Duration of Metal Corrosion: Plumbing and Construction Materials

摘要

The forensic engineer recognizes the importance of metal corrosion as a diagnostic tool when conducting a building investigation. This study advances the scientific community's use of qualitative analysis by reporting the results from three long-term moisture exposure studies. The study was divided into two tasks: 1) creation of a moisture exposure chamber that would allow repeated exposure of study exemplars to fresh water and salt water mists repeatedly over extended periods of time (months), and 2) documentation of the gradual changes that occurred in the specimens as they experienced surface oxidation, discoloration, and the presence of advanced surface corrosion. The study was conducted over three test periods. The first and second test periods were conducted over 244 days and 461 days, respectively. These tests documented qualitative changes to galvanized steel pieces (i.e., corner bead, framing, sill plate, electrical conduit, metal lath, galvanized pipe, and brass fitting). The third study was conducted over 122 days and documented changes to metal components commonly found in the plumbing/building materials for bathrooms and kitchens. These components consisted of stainless steel water supply lines, angle stop valve handles, escutcheon plates, under sink mount brackets, concealed and face cabinet door hinges. The components were exposed to fresh water and seawater using modified methods from ASTM Standard Bl 17. Controlled tests were conducted within an acrylic and polycarbonate test chamber equipped with a recirculating solution system. Frequent time-lapsed photography documented the corrosive effects facilitated by continuous fresh and salt water exposure. The test procedure enabled evaluation between both wetted, humid, and un-wetted (control) specimens. The photographs document qualitatively equivalent exemplars that were compared to "real world" component installations affected by a water loss. These comparisons facilitate determinations of loss duration under conditions of a worst-case, water exposure scenario.