spectacle and butterfly valve

I have a 20" 600# gas line--outlet of the high pressure gas arm--P&ID shows Spectacle Blind + Butterfly valve connected together.

I read the above post for spec. blind, do you mean I should follow the same logic & add another pair of flaneges seperately for spade in my case of spade as well?

I'm afraid I can't agree with my colleague on this one. ..."WHY" would/do you put in a spec. blind ...bottom-line SAFETY ...you don't want that valve opened for any reason during certain operations, hence the spec. (or paddle) blind. SO IF someone broke the valve trying to open it against the blind, then the blind is doing its job! ...YES you could add another set of flanges up or down stream to deal with the blind but that kind of flies in the face of "good economic design" ...adding components to a piping system that are unnecessary (and at 20"-600# the cost of those components quickly rises). …My $0.02!

Thanks for your inputs, I think there is surely a chance of interface between the blind (inside) & the valve internals while operation so we need a seperation & hence the additional pair of flanges which are reasonable (not a wish it is a need).

If you are so worried that "somebody" would try to operate a butterfly valve with a closed spec blind and the valve disk might "touch" the blind, then have the valve chained in position (closed)! A length of chain is far cheaper then adding an additional pair of 20"-600# flanges! ...Plus I have to add, I personally have never seen a butterfly, used with a spec blind, and have a set of "remote flange set" to deal with the blind. ...and I seen a lot of butterfly valves!