High temperature electromagnetic acoustic transducer for guided wave testing

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis research focuses on the theoretical analysis, development and experimental evaluation of a water cooled Electromagnetic Acoustic Transducer (EMAT) specifically designed for high-temperature Guided Wave Testing (GWT). Its novel design and detailed calculation of its optimum operating conditions resulted in its effectiveness at high temperatures for both short (500oC) and long-term inspection (250oC). All the steps followed for the theoretical and experimental investigation of the limitations of the existing technology and the development of a probe that can overcome these boundaries are presented. Finite Element Analysis (FEA) was performed for the optimization of the EMAT design and estimation of its ultrasonic and thermal properties at room and high temperatures over time. The wave mode purity profile of the Periodic Permanent Magnet (PPM) EMAT was theoretically studied as well as the effect of temperature rise on its ultrasonic performance. Thermal and Computational Fluid Dynamics (CFD) analysis was accomplished for the EMAT design optimization and calculation of its optimum operating conditions. The experimental validation of the theoretical study was also accomplished. The novel water cooled EMAT was developed and experimentally evaluated regarding its ultrasonic and thermal response at room and high temperatures. An empirical method for the enhancement of EMAT performance and its SNR was established. The wave mode purity characteristics of PPM EMAT were experimentally investigated via Laser vibrometry tests, which agreed with FEA results. The impedance analysis and ultrasonic evaluation of the EMAT at both room and high temperatures against various operating conditions were linked and compared to the results obtained from the ultrasonic, thermal and fluid FEA. In all cases, the experimental study is in good agreement with the theoretical results

High temperature shear horizontal electromagnetic acoustic transducer for guided wave inspection

Guided Wave Testing (GWT) using novel Electromagnetic Acoustic Transducers (EMATs) is proposed for the inspection of large structures operating at high temperatures. To date, high temperature EMATs have been developed only for thickness measurements and they are not suitable for GWT. A pair of water-cooled EMATs capable of exciting and receiving Shear Horizontal (SH0) waves for GWT with optimal high temperature properties (up to 500 °C) has been developed. Thermal and Computational Fluid Dynamic (CFD) simulations of the EMAT design have been performed and experimentally validated. The optimal thermal EMAT design, material selection and operating conditions were calculated. The EMAT was successfully tested regarding its thermal and GWT performance from ambient temperature to 500 °C

Inspection and structural health monitoring techniques for concentrated solar power plants

Parabolic trough concentrators are the most widely deployed type of solar thermal power plant. The majority of parabolic trough plants operate up to 400 °C. However, recent technological advances involving molten salts instead of oil as working fluid the maximum operating temperature can exceed 550 °C. CSP plants face several technical problems related to the structural integrity and inspection of critical components such as the solar receivers and insulated piping of the coolant system. The inspection of the absorber tube is very difficult as it is covered by a cermet coating and placed inside a glass envelope under vacuum. Volumetric solar receivers are used in solar tower designs enabling increased operational temperature and plant efficiency. However, volumetric solar receiver designs inherently pose a challenging inspection problem for maintenance engineers due to their very complex geometry and characteristics of the materials employed in their manufacturing. In addition, the rest of the coolant system is insulated to minimise heat losses and therefore it cannot be inspected unless the insulation has been removed beforehand. This paper discusses the non-destructive evaluation techniques that can be employed to inspect solar receivers and insulated pipes as well as relevant research and development work in this field

A New Condition Monitoring Approach for Maintenance Management in Concentrate Solar Plants

The concentrated solar energy is one of the most important renewable energy source. It is crucial to ensure that the solar receivers work properly to avoid failures, and to increase the reliability, availability, safety and maintainability. Non-destructive testing (NDT) is used in structural health monitoring systems for fault detection and diagnosis (FDD). The main purpose of this paper is to present a novel approach for FDD based on long range ultrasonic technology, together with a signal processing of ultrasonic waves (Shear waves) employing wavelet transforms using a variable window size. A new electromagnetic acoustic transducer (EMAT) generates high frequency waves that flow through the material. A similar transducer is also employed as a sensor to collect the guided wave. These waves have a particular behaviour according to the condition of the material. It is analyse the influence of the temperature in the propagation of an ultrasonic pulse through the material. This information is very useful to carry out a proper signal analysis in order to find cracks or failures on the pipes, the correct operation of the system, etc

Calculus of the defect severity with EMATs by analysing the attenuation curves of the guided waves

The aim of this paper is to develop a novel method to determine the severity of a damage in a thin plate. This paper presents a novel fault detection and diagnosis approach employing a new electromagnetic acoustic transducer, called EMAT, together with a complex signal processing method. The method consists in the recognition of a fault that exists within the structure, the fault location, i.e. the identification of the geometric position of damage, and the determining the significance of the damage, which indicates the importance or severity of the defect. The main scientific novelties presented in this paper is: to develop of a new type of electromagnetic acoustic transducer; to incorporate wavelet transforms for signal representation enhancements; to investigate multi-parametric analysis for noise identification and defect classificatoin; to study attenuation curves properties for defect localization improvement; flaw sizing and location algorithm development

Electromagnetic Acoustic Transducers Applied to High Temperature Plates for Potential Use in the Solar Thermal Industry

Concentrated Solar Plants (CSPs) are used in solar thermal industry for collecting and converting sunlight into electricity. Parabolic trough CSPs are the most widely used type of CSP and an absorber tube is an essential part of them. The hostile operating environment of the absorber tubes, such as high temperatures (400–550 °C), contraction/expansion, and vibrations, may lead them to suffer from creep, thermo-mechanical fatigue, and hot corrosion. Hence, their condition monitoring is of crucial importance and a very challenging task as well. Electromagnetic Acoustic Transducers (EMATs) are a promising, non-contact technology of transducers that has the potential to be used for the inspection of large structures at high temperatures by exciting Guided Waves. In this paper, a study regarding the potential use of EMATs in this application and their performance at high temperature is presented. A Periodic Permanent Magnet (PPM) EMAT with a racetrack coil, designed to excite Shear Horizontal waves (SH0), has been theoretically and experimentally evaluated at both room and high temperatures

Clasificación automática de anomalías asociadas con ausencia de información en superficies tridimensionales de objetos de forma libre

En este trabajo se propone un método computacional para clasificar anomalías relacionadas con ausencia de información sobre modelos tridimensionales de forma libre. Para ello, se hizo una exploración descriptiva de las propiedades geométricas globales y locales de las anomalías y una evaluación posterior de distintos métodos de clasificación utilizados en visión artificial y aplicaciones de reconstrucción tridimensional. El método propuesto logra un nivel de clasificación cercano al 90% y un tiempo de ejecución de alrededor de 100 milisegundos. Restringir la clasificación de acuerdo a la aplicación en específico se propone como trabajo futuro./Abstract. In this work it is proposed a computational method to classify anomalies related with information absence over free-form tridimensional models. For that, it was made a descriptive exploration of global and local geometric properties of anomalies and a posterior evaluation of different classification methods widely used in artificial vision and tridimensional reconstruction applications. The proposed method achieved a classification level near to 90% and an execution time near to 100 miliseconds. Constrain classification according to the specific application is suggested as future work.Maestrí