My submission is as follows:-
Stelliting is used for getting harder seating surfaces.
ENP is used as cost saving to substitute solid stainless balls of ball valve by CS-ENP balls.
Piping Elders,
Agreed, there is no justification for 100 mm requirement.
Maximum movement of 100mm is a conservative number. If one restricts axial movement to 100mm, no additional precaution is required.
I had also come across higher values with longer shoes or off center shoes. But these...