Corrosion and metal release mechanisms of CoCrMo alloys are at human biological conditions not fully understood. The main objective of this master thesis was to investigate whether the Vroman effect influences the extent of metal release from CoCrMo alloy in mixed protein solutions. The project focuses on the corrosion properties and release of cobalt (Co), chromium (Cr) and molybdenum (Mo) from a CoCrMo alloy into simulated physiological solutions of pH 7.2-7.4 in the presence of proteins. The metal release study was performed in phosphate buffered saline (PBS) for 4 and 24 h at 37 °C with and without different concentration of proteins (bovine serum albumin-BSA and fibrinogen-Fbn from bovine plasma). In order to investigate whether any Vroman effect could affect the extent of released metals in solutions, sequential tests were performed by sampling after 1, 4, 6 and 24 h in solutions that were partially replenished after 5 h. Significant metal-induced protein aggregation and precipitation were observed in solutions of physiologically-relevant protein concentrations (40 g/L BSA and 2.67 g/L Fbn). Cr was strongly enriched in the surface oxide of CoCrMo after exposure in all solutions. This was for all solutions accompanied by metal release processes dominated by Co. Based on electrochemical investigations, the electrochemical activity did not increase, but rather decreased, in protein-containing solutions as compared to PBS alone. This could possibly be explained by blocking of cathodic areas as a result of protein adsorption.

The power transformer is a critical equipment in which the protection process is essential for modern societies where continuous electric power supplies are required. Copper corrosion problems due to the formation of sulfur deposits on the copper windings of mineral oil-filled power transformers are considered a major issue that can lead to sudden failures, and in some cases, to costly fire and explosion accidents in the power plants. These kinds of problems are still being reported regardless of available condition monitoring (CM) parameters applied in power transformers' maintenance strategy. The currently applied CM parameters are based on three different types of technologies. The first is oil analysis focuses more on measurable variables such as measuring the concentration of the corrosive sulfur compounds in the insulating oil, evaluating the oil's capability to form sulfur deposits, and measuring an increase in the concentration of specific gases. The second is on-site electrical testing focuses on the variation of the transformer's electrical properties due to the sulfur deposits. The measurable variables used in the electrical testing are Frequency Domain Spectroscopy test and Polarization/Depolarization Current test. The last is online sensor technology using Corrosive Sulfur Sensor, where the sensor's outcome data provide information about the oil's capability to form sulfur deposits. The research problem addressed is how to establish more effective CM parameters for early detection of copper corrosion problems.  The research problem is divided into three concretized research problems: What are the strengths and weaknesses of the currently applied condition monitoring parameters? Which measurable variables could be utilized to improve the currently applied condition monitoring parameters to be more effective for early detection of copper corrosion problems? And how to establish a procedure for the condition monitoring for detecting copper corrosion? Two research methodologies were applied to answer these questions, literature review and experimental work. The literature review showed significant gaps in the currently applied CM parameters for early detection of copper corrosion problems due to incomplete data of the corrosion reaction mechanism. Therefore, qualitative and quantitative investigations in the experimental work were carried out. The most important result was finding new relevant measurable variables, i.e. hydrogen sulfide gas and toluene compound, which are by-products of corrosion reaction. These measurable variables are utilized to establish more effective CM parameters for early detection of copper corrosion problems. The main conclusion of this thesis is the importance of detection corrosion problems in the initial stage by implementing more effective CM parameters to prevent catastrophic and costly failures, reduce the negative impacts on human life and the environment, and save the economic losses. Another conclusion is the importance of regularly following the measurable variables' uptrend during transformer useful life to avoid incorrect evaluation of corrosion conditions.

The purpose of this study was to extract galvanized steel wire reinforcement coupons from mechanically stabilized earth (MSE) walls along I-15 and determine the rate of corrosion that has taken place since Phase I, which was conducted by Gerber and Billings (2010). The galvanized steel reinforcement analyzed in this study has been in place for 19 to 20 years at the time of extraction. A total of 85 coupons were extracted and laboratory analysis was performed to determine the thickness of remaining zinc galvanization on each coupon. Soil samples were obtained from each one-stage wall extraction location to determine moisture content for correlation with corrosion. After laboratory testing was performed, the measured zinc coating thickness was compared to that determined in Phase I. An average corrosion rate of approximately 0.032 oz/ft²/year has occurred since Phase I. According to the AASHTO (2017) design corrosion rate of 0.35 oz/ft²/year for the first two years and 0.09 oz/ft²/year until the depletion of the zinc, the zinc coating would have been completely depleted after 16 years. Based on the results of laboratory testing, the initial galvanization coating was likely greater than the specified thickness of 2.0 oz/ft² (86 μm). The zinc galvanization is corroding at a slower rate than the AASHTO design rate. The AASHTO design rate for depletion of zinc coating and subsequent corrosion of the steel reinforcement is conservative for the corrosion conditions present in the MSE wall reinforcement coupons tested. The integrity of the steel reinforcement that is currently in place is not likely to be compromised by corrosion.

Chloride-induced stress corrosion cracking (CISCC) has been identified as the main degradation mechanism for spent nuclear fuel dry storage canisters. This type of induced cracking is complex and depends on several factors, such as material composition, exposure temperature, relative humidity, applied tensile stress, and atmospheric salt concentration. An accelerated experiment was designed to simulate marine environments in a controlled fogging chamber to examine 304 and 304L stainless steel U-bend and welded U-bend samples. The samples were exposed to chloride rich and humid fogging in a corrosion chamber at 35℃ continuously for 4 weeks, 8 weeks, and 12 weeks. The same experiment was repeated at 50℃ for 4 weeks, 8 weeks, and 14 weeks to study the sensitivity of CISCC to temperature changes. A qualitative evaluation of optical micrographs from a 3D Surface Profiler was performed for 16 corroded samples and compared with 2 reference samples. Cracking was observed on 12 out of 16 samples exposed to 35℃ and 50℃ for durations ranging from 8 to 14 weeks. Likely cracking observations were noted on 4 out of 16 samples. A quantitative statistical analysis was also performed using surface profile depth (valley) data from corroded and reference samples. The quantitative analysis examined the effect of temperature, welding, exposure duration, and material composition. The quantitative results were compared with the qualitative results and literature published in CISCC. / Master of Science / Most nuclear power plants are currently using dry storage canisters (DSCs) which are made of a concrete vault and a stainless steel canister that houses the spent nuclear fuel (SNF) assemblies. Multiple conditions must be present simultaneously for chloride-induced stress corrosion cracking (CISCC) to develop, such as the presence of a susceptible alloy, high relative humidity, high temperature, high atmospheric salt concentrations, and applied tensile stresses. DSCs are typically made from 300-series austenitic stainless steels which are susceptible to this type of corrosion during long-term storage near marine environments. Therefore, understanding of the factors leading to CISCC is critically important for proper management and mitigation and to estimate the service life of DSCs for the safe long-term storage of SNF. An accelerated experiment was designed to examine the effects of temperature, exposure duration, and welding on pitting and cracking for 304 and 304L U-bend samples. The experimental results concluded that stainless-steel grades 304 and 304L are susceptible to CISCC when exposed for 8 weeks or longer to fogging at temperatures between 35℃ and 50℃, 95% relative humidity, and 5% salt concentration. This study also concluded that increasing exposure duration from 8 to 12 weeks or the temperature from 35℃ to 50℃ had no significant effect on the acceleration of CISCC. Also, unwelded samples were deemed more susceptible to CISCC than welded samples and the susceptibility of 304 and 304L grades were relatively similar.

Pitting corrosion is a prevalent form of corrosive damage that can weaken, damage, and initiate failure in corrosion-resistant metallic materials. For instance, 304 stainless steel is commonly utilized in various structures (e.g., miter gates, heat exchangers, and storage tanks), but is prone to failure through pitting corrosion and stress corrosion cracking under mechanical loading, regardless of its high corrosion resistance. In this study, to better understand the pitting corrosion damage development, controlled corrosion experiments were conducted to generate pits on 304 stainless steel specimens with and without mechanical loading. The pit development over time was characterized using a high-resolution laser scanner. In addition, to achieve scalable and automatic assessment of pitting corrosion conditions, two convolutional neural network-based computer vision algorithms were adopted and implemented to evaluate the efficacy of networks to identify existence of pitting damage. One was a newly trained convolutional neural network (CNN) using MATLAB software, while the other one was a retrained version of GoogLeNet. Overall, the experimental results showed that time is the dependent variable in predicting pit depth. Meanwhile, loading conditions significantly influence pit morphology. Under compression loading, pits form with larger surface opening areas, while under tension loading, pits have smaller surface opening areas. Deep pits of smaller areas are dangerous for structural members, as they can lead to high stress concentrations and early stress corrosion cracking (SCC). Furthermore, while the training library was limited and consisted of low-resolution images, the retrained GoogLeNet CNN showed promising potential for identifying pitting corrosion based on the evaluation of its performance parameters, including the accuracy, loss, recall, precision, and F1-measure.

This thesis reports on the research outcome of corrosion mechanism and corrosion rate of mild steel in different environments (saline, alkaline solutions and concrete media) using potentiodynamic polarization technique. The study also included the effect of corrosion on bond strength between reinforcing steel and concrete using pull-out test. Corrosion of mild steel and 316L stainless steel with different surface conditions in 1, 3 and 5% saline (NaCl + Distilled water) was investigated. Specimens ground with 200 and 600 grit silicon carbide grinding paper as well as 1¿m surface finish (polished with 1¿m diamond paste) were tested. In case of mild steel specimens, reduction in surface roughness caused increase in corrosion rate, while in 316L stainless steel corrosion rate decreased as the surface roughness improved. Metallographic examination of corroded specimens confirmed breakdown of passive region due to pitting corrosion. Corrosion of mild steel was also investigated in alkaline solution (saturated calcium hydroxide, pH =12.5) contaminated with 1, 3 and 5% saline. A series of corrosion experiments were also conducted to examine the efficiency of various concentrations of calcium nitrite (CN) on corrosion behaviour of both as-received and polished mild steel in alkaline solution containing 3% saline after 1 hour and 28 days of exposure. Corrosion rate was higher for the as-received than polished mild steel surface under the same testing conditions in NaCl alkaline solution with and without nitrites due to the effect of surface roughness. Morphology investigation of mild steel specimens in alkaline solution ii containing chlorides and nitrites showed localized pits even at nitrite concentration equal to chloride concentration. Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46MPa was also investigated. The effect of 2 and 4% CN by weight of cement on corrosion behaviour of steel bar in low and high concrete strengths specimens were also studied. All reinforced concrete specimens were immersed in 3% saline solution for three different periods of 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4A was applied. Corrosion rate was measured by retrieving electrochemical information from polarization tests. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and bond strength were dependent on concrete strength, amount of CN and acceleration corrosion period. As concrete strength increased from 20 to 46MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration showed a slight increase in steel/concrete bond strength, whereas severe corrosion due to 7 and 15 days corrosion acceleration significantly reduced steel/concrete bond strength. Addition of only 2% CN did not give corrosion protection for steel reinforcement in concrete with 20MPa strength at long time of exposure. However, the combination of good quality concrete and addition of CN appear to be a desirable approach to reduce the effect of chloride induced corrosion of steel reinforcement. At less time of exposure, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 days of corrosion acceleration, the higher concentration of CN gave higher bond strength in both concrete mixes. The same trend was observed at 15 days of corrosion acceleration except for the specimen with 20MPa compressive strength and 2% CN which recorded the highest deterioration in bond strength.

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