Which gas may be used to test refrigerant piping?

The correct answer is R-717, which is ammonia. Ammonia is commonly used in various industrial refrigeration systems and is often utilized to test refrigerant piping due to its physical properties and the ability to detect leaks effectively. Using ammonia can help ensure the integrity of the piping system, as it is easier to spot leaks, given its pungent odor.

In testing applications, R-717 can withstand higher pressures compared to many synthetic refrigerants. This characteristic is beneficial when performing pressure tests to identify any weaknesses or defects in the piping. Additionally, ammonia is less expensive than some synthetic refrigerants, making it a cost-effective choice for pressure testing.

Other refrigerants like R-410A, R-134A, and R-22 are primarily used for refrigeration and air conditioning but are not suitable for testing refrigerant piping due to reasons such as expense, specific application usage, or non-detectable leak characteristics.