The main disadvantage of using magnesium anodes is:

Magnesium anodes are often preferred for their high driving potential in cathodic protection systems, particularly in freshwater and soil applications. However, one significant disadvantage is their shorter lifespan compared to other anode materials like zinc or aluminum.

The basic reason for the shorter lifespan is that magnesium has a higher electrochemical potential which can lead to a rapid depletion rate as it corrodes more quickly when used in certain conditions. This rapid consumption can limit the duration of effective protection, especially in harsh environments where aggressive electrolytes or high currents are present. Consequently, the need for more frequent replacements can make them less practical in some long-term applications.

This characteristic of magnesium not only affects the operational efficiency of the cathodic protection system but also can increase the overall maintenance and operational costs involved in replacing the anodes more frequently than others with longer lifespans.