Which type of connection is generally considered illegal?

Flexible hoses are typically deemed unsuitable for permanent connections in gas piping systems due to their inherent characteristics. These hoses can be more susceptible to wear and tear, making them prone to leaks over time. Gas systems demand a high level of safety and integrity, as leaks can lead to dangerous situations, including explosions or fire hazards. Therefore, using flexible hoses for permanent connections undermines the reliability and safety standards that must be upheld in gas installations.

In contrast, rigid steel piping, polyethylene gas pipes, and soldered copper tubes are all materials commonly accepted in gas piping systems when installed according to the appropriate codes and standards. Rigid steel piping is valued for its robustness, polyethylene offers chemical resistance and flexibility where needed, and soldered copper tubes can provide solid, durable connections. These materials are designed to withstand the pressures and conditions associated with gas transport, making them reliable choices for installation.