What should NOT be used to test piping equipment or systems for leaks?

The use of flame is not appropriate for testing piping equipment or systems for leaks due to the significant safety hazards it presents. When testing for leaks, particularly in systems that may contain flammable gases or liquids, introducing a flame can lead to dangerous fires or explosions. Flame can ignite any leaked flammable substances, creating an immediate hazard to personnel and the surrounding environment.

In contrast, other methods such as using compressed air, water, or a soap solution are commonly employed for leak testing. Compressed air can provide a way to pressurize the system and observe for leaks, while water is often used in a hydrostatic test, where pressure is applied through liquid. A soap solution can indicate leaks through bubble formation at points where gas escapes. These alternatives are much safer for verifying the integrity of piping equipment or systems.