What gas should a new piping system NOT be tested with?

A new piping system should never be tested with oxygen due to the significant safety hazards it presents. Oxygen is a highly reactive gas that can support combustion and increase the risk of fires and explosions, especially in the presence of flammable materials or sources of ignition. Testing with oxygen can create a dangerous environment, particularly if any components of the piping system contain residues or materials that could ignite in high-oxygen conditions.

In contrast, nitrogen is commonly used for pressure testing because it is inert and does not support combustion, making it a safe choice for ensuring system integrity. Hydrogen may be used in specialized applications but often requires specific safety considerations due to its flammability. Natural gas is typically used in operational systems rather than for testing purposes, as test pressures and conditions differ from normal operating conditions. Therefore, oxygen stands out as the improper choice for testing a new piping system due to its inherently dangerous properties.