Which type of fittings should not be used for concealed gas piping connections?

Concealed gas piping connections should not utilize compression couplings and unions due to safety and reliability concerns. These types of fittings are designed for easy assembly and disassembly, which can create the potential for leaks when they are not accessible for regular inspection. In concealed applications, where joints may not be seen or easily accessed, the risk of undetected gas leaks increases significantly.

Compression fittings are typically more vulnerable to movement and stress, which can cause the fittings to loosen over time, especially in environments where vibration or thermal expansion is common. This potential for failure makes them unsuitable for concealed installations, where a secure and leak-free connection is critical for safety.

In contrast, welded joints, pipe fittings, and screwed joints provide a more permanent and secure means of joining pipes, making them more reliable choices for concealed applications. These options, when properly installed, create a solid bond that minimizes the risk of leaks, thus ensuring safer operation of the gas piping system.