Development of a petroleum pipeline monitoring system for characterization of damages using a Fourier transform

Significant damage to the environment and huge economic losses are potential problems caused by leakage from petroleum pipelines. The occurrence of a leakage in a pipeline throughout its lifetime is very difficult to prevent. To minimize environmental damage and high economic losses, an efficient pipeline monitoring system is required to carry out damage characterization thereby enhancing quick response. The signal processing technique of sampling and reconstruction was adopted and mathematical algorithms for the characterization of damages in pipes were developed using the Fourier transform method. These were simulated with the results showing a good agreement between the shapes and magnitudes of the measured original and reconstructed pulses. The simulation was verified with experiments on the test rig. The results showed an underestimation in the magnitudes of the reconstructed pulses in the range of 40 – 45 %. This problem was solved by using a factor K obtained by dividing the maximum amplitude value of the original pressure pulse by that of the reconstructed pulse. Reconstruction of the measured original pulse at a damage location was achieved from combining the measured pulses from two other close locations using the developed Fourier transform based model. Keywords: Damage Pipeline-monitoring Characterization Fourier transform Reconstructio

PZT Sensor Arrays for Integrated Damage Monitoring in Concrete Structures

The broad objective of the work reported here is to provide a fundamental basis for the use of Lead Zirconate Titanate (PZT) patches in damage detection of concrete structures. Damage initiation in concrete structures starts with distributed microcracks, which eventually localize to form cracks. By the time surface manifestation in the form of visible cracking appears there may be significant degradation of the capacity of the structure. Early detection of damage, before visible signs appear on the surface of the structure is essential to initiate early intervention, which can effectively increase the service life of structures. Development of monitoring methodologies involves understanding the underlying phenomena and providing a physical basis for interpreting the observed changes in the parameters which are sensed. PZT is a piezoelectric material, which has a coupled constitutive relationship. In the case of the PZT patches bonded to a concrete structure, any sensing strategy requires developing an understanding of the coupled electromechanical (EM) response of the PZT-concrete system. The challenges associated with the use of PZT patches for damage monitoring in a concrete substrate include providing the following: a clear understanding of the fundamental response of the PZT patch when bonded to a concrete substrate; interpretation of the coupled response of the PZT patch under load induced damage; and development of an efficient, continuous monitoring methodology to sense a large area of the concrete substrate. Due to a lack of a fundamental basis, the use of PZT patches in concrete structures often involves inferring the measured response using model-based procedures. The work outlined in this thesis addresses the key issue of developing the theoretical basis and providing an experimental validation for PZT-based damage monitoring methodology for concrete structures. A fundamental understanding of response of the PZT patch when bonded to concrete substrate is developed. The outcome of the work is an integrated local and distributed sensing methodology for concrete structures by combining the electromechanical impedance and stress wave propagation methods using an array of bonded PZT patches. The work presented in this thesis is focused on using PZT patches bonded to a concrete substrate. A fundamental understanding of the coupled electromechanical behaviour of a PZT patch under an applied electrical excitation in an electrical impedance (EI) measurement, is developed. The influence of the substrate size and its material properties on the frequency dependent EI response of a PZT patch is investigated using concrete substrates of different sizes. The dynamic response of a PZT patch is shown to consist of resonance modes of the PZT patch with superimposed structural response. The resonance behaviour of the PZT patch is shown to be influenced by the material properties of the substrate. The size dependence in the EI response of a PZT patch bonded to a concrete substrate is produced by the dynamic behaviour of the structure. The size of the local zone of the concrete material substrate in the vicinity of the bonded PZT patch, which influences the frequency dependent EI response of the PZT patch is identified. For each resonant mode, a local zone of influence, which is free from the influence of boundary is identified. The dynamic response of the PZT resonant mode is influenced by the elastic material properties and damping within the zone of influence. The structural effects of the concrete substrate produced by the finite size of the specimen are separated from the material effects produced by the material properties and the material damping in the coupled EM response of the bonded PZT patch. The influence of size of the concrete substrate on the coupled impedance response of the PZT is identified with peaks of structural resonance, which are superimposed on the resonant peaks of the bonded PZT patch The EI response of the PZT patch when bonded to concrete for detecting load-induced damage from distributed microcrack to localized cracks within the zone of influence of the PZT patch is investigated. Using an approach which combines an understanding of the coupled EM constitutive behaviour of PZT with experimental validation, a methodology is developed to decouple the effects of stress and damage in the substrate on the coupled EM response of a PZT patch. The features in the EI signature of a bonded PZT patch associated with stress and damage are identified. An increasing level of distributed damage in the concrete substrate produces a decrease in the magnitude and the frequency of the resonant peak of the bonded PZT patch. The substrate stress produces a counter acting effect in the EI spectrum of the bonded PZT patch. A measurement procedure for the use of bonded PZT patches for continuous monitoring of stress-induced damage in the form of distributed microcracks in a structure under loading is developed. An integrated methodology for damage monitoring in concrete structures is developed by combining the EI method for local sensing and the stress wave propagation-based method in a distributed sensing mode. An array of surface mounted PZT sensors are deployed on a concrete beam. The EI measurements from individual PZT sensors are used for detecting damage within the local zone of influence. PZT sensor pairs are used as actuators and sensors for distributed monitoring using stress wave propagation. A stress-induced crack is introduced in a controlled manner. It is detected very accurately from the full-field displacement measurement obtained using digital image correlation. The crack opening profile in concrete produced by the fracture is established from the surface displacement measurements. From the measurements of bonded PZTs, the localized crack is detected in the zone of influence by EI. The change in compliance of the material medium due to a localized crack is small and it is reflected in the smaller change in the measured EI when compared to distributed damage. Stress wave based measurements sensitively detect crack openings on the order of 10m. The material discontinuity produced by a closed crack, after removal of the stress is also detected. A damage matrix is developed for stress wave based method which is independent of transmission path to assess the severity of damage produced by the crack in a concrete structure

Preload monitoring of bolted L-shaped lap joints using virtual time reversal method

L-shaped bolt lap joints are commonly used in aerospace and civil structures. However, bolt joints are frequently subjected to loosening, and this has a significant effect on the safety and reliability of these structures. Therefore, bolt preload monitoring is very important, especially at the early stage of loosening. In this paper, a virtual time reversal guided wave method is presented to monitor preload of bolted L-shaped lap joints accurately and simply. In this method, a referenced reemitting signal (RRS) is extracted from the bolted structure in fully tightened condition. Then the RRS is utilized as the excitation signal for the bolted structure in loosening states, and the normalized peak amplitude of refocused wave packet is used as the tightness index (TIA). The proposed method is experimentally validated by L-shaped bolt joints with single and multiple bolts. Moreover, the selections of guided wave frequency and tightness index are also discussed. The results demonstrate that the relationship between TIA and bolt preload is linear. The detection sensitivity is improved significantly compared with time reversal (TR) method, particularly when bolt loosening is at its embryo stage. The results also show that TR method is an effective method for detection of the number of loosening bolts

Electromechanical Impedance-based Techniques for Structural Health Monitoring

New developments on electromechanical impedance (EMI) based structure health monitoring techniques are presented in this thesis. Time frequency auto-regressive moving average (TFARMA) model based damage indicator is developed to enhance the sensitivity of EMI based method for structural damage detection. An innovative approach by using impedance sensitivity-based model updating and sparse regularization techniques is developed for structural damage localization and quantification. Numerical and experimental studies are conducted to verify the performance of the proposed approaches

New ultrasonic methods for detecting damage in metals and composite materials

Recent requirements in the field of non-destructive testing are techniques that quantify micro-structural damage in a wide variety of materials during their manufacture and life cycle for ensuring both their quality and durability. Traditional evaluation techniques such as acoustic pulse echo, impact echo, resonance, ultrasonic transmission, electromagnetic and visual inspection methods are not sufficiently sensitive to the presence and development of domains of incipient and progressive damage. The research presented in this thesis details work undertaken by the author while working at the University of Exeter and is concerned with the development and validation of innovative methods to inspect micro-damage. Various non-linear acoustic measurement techniques, such as detecting defects by measuring the generation of harmonic and inter-modulation products, pulse inversion and resonant frequency deviation has been investigated. In addition to the experimental work new transducers and instrumentation has been developed and used in experimental validation tests on a variety of objects and differing materials. It has been found that the non-linear acoustic testing method provides a practical means by which low levels of progressive damage can be detected and quantified with sensitivities far in excess of that provide by conventional ultrasonic testing methods

Inspection of Parts with Complex Geometry and Welds with Structural Health Monitoring Techniques

Structural Health Monitoring (SHM) systems were developed to evaluate the integrity of a system during operation, and to quickly identify the maintenance problems. They will be used in future aerospace vehicles to improve safety, reduce cost and minimize the maintenance time of a system. Many SHM systems were already developed to evaluate the integrity of plates and used in marine structures. Their implementation in manufacturing processes is still expected. The application of SHM methods for complex geometries and welds are two important challenges in this area of research. This research work started by studying the characteristics of piezoelectric actuators, and a small energy harvester was designed. The output voltages at different frequencies of vibration were acquired to determine the nonlinear characteristics of the piezoelectric stripe actuators. The frequency response was evaluated experimentally. AA battery size energy harvesting devices were developed by using these actuators. When the round and square cross section devices were excited at 50 Hz frequency, they generated 16 V and 25 V respectively. The Surface Response to Excitation (SuRE) and Lamb wave methods were used to estimate the condition of parts with complex geometries. Cutting tools and welded plates were considered. Both approaches used piezoelectric elements that were attached to the surfaces of considered parts. The variation of the magnitude of the frequency response was evaluated when the SuRE method was used. The sum of the square of the differences was calculated. The envelope of the received signal was used for the analysis of wave propagation. Bi-orthogonal wavelet (Binlet) analysis was also used for the evaluation of the data obtained during Lamb wave technique. Both the Lamb wave and SuRE approaches along with the three methods for data analysis worked effectively to detect increasing tool wear. Similarly, they detected defects on the plate, on the weld, and on a separate plate without any sensor as long as it was welded to the test plate

Structural Health Monitoring (SHM) systems in aircraft: wing damage detection employing guided waves techniques

The doctoral thesis provides a detailed description of the implementation of methodologies and technologies based on ultrasonic guided waves for Structural Health Monitoring (SHM) on wing structural elements made of composite materials for BVID or hidden flaws detection. The developed methodologies have been first technologically integrated and applied on small scale structural elements, unstiffened and stiffened plates. Subsequently the SHM system was integrated on a full scale wing box demonstrator in order to perform the delamination detection. The implemented SHM system is capable to control a network of surface mounted piezoelectric transducers, to perform Electromechanical Impedance measurement at each transducer, to check the reliability as well as the bonding strength, and to perform an active guided wave screening

Ultrasonic lamb wave energy transmission system for aircraft structural health monitoring applications

In this project an investigation of a wireless power transmission method utilising ultrasonic Lamb waves travelling along plates was performed. To the author’s knowledge, this is the first time such a system was investigated. The primary application for this method is the supply of power to wireless structural health monitoring (SHM) sensor nodes located in remote areas of the aircraft structure. A vibration generator is placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device travel through the aircraft structure to a receiver in a remote wireless sensor node. The receiver converts the mechanical vibration of the ultrasonic waves back to electricity, which is used to power the sensor node. An experimental setup comprising a 1000 × 821 × 1.5 mm aluminium plate was designed to model an aircraft skin panel. Pairs of piezoelectric transducers were positioned along the longer edges of the plate. The electric impedance characteristics of three transducer types were measured. A circuit simulation MATLAB code was written. An input and output power measurement system was developed. The MFC M8528-P1 transducer type was identified as providing the best performance. The use of inductors to compensate for the capacitive characteristics of transducers was shown to provide up to 170-fold power throughput increase. The propagation of Lamb waves in the experimental plate was mapped using a scanning laser vibrometer and simulated using LISA finite difference method software. An optimised laboratory system transmitted 17 mW of power across a distance of 54 cm while being driven by a 20 V, 224 kHz signal. This figure can be easily increased by using a higher drive voltage. This shows that the system is capable of supplying sufficient power to wireless SHM sensor nodes, which currently have a maximum power requirement of approximately 200 mW

Thick film PZT transducer arrays for particle manipulation

This paper reports the fabrication and evaluation of a two-dimensional thick film PZT ultrasonic transducer array operating at about 7.5 MHz for particle manipulation. All layers on the array are screen-printed and sintered on an Al2O3 substrate without further processes or patterning. The measured dielectric constant of the PZT is 2250 ± 100, and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis has been used to predict the behaviour of the array and impedance spectroscopy and laser vibrometry have been used to characterise its performance. The measured deflection of a single activate element is on the order of tens of nanometres with 20 Vpp input. Particle manipulation experiments have been performed by coupling the thick film array to a capillary containing polystyrene microspheres in water

Investigating the motility of Dictyostelium discodeum using high frequency ultrasound as a method of manipulation

Cell motility is an essential process in the development of all organisms. The earliest stages of embryonic development involve massive reconfigurations of groups of cells to form the early body structures. Embryos are very complex systems, and therefore to investigate the molecular and cellular basis of development a simpler genetically tractable model system is used. The social amoeba Dictyostelium Discoideum is known to chemotax up a chemical gradient. From previous work, it is clear that cells generate forces in the nN range. This is above the limit of optical tweezers and therefore we are investigating the use of acoustic tweezers instead. In this paper, we present recent progress of the investigation in to the use of acoustic tweezers for the characterisation of cell motility and forces. We will describe the design, modelling and fabrication of several devices. All devices use high frequency (>15MHz) ultrasound to exert a force on the cells to position and/or stall them. Also, each device is designed to be suitable for the life-sciences laboratory where form-factor and sterility is concerned. A transducer (LiNo) operating at 24 MHz excites resonant acoustic modes in a rectangular glass capillary (100um by 2mm). This device is used to alter the directionality of the motile cells inside the fluid filled capillary. A quarter-ring PZT26 transducer operating at 20.5MHz is shown to be useful for manipulating cells using axial acoustic radiation forces. This device is used to exert a force on cells and shown to pull them away from a coverslip. The presented devices show promise for the manipulation of cells in suspension. Currently the forces produced are below that required for adherent cells; the reasons for this are discussed. We also report on other issues that arise when using acoustic waves for manipulating biological samples such as streaming and heating