International Journal of Material and Mechanical Engineering (IJMME) Volume 2 Issue 3, August 2013 www.ijm‐me.org 43 The Premature Deterioration of Zinc‐coated Steel Pipes in Water Distribution System B. Pawlowski, J. Krawczyk, P. Bala AGH University of Science and Technology, Krakow, Poland bpawlow@agh.edu.pl Abstract This paper presents examples of improper materials selection in choosing a pipe for a hot water distribution system. Despite the recommendations of both European Standards and Polish Research & Development Centre COBRTI zinc‐coated steel pipes were used for piping in conditions under which the premature corrosion failure was observed. Keywords Zinc‐Coated Steel Pipe; Internal Corrosion; Water Distribution System Introduction Iron and steel pipes have been used in water distribution systems for over five centuries (Sarin et al., 2001). Economically, modern zinc‐coated steel pipes are inexpensive and recyclable. With a long life span, such material is very attractive. Zinc coatings protect steel by providing a physical barrier as well as cathodic protection for the underlying steel. In this process, zinc as more ignoble metal is acting as a sacrificial anode while the steel(as cathode) will not be attacked. However, there are many reports of galvanized steel water pipe failures due to corrosion, after several months or few years of service life(Wilmot et al., 2006, Bae et al., 2007). Accelerated corrosion occurs under certain conditions of flow water chemistry. The internal wall of the steel pipe exposed to aqueous environment (flow water) usually suffers more severe corrosion (so‐called internal corrosion) than the external wall exposed to indoor conditions (Wang et al., 2012). Many water distribution systems begin to experience pinhole leaks caused by pitting corrosion on the internal surfaces of the piping. Corrosion of zinc in flow water is a complex process controlled largely by water chemistry and temperature. Relatively small differences in water chemistry can produce relatively substantial changes in corrosion products and rate(Amer. Galv. Ass., 2000).A coating of zinc protects galvanized pipe, but when corrosion occurs, depositing high levels of zinc and iron into the tap water.The zinc coating on galvanized pipe may contain lead, copper, cadmium, chromium, aluminum, barium, and other impurities. As a result of these impurities, corrosion of galvanized pipe may result in the release of trace metal concentrations(Amer. Water Works Ass., 2011). Contemporary regulations in many countrieseven prohibit the use of galvanized steel pipes in drinking water systems and do not recommend for hot water circuit(The Austr. & NZ Stand., 2003). Today, almost all installations in Denmarkare built with pipes of stainless steel and polymer materials. In many other European countries copper pipes arestill widely used, whereas the use of hot dip galvanized steel pipes is decreasing(Hilbert et al., 2010). In some countries, including Poland, galvanized steel piping is still popular and this paper presents the investigations of hot water piping failure due to the use of galvanized steel in two regions (north‐east and south‐east of Cracow, Poland) supplied by two different public‐ supplied water sources in the city. Material and Method The pipe samples which forms a part of two hot water distribution systems exposed approximately: first one for 2 years (region I) and second one for 5 years (region II) to flow water delivered by two public‐ supplied sources in the city has been considered for the study. After this short service life galvanized pipes experiencing pitting failures, as it shown in Figure 1 (after 2 years of service) and Figure 2 (after 5 years of service). FIG. 1. PITTING PERFORATION ALONG THE WELD SEAM, 3/4“ PIPE AFTER 2 YEARS OF SERVICE, REGION I FIG. 2. MAGNIFIED IMAGE OF PITTING PERFORATION ALONG THE WELD SEAM, 5/4” PIPE AFTER 5 YEARS OF SERVICE, REGION II