Which material is seldom used to make a pressure vessel but is common in heat exchanger tubes?

The correct choice is that copper alloys are seldom used to make pressure vessels but are commonly found in heat exchanger tubes. This is primarily due to their excellent thermal conductivity, which makes them ideal for applications where efficient heat transfer is paramount, such as in heat exchangers.

In pressure vessels, the material needs to withstand high pressures and is typically selected based on its strength characteristics and ability to deal with the mechanical and thermal stresses involved. Copper alloys, while effective in heat exchange applications, may not have the strength or ductility needed for high-pressure contexts, which is why they are not widely used for pressure vessels.

In contrast, steel is often favored for pressure vessels due to its high tensile strength and ability to be fabricated into thick-walled designs. Plastic can be effective in applications with lower pressure and temperature requirements but is generally not suitable for high-pressure uses. Aluminum is lightweight and corrosion-resistant, making it suitable for certain applications, but it also does not possess the same strength characteristics as steel when it comes to pressure vessels.