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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15 MATERIALS PERFORMANCE: VOL. 57, NO. 8 AUGUST 2018 Continued on page 16 Initial surfaces of the samples. Source: CORROSION 2018 paper no. 11418. had formed oxide scales that were expected to provide the metal with corrosion resistance during the im mersion test. After surface preparation, the sam- ples were weighed and then placed into 500 mL bottles f illed with different solu- tions: non-chlorinated natural seawater, non-chlorinated artif icial seawater, and chlorinated natural seawater with differ- ent residual Cl concentration levels (0.5, 1.0, and 5.0 ppm). The natural seawater was collected near the Samsung Heav y Industry shipyard on Geoje Island in the southern part of South Korea. The artif i- cial seawater was made using commercial sea salts and distilled water so that it had the same salinity as the natural seawater but did not contain microorganisms (sterile condition). Sodium hy pochlorite (NaClO) was used for chlorination. The bottles were then capped and securely closed to create a closed system. The samples were immersed for one, three, and six months to study corrosion of the Cu-Ni alloy under different condi- tions. Weight loss of the samples from the corrosion process was estimated by mea- suring the weight change of the samples. Optical microscopy was used to observe sample surfaces before and after immer- sion. Additionally, the samples were cross-sectioned to reveal the corrosion product layers so the corrosion develop- ment sequence could be studied. Corro- sion products were identif ied using scan- ning electron microscopy (SEM) with energ y dispersive spectroscopy (EDS). Potentiodynamic polarization experi- ments were also performed in artif icial seawater with 1, 5, 10, 50, and 100 ppm of residual chlorine to further investigate the chlorination effect on corrosion of Cu-Ni alloys. The dosing level to achieve 100 ppm of residual chlorine simulated the extreme chlorination case (e.g., near the chemical injection point). Polariza- tion curves were drawn with a potential range of ±300 mV at the rate of 10 mV/ min. A saturated calomel electrode was used as a reference electrode. The samples in non-chlorinated sea- water were retrieved after one, three, and six months, and their surfaces were observed. Green corrosion products had peeled off the samples and were on the bottom of the bottles. Because the sur- faces of the samples immersed for six months were more corroded, it was apparent that corrosion developed over time. The authors note that the as-is sam- ples were the least corroded, while the polished samples experienced very active surface corrosion. The polished samples immersed in artif icial seawater, however, did not show amounts of corrosion simi- lar to the samples in the natural seawater. A lthough the salinity of the natural sea- water and artif icial seawater was almost identical, they possessed different levels Information on corrosion control and prevention

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