Where shall aluminum alloy pipe not be used according to code?

The correct choice highlights that aluminum alloy pipe should not be used in exterior and underground locations according to code. This is primarily because aluminum alloys can be susceptible to corrosion when exposed to the environmental elements or when buried in the ground.

In outdoor settings, moisture, temperature fluctuations, and other environmental factors can lead to the degradation of aluminum over time. Similarly, when aluminum pipes are buried underground, they may come into contact with moisture and soil chemistry that can further compromise the integrity of the material, increasing the risk of leaks and failures.

Therefore, building codes and standards often restrict the use of aluminum pipe in these specific environments to ensure the longevity and safety of plumbing systems. This is especially vital in residential and light commercial applications, where the reliability of the systems is crucial for proper function and safety. Proper materials selection is essential in maintaining the integrity of both the plumbing system and the structure overall.