Interplay of Water Chemistry and Entrained Particulates in Erosion Corrosion of Copper and Nonleaded Alloys in Potable Water Systems

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Virginia Tech

Erosion corrosion of plumbing materials in domestic water systems is a complex phenomenon driven by water quality, hydrodynamic and electrochemical factors. Erosion corrosion accounts for over a third of copper hot water system failures in the U.S., hundreds of millions in damage, and may be expected to increase with newer Legionella control strategies including increased use of water recirculation and high temperatures. Additionally, some nonleaded alloys introduced after the passage of a new federal law restricting lead content in plumbing, have been anecdotally implicated as failing prematurely from erosion corrosion compared to traditional alloys.

This dissertation includes 1) a critical review of the literature, 2) investigation of a recent rapid erosion corrosion failure in a large building plumbing system, 3) replication of this phenomena in copper and nonleaded brass in laboratory studies, and 4) evaluation of 12 nonleaded alloys against conventional leaded brass. Current plumbing codes and guidelines to prevent erosion corrosion were found to be widely inconsistent and lacking scientific evidence. Large-scale recirculating hot water pipe-loop experiments demonstrated that an aggressive hard water with entrained aragonite (CaCO3) particles could cause fully penetrative failures (i.e., leaks) in brand new copper pipe and nonleaded brass fittings in just 3-49 days. This represents the first time rapid erosion corrosion failures have ever been replicated in the laboratory under conditions similar to those encountered in practice. The entrained particulates dramatically accelerated attack on metals, especially at pipe bends. In general, lowering pH, increasing flow velocity, increasing temperatures, entrainment of particles (of bigger sizes), and addition of chlorine disinfectant increased erosion corrosion rates. These results scientifically proved that hard waters are not inherently less aggressive than soft water, and in fact if CaCO3 solids form they can be much more aggressive. Finally, cavitation and erosion corrosion resistance of 12 nonleaded alloys was evaluated against leaded brass; stainless steels demonstrated superior performance, silicon brass had the greatest susceptibility and remaining alloys were in the middle. This performance data can aid decision making regarding choice of alloys for various water applications.

Our work over the years, including involvement in the Flint Water Crisis, demonstrated that practicing trustworthy science as a public good requires commitment to scientific rigor, truth-seeking, managing conflicts of interest, and comprehensible evidence-based science communication. Critical problems in 21st century public science were highlighted including perverse incentives, misconduct, postmodernist "science anarchist" thought, and ineffectiveness of U.S. water utilities in communicating tap water safety to the American public.

aragonite, flow-induced failures, hot water, particle impingement, water infrastructure