Which brazing rods should not be used for natural gas/propane due to their reaction with sulfur?

Brazing rods that contain phosphorus should not be used for natural gas or propane applications primarily due to their reactivity with sulfur. When phosphorus is exposed to high-temperature environments, especially in the presence of combustion gases that may contain sulfur compounds, it can form phosphides. These phosphides can create brittle and weak joints in the brazed connections, leading to potential failure.

Using phosphorus-containing brazing materials can result in unreliable seals in gas lines that are critical for safety. In contrast, the other materials listed, such as copper, aluminum, and silver, do not pose the same risks regarding sulfur reactions, making them more appropriate choices for brazing applications involving natural gas and propane. Copper is widely used in many applications due to its good thermal conductivity and strength, while silver is often preferred for high-strength requirements and corrosion resistance. Aluminum is used in some specific applications where appropriate; however, its use is typically more specialized compared to copper and silver.

Overall, understanding the chemical interactions of brazing materials with sulfur helps in making informed choices that ensure safe and durable gas connections in various installations.