Which test medium should NEVER be used to pressure test gas piping?

The use of oxygen as a test medium to pressure test gas piping is highly discouraged because of its inherent combustion properties. Oxygen supports and accelerates combustion, making it extremely hazardous if any leaks are present in the gas piping system. In the event of a spark or other ignition source, the presence of oxygen can lead to explosive situations, creating serious safety risks not only for personnel but also for surrounding infrastructure.

In contrast, other mediums such as air, nitrogen, and carbon dioxide, while not ideal in all situations, do not have the same level of risk associated with combustion. Nitrogen, for example, is an inert gas that does not react with the materials typically found in gas piping, making it a safe option for pressure testing. Similarly, air can be used under certain conditions, although it may not provide the precision or control that nitrogen can.

The critical aspect to remember is that safety is the foremost priority when conducting pressure tests, and using oxygen violates the fundamental safety protocols necessary to prevent accidents during such processes.