Materials Performance

NOV 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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51 MATERIALS PERFORMANCE: VOL. 57, NO. 11 NOVEMBER 2018 Electrical Concrete Resistance Figure 5 shows variations of mean R data in the tidal zone in terms of sensor type and structure orientation. As expected, R tends to be sensitive to moisture, where sensors at the lower eleva- tions exhibited lower R than those at the higher elevations. For example, the sensors placed in the atmospheric zone showed ~10 tim es great er R than those in th e splash, tidal, and submerged zones. One exception to this trend is the R of a single pro b e sen s or in th e subm erged zon e, which was the greatest. Since the unusu- ally high R data were collected from a sin- gle sensor, the reliability of this sensor's data is questionable. The single probe sensors yielded much higher R than the multi-probe ones due to their different shapes. It is apparent that b oth sens or typ e s showed lower R in warmer seasons ( June and September) than in colder seasons (December and March), but the sea-facing side and lake- facing side probes exhibited similar R under identical conditions. Macro-Cell Corrosion Current and Corrosion Rate Figure 6 shows how mean I macro and CR data in the tidal zone varied during three years of monitoring. Although none of the sensors exhibited active corrosion accompanied by very high I macro , the multi-probe sensors in the sub- merged and tidal zones exhibited about 10 times greater mean I macro than those in the splash and atmospheric zones. Increased c on cret e re si st an c e in dri er c on cret e should be, at least partially, responsible for low I macro of the latter zones. The sea side multi-prob e sensors in th e ti d al zon e started producing higher mean I macro on the 10th measurement and onward . If this trend holds in the future, it may indicate that corrosion initiates in the tidal zone. The lake side constituted a much less cor- ro sive env ironm ent than th e sea si d e because the former exhibited only 1% of the mean I macro observed in the latter. One observation made with the multi- probe sensors is that R and the correspond- ing I macro measured between each of the four FIGURE 5 Variations of mean concrete resistance with time in the tidal zone. FIGURE 6 Variations of mean macro-cell corrosion currents and CRs with time in the tidal zone. macro-anode probes and the macro-cath- ode did not follow a theoretical relation- ship among distance of the probes from the concrete surface, R, and I macro . Mean C R s of th e lake side sensors remained near zero, regardless of time and exposure zone, whereas sea side sensors in the submerged and tidal zones exhibited higher mean CRs than those in the splash and atmospheric zones. The mean CR in the tidal zone of the sea side gradually decreased with time. The single sensor in the submerged zone produced erroneous CR data from the 8th measurement. Like th e malfunctionin g MnO 2 , thi s sens or might have deteriorated and failed to func- tion properly. Corrosion Monitoring of World's Largest Tidal Power Plant

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