## 3 Experimental Results and Discussions
The coupled potential and the OCP of the electrodes had a slight reduction after the inhibitor was added for nearly \(36\) h. The small decrease of the OCP may be caused by the decrease in the pH of the test solution. The negative potential transients reappeared which can be seen from Figure 3d. The transient frequency was lower than that shown in Figure 3b. ### Measurement Results of the Coupled Potential and the OCP  
More intuitive corrosion processes and anodic transients can be reflected by the galvanic current flowing through each electrode. It is seen from Figure 4a, the anodic and cathodic currents were all close to zero at the initial period. With the sudden decrease of the coupled potential. The WE 3 became the only anode and the anodic current of WE 3 which had an intensive increase to nearly \(6\times 10^{-5}\) A. After the introduction of the inhibitor, both anodic current and cathodic current recovered to a small order of magnitude close to \(10^{-6}\) A.  
Figure 3: Time dependence of the coupled potential (**a**), the coupled potential at \(0\) h to \(28\) h (**b**), the coupled potential at \(35\) h to \(61\) h (**c**), and the coupled potential at \(61\) h to \(110\) h (**d**). Figure 4: Time dependence of the galvanic currents among the electrodes (**a**), the galvanic currents at 0 h to 28 h (**b**), the galvanic currents at 35 h to 61 h (**c**), and the galvanic currents at 61 h to 110 h (**d**). More detailed information of the currents distribution at a different time can be seen from Figure 4b-d. As shown in Figure 4b, during the initial 28 h test, WE 2, WE 3, WE 4, WE 5, and WE 6 presented as anodic areas. The anodic currents of WE 2 and WE 4 were very small. WE 3 and WE 5 performed as major anodic areas. The maximum anodic current \(I_{\mathrm{max}}\) was near 8 \(\times\) 10\({}^{-8}\) A and the maximum corrosion rate CR\({}_{\mathrm{max}}\) caused by the anodic current can be calculated as [41]:  
\[\mathrm{CR}_{\mathrm{max}}=I_{\mathrm{max}}\mathrm{M}/A\rho\mathrm{r}\mathrm{F} \tag{1}\]  
where M is the molecular weight of the metal, \(A\) is the working surface area of the electrode, \(\rho\) is the mass density of metal, \(n\) is valence, and F is Faraday's constant. The max corrosion rate caused by the galvanic current was 9.42 \(\times\) 10\({}^{-4}\) mm/a. Note that CR\({}_{\mathrm{max}}\) is the corrosion rate caused by the anodic galvanic current. It cannot represent the real corrosion rate of the electrode. Only when most of the metal loss was induced by the galvanic current, the CR\({}_{\mathrm{max}}\) can be considered as the real corrosion rate of the electrode. It can be found that the max corrosion rate caused by the anodic current was quite low which indicated the galvanic current nearly did not influence the damage of the passive film. However, through the comparison of the OCP and galvanic currents, it can be deduced that the preferential corrosion was potentially occurring on the WM zone and HAZ 1. Frequent current spikes also can be observed from Figure 4b which suggests metastable corrosion processes on the surfaces of the electrodes. It can be seen from Figure 4c that when WE 3 became the stable anodic area, the other electrodes soon transferred to the cathodic area. The maximum anodic current reached nearly 7 \(\times\) 10\({}^{-5}\) A which means the CR\({}_{\mathrm{max}}\) was 0.82 mm/a. The CR\({}_{\mathrm{max}}\) was nearly 4 times higher than the general corrosion rate measured by the LPR method in pore solution with 3.5% NaCl added [34]. In this situation, the anodic galvanic current is the main cause of the localized corrosion and CR\({}_{\mathrm{max}}\) can be used as the highest localized penetration rate of the electrode. It is known that localized corrosion is the most dangerous corrosion pattern for reinforcements. The corrosion rate of 0.82 mm/a will cause the soon failure of the structure.