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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26 DECEMBER 2018 W W W.MATERIALSPERFORMANCE.COM polarization of the cathode coupon exceeded that of the anode coupon, resulting in a "–ve" I CORR value (i.e., ~ –100 µA). 6. Cathodic current was reduced to I CP = 9.5 mA and I CORR was brought back to zero. 7. Another gram of VCI (A) was added to the solution and I CP and I CORR were monitored over 70 h . Both coupon potentials shifted electro- n e ga tiv e , i n di c a ti n g th e y w e re being cathodically polarized. The cathodic polarization of the cath- ode coupon exceeded that of the anode coupon, resulting in a "–ve" I CORR value (i.e., ~ –350 µA). 8. Cathodic current was reduced to I CP = 5.9 mA and I CORR was brought back to zero. 9. A third gram of VCI (A) was added to the solution and I CP and I CORR were monitored over 20 h. Both coupon potentials shifted electronegative, indicating they were being cathodi- cally polarized. The cathodic polar- i zation of th e catho d e c oup on exceeded that of the anode coupon, resulting in a "–ve" I CORR value (i.e., ~ –200 µA). 10. Cathodic current was reduced to I CP = 6.4 mA and I CORR was brought back to zero. 11. At the end of the experiment, the CP system was turned off. Volatile Corrosion Inhibitor (B) Test Results Figure 3 shows the following: 1. Both coupons were bonded and left to stabilize to –795 mV. 2. A macrocell was created by aera- ti on to a chi e v e a st e a dy st at e p ot enti al dif ference of ~40 mV between coupons and an I CORR of ~ 3 6 0 µ A . Th e a e ra t i o n c a u s e d potentials of both coupons to shift electropositive because of cathodic depolarization. 3. The application of CP with I CP = 6.9 mA caused the cathode coupon to cathodically polarize toward the pot ential of th e anode coupon , 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 = 7.9 mA to maintain zero I CORR . 5. One gram of VCI (B) was added to the solution and I CP and I CORR were monitored over 18 h. Both coupon potentials shifted in the electropos- itive direction, indicating they were being anodically polarized. How- ever, the anodic polarization rate of the anode coupon was more than the cathode coupon, resulting in a "–ve" I CORR value (i.e., ~ –68 µA). FIGURE 2 Test results for VCI (A). CATHODIC PROTECTION

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