Brass components are widely used in drinking water distribution systems as valves, faucets and other fixtures. They can be corroded by "dezincification," which is the selective leaching of zinc from the alloy. Dezincification in potable water systems has important practical consequences that include clogged water lines, premature system failure and leaks, and release of contaminants such as lead. Brass failures attributed to dezincification are known to occur at least occasionally all over the world, and have emerged as a significant problem in the U.S. recently due to the use of inexpensive high zinc brass fittings in cross-linked polyethylene (PEX) plumbing systems. As PEX systems gain popularity and leaded brass is recognized as an important source of lead in potable water systems, it is important to examine dezincification corrosion in more detail. An in-depth literature review revealed that conventional wisdom about dezincification was no longer adequate in explaining failures observed in modern water systems. Little research has been conducted since the landmark work of Turner et al. nearly half a century ago. The potential role of chloramines, phosphate inhibitors, and modern understanding of water chemistry need evaluation. The role of physical factors including stirring, heating and galvanic connections are also potentially influential. A mechanistic study of zinc solubility and corrosion of copper: zinc couples provided insight to factors that might mitigate and exacerbate zinc leaching from brass. Zinc solubility and corrosion was reduced by higher pH and bicarbonate, but was enhanced by higher chloride. Hardness ions including Mg⁺² and Ca⁺² had little effect. Alloys with higher zinc content had a greater propensity for dezincification corrosion. Stirring and galvanic connections caused brass to leach more metals and have higher weight loss. Heating may contribute to corrosion scale accumulation. A comprehensive examination of dezincification as a function of water chemistry used numerous techniques that include measurement of galvanic currents, metal leaching, and weight loss. In general, as would be predicted based on results of the study of solubility and corrosion of pure zinc, chloride emerged as an aggressive ion whereas bicarbonate was beneficial to brass corrosion. Hardness had little impact, and phosphates, silicates and Zn+2 inhibitors had a significant short-term benefit but little long-term benefit. The relationship between dezincification corrosion, lead leaching from brass, and water chemistry was investigated in Chapter 5. Surprisingly, lead and zinc leaching from a range of brasses were found to be negatively correlated. Hence, use of brasses that minimize dezincification problems might increase lead leaching. This thesis represents a comprehensive analysis of factors that are influential for dezincification and lead leaching from brass in premise water distribution systems through literature reviews, mechanistic investigations, bench-scale experiments, and case studies. Results can be used by water utilities, plumbing engineers, manufacturers and home owners to better prevent, recognize, and mitigate brass and dezincification corrosion problems. / Master of Science

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Grade 91 (Gr.91) is a common structural material used in boiler applications and is favored due to its high temperature creep strength and oxidation resistance. Under cyclic stresses, the material will experience creep deformation eventually causing the propagation of type IV cracks within its heat-affected-zone (HAZ) which can be a major problem under short-term and long-term applications. In this study, we aim to improve this premature failure by performing a computational thermodynamic study through the Calculation of Phase Diagram (CALPHAD) approach. Under this approach, we have provided a baseline study as well as simulations based on additional alloying elements such as manganese (Mn), nickel (Ni), and titanium (Ti). Our simulation results have concluded that high concentrations of Mn and Ni had destabilized M23C6 for short-term creep failure, while Ti had increased the beneficial MX phase, and low concentrations of nitrogen (N) had successfully destabilized Z-phase formation for long-term creep failure.