Bolted joints performance requirements

In the plant experience, even cases of valves on welded lines are recorded where maintenance could not be performed because a relative displacement of the two parts of the valve along the welded pipe axis was required (for example, non-retum valves with a diagonal bolted joint on the valve body). 

Bolted joints are subject to cychc changes in forces that want to pull the joints apart. That s why all threads in a stud and nut are required to assure full performance of the connection. Missing threads put excessive stress on the remaining threads which can lead to their pressure failure. 

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