Structural Health Monitoring (SHM) and Determination of Surface Defects in Large Metallic Structures using Ultrasonic Guided Waves

Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws

Corrosion Behaviour of Cupronickel 90/10 Alloys in Arabian Sea Conditions and its Effect on Maintenance of Marine Structures

The composition of seawater plays a very significant role in determining the severity of corrosion process in marine assets. The influential contributors to the general and pitting corrosions in marine structures include temperature, dissolved oxygen (DO), salinity, PH, chlorides, pollutants, nutrients, and microbiological activities in seawater. The Cu-Ni (90/10) alloy is increasingly used in marine applications such as heat exchangers and marine pipelines because of its excellent corrosion resistant properties. Despite the significant advancements in corrosion shielding procedures, complete stoppage of corrosion induced metal loss, especially under rugged marine environments, is practically impossible. The selection of appropriate metal thickness is merely a multifaceted decision because of the high variability in operating conditions and associated corrosion rate in various seawater bodies across the globe. The present research study aims to analyze the early phase of corrosion behavior of Cu-Ni (90/10) alloy in open-sea conditions as well as in pollutant-rich coastal waters of the Arabian Sea. Test samples were placed under natural climatic conditions of selected sites, followed by the mass loss and corrosion rate evaluation. The corrosion rate in the pollutant-rich coastal waters was around five times higher than in the natural seawater. A case study on marine condenser (fitted with of Cu-Ni 90/10 alloy tubes) is presented, and a risk-based inspection (RBI) plan is developed to facilitate equipment designers, operators, and maintainers to consider the implications of warm and polluted seawater on equipment reliability, service life, and subsequent health inspection/ maintenance

The Effect of Foreign Bank Presence on Domestic Banks Performance: An Evidence from a Developing Economy

This study examines the effect of foreign bank presence on the behaviour of domestic banks by using the annual data of 37 commercial banks comprising of 7 foreign and 30 domestic banks for the time period of 2007 to 2011, to investigate the effect of foreign bank presence  five banking ratios, net interest margin, return on assets, overhead, cost to income and nonperforming loans using panel regression analysis employing bank specific fixed effect model. As a developing country case, the results suggest that the increase in foreign bank share effects the interest margins and profitability of domestic banks in a decreasing manner. It wouldn't be erroneous to express that foreign banks have a positive effect on the competitive environment of domestic banks increasing overall banking standard in Pakistan, the licensing policies should be further liberalized to let new entrants further improve the domestic financial intermediation system.&nbsp

Competition and market contestability of banks: evidence from emerging financial market

The study is an attempt to investigate the nature of competition and market contestability of 35 Pakistani banks for the period of 2007-2011 by employing Panzar and Rosse (PR-model). The test of competition overall sample (2007-2011) suggest that banks in Pakistan in state of monopolistic competition and market is in equilibrium. The sub sample (2007-2009) result of competition and equilibrium are similar as for sample period (2007-2011) suggesting that revenue produced during this period is state of monopolistic competition. Finally the results of sample period (2010-2011) suggest that banks in Pakistan are instate of perfect competition however, the market in not in long-run equilibrium. The results have interesting policy implications; it is suggested to encourage the foreign banks presence to improve the competitive condition of banking industry so that to ensure the exit and entrance of banks in the industry to increase the competition and produce the variety of product to improve banks performance and customer satisfaction.&nbsp

An Overview of Maintenance Management Strategies for Corroded Steel Structures in Extreme Marine Environments

Maintenance is playing an important role in integrity management of marine assets such as ship structures, offshore renewable energy platforms and subsea oil and gas facilities. The service life of marine assets is heavily influenced by the involvement of numerous material degradation processes (such as fatigue cracking, corrosion and pitting) as well as environmental stresses that vary with geographic locations and climatic factors. The composition of seawater constituents (e.g. dissolved oxygen, salinity, temperature content, etc.) is one of the major influencing factors in degradation of marine assets. Improving the efficiency and effectiveness of maintenance management strategies can have a significant impact on operational availability and reliability of marine assets. Many research studies have been conducted over the past few decades to predict the degradation behaviour of marine structures operating under different environmental conditions. The utilisation of structural degradation data – particularly on marine corrosion – can be very useful in developing a reliable, risk-free and cost-effective maintenance strategy. This paper presents an overview of the state-of-the-art and future trends in asset maintenance management strategies applied to corroded steel structures in extreme marine environments. The corrosion prediction models as well as industry best practices on maintenance of marine steel structures are extensively reviewed and analysed. Furthermore, some applications of advanced technologies such as computerized maintenance management system (CMMS), artificial intelligence (AI) and Bayesian network (BN) are discussed. Our review reveals that there are significant variations in corrosion behaviour of marine steel structures and their industrial maintenance practices from one climatic condition to another. This has been found to be largely attributed to variation in seawater composition/characteristics and their complex mutual relationships

Analysis of the Surface Quality and Temperature in Grinding of Acrylic-Based Resin

Polymeric resins are becoming increasingly popular in medical and engineering applications due to their properties, such as their low weight, high strength, corrosion resistance, non-allergenicity, and extended service life. The grinding process is used to convert these materials into desired products, offering high accuracy and surface quality. However, grinding generates significant heat, which can potentially degrade the material. This study investigates the grinding of acrylic-based resins, specifically focusing on the interplay between the grind zone temperature and surface finish. The low glass transition temperature (57 °C) of the acrylic necessitates the precise control of the grinding parameters (spindle speed, feed rate, depth of cut, and grinding wheel grain size), to maintain a low temperature and achieve high-quality machining. Thermal imaging and thermocouples were employed to measure the grind zone temperature under various grinding conditions. This study investigates the influence of four parameters: spindle speed, feed rate, depth of cut, and grinding wheel grain size. The best surface finish (Ra: 2.5 µm) was obtained by using a finer-grained (80/Ø 0.18 mm) grinding wheel, combined with slightly adjusted parameters (spindle speed: 11.57 m/s, feed rate: 0.406 mm/rev, depth of cut: 1.00 mm), albeit with a slightly higher grind zone temperature (~54 °C). This study highlighted the importance of balancing the grind zone temperature and surface finish for the optimal grinding of acrylic-based resins. Further, this research finds that by carefully controlling the grinding parameters, it is possible to achieve both a high surface quality and prevent material degradation. The research findings could be highly valuable for optimizing the grinding process for various medical and engineering applications

An advanced Wigner-Ville time-frequency analysis of lamb waves signals based upon AR model for efficient damage inspection

The generation and acquisition of the ultrasonic guided wave in metallic or composite structures to investigate the structural defects are quite straightforward; however, the interpretation and evaluation of the reflected/transmitted signal to extract the useful information is a challenging task. It is primarily due to the dispersion, and multi-modal behavior of the Lamb waves which is dependent on the exciting wave frequency and thickness of the material under investigation. These multi-modes and dispersion behavior lead to a complex waveform structure, and therefore, require an advanced signal processing technique to decipher the useful information in time and frequency domain. For this purpose, Wigner-Ville Distribution, due to its desirable mathematical properties, is considered as a powerful tool for estimating temporal and spectral features of this type of complex signals. However, because of its quadratic nature, the undesirable cross-terms and spurious energies are also generated, which limit the readability of the spectrum. To suppress this effect, the autoregressive model based upon Burg's Maximum Entropy method was employed that modified the kernels of the discrete Wigner-Ville Distribution. This technique was applied to ultrasonic Lamb wave signals, obtained numerically and experimentally, to extract useful discriminating spectral and temporal information that was required for mode identification, damage localization, and its quantification. For damage localization, based upon excellent time-frequency energy distribution, the proposed method precisely estimated the distance between two closely spaced notches in a plate from different simulated noisy signals with a maximum uncertainty of 5%. Moreover, time-frequency energy concentration in a combination with variation of its instantaneous frequency was also effective in identifying the overlapping modes of the Lamb wave signal. Lastly, for damage quantification, three time-frequency based damage indices namely, energy concentration, time-frequency flux, and instantaneous frequency were extracted from the five sets of specimens using the proposed time-frequency scheme and trained them for the regression model. The model testing proved that the damage indices has the potential to predict the crack sizes precisely and reliably

Evaluation of the effects of highly saline and warm seawaters on corrosivity of marine assets

In marine environment, the corrosion rate of metallic structures vary remarkably with the change in climatic conditions and seawater composition across geographical locations. The corrosion in brackish and polluted seawaters is even more complicated due to the presence of different chemical species and untreated effluents. The complex correlation between the above average temperature and salinity with the high nutrient content in polluted seawater tends to accelerate the rate of biological activities and microbiological induced corrosion (MIC). This research paper has investigated the short-term corrosion of cupronickel (Cu-Ni) 90/10 alloy, and mild steel in the highly saline and warm seawaters. Field experiments for general corrosion under fully immersed condition were conducted at two site locations, represented as site 1 for pollutantrich seawaters and site 2 for natural seawaters in the North Indian Ocean. The experiments were conducted for a period of up to two months and coupons for each metal alloy were recovered from both sites after an exposure period of 15, 30, 45, and 60 days, respectively. In both environmental conditions, significantly high mass loss and corrosion rates were recorded for each metal alloys. Despite the same temperature of seawater and immersion depth at both sites, average corrosion losses at site 1 were found to be 5 and 3 times higher than that of site 2 for Cu-Ni alloy 90/10, and mild steel coupons, respectively

Performance evaluation of Cu-Ni 90/10 alloyed structures exposed to various seawater compositions and their remaining service life estimation

The Cu-Ni 90/10 alloy is extensively used in seawater applications mainly because of its excellent heat transferability, resistance toward corrosion and marine fouling. The corrosion resistance of Cu-Ni 90/10 has been found to be far superior in open natural seawater, however, several premature failures have often been reported during their exposure in the pollutant-rich seawater typically found near harbours, jetties and coastlines. This paper investigates the corrosion behaviour of Cu-Ni 90/10 alloyed coupons exposed to natural seawater, and pollutant-rich harbour seawater in a submerged position. Moreover, this research also investigates the corrosion mechanism on marine heat exchanger tubes of material that failed prematurely while operating in similar seawater compositions. The field experimental results for short-term corrosion results from coupons, and the long-term corrosion results from heat exchanger tubes have been evaluated, to formulate a relationship and corrosion modelling

Environmental impact on the corrosion behavior of marine grade steel in the Arabian Sea conditions - a comparative analysis of field and laboratory based corrosion tests

Corrosion-induced degradation of marine steel structures is highly dependent on the surrounding environmental conditions and so varies significantly around global seawaters. This research has investigated the dependence of corrosion of carbon steel alloy for marine service on seawater composition and climatic conditions typical of the Arabian Sea. Natural and polluted seawater sites in the Arabian Sea were selected for field exposures. In addition, environmental conditions spanning those anticipated for the shipping structures operating in the Arabian Sea have been simulated in laboratorybased experiments by using heated and aerated artificial seawater. Following their exposures, the performance of samples have been investigated using the weight-loss and dimensional metrology methods. High overall corrosion losses were observed in the polluted seawaters than in the natural seawater conditions of Arabian Sea