The Center for Ocean Energy Technology at Florida Atlantic University is developing an ocean energy turbine system to investigate the feasibility of harnessing Florida's Gulf Stream current kinetic energy and transforming it into a usable form. The turbine system has components which are prone to marine corrosion given the materials they are made of and to the harsh environment they will be exposed to. This study assumes a two-part system composed of a coating system acting as a barrier and sacrificial anode cathodic protection which polarizes the metal structures to a potential value where corrosion is significantly reduced. Several configurations (varying in anode quantity, size and location) were considered in order to cathodically protect the structures with various coating qualities (poor, good and excellent). These cases were modeled and simulated via Boundary Element Method software and analyzed so as to assess the most appropriate design. / by Nicolas Gantiva. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Dutos metálicos revestidos, enterrados e protegidos catodicamente, quando são instalados nas proximidades de linhas de transmissão e distribuição de energia elétrica, vêm apresentando problemas de corrosão, sendo esta atribuída às interferências de corrente alternada dispersas no solo. São muitos os critérios propostos na literatura para verificar se um duto está ou não sujeito a esse tipo de problema, mas tais critérios são contraditórios e ineficientes, uma vez que não levam em conta parâmetros termodinâmicos e não contemplam o acoplamento dos potenciais originados de corrente contínua com os potenciais oriundos de corrente alternada. O objetivo do presente trabalho foi estudar a corrosão causada por corrente alternada, selecionar um critério seguro de verificação da probabilidade de ocorrência dessa corrosão e desenvolver uma nova metodologia para a obtenção dos parâmetros necessários para a aplicação do critério proposto. Com base em uma ampla pesquisa bibliográfica, em resultados experimentais obtidos em laboratório e em campo, foi possível a seleção do seguinte mecanismo: a corrosão por corrente alternada é decorrente da oscilação do potencial da interface duto/solo que, dependendo do valor do pH nas suas vizinhanças, leva o sistema alternadamente ao domínio da corrosão e da imunidade ou alternadamente ao domínio da formação de óxidos (com e sem passivação) e da imunidade. Nessas condições, a corrosão do aço-carbono ocorre devido à irreversibilidade da reação Fe2+ + 2e- Fe, nos casos de alcalinização limitada, e à impossibilidade de formação de uma camada passiva protetora decorrente da flutuação de potencial entre o domínio de formação de óxidos e da imunidade, nos casos de alcalinização moderada. Como critério de verificação da ocorrência ou não de interferência de corrente alternada em dutos enterrados e catodicamente protegidos foi proposta, neste estudo, a obtenção da forma de onda do acoplamento entre os potencias originados de corrente contínua e os oriundos de corrente alternada sem a influência da queda ôhmica e a comparação do potencial de pico dessa forma de onda com o potencial estabelecido como limite aceitável do sistema de proteção catódica tradicional. Esta proposição foi feita com base na termodinâmica, o que garante que a previsão seja usada com mais segurança. Finalmente, foi desenvolvida uma sonda que, juntamente com uma instrumentação adequada, é capaz de fornecer a forma de onda do referido acoplamento em dutos enterrados e catodicamente protegidos, sem a interferência da queda ôhmica. / Corrosion problems have been observed in cathodically protected pipelines installed in the vicinity of high voltage power lines or electrical distribution systems. Many of these problems have been attributed to interferences coming from stray alternating currents. In the literature, there are many criteria proposed aiming at verifying the AC corrosion probability. However, such criteria are contradictory and ineffective since they do not take into account thermodynamic parameters and do not include the coupling of potential coming from direct current and the potential due to stray alternating current. The aim of this work was to study pipeline corrosion induced by stray alternating current, to select a safe criterion for the probability of this corrosion and to develop a new methodology for obtaining the required parameters for the application of the selected criterion. A broad literature review and the results obtained from a series of tests and analyses have allowed choosing the following mechanism: AC corrosion is a result of the fluctuation of the pipe/soil potential which, depending on the pH of the soil near the pipe, takes the system alternatively to the corrosion and to the immunity domains or alternatively to the oxide formation (with or without passivation) and to the immunity domains. Under these conditions, the corrosion of carbon steel occurs due to the irreversibility of the reaction Fe2+ + 2e- Fe reaction in cases of limited alkalinization and due to the impossibility of forming a protective passive layer caused by the potential fluctuation between the oxide formation and the immunity domains in cases of moderate alkalinization. In this study, a method to obtain the waveform of the AC+DC potential, without the ohmic drop, was proposed. The comparison of the peak potential of the AC + DC waveform with the potential value established as an acceptable threshold for traditional cathodic protection systems was used as a criterion for AC corrosion assessment. This criterion is proposed based on thermodynamic principles which ensure that the prediction is reliable. Finally, a probe was developed. This probe, along with a proper instrumentation, is able to provide the desired waveform for a safe application of the proposed criterion.

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.

Steel corrosion in reinforced concrete is a major concern to transportation agencies nationwide because of the expenses incurred for repair and ultimate shortening of bridge life. Cathodic protection (CP), as a remedy, has been applied to reinforced bridges in the US since 1974. However, application of this technique is largely empirical, lacking fundamental understanding. In order to optimize the performance of a CP system, it is important to monitor the rebar potential with respect to a reliable reference electrode. Moreover, because of potential variation in the concrete, reference cell placement is fundamental to ensure effective protection. The work plan was divided into two parts: laboratory scale experimentation and computer simulation. In the experimentation section, the response of graphite probes was compared to that of an Orion silver-silver chloride electrode. Graphite probes behaved as well as the standard electrode. Furthermore, the home-made graphite probes behaved the same as the commercial ones. This will allow much greater experimental latitude since the home-made probes are much more economical than the commercial ones. A finite difference code was developed to assess the performance of cathodic protection. The potential distribution in a two dimensional geometry of a concrete block with a sprayed zinc anode at one boundary and an iron cathode at the other side was calculated under cathodic protection. The equations were solved by means of a Gauss-Seidel iterative method with the help of an overrelaxation factor. An interval halving method was used to solve for nonlinear boundary condition at the iron. The effects of concrete pore saturation, concrete cover, and applied potential were studied to determine the degree of protection and proper placement of the reference electrode in concrete. Furthermore, a sensitivity analysis was performed versus input parameters: concrete conductivity, oxygen mass transfer coefficient, and oxygen reduction polarization parameters. The results of the simulation showed that the center of the rebar is less protected than the other locations. Therefore, the reference electrode should be located as close to the center as possible. / Graduation date: 1995

The polarization performance of two types of commercial galvanic point anodes for protection of reinforced steel around patch repairs was investigated. Experiments included measurement of the polarization history of the anode under constant current impressed by galvanostatic circuits and in reinforced concrete slabs. The tests revealed, for both types of anodes, a potential-current function (PF) indicating relatively little anodic polarization from an open circuit potential at low current levels, followed by an abrupt increase in potential as the current approached an apparent terminal value. Aging of the anodes was manifested by a continually decreasing current output in the concrete tests, and by increasingly more positive potentials in the galvanostatic tests. Those changes reflected an evolution of the PF generally toward more positive open circuit potentials and, more importantly, to the onset of elevated polarized potentials at increasingly lower current levels. There was considerable variability among the performance of replicate units of a given anode type. Modest to poor steel polarization levels were achieved in the test yard slabs. Modeling of a generic patch configuration was implemented with a one-dimensional approximation. The model calculated the throwing distance that could be achieved by a given number of anodes per unit perimeter of the patch, concrete thickness, concrete resistivity, amount of steel and amount of polarization needed for cathodic prevention. The model projections and aging information suggest that anode performance in likely application scenarios may seriously degrade after only a few years of operation, even if a relatively optimistic 100 mV corrosion prevention criterion were assumed. Less conservative criteria have been proposed in the literature but are yet to be substantiated. Other investigations suggest a significantly more conservative corrosion prevention may apply instead. The latter case would question the ability of the point anodes to provide adequate corrosion prevention.

No description available.

Thesis (PhD) - Swinburne University of Technology, School of Engineering and Science, 2008. / A thesis submitted for the degree of Doctor of Philosophy, School of Engineering and Science, Swinburne University of Technology, 2008. Typescript. Includes bibliographical references (p. 189-204).

A ortodontia pressupõe o uso de artefatos. Os bráquetes são ligados por fios ortodônticos, denominado arcos, para que possam ser movimentados juntamente com os dentes por sistemas de molas e ancoragens de vários materiais unidos por diferentes processos. Isto propicia uma pilha galvânica e liberação de níquel pelo aparelho. Atualmente existem materiais livres de níquel, porém os aços inoxidáveis possuem menor custo e maior facilidade de uso. A alergia ao níquel contido no aço inoxidável do aparelho causa desconforto e, em alguns casos, a interrupção do tratamento. Tal alergia provém dos íons de níquel liberados pelo aço inoxidável e transportados pela saliva até os tecidos do paciente. Este trabalho teve por objetivo aplicar a técnica dos anodos de sacrifício utilizada para a proteção catódica de estruturas metálicas expostas a meios salinos. Esta técnica foi aplicada na proteção do aço inoxidável e suas combinações com outros metais usados em tratamentos ortodônticos. Foram efetuadas várias combinações de anodos de sacrifício e eletrólitos em duas etapas de testes, com arranjos compostos por uma banda soldada com solda prata a um meio arco pré-contornado mais cinco bráquetes presos nele por um fio de amarril. Na primeira etapa foram avaliados quatro anodos de sacrifício amarrados aos arranjos e soluções aquosas com três salinidades obtendo-se em torno de cinquenta por cento de redução na liberação de níquel. A segunda etapa foi melhor sucedida e, a quantidade de níquel liberada, ficou abaixo do limite de detecção do equipamento de absorção atômica eletroquímica que foi utilizado neste trabalho. Nessa segunda etapa foram utilizados anodos de zinco e magnésio para a proteção e soro fisiológico com e sem fluoreto de sódio. O contato elétrico dos anodos de sacrifício com o aço inoxidável foi melhorado e, possivelmente, causou a menor liberação de níquel nesta etapa. Isto valida o método de proteção catódica na diminuição da liberação de níquel pelos aparelhos ortodônticos de aço inoxidável. / Orthodontics involves the use of artifacts. The orthodontic brackets are connected by wires, called arches, so that they can be moved together with the teeth by springs and anchoring systems of different materials together by different processes. This possibly creates a galvanic cell, and release of nickel by the device. Currently there are nickel-free materials. However stainless steels have lower value and ease of use. Allergy to nickel contained in the stainless steel unit causes discomfort and in some cases to discontinuation of treatment. This allergy comes from nickel ions released by stainless steel through the patient's saliva. This study aimed to apply the technique of sacrificial anodes used for cathodic protection of steel structures exposed to saline. This technique was applied to the stainless steel protection and their combinations with other metals used in orthodontic treatments. Various combinations of sacrificial anodes and electrolytes were made. Two stages of tests were carried out and arrangements consist of a welded band with silver solder in the middle pre-skirted five brackets bow stuck in it with amarril wire. In the first stage were evaluated four anodes sacrifice tied to the arrangements and aqueous solutions with various salinities yielding around fifty percent reduction in nickel release. The second step was more successful and the amount of nickel released, was below the detection limit of electrochemical atomic absorption device used in this work. In the second stage we used zinc and magnesium anodes for the protection and saline with and without sodium fluoride. The electrical contact of sacrificial anodes with stainless steel has been improved and possibly caused the lower nickel release at this stage. This validates the method of cathodic protection in the reduction of the release of nickel stainless steel orthodontic appliances.

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.

Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído. / Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.