What medium must be used for testing all gas piping?

The correct choice for testing all gas piping is air pressure. Testing gas piping with air pressure is crucial because air is non-toxic and does not pose the same risks as other fluids if there is a leak. This method allows for the detection of leaks by introducing air into the system and monitoring for any drop in pressure over time, a clear indicator of a potential leak.

Unlike water, which can introduce risks such as corrosion or water damage to the gas piping and fittings, air does not have this drawback. Hydraulic fluid, while it can be used in other applications, is not suitable for gas piping tests due to potential contamination and hazards if it interacts with gas. Natural gas itself is not appropriate for testing due to the risks involved, as it is flammable and could lead to dangerous situations if leaks occur during testing.

Using air pressure is a widely accepted industry practice because it ensures the integrity of the piping system without introducing additional safety risks. This practice conforms with safety standards and regulations concerning gas piping maintenance and installation.