Which method of joined steel piping is NOT acceptable for natural gas systems?

Flared fittings are typically not acceptable for use in natural gas systems primarily due to safety and integrity concerns. These fittings rely on a conical shape to create a seal when the two pieces of tubing are joined together. While this type of connection is effective in some applications, it could pose risks in a natural gas setting.

Natural gas systems require joints that can withstand high-pressure conditions and resist leaks. Flared fittings can be more prone to failure under the extreme conditions that can occur in gas systems, especially if not installed or maintained properly. This increases the likelihood of gas leaks, which can be dangerous and potentially lead to catastrophic events.

In contrast, soldered, welded, and threaded fittings provide more robust connections suited for the higher pressure and safety needs of natural gas installations. Soldered fittings, while traditionally used in plumbing, should be avoided as well in gas applications due to the potential for solder melting under high heat. Welded and threaded fittings offer secure connections that comply with safety codes and industry standards for gas handling. Therefore, understanding the appropriateness and safety of different types of fittings is crucial for ensuring the integrity of natural gas systems.