of seconds. No obvious chemical structure changes in SiO2 thin film were observed through Fourier-transform infrared spectroscopy (FTIR) analysis after the film was exposed to the alkaline media for 30 min. However, the sensing layers were found to become thinner due to corrosion when tested in strong alkaline solutions with the pH up to 14 for 3 days, especially for the pure SiO2 coating. The incorporation of Au nanoparticles was found to stabilize the pH sensing signals and prolong the lifetime of the pH sensitive layer. Importantly, with the coating of SiO2 based sensitive materials, spatially distributed pH sensing was enabled. The intensity of the backscattered light increased with the increasing pH values along the coated segments on the fiber optic sensors.

Review on corrosion sensors for structural health monitoring of oil and natural gas infrastructure

Abstract: Corrosion has been a great concern in the oil and natural gas industry. A variety of corrosion sensor technologies have been developed based on different sensing principles. Conventional corrosion sensors and emerging sensor technologies are critically reviewed in terms of sensing principles, sensor designs, advantages, and limitations. Conventional corrosion sensors encompass corrosion coupons, electrical resistance probes, electrochemical sensors, ultrasonic testing sensors, magnetic flux leakage sensors, electromagnetic sensors, and inline inspection tools. Emerging sensor technologies include optical fiber sensors (OFS) and passive wireless sensor technology such as surface acoustic wave (SAW) sensors. OFS have advantages of nondestructive monitoring, in-situ distributive measurements, long reach, small size, light weight, inherent immunity to electromagnetic interference, compatibility to optical fiber data communication systems, and improved safety in the presence of flammable gas/oil as compared to electrical based sensors. Passive SAW sensors have advantages of small size, cost efficiency, ease of fabrication, compatibility with wireless telemetry, and adaptability to many applications. Both emerging technologies are promising in corrosion monitoring in the oil and natural gas applications. The ability to monitor corrosion online before the structural integrity is compromised can have a significant impact on preventing catastrophic events resulting from corrosion. Distributed chemical sensing shows promising potential to detect early corrosion onset and monitor corrosive environments for corrosion mitigation management. Additionally, high durability and stability are required for corrosion sensors in extreme service conditions such as high temperature and high pressure during drilling, production, and refining.

Metal oxides-based fiber optic pH sensors for elevated temperature sensing applications

Abstract: Metal oxides based materials are often employed for harsh environment applications since they tend to be stable at high-temperature and high-pressure conditions. In this work, TiO2 and ZrO2 based materials coated fiber optic pH sensors were evaluated with respect to pH sensitivity and stability by measuring the pH-dependent transmission at elevated temperature and high pH range, which are relevant to the wellbore cement monitoring. The TiO2 thin film coated fiber optic sensor showed reversible pH sensitivity during the pH cycling between DI water and pH 12 at room temperature and 80 °C. It demonstrated improved stability and reversibility as compared to the SiO2 or ZrO2 based materials at 80 °C. Au-nanoparticles incorporated TiO2 coating was showed to maintain the pH sensing capability for about 30 hours at 80 °C. This finding is beneficial for future development and deployment of robust distributed optical pH sensors for harsh environment applications in the wellbores.

Distributed carbon dioxide sensor based on sol-gel silica-coated fiber and optical frequency domain reflectometry (OFDR)

Abstract: Monitoring carbon dioxide (CO2) for carbon capture, gas pipelines, and storage as well as early detection of CO2 leakage is important to mitigate greenhouse gas emissions and have a high atmospheric concentration for a long lifetime. Moreover, the main cause of the corrosion in natural gas pipelines is owed by CO2. Therefore, real-time and effective CO2 monitoring is essential to improve efficiency, reduce pipeline emissions, and improve the economics of the natural gas industry. In this paper, we propose and experimentally demonstrate a distributed CO2 sensor based on the measurement of evanescent wave absorption by using optical frequency domain reflectometry (OFDR). A coreless fiber is re-coated with tetraethyl orthosilicate (TEOS) through a dip-coating process with well-defined fabrication conditions. Rayleigh scattering OFDR system is optimized to provide high spatial resolution and large dynamic range to trace gas detection. The proposed distributed fiber gas sensor exhibits continuous real-time measurement of CO2 gas concentrations from 5% to 100% calibrated with nitrogen (N2) as a background gas. The results provide confidence that the proposed sensing technology represents a novel paradigm and holds a potential tool for the early detection of CO2 leaks with high sensitivity in a distributed fashion.

Distributed optical fiber sensing: Review and perspective

Abstract: Over the past few decades, optical fibers have been widely deployed to implement various applications in high-speed long-distance telecommunication, optical imaging, ultrafast lasers, and optical sensors. Distributed optical fiber sensors characterized by spatially resolved measurements along a single continuous strand of optical fiber have undergone significant improvements in underlying technologies and application scenarios, representing the highest state of the art in optical sensing. This work is focused on a review of three types of distributed optical fiber sensors which are based on Rayleigh, Brillouin, and Raman scattering, and use various demodulation schemes, including optical time-domain reflectometry, optical frequency-domain reflectometry, and related schemes. Recent developments of various distributed optical fiber sensors to provide simultaneous measurements of multiple parameters are analyzed based on their sensing performance, revealing an inherent trade-off between performance parameters such as sensing range, spatial resolution, and sensing resolution. This review highlights the latest progress in distributed optical fiber sensors with an emphasis on energy applications such as energy infrastructure monitoring, power generation system monitoring, oil and gas pipeline monitoring, and geothermal process monitoring. This review aims to clarify challenges and limitations of distributed optical fiber sensors with the goal of providing a pathway to push the limits in distributed optical fiber sensing for practical applications.

Corrosion Sensors for Structural Health Monitoring of Oil and Natural Gas Infrastructure: A Review

Abstract: Corrosion has been a great concern in the oil and natural gas industry costing billions of dollars annually in the U.S. The ability to monitor corrosion online before structural integrity is compromised can have a significant impact on preventing catastrophic events resulting from corrosion. This article critically reviews conventional corrosion sensors and emerging sensor technologies in terms of sensing principles, sensor designs, advantages, and limitations. Conventional corrosion sensors encompass corrosion coupons, electrical resistance probes, electrochemical sensors, ultrasonic testing sensors, magnetic flux leakage sensors, electromagnetic sensors, and in-line inspection tools. Emerging sensor technologies highlight optical fiber sensors (point, quasi-distributed, distributed) and passive wireless sensors such as passive radio-frequency identification sensors and surface acoustic wave sensors. Emerging sensors show great potential in continuous real-time in-situ monitoring of oil and natural gas infrastructure. Distributed chemical sensing is emphasized based on recent studies as a promising method to detect early corrosion onset and monitor corrosive environments for corrosion mitigation management. Additionally, challenges are discussed including durability and stability in extreme and harsh conditions such as high temperature high pressure in subsurface wellbores.

Pipeline In-Line Inspection Method, Instrumentation and Data Management.

Abstract: Pipelines play an important role in the national/international transportation of natural gas, petroleum products, and other energy resources. Pipelines are set up in different environments and consequently suffer various damage challenges, such as environmental electrochemical reaction, welding defects, and external force damage, etc. Defects like metal loss, pitting, and cracks destroy the pipeline's integrity and cause serious safety issues. This should be prevented before it occurs to ensure the safe operation of the pipeline. In recent years, different non-destructive testing (NDT) methods have been developed for in-line pipeline inspection. These are magnetic flux leakage (MFL) testing, ultrasonic testing (UT), electromagnetic acoustic technology (EMAT), eddy current testing (EC). Single modality or different kinds of integrated NDT system named Pipeline Inspection Gauge (PIG) or un-piggable robotic inspection systems have been developed. Moreover, data management in conjunction with historic data for condition-based pipeline maintenance becomes important as well. In this study, various inspection methods in association with non-destructive testing are investigated. The state of the art of PIGs, un-piggable robots, as well as instrumental applications, are systematically compared. Furthermore, data models and management are utilized for defect quantification, classification, failure prediction and maintenance. Finally, the challenges, problems, and development trends of pipeline inspection as well as data management are derived and discussed.

Highly Sensitive Humidity Sensor With Low-Temperature Cross-Sensitivity Based on a Polyvinyl Alcohol Coating Tapered Fiber

Abstract: A highly sensitive humidity sensor with low-temperature sensitivity is proposed and demonstrated using a polyvinyl alcohol (PVA) coating tapered fiber. The taper fiber is highly sensitive to the environmental medium due to its microscale diameter. Thus, a humidity sensor can be prepared by plating a PVA moisture-sensitive film in a tapered region. The experimental results show that the sensor has a high humidity sensitivity of 0.1194 nm/%RH but with a relatively low-temperature sensitivity of 0.029 nm/°C. Thus, the sensor can eliminate temperature interference and achieve accurate measurement of environmental humidity. At the same time, the sensor has excellent reversibility, stability, and advantages common to optical fiber sensors, such as small size, antielectromagnetic interference, and remote measurement.