What must be done to most socket welded valves before welding them in place?

When preparing socket welded valves for welding, it is essential to open the valve completely. This practice is necessary to prevent damage to the valve during the welding process. By opening the valve fully, the internal mechanisms are not subjected to the extreme heat generated by welding, which could warp or distort the valve components.

Additionally, having the valve open allows for any potential expansion or contraction of materials as they heat up or cool down, reducing the risk of creating stresses that could lead to failure once the valve is in service.

Therefore, opening the valve completely is a critical step in ensuring that the valve maintains its integrity and will function properly after it has been welded into place.