What is a common disadvantage of using magnesium anodes?

The limited lifespan of magnesium anodes is a significant disadvantage due to their anodic dissolution process, which occurs when they corrode to protect the surrounding metal structures from electrolysis. This sacrificial action is effective in cathodic protection; however, it also means that magnesium anodes wear out relatively quickly compared to other anode materials such as zinc or aluminum. Depending on environmental conditions, such as soil resistivity and moisture content, magnesium anodes may need to be replaced more frequently to maintain effective cathodic protection.

In contrast, other choices present factors that, while they may have importance, do not typically characterize magnesium anodes in the same way. For instance, the high cost is generally not seen as a common disadvantage when compared to the effectiveness of magnesium anodes in certain applications. In terms of seawater compatibility, magnesium can be less effective in that environment, but it is not inherently incompatible. Finally, while maintenance is necessary for any cathodic protection system, the level of maintenance required for magnesium anodes is not typically considered high compared to other systems. Thus, the limited lifespan stands out as the primary disadvantage in the context of magnesium anodes used for cathodic protection.