Which type of coupling is prohibited in concealed gas piping?

Compression couplings are prohibited in concealed gas piping primarily because they do not provide a permanent joint that is as secure as other types of connections. Concealed gas piping is typically installed within walls or other inaccessible areas, making it crucial that any joints are highly reliable and less prone to leaks. Compression fittings rely on a mechanical grip and can be more susceptible to loosening over time, especially under thermal expansion, vibration, or other stresses.

The use of welded, flanged, or threaded couplings is acceptable for concealed gas piping because these methods create more permanent and robust connections. Welded couplings form a continuous joint that is free from the potential looseness associated with compression fittings. Flanged and threaded connections, when installed properly, can also ensure a strong and gas-tight seal that is suitable for concealed applications. This makes them safer and better suited for gas systems where any leakage could pose significant hazards.