ANS:B - marine structure & underground pipelines.

Cathodic protection is widely used in controlling corrosion in marine structures and underground pipelines. Marine structures, such as offshore platforms, ships, piers, and docks, are constantly exposed to corrosive environments due to the presence of seawater, which is highly conductive and accelerates the corrosion process. Cathodic protection is commonly employed in these structures to mitigate corrosion and extend their service life. Additionally, underground pipelines, such as those used for transporting oil, gas, water, or sewage, are also susceptible to corrosion, especially in environments where moisture, soil conditions, and stray currents can promote corrosion. Cathodic protection systems are extensively utilized to protect underground pipelines from corrosion and prevent leaks or failures. While cathodic protection can also be applied to high-pressure vessels to mitigate corrosion, it is more commonly used in marine structures and underground pipelines due to the prevalent corrosive conditions in these environments and the effectiveness of cathodic protection systems in controlling corrosion.