What should a new piping system not be tested with?

A new piping system should not be tested with oxygen due to the safety risks associated with its use. Oxygen is a highly reactive gas that can support and accelerate combustion. In the presence of fuel and heat, even non-flammable materials can ignite when they are exposed to a high concentration of oxygen. This poses a significant risk in case of any leaks or failures during the testing process, potentially leading to explosions or fires.

Instead, inert gases like nitrogen or less reactive gases like helium are preferred for testing because they do not react chemically with the materials of the piping system and ensure safer testing conditions. Carbon dioxide, although not as reactive as oxygen, also carries some risks and is not commonly used for pressure testing in piping systems. Therefore, oxygen is the most inappropriate choice for testing the integrity of a new piping system.