Acoustic emission analysis for quality assessment of thermally sprayed coatings

This study describes a new approach to the quality assessment of thermally sprayed carbide and ceramic coatings produced by High Velocity Oxy-Fuel (HVOF) and Air Plasma Spray (APS) processes. The aim of the work was to develop an experimental methodology based on Acoustic Emission (AE) monitoring of a dead-weight Vickers indentation to assess the degree of cracking and hence the toughness of the coating. AE monitoring was also applied to an industrial process as a contribution to the possibility of quality assessment during the deposition process. AE data were acquired during indentation tests on samples of coating of nominal thickness 250-325 μm at a variety of indentation loads ranging from 49 to 490 N. Measurements were carried out on six different thick-film coatings (as-sprayed HVOFJP5000/ JetKote WC-12%Co, HIPed HVOF-JetKote WC-12%Co, as-sprayed HVOFJP5000 WC-10%Co-4%Cr, conventional powder APS-Metco/9MB Al2O3 and fine powder HVOF-theta gun Al2O3) and also on soft and hard metallic samples and metals. The raw AE signals were analysed along with force and displacement history and the total surface crack length around the indent determined. Also, a selection of the indents was sectioned in order to make some observations on the sub-surface damage. The results show characteristic AE time evolutions during indentation for tough metals, hard metals, and carbide and ceramic coatings. Within each category, AE can be used as a suitable surrogate for crack length measurement for assessing coating quality. Finally, a preliminary observation on AE monitoring during HVOF (JP5000) WC- 10%Co-4%Cr thermal spraying was made. It was found that AE is sensitive to individual particle landings during thermal spraying and therefore can, in principle, be used to monitor the spray process

Parametric sensitivity analysis to maximise auxetic effect of polymeric fibre based helical yarn.

Studies on designing polymeric fibres based helical auxetic yarn (HAY) to maximise their auxetic effect are yet to propose optimised design configurations for general impact mitigation applications. This study therefore presents optimal design parameters through analytical calculations and finite element (FE) method. Three main design parameters were considered which includes Poisson's ratio, core/wrap diameter ratio, and starting wrap angle. The Poisson's ratio of the HAY was calculated by measuring its total diameter at a given rate of strain. The investigation found here to be a starting wrap angle of a HAY (critical angle) that resulted in the highest possible exhibiting of the auxetic effect. The critical angle was determined to be 7°, and a maximum NPR of −12.04 was achieved with this design

Modeling aerosol cloud aerodynamics during human coughing, talking, and breathing actions.

In this paper, we investigate the aerosol cloud flow physics during three respiratory actions by humans (such as coughing, talking, and breathing). With given variables (i.e., velocity, duration, particle size and number of particles, and ambient conditions), the standoff safe distance during coughing, talking, and breathing should be the distance where virus-laden droplets and aerosols do not have significant transmission to another person. However, at a critical distance, the aerosol cloud flux can still be extremely high, which can immediately raise the transmission in a localized area to another person during a static condition. In this study, computational fluid dynamics analysis of selective respiratory actions has been carried out to investigate the effect of the standoff distance and assess the importance of social distancing in indoor places. The prediction of the aerosol transport due to flow generated from coughing, talking, and breathing was obtained by applying the Eulerian-Lagrangian approach. From the simulation results, it can be concluded that the aerosols released due to continuous talking travel a similar distance to that released due to sudden coughing. On the other hand, aerosols exhaled from breathing do not travel a long distance but float in air for a long time

An evaluation of the morphological, microstructural and mechanical behaviour of the glass fibre/HDPE thermoplastic composite pipe.

Composite pipes are increasingly being used as an alternative solution to conventional metal-based pipes. This development is in response to significant corrosion failures with the metallic pipes and enables better decision making especially for the plausibility of alternative offshore energy sources. Flexible pipes which thermoplastic composite pipes (TCP) belong to have proven to have beneficial features. The aim of this research is to experimentally investigate TCP and the layers based on the morphological and mechanical properties, identify and utilize the methods to obtain relatively precise material properties of the TCP which are currently barely known

Application of acoustic emission to predict corrosion.

Non-destructive testing (NDT) techniques used for petroleum pipelines and offshore windturbines can only detect corrosion after it has occurred. Therefore, intrusive inspections are required regularly, potentially causing disruption to operation and production. Acoustic Emission (AE) is a non-destructive testing (NDT) sensor based technique which measures the detection and the conversion of high frequency (between 100 kHz to 1 MHz) elastic waves generated by the rapid release of energy to electrical signals. AE is released when crack propagates in the specimens during corrosion. This presentation will summarise AE sensor based technique for monitoring corrosion and offer examples of practical applications. Samples tested include aluminium and steel thin plates (rectangular shape) in different corrosive environments. AE from corrosion usually releases much less energy than emission from crack growth, and so is more difficult to detect in the field environment. However, the results present an exponential curve showing a trend between the concentration of the corrosive environment and the energy of the acoustic emission signal

Evaluation of caprock integrity for underground storage of CO2 in depleted oil and gas reservoirs using machine learning approaches.

Carbon Dioxide (CO2) geosequestration represents one of the most promising options for reducing atmospheric emissions of CO2. Caprock integrity - ascertained based on the petrophysical and geomechanical properties of caprock - is vital to ensure safe and sustainable storage of CO2 (Liu et al., 2020). Shale and carbonate rocks are typical caprock for CO2 geological storage, but their failure behaviours have not been fully understood due to their severe heterogeneity and anisotropy (Liu et al., 2020). It is therefore vital to apply machine learning techniques in order to understand caprock behaviour under several conditions. No other study so far has focused on caprock integrity using machine learning to select the best depleted petroleum reservoirs for CO2 storage, based on caprock mechanical and petrophysical properties. The aim of this research is to evaluate caprock integrity under cyclic stress loadings based on variation in pressure and CO2 injection temperature

Numerical Modelling of the Effect of Wettability, Interfacial Tension and Temperature on Oil Recovery at Pore-Scale level

A numerical investigation into the effect of wettability and temperature on oil recovery with a hot water injection at different temperatures is reported in this paper. The computational domain is a two-dimensional porous medium (reservoir) maintained at a fixed temperature with pore spaces of varying sizes and interconnected pore-throats. ANSYS-Fluent VOF (volume of fluid) model was used to simulate the two-phase transport through the reservoir with hot water injections at varying temperatures (20, 40 and 60 °C) and wettability contact angles of 45°, 90° and 150°. In addition, an investigation was conducted on the effect of combined interfacial tension and matrix wettability on oil recovery process at low and high interfacial tension of 0.025 N/m and 0.045 N/m respectively for the three different wettability contact angles. The results showed that, the displacement behaviour of water and oil-wet system is affected significantly by the contact angle with a profound effect on the oil recovery factor. In the water-wet case (with the water wetting the matrix wall and the oil phase surrounded by water), relatively more oil is displaced from the domain thereby improving the oil recovery factor. The water-wetter system resulted in about 35–45% oil recovery than the oil-wet system, with the unrecovered oil mainly adhering to the wall region of the pore bodies for oil-wet system. For the intermediate wet case, initial fluid distribution is seen to have a more significant effect on the displacement behaviour than the contact angles. In conclusion, by altering the wettability from oil-wet to water-wet condition, the oil recovery rate is improved. The results from this study are consistent with the experimental and numerical studies in literature and it will further enhance the understanding of the phenomenon that is critical to the mechanism of recovery such as surfactant and polymer flooding process

Sand production due to chemical-rock interaction: a review.

Oilfield chemicals are utilized in treating reservoir formations, wellbore completions, wellbore drilling, and to enhance reservoir productivity, which exerts pressure on the formation. Pressure from these processes cause the formation rock to weaken, and the weakened rock begins to detach, thereby producing formation sand as well as reservoir fluid (petroleum). In petroleum industry, sanding poses major challenges with significant financial consequences. The negative financial implications of sand production make it crucial to reduce sand production at the same time as optimizing reservoir fluid production and maintaining facility integrity. An effective way to manage sand production depends on several factors, so a methodical approach is needed. The paper discusses sand production from oilfield chemicals-rock interactions, models that are used to forecast sand production, personnel safety, and maintaining production facilities. In addition to determining sanding onset, some models can detect the rate or quantity of sand produced, which can help with sand management

Application of pencil lead break (PLB) point source in the detection of interfacial defects in adhesive bonds.

The presence of kissing bonds (zero-thickness disbond) along the interface of an adhesive bond is highly detrimental to its strength and longevity. The detection of these kind of defects has previously been attempted using several techniques such as ultrasonic, infrared thermography, and X-ray spectroscopy, etc. This study aims to assess the effectiveness of pencil lead break (PLB) tests as a source in detecting the defects distributed along the interface of an adhesive bond. The defects were introduced artificially using polytetrafluoroethylene (PTFE) spray along one of the interfaces of the adhesive bond fabricated with aluminium plates bonded with an epoxy adhesive. Three different interfacial defect area percentages, 0%, 25% and 40% and three adhesive layer thicknesses (i.e., 0.1mm, 0.25mm, and 0.5mm) were considered. The PLB tests were conducted, and the recorded signals were analysed to assess the variation of AE features with the defect area percentage and adhesive layer thicknesses. Different source-sensor location configurations were also considered. The 200 kHz-highpass component of the recorded signals was found to be sensitive to the presence of the interfacial defects. The duration above a chosen threshold was found to be the distinguishing factor between the different defective specimens. Of the different sensor-source configurations tried, the configurations with the PLB on the 0.5mm side were seen to be sensitive to the presence of defects

Materials for molten salt facing parts: challenges and opportunities for nuclear thermochemical cycle electrolysis.

One of the important challenges is to develop coating materials for thermochemical containment vessels and pipes that encounters the highly corrosive and harsh environment produced by the molten salt at high temperature. The aim of this review is to summarise structural and coating materials (mainly thermally sprayed) that can withstand thermochemical cycle corrosive environment. This review presents findings published in the scientific literature related to high temperature aggressive corrosion of materials, specifically geared towards nuclear thermochemical cycles leading to hydrogen production. Data related to materials, composition, synthesis have been gathered. Corrosion environment data such as environment, test time, test results have been reviewed. Structure-property relations of different materials reviewed as a part of this exercise will aid in the material selection process for future development. The overall assessment based on the evidence from previous investigations in this area is that none of the high-performance structural materials (coating, substrates) are likely to survive for an extended period in the high temperature corrosive environment. However, there are means and methods which could be considered to have sustainable coating-substrate assembly and extended lifetime. This review presents challenge and assess opportunities that will warrant efficient hydrogen production with stable thermochemical structure for operation at molten salt reactor (MSR) nuclear plants (e.g., thermochemical electrolysis leading to water splitting and hydrogen production) as well as other power plants, boilers, and waste incinerators