Which material is commonly used for water and instrument air piping in power plants?

The correct choice for commonly used material for water and instrument air piping in power plants is copper.

Copper is favored in these applications due to its excellent corrosion resistance, which is crucial for maintaining the integrity of piping systems that carry water and instrument air. It also has good thermal conductivity and is relatively easy to work with, allowing for flexibility in installation and repair. Additionally, copper's inherent antimicrobial properties make it a suitable option for systems where hygiene and the prevention of bacterial growth are important.

In contrast, while galvanized steel, cast iron, and bronze might be used in certain situations, they are not as prevalent for these specific applications. Galvanized steel can be subject to corrosion over time, especially in water systems, which could lead to issues with scaling and reduced flow. Cast iron is heavier and often used for drainage or heavy-load applications rather than for water supply or instrument air. Bronze can be good for specific applications due to its resistance to corrosion, but it is generally more expensive and less common for larger scale piping compared to copper.