Previous research by Rushing et al. (2002) identified key factors contributing to the formation of pinhole leaks in copper plumbing. These factors included high chlorine, pH levels and the presence of aluminum solids. Experiments were conducted to 1) examine the interplay between these constituents, 2) confirm that the water was aggressive enough to eat a hole through a pipe, 3) examine phosphate inhibition, and 4) try to determine the scope of this pitting problem in other distribution systems and on a national level. The first set of experiments clearly defined the controversial trends from earlier work. At certain pH values, the presence of chlorine and aluminum solids does seem to initiate pitting corrosion of copper. Although the problem is most severe at higher pH, it is likely that long-term exposure at lower values such as pH 8 could lead to pitting. There is a concentration effect of aluminum solids at pH 9.0, in that higher concentrations cause an earlier rise in the potential for copper to corrode if sufficient chlorine is present. The second phase of experiments are the first to prove that a potable water containing aluminum, high chlorine residual, and relatively high pH can cause pinholes in copper tube. To our knowledge this is the first time the phenomenon of pinhole leaks has been reproduced in the laboratory as it occurs in the field. It therefore proves that "aggressive water" alone can cause the problem of pitting. The role of flow, pipe orientation and hypothesized surface defects was directly examined as part of this evaluation. Pitting increased with greater water usage and for sections of straight pipe exposed to hydraulic conditions near bends. Copper pipe sections polished to a mirror like finish to remove surface defects were also severely attacked. The role of phosphate in mitigation of copper pitting corrosion was defined in a subsequent experiment using synthesized water. Phosphates did not have an effect at pH 7.7 and were found to reduce electrochemical indications of pitting in the synthetic water at the pH of 8.3. Phosphates had lesser benefits at higher pH even in synthetic water, but overall, even at pHs as high as 10, some benefits from orthophosphate dosing might be anticipated. Effects of orthophosphate on the inhibition of copper pitting corrosion were then applied to treated water from a utility in Washington D.C., whose consumers have experienced an outbreak of pinhole leaks in household copper plumbing. After comparing electrochemical results from synthetic and actual water from the treatment plant, there was evidence of a natural inhibitor to pitting corrosion in WSSC water that is not present in the synthetic water. The higher chloride concentration in the water after ferric chloride was dosed at the treatment plant may have reduced the pitting propensity of the water. The effects of phosphates seemed to reduce the pitting propensity of real water at pH 8.3 although little benefit was seen at pH 9.1. These defined characteristics of copper pitting were then applied in a systematic evaluation of a water utility experiencing pitting corrosion in Roanoke, VA. This case study further supported the hypothesis that high levels of aluminum, chlorine, and pH may be combining to catalyze copper pitting in practice. Recommendations to alter the treatment strategies at these utilities were proposed to help mitigate the pitting corrosion problems in these areas. A national survey then confirmed pitting is occurring at a significant frequency at other large utilities across the U.S. / Master of Science

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Interactions between copper and chlorine disinfectants were examined from the perspective of disinfectant decay and copper pitting corrosion. Sparingly soluble cupric hydroxide catalyzed the rapid decay of free chlorine, which in turn, led to production of less soluble and more crystalline phases of cupric hydroxide. The catalytic activity of the cupric hydroxide was retained over multiple cycles of chlorine dosing. Experiments with chloramine revealed that copper species could also trigger rapid loss of chloramine disinfectant. In copper pipes, loss of free chlorine and chloramine were both rapid during stagnation. Reactivity of the copper to the disinfectants was retained for weeks. Phosphate tended to decrease the reactivity between the copper pipe and chlorine disinfectants. A novel, inexpensive and real-time test to monitor copper pitting corrosion was developed. In a normal pipe, it is not possible to measure the electron flow or pitting current from the pit anode to the cathode. But a new method was developed that can form an active pit on the tip of a copper wire, which in turn, allows the pitting current to be measured. Preliminary experiments presented herein have proven that this technique has promise in at least one water condition known to cause pitting. The method also quickly predicted that high levels of orthophosphate could stop pitting attack in this water, whereas low levels would tend to worsen pitting. Future research should be conducted to examine this technique in greater detail. / Master of Science

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Pitting corrosion is a form of highly localized corrosion that can lead to crack and failure of a structure. Study on pitting corrosion is necessary in order to predict and prevent the risk of failure of structure susceptible to corrosion. In this thesis, a combination of Cellular Automata (CA) and Boundary Element Method (BEM) was developed to simulate pitting corrosion growth under certain environment. It is assumed that pitting corrosion can be simplified to electrochemical corrosion cell. The distribution of potential around this corrosion cell can then be simulated by BEM. This distribution potential represents cathodic and anodic reactions around the corrosion cell. A CA model was developed that uses transition rules reflecting mechanism of pitting corrosion. The CA model has two types of cell states, one reflecting BEM simulation results and the other reflecting the status of corrosion cell (anode, cathode, and passive metal’s surface). For every CA iteration, the CA decides the state of the corrosion cells (the location and size of anode, cathode) while BEM simulate the level of electrochemical activity at discrete location on the surface (represented by potential distribution). In order to demonstrate the methodology, a simple case of rectangular corrosion cell with varied dimensions and under different polarization functions is considered. Results show certain shapes tend to grow at certain type environment and these pits are comparable to commonly observed pit shapes. In addition, stress analysis was carried out to investigate the severity of corrosion pits of varying shapes and sizes. Results show that certain pits induced highly varying stress concentration as it grows over time, while others have more steady increase of stress concentration.

A resistência à corrosão das ligas de alumínio está relacionada ao meio de exposição, composição química, presença de intermetálicos e microestrutura do metal, entre outras. Neste trabalho investigou-se a corrosão nas ligas de alumínio 3105 H16 e 5052 H34, comumente utilizadas na indústria de carrocerias de ônibus, em meio aquoso continham íons agressivos, tais como cloretos, sulfatos e hidroxilas. Avaliou-se comparativamente o comportamento destas ligas com os revestimentos de proteção de Nanocerâmico, Cromo VI, Cromo III e Sistema de Pintura em exposição atmosférica acelerada e imersão em diferentes meios agressivos. Estudos mais aprofundados restringiram-se às ligas sem tratamento, para as quais foram realizados ensaios de exposição acelerada em névoa salina neutra, névoa salina acética, câmara de umidade e exposição atmosférica natural. Microscopia eletrônica de varredura por emissão de campo foi empregada para caracterizar a superfície das ligas antes e após os ensaios de névoa salina neutra e acética. O comportamento eletroquímico das ligas sem tratamento foi determinado através do monitoramento do potencial de circuito aberto, curvas de polarização potenciodinâmica anódicas e espectroscopia de impedância eletroquímica. Os resultados mostraram que o tratamento de Cromo VI foi o que obteve melhor desempenho na proteção de ligas de alumínio, particularmente para a liga 5052. De um modo geral, a liga 5052 apresentou maior resistência à corrosão nos meios testados em presença ou não de tratamentos superficiais. Na exposição à névoa salina, a corrosão manifestou-se principalmente na forma de pites. Ficou comprovado que o efeito do íon Cl- é importante, porém o fator preponderante do comportamento à corrosão das ligas de alumínio está relacionado ao pH do meio de exposição, sendo este recomendado para avaliar revestimentos protetores. Além das condições do meio ao qual o metal será exposto, na seleção de tratamentos anticorrosivos é importante considerar as particularidades de cada liga, uma vez que suas características composicionais e microestruturais exercem relevante influência no desempenho à corrosão. / The corrosion resistance of aluminum alloys is related to the exposure medium, chemical composition, presence of intermetallic particles and metallic microstructure, among others. This work investigated corrosion of 3105 H16 and 5052 H34 aluminum alloys commonly used in the bus body industry in aqueous media containing aggressive ions, such as chlorides, sulfates and hydroxyls. The behavior of these alloys with the protective coatings of Nanoceramic, Chromium VI, Chromium III and Paint System in accelerated atmospheric exposure and immersion in different aggressive media was evaluated comparatively. Further studies were restricted to untreated alloys for which accelerated exposure tests were performed on neutral salt spray, acetic salt spray, moisture chamber and natural atmospheric exposure. Field scanning electron microscopy was used to characterize the alloys surface before and after neutral and acetic salt spray tests. The electrochemical statement of the untreated alloys was determined by monitoring the open circuit potential, anodic potentiodynamic polarization curves and electrochemical impedance spectroscopy. Results have shown that the treatment with Chromium VI was the one that obtained better performance in the protection of the aluminum alloys, particularly for 5052 alloy. In general, 5052 aluminum alloy presented greater resistance to corrosion in all tested media, with or without surface treatments. Under salt spray exposure, the corrosion attack appeared mainly in the form of pitting. It has been proven that the effect of Cl- ion is important, but the predominant factor on the corrosion behavior of aluminum alloys is related to the pH of the exposure medium, which is recommended to evaluate protective coatings. Besides the conditions of the medium to which the metal will be exposed, in the selection of anticorrosive treatments it is important to consider the particularities of each alloy, since its compositional and microstructural characteristics exert a relevant influence on the corrosion performance.

Fault feature analysis of gear tooth spall plays a vital role in gear fault diagnosis. Knowing the characteristic of fault features and their evolution as a gear tooth fault progresses is key to fault severity assessment. This thesis provides a comprehensive (both theoretical and experimental) analysis of the fault vibration features of a gear transmission with progressive localized gear tooth pitting and spalling. A dynamic model of a one-stage spur gear transmission is proposed to analyze the vibration behavior of a gear transmission with tooth fault. The proposed dynamic model considers the effects of Time Varying Mesh Stiffness (TVMS), tooth surface roughness changes and geometric deviations due to pitting and spalling, and also incorporates a time-varying load sharing ratio, as well as dynamic tooth contact friction forces, friction moments and dynamic mesh damping ratios. The gear dynamical model is validated by comparison with responses obtained from an experimental test rig under different load and fault conditions. In addition, several methods are proposed for the evaluation of the TVMS of a gear pair with tooth spall(s) with curved bottom and irregular shapes, which fills the current research gap on modelling tooth spalls with irregular shapes and randomly distribution conditions. Experiments are conducted and the fault vibration features and their evolution as the tooth fault progresses are analyzed. Based on feature analysis, a new health indicator is proposed to detect progressive localized tooth spall.