In which situation is it most crucial to open a valve completely before welding?

Opening a valve completely before welding is particularly crucial when using socket welded valves, which is why this response is the most accurate. This procedure ensures that the valve is not damaged during the welding process and enables proper access to the internal structure of the valve.

Socket welded valves often have a cylindrical socket where the pipe fits. If the valve is not fully opened during the welding process, excessive heat and shrinkage can occur, leading to warping or unwanted stresses in the valve. This can compromise the integrity of the valve seals and affect the overall functionality.

Moreover, opening the valve completely allows for better heat dissipation during welding, reduces the likelihood of burns and internal distortion, and provides a clear passage for any contaminants that may be released from the system, facilitating a cleaner welding environment.

In contrast, while it’s important to consider valve operation in the other situations listed, the critical nature of fully opening a socket welded valve before welding focuses on structural integrity and performance, making it the most essential choice in this context.