Development of techniques for detection and dissolution enhancement of mineral deposits in petroleum pipelines using ultrasound.

Scale formation in petroleum pipelines causes progressive flow reductions, leading to large production losses and operating costs. The composition and thickness of the scale deposits vary widely, but with present technology they cannot be accurately quantified or monitored. Remedial treatments such as chemical de-scaling etc. are therefore largely based on guesswork, which can lead to expensive chemical wastage and production shutdowns. This project is intended to address some of the above problems using ultrasonic techniques. Work presented in this thesis branches out into two main areas of interest, namely: (a) developments concerning location of deposits from both top-side and down-hole locations; and (b) developments relating to enhancement of scale removal, using ultrasound. With regard to top-side scale detection, the major challenge in this work was to develop a technique by which acoustic signatures are synthetically generated, which can be used with the techniques previously developed for pipeline inspection. This required the determination of a suitable type of transducer and the study of its radiation characteristics in developing comprehensive mathematical models for artificially generating reference echoes. The model allowed the first three multiple echoes (in steel objects) to be computed for given test parameters. Close agreement of the synthesised echoes with practical measurements was demonstrated with good repeatability. An essential requirement for the detection of deposits in down-hole is the accurate alignment of the test probes with respect to the pipe-wall. In this regard, a novel technique for remote alignment of the transducers was successfully formulated. It is based on identifying symmetrical properties of the signals received from the test probe itself when scanned around the correct angular position with respect to the target. However, through extensive practical measurements, it was found that an important requirement for applying this technique is to know in advance whether a particular combination of probe, target diameter and separation distance would give satisfactory angular resolution. Extensive practical examination of these factors showed that no general conclusion can easily be drawn with respect to this requirement. Therefore a mathematical model was successfully developed, which would predict the suitability of given probe/target parameters. It has been reported in previous studies that ultrasonic irradiation could greatly enhance the chemical dissolution of localised deposits during de-scaling operations. In this regard, a major challenge was to improve the efficiency of power transducers radiating into confined spaces at elevated temperatures. That required the study of radiation characteristics of ultrasonic power transducers and compensation techniques to regain loss of efficiency at elevated temperatures. Alternative types of transducers - based on flexural-horn designs - were also investigated and their relative merits presented. Significant findings related to the performance variations of ultrasonic transducers and transmission cables at elevated temperatures have been made. After examining the transducer efficiency drop with temperature, a closed-loop compensation strategy was proposed for maintaining optimal performance. The matching requirements of the cables transmitting power from top-side to down-hole power transducers were also investigated as part of optimisation of ultrasonic power output. From this study it was found that, within the temperature range of interest, the cable in itself does not require changes to the matching requirements as the environmental temperature fluctuates. However, it was noted that the transducer impedance changes rapidly with temperature and therefore a unified compensation strategy incorporating both cable and transducer impedances was proposed as a better solution. Overall, the main objectives of the project concerning pipeline scale detection were well achieved, namely: (a) modelling of a suitable type of ultrasonic transducer to synthesise the reference multiple echoes to aid top-side scale detection; and (b) development of a remote sensing technique for ultrasonic probe alignment in downhole pipes. With regard to dissolution enhancement, techniques for enhancing power output of ultrasonic transducers to aid dissolution enhancement of scale deposits have been determined. Further work includes the improvements to software algorithms developed and hardware integration to achieve the expected performance of the techniques presented

Measurement techniques and instruments suitable for life-prediction testing of photovoltaic arrays

Array failure modes, relevant materials property changes, and primary degradation mechanisms are discussed as a prerequisite to identifying suitable measurement techniques and instruments. Candidate techniques and instruments are identified on the basis of extensive reviews of published and unpublished information. These methods are organized in six measurement categories - chemical, electrical, optical, thermal, mechanical, and other physicals. Using specified evaluation criteria, the most promising techniques and instruments for use in life prediction tests of arrays were selected

A reconfigurable all-optical ultrasound transducer array for 3D endoscopic imaging

A miniature all-optical ultrasound imaging system is presented that generates three-dimensional images using a stationary, real acoustic source aperture. Discrete acoustic sources were sequentially addressed by scanning a focussed optical beam across the proximal end of a coherent fibre bundle; high-frequency ultrasound (156% fractional bandwidth centred around 13.5 MHz) was generated photoacoustically in the corresponding regions of an optically absorbing coating deposited at the distal end. Paired with a single fibre-optic ultrasound detector, the imaging probe (3.5 mm outer diameter) achieved high on-axis resolutions of 97 μm, 179 μm and 110 μm in the x, y and z directions, respectively. Furthermore, the optical scan pattern, and thus the acoustic source array geometry, was readily reconfigured. Implementing four different array geometries revealed a strong dependency of the image quality on the source location pattern. Thus, by employing optical technology, a miniature ultrasound probe was fabricated that allows for arbitrary source array geometries, which is suitable for three-dimensional endoscopic and laparoscopic imaging, as was demonstrated on ex vivo porcine cardiac tissue

Wavelet Transform Applied to Internal Defect Detection by Means of Laser Ultrasound

Laser-generated ultrasound represents an interesting nondestructive testing technique that is being investigated in the last years as performative alternative to classical ultrasonic-based approaches. The greatest difficulty in analyzing the acoustic emission response is that an in-depth knowledge of how acoustic waves propagate through the tested composite is required. In this regard, different signal processing approaches are being applied in order to assess the significance of features extracted from the resulting analysis. In this study, the detection capabilities of internal defects in a metallic sample are proposed to be studied by means of the time-frequency analysis of the ultrasonic waves resulting from laser-induced thermal mechanism. In the proposed study, the use of the wavelet transform considering different wavelet variants is considered due to its multi-resolution time-frequency characteristics. Also, a significant time-frequency technique widely applied in other fields of research is applied, the synchrosqueezed transform

Thermographic non-destructive evaluation for natural fiber-reinforced composite laminates

Natural fibers, including mineral and plant fibers, are increasingly used for polymer composite materials due to their low environmental impact. In this paper, thermographic non-destructive inspection techniques were used to evaluate and characterize basalt, jute/hemp and bagasse fibers composite panels. Different defects were analyzed in terms of impact damage, delaminations and resin abnormalities. Of particular interest, homogeneous particleboards of sugarcane bagasse, a new plant fiber material, were studied. Pulsed phase thermography and principal component thermography were used as the post-processing methods. In addition, ultrasonic C-scan and continuous wave terahertz imaging were also carried out on the mineral fiber laminates for comparative purposes. Finally, an analytical comparison of different methods was give

Detector limited resolution in ultrasound visualization

Imperial Users onl

Ultrasound metrology and phantom materials for validation of photoacoustic thermometry

High intensity focused ultrasound is an emerging non-invasive cancer therapy during which a focused ultrasound beam is used to destroy cancer cells within a confined volume of tissue. In order to increase its successful implementation in practice, an imaging modality capable of accurately mapping the induced temperature rise in tissue is necessary. Photoacoustic thermometry, a rapidly emerging technique for non-invasive temperature monitoring, exploits the temperature dependence of the Grüneisen parameter of tissues, which leads to changes in the recorded photoacoustic signal amplitude with temperature. However, the implementation of photoacoustic thermometry approaches is hindered by a lack of rigorous validation. This includes both the equipment and methodology used. This work investigates the effect of temperature on ultrasound transducers used in photoacoustic thermometry imaging as well as characterisation of potential phantom materials for its validation. The variation in transducer sensitivity with temperature is investigated using two approaches. The first one utilises a reference transducer whose output power is known as a function of temperature to characterise the sensitivity of the hydrophone. As the knowledge of variability of transducer output with temperature is not readily available, two standard metrology techniques using radiation force balances and laser vibrometry are extended beyond room temperature to characterise the effect of temperature on the output of PZT tranducers. For the second approach to transducer sensitivity calibration, a novel method is developed utilising water as a laser-generated ultrasound source and validated using the self-reciprocity calibration method. The calibrated hydrophone is then used to characterise the relevant temperature-dependent properties of several phantom materials in a custom-built setup. The measurement results are used to determine the most suitable phantom for photoacoustic thermometry. Finally, the phantom is heated and imaged in a proof-of-concept photoacoustic thermometry setup using a linear array. These contributions are of vital importance for allowing the translation of photoacoustic thermometry into clinical practice