Materials Performance

AUG 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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14 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM Chlorination Effect on Corrosion of CuNi 90/10 in Seawater C u-based alloys are frequently used for seawater piping because of their resistance to chloride pitting as well as their antifouling characteristics. One Cu-based alloy that is a preferred choice for its reli- able performance in seawater applica- tions (such as ballast water systems) is CuNi 90/10 alloy (UNS C70600), which is 10 mass% of Ni alloyed to Cu. Seawater for ballast water tanks is normally treated with disinfectants (e.g., chlorine) by ballast water treatment sys- tems to control invasive species in ballast water. These invasive species can become an environmental threat if released untreated. A lthough the level of chlorine is thought to inf luence corrosion of the exposed metal, the criteria for chlorina- tion dosing for seawater treatment have yet to be well established for Cu-Ni pip- ing, despite the long history of the alloy being used for seawater systems. When CuNi 90/10 alloy is used for sea- water applications, it is ty pically recom- mended that the seawater f low be main- tained above a minimum f low rate of 1 m/s because slow f low makes it easier for marine organisms to attach them- selves to a metal surface, which can lead to microbiologically inf luenced corrosion (MIC). The f low rate of 1 m/s, however, is rarely reached during the normal opera- tion of certain seawater lines such as bal- last water or f ire-f ighting systems, as these systems f low only under specif ic circumstances. Whether chlorinating seawater is effective for suppressing marine fouling and causes subsequent corrosion of CuNi 90/10 alloy under stag- nant conditions is unclear. In CORROSION 2018 paper no. 11418, "Effect of Chlorination on Corrosion of 90-10 Cu-Ni A lloy for Ballast Water Sys- tem," authors Geunsu Jung, Byoung Young Yoon, Jae Kwang Lee, and Chae- Seon Lim with Samsung Heav y Industry (Gyeongsangnam-do, South Korea) dis- cuss a study where biofouling and corro- sion issues for CuNi 90/10 alloy were examined. Samples of the alloy were pre- pared and immersed in bottled seawater with various chlorination levels for up to six months for two main research objec- tives: to investigate the effective dosing level of chlorination for CuNi 90/10 alloys in seawater for effectively suppressing marine fouling, and to evaluate the effect of chlorination on the corrosion of CuNi 90/10 alloy in seawater under stagnant conditions. For the experiment, 10- by 30- by 5-mm samples were taken from a com- mercially available CuNi 90/10 pipe and prepared with various surface prepara- tions: as received (as-is); mirror polished to 1 μm using conventional methods (pol- ished); and polished and immersed in clean, fresh water for a month (condi- tioned). The surface of the samples was observed with an optical microscope before the immersion test. The as-is and conditioned samples showed similar sur- face morphologies, although the condi- tioned sample—through polishing—no longer had grooves from the manufactur- ing process, which could be seen on the surface of the as-is sample. The glossy surface of the polished sample was antici- pated to be the most sensitive to corrosive media as the protective oxide scales were removed when the metal was polished. The surface of the conditioned sample MATERIAL MATTERS

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