When referencing E2, what is the minimum shift for full cathodic protection?

In the context of cathodic protection, particularly when referencing the E2 potential, the minimum shift required for effective full cathodic protection is indeed -200 mV. This threshold is significant because it indicates a shift in potential that is necessary to ensure that the structure being protected has sufficient cathodic polarization to prevent corrosion.

The -200 mV shift is derived from the electrochemical behavior of the metal being protected. It represents a change from the initial open circuit potential toward a more negative potential, which is indicative of a protected state. When this shift is achieved, it reflects that the cathodic protection system is sufficiently driving down the potential of the metal surface to mitigate corrosion processes, effectively pushing the metal into a more noble electrochemical state.

In marine environments, where structures often face accelerated corrosion due to saltwater and other factors, achieving this level of cathodic protection is crucial for extending the life of metallic components. The -200 mV benchmark helps in assessing the adequacy of the protection being applied, ensuring that any protective measures are not only in place but are functioning effectively.