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No description available.

No description available.

No description available.

No description available.

Non-uniform corrosion of copper and brass in potable water systems poses both economic and environmental problems associated with premature plumbing failures and release of metals. With respect to copper pitting corrosion, it was found that forensic testing (i.e., in pipe-loops) is the only investigative technique that can closely mimic conditions found in real water systems and produce unambiguous results; and, if used in combination with electrochemical techniques, it may also provide some mechanistic insights into the pitting process. Using pipe-loops, it was demonstrated that copper pitting in aggressive water qualities (i.e., chlorinated, high pH and low alkalinity) is deterministic and reproducible. Additionally, the effects of various chemical and physical factors on pitting were investigated. Overall, increased flow velocity and frequency, increased chlorine residual and decreased hardness were found to accelerate pitting; whereas increased phosphate and silica were found to decelerate pitting. Several mitigation strategies for copper pitting in aggressive water were further investigated, and experimental data were interpreted utilizing electrochemical theory to evaluate specific effects on the initiation and propagation phases of pitting. Surprisingly, it was found that decreased chlorine may delay pit initiation, however, even relatively low levels of chlorine may eventually initiate and propagate pits. Increased alkalinity appears to decelerate pit growth, but does not prevent pit initiation. NOM can delay pit initiation and propagation, although the potential for DBP formation in chlorinated waters makes inhibition by NOM an unfavorable alternative. At sufficient dosages, phosphate and silica corrosion inhibitors may completely stop pitting, consistent with the success of several field trials. At very low dosages, phosphate and silica may actually accelerate pinhole failures, so these inhibitors should not be under-dosed. While brass alloys exist that can limit dezincification problems, they are not always utilized in potable water applications due to high costs, and so dezincification is a re-emerging issue in some countries, including the US. Little research has been conducted in the past several decades regarding the effects of water chemistry, and almost no work has addressed the roles of physical factors associated with real plumbing systems. Thus, a comprehensive review of these topics was conducted. To better understand the effects of some factors associated with specific plumbing installations on dezincification and other brass corrosion types, a series of pipe-loop studies was carried out. It was confirmed that increased oxidant delivery rates to cathodic surfaces, either via increased oxidant concentration or increased flow velocity, can increase corrosion rates. Several key differences were observed with respect to corrosion of brass located in copper plumbing tube systems as opposed to plastic. When copper tubes contribute copper ions to water, brass corrosion becomes more selective for zinc; but if galvanic connections are made between the copper tubes and brass, selectivity for zinc is reduced while overall corrosion rates are accelerated. As opposed to copper tubing, plastic maintains oxidant (e.g., free chlorine) levels, and may thereby increase brass corrosion and build-up of corrosion by-products. Finally, it was found that increased temperature can significantly increase lead leaching from brass. Following recent outbreaks of brass dezincification failures, NSF/ANSI Standard 14 has been revised to require that all NSF 14-listed brass is dezincification resistant, as certified by satisfactory results from an accelerated test method (ISO 6509). Various brasses were tested using this method as well as a longer-term jar method utilizing real potable water. Results of the two tests were in good agreement with respect to dezincification, specifically; but some inconsistencies were observed with respect to uniform corrosion and lead leaching. / Ph. D.

Water chemistry and fluid velocity are factors that can perpetuate certain types of non-uniform pitting corrosion in copper tube, specifically in waters with high chlorine and a high pH. These two parameters can further act synergistically to alter pitting propensities in copper pipes subjected to this type of water. A preliminary short-term experiment considered pitting propensity in copper pipe as a function of water chemistry. This study used a water chemistry that had been documented to promote and sustain pitting in copper tube that further developed into fully penetrating pinhole leaks. Modifications to this base water chemistry found that dosing a chloramine disinfect (rather than free chlorine) or the addition of silica greatly reduced corrosion activity and pitting propensity on copper pipes. In another short-term experiment, copper pitting propensity was considered as a function of fluid velocity. A number of different fluid velocities were tested in several different pipe diameters using the same documented pitting water. Velocity was observed to significantly increase pitting propensity in all pipe diameters considered. At the highest fluid velocity tested (11.2 fps) a pinhole leak formed in ¼â tubing after only 2 months of testing. Larger pipe diameters were also found to increase the likelihood of forming deeper pits on the pipe surface at the same fluid velocity. Chlorine was a driving factor in corrosion for preliminary tests conducted using this pitting water. The reduction of chlorine to chloride is believed to be the primary cathodic reaction limiting the overall rate of corrosion in this type of water. As such, a subsequent study considered the relationship between the rate of chlorine reduction and corresponding corrosion activity. Chlorine reduction or demand rates were found to be good indicators for pitting propensity and corrosion activity for this particular type of water. All preceding work led to the development and design of a large scale, long-term, copper pitting study. A matrix of 21 unique conditions tested various water chemistries, flow conditions, corrosion inhibitors, and galvanic connections of copper pipes to other metallic plumbing materials. The severity of pitting corrosion was observed to be dramatically decreased by lower free chlorine residual concentrations, high alkalinity, and sufficient doses of copper corrosion inhibitors such as natural organic matter, silica, and orthophosphate. Pitting severity was consequently observed to increase at a low alkalinity, indicating that this parameter has a significant effect on corrosion reactions. Furthermore, the addition of aluminum solids to the base pitting water chemistry dramatically increased the formation of tubercle mounds on the inside of the copper pipes in contact with the waster. Aluminum solids have been observed to be a vital constituent for sustaining pit growth in this specific water at lower pHs, however, the role of this constituent at the high pH levels tested in this study was previously unknown. From simple visual observation, aluminum solids appear to increase the aggressiveness of this water even at higher pHs. / Master of Science

When severe copper pitting problems impacted customers at a large utility, studies were begun to attempt to diagnose the problem and identify potential solutions. A series of tests were conducted to characterize the nature of pitting. Desktop comparisons of pinhole leak frequency and treatment practices at nearly utilities were also documented to identify treatment factors that might be influencing the initiation and propagation of leaks. Factors identified included the presence of relatively high levels of free chlorine and aluminum in the distribution system. Experiments were conducted to examine the effect of these constituents on copper pitting under stagnant and flow conditions. That led to discovery of a synergistic redox reaction between chlorine, aluminum solids, and copper metal as evidenced by increased chlorine decay rates, non-uniform corrosion, and rising corrosion potentials. Temperature changes had been suspected to increase copper pitting frequency and copper release to drinking water. Experiments examined the effect of temperature gradients on copper pipe corrosion during stagnant conditions. The pipe orientation in relation to the temperature gradient determined whether convective mixing would occur, which influenced temperature gradients within the pipe. This work is the first to demonstrate that temperature gradients lead to thermogalvanic currents, influences copper leaching and scale type. Iron release from corroding water mains is another concern of many water utilities, but little is known about chemistry factors that influence the problem. In laboratory experiments, higher levels of silica caused more iron release to the water and decreased the size of suspended iron particles. Silica levels also changed during the experiment: it decreased through incorporation into a dense scale, and increased by release from cast iron during corrosion. Silica slightly decreased iron corrosion rates near the end of this 6-month test. / Master of Science

Les aciers inoxydables duplex (DSS) sont caractérisés par une structure biphasée comprenant un mélange de ferrite et d’austénite. La proportion entre les deux phases est d'habitude environ 50 %. Ils sont de plus en plus employés dans les industries chimiques, pétrochimiques, nucléaires, marines et de papier, principalement en raison de leurs excellentes propriétés mécaniques couplées à une bonne résistance à la corrosion par piqûre (basse teneur en nickel et molybdène). L’austénite ayant une composition chimique différente de celle de la ferrite, un film hétérogène se forme à la surface des aciers inoxydable duplex. Par ailleurs, les deux phases métalliques ayant des propriétés mécaniques différentes, un champ de contrainte hétérogène est généré dans les grains. Sous certaines conditions, l’existence de gradients de contraintes peut conduire à des hétérogénéités du film passif. Dans ce travail , on étudie l’effet des éléments d’alliages sur les propriétés physico-chimiques du film passif et le comportement en corrosion par piqures avant et après vieillissement en milieu chlorurés, pour une surface de référence respectant certains critères à savoir une surface lisse exempt de tout défauts (pas de couche écrouie, rugosité faible..). Les propriétés physico- chimiques du film sont étudiés à l’aide des analyses Auger et XPS à l’échelle locale et globale. Le comportement en corrosion des alliages duplex a été ensuite déterminé à partir d’essais TCP (détermination de la température critique de piqûration). Les résultats avant vieillissement ont montré que le film passif est homogène à l’échelle macroscopique et que l’amorçage des piqûres semblent être liée à la taille des grains et à la texture cristallographique décrit par le GOS. Après vieillissement de longue durée en milieu représentatif, les analyses de surface montrent un renforcement de la passivité par un épaississement du film passif, une augmentation significative du rapport Cr/Fe ce qui ont pour effet d’améliorer le comportement en corrosion par piqures des alliages. Des critères métallurgiques ont été proposés pour expliquer l’amorçage de piqûres pour ces alliages. / Duplex stainless steels (DSS) are characterized by a two-phase structure comprising a mixture of ferrite and austenite. The proportion between the two phases is usually about 50%. They are increasingly used in the chemical, petrochemical, nuclear, marine and paper, mainly because of their excellent mechanical properties coupled with good resistance to pitting corrosion (low grade nickel and molybdenum). The austenite having a different chemical composition than the ferrite, a heterogeneous film is formed on the surface of duplex stainless steels. Furthermore, the two metallic phases having different mechanical properties, a field of heterogeneous stress is generated in the grains. Under certain conditions, these differences may also yield formation of a heterogeneous passive film. In this work, we study the effect of alloying elements on the physico-chemical properties of the passive film and behavior pitting corrosion before and after ageing in chloride media for a reference surface that meet certain criteria ie a smooth surface free from any defects (no hardened layer .. low roughness). The physicochemical properties of the film are studied using Auger and XPS analysis at the microscale. The corrosion behavior of duplex alloys was then determined from CPT tests (determination of the Critical Pitting Temperature). The results before ageing have shown that the passive film is homogeneous on a macroscopic scale and that pitting corrosion appear to be related to the grain size and crystallographic texture described by GOS. After ageing, surface analysis shows a strengthening of passivity by thickening of the passive film and the ratio Cr/Fe are significantly increased which has the effect of improving behavior pitting alloys. Metallurgical criteria for pitting were proposed.

Klimatutmaningar, lagändringar och ett ökat miljötänk har tvingat transportsektorn att ställa om till eldrift. Batterier och elmotorer har utvecklats kraftigt och är nu ett alternativ även för tunga fordon. Ett vanligt förekommande problem med elmotorer i fordon är lagerströmmar, här kallat gnista eller blixthändelser. Dessa uppstår på grund av oönskade urladdningar i motorn och förorsakar skador på lagren i motorn. Syftet med motorlager är att avlasta och minska friktionen kring motoraxeln. För att förebygga problemet och se förbättringar eller försämringar av olika åtgärder som görs krävs att lagerströmmar kan identifieras utifrån mätdata. Detta examensarbete analyserar relevant forskning inom området för att sedan introducera en metod och en algoritm för att identifiera lagerströmmar i samarbete med Scania CV. Algoritmen består av tre olika parametrar som påverkar identifieringen av de oönskade strömmarna på olika sätt. Verktyget lyckades identifierade lagerströmmar i olika mätdata, och hittade skillnader i antalet blixthändelser mellan olika körningar av provobjektet. Dock krävs vidare utveckling av verktyget och möjligheten att bearbeta annan typ av data som exempelvis spänningar i motorn för atthitta bättre samband. / A changing climate, changing laws and an increased environmental consciousnesshas forced the transport sector to transition to electric power. Batteries and electric motors have seen a quick and powerful development which means that they are now an alternative even for heavy vehicles. A common problem with electric motors forvehicles is bearing currents. The bearing currents occur as a result of electrical discharges in the motor and can damage the bearings inside the motor. The purpose of motor bearings is to offload and reduce friction for the motor shaft. To prevent the issue and to see improvements or deteriorations from different preventativemeasures it is critical to be able to identify bearing currents from data. This thesis analyzes relevant research in the area before introducing a method and an algorithm for detecting bearing currents in cooperation with Scania CV. The algorithm is composed of three different parameters which affects the identification in different ways. The tool was able to identify bearing currents from various data and found differences between the number of bearing currents between different test runs of the motor. However, more development of the tool and the possibility to process different kinds of data like voltages inside the motor is needed to be able to find better patterns in the data.