Materials Performance

DEC 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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27 MATERIALS PERFORMANCE: VOL. 57, NO. 12 DECEMBER 2018 6. Cathodic current was reduced to I CP = 7.5 mA and I CORR was brought back to zero. 7. Another gram of VCI (B) was added to the solution and I CP and I CORR were monitored over 20 h . Both coupons were anodically polarized. Howe ver, th e polari zation hap- pened for both coupons at the same rate, resulting in a minimal differ- ence between the potential of the cathode coupon and the anode, which consequently resulted in a ver y small "+ve" I CORR value (i .e., ~12 µA). 8. CP current was kept at I CP = 7.7 mA as I CORR remained at zero. 9. A third gram of VCI (B) was added to the solution and I CP and I CORR were monitored over 22 h. Like the behavior in step 7, both coupons were anodically polarized at the same rate, resulting in a minimal difference in potential and hence I CORR remained around zero value. 10. CP current was kept at I CP = 7.7 mA and I CORR at zero. At the end of the experiment, the CP system was turned off. Volatile Corrosion Inhibitor (C) Test Results Figure 4 shows the following: 1. Both coupons were bonded and left to stabilize to ~ –790 mV. 2. A macrocell was created by aeration to achieve a steady state potential difference of ~30 mV between cou- pons and an I CORR of ~300 µA. The aeration caused potentials of both coupons to shift electropositive because of cathodic depolarization. 3. The application of CP with I CP = 5.5 mA caused the cathode coupon to cathodically polarize toward the pot ential of th e anode coupon , FIGURE 3 Test results for VCI (B). thereby reducing I CORR to 0 µA and effectively mitigating the macro- cell. CP current was left to stabilize for 20 h. 4. CP current was adjusted to I CP = 5.7 mA to maintain zero I CORR . 5. One gram of VCI (C) was added to the solution and I CP and I CORR were monitored over 20 h. The inhibitor didn't seem to have any cathodic or anodic polarization effect. How- ever, it resulted in a small "+ve" I CORR value (i.e., ~ +20 µA). 6. Cathodic current was increased to I CP = 6 mA and I CORR was brought back to zero. 7. Another one gram of VCI (C) was added to the solution and I CP and I CORR were monitored over 20 h. The inhibitor continued not to show any anodic or cathodic polarization and resulted in a small "+ve" I CORR value (i.e., ~ +25 µA). Effect of Volatile Corrosion Inhibitors on Cathodic Protection

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