Lug Type Butterfly Valves

Using threaded studs on threaded lugged butterfly valves is NOT a wise way to go! To do this you need a "break out spool" up against the valve or pretty close to it. Because there is no "easy way" to remove the studs to be able to remove the valve by just "dropping it out".
What we normally do in my area is used threaded hex head bolts, ones that thread half way into the threaded lug section of the valve. That way we can use butterfly valves as block valves on tanks and in locations that having break out spools is not appropriate. As I view this you need to remember your piping design configurations is for the operators of the facility, and making maintenance an easy operation is key to a "good design".