Which of the following are approved cathodic protection methodologies?

The approved cathodic protection methodologies include both sacrificial anodes and impressed current systems.

Sacrificial anodes function by providing a more anodic (less noble) metal that corrodes instead of the protected metal, thereby extending the lifespan and integrity of underground storage tanks or pipelines. When the sacrificial anode is electrically connected to the structure, it serves to protect the metal from corrosion by becoming the anode in the electrochemical reaction.

On the other hand, impressed current systems utilize an external power source to provide direct current to the structure that needs protection. This method is often more effective in high resistivity environments or where large areas need to be protected, as it allows for greater control over the cathodic protection process.

The combination of these two methodologies ensures robust protection against corrosion, making this answer the most comprehensive choice for approved cathodic protection methods. The other options do not fully encompass the accepted techniques used for this purpose. Chemical barriers and coatings, as well as plastic linings, serve as corrosion prevention methods but are not classified as cathodic protection methodologies.