In one of refinery revamp , both hot air and steam service, the piping spec calls out valves 3" and above with no exception flanged gate valve.The service is 500F - 800 F and 40 psi. Class 150.I wondered. I am thinking of butt-weld would be superior to flange considering from weight, leak path or reliability.I am also thinking of ball valve or butterfly valve (over 8")as of better block valve options for these two services than gate valve. Is gate cheaper?"the piping spec calls out"....If this is a fact then why are you questioning it.a) Normally the assigned Piping Material Engineer would do a lot of study to determine the best (technical vs. cost) valve and other material.b) The piping Specs are then sent to the Client for review and approval. I assume this was done.c) Piping design is responsible for routing the pipe and making the fabrication and installation drawings using the material in the specs.d) The purchasing department is responsible for buying what is in the spec. in the quantities that are on the Material Summary. e) Construction is responsible for installing what is on the drawings with the material from the specs.

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