Materials Performance Supplements

CORTEC 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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ples in boiling water are shown in Figures 1 and 3. Corrosion rates were monitored for 700 h of continuous immersion at boiling temperature. The corrosion rate was 5.3 mpy (determined from weight loss measurement) for the steam environment with no inhibitor. When 50 mg/L of VCI was added, the corro- sion rate decreased to 1.94 mpy and for 100 mg/L VCI addition, corrosion rate dropped to 1.36 mpy. The addition of 200 mg/L VCI decreased the corrosion rate to 0.97 mpy, while the addition of 500 mg/L resulted in a very low corrosion rate of 0.37 mpy. The corrosion rates for the solutions with differ- ent amounts of VCI had become steady at roughly 120 h (corrosion rate showed a log- arithmic rate) while the nonprotected steel samples showed an increasing trend for the corrosion rate. From observation, the non- protected steel samples (control-reference) showed heavy corrosion attack with hema- tite (Fe 2 O 3 ) (brown color solution, an indica- tion of heavy rust formation). To the contrary, the presence of VCI in low dosages (50 to 100 mg/L addition) resulted in an oxide forma- tion of magnetite (Fe 3 O 4 ) and no significant change in solution color was observed. At higher dosages (200 to 500 mg/L), no color change was observed on the steel samples or their solutions, which correlates with the (measured) low corrosion rates. Elevated temperature corrosion tests on CS pipe samples in the steam/water loop with VCI and without inhibitor (control ref- erence) were conducted using the electric boiler steam/water in a closed loop system that could circulate and maintain hot steam at 90 psi and 118 °C. The control reference test (without inhibitor addition) was con- ducted for 1,100 h and the corrosion rate was monitored using ER techniques. Figure 4 shows the corrosion rate over time for the reference sample without using any water treatment or inhibitor. The average corrosion rate was measured to be 8.2 to 8.9 mpy. After 1,100 h, 500 mg/L of VCI was injected into the closed loop system. This addition resulted in a significant drop in the corrosion rate to 0.72 mpy. This indicates that the VCI had successfully retarded the corrosion reaction and managed to stabilize formation of protective magnetite on the internal surfaces. The corrosion test in the steam/water closed loop was continued for 1,900 h in total (800 h beyond introduction of inhibitor to the closed loop system) and the dosage of inhibitor was maintained at 100 mg/L. The ER probe showed a steady corro- sion rate of 1.30 mpy. This is a very impres- sive result, indicating that a corroding closed loop steam/water system can be success- fully recovered by introduction of inhibitor treatment to lower its corrosion rate to an acceptable level. Figure 5 also shows the cor- rosion rate over time for the corrosion test in the steam/water closed loop with 100 mg/L VCI addition for 2,200 h. The average corro- sion rate was measured at 1.09 to 1.24 mpy. During the boiler drainage (blowout), no sign of any rust formation in the discharged water was observed. Figure 5 shows the comparison of the ER probes that were used to monitor corro- sion rate during these investigations. Figure 6 shows the comparison of corrosion rate measurements for the inhibitor treated loop and control reference after 2,200 h corrosion in the hot steam/water closed loop. The con- trol probe showed heavy rust formation on its surface, while the 100 mg/L VCI ER probe showed a thin layer of black magnetite and relatively clean surfaces. Figure 6 shows the section of the closed loop steel pipe after corrosion tests. Comparison of these inter- nal surfaces show that the control pipes internal surfaces are covered by hematite (rust formation due to their high corrosion rate) while the test conducted with corro- sion inhibitor VCI is mainly covered by a thin magnetite oxide. XPS analyses were conducted on the inter- nal surfaces of both the control sample and inhibitor-treated steel pipe. Results are shown in Figure 7. High-resolution XPS analysis was also conducted on both the control and inhib- itor-treated steel pipes (Figure 8). The nature of the surface oxide was compared after 2.0 nm of the top surface deposits were etched to remove ambient changes or accidental sur- face contamination. XPS data showed that the oxide on the internal surface of the control sample (no inhibitor) is hematite, Fe 2p, with binding energy 710.4 eV, while the oxide on the Amine-Based Vapor Phase Corrosion Inhibitor Alternatives to Hydrazine for Steam-Generating Systems and Power Plants FIGURE 4 Comparison of corrosion rate measurements of the inhibitor treated loop and control test after 2,200 h corrosion test in hot steam/water closed loop. FIGURE 5 Comparison of corrosion ER probe surface condition of the inhibitor treated loop and control test after 2,200 h corrosion test in hot steam/water closed loop. 13 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2018

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