Resistance to Corrosion
As far as resistance to corrosion, copper and copper alloys are among the best choices for piping. The oxide film that forms on copper and turns it green (like the Statue of Liberty) actually works as a protection against the elements when copper pipes are exposed, and allows for the flow of water through pipes without the worry of buildup. When water of a certain pH level is allowed to flow through copper pipes, ferrous sulfate is often added to speed up the process of building a healthy film. Depending on the velocity of fluids flowing through copper pipes, the pipes may last for decades without falling prey to corrosion from outside materials.
The strength of copper piping is unparalleled by many other materials commonly used. While it is not quite as hard as steel, copper is far less brittle, a property known as ductility. Whereas other strong metals such as steel or iron will crack and break under stress, copper's ductility allows it to bend a little bit when pressure is applied. It is also malleable, which means it will not become deformed under compression. It can be hammered, bent, rolled, and shaped into the exact right pipe size without having to be melted down and poured into a mold. The strength of copper is a huge reason for its widespread use in piping systems.
Copper, particularly when combined with other metals in an alloy, works well in condenser and heat exchanger tubes due to a property known as thermal conductivity. It is unmatched in its ability to hold and carry heat---only much more expensive materials such as silver and diamond have better thermal conductivity than copper. Copper pipes can hold transfer cold and hot temperatures very easily, accounting for its popularity in cooling, refrigeration, and heating systems. Alloys of copper sometimes work even better than copper itself due to their durability.