The piping design usually dictates the flange face and process dictates the gasket materials. This is where a competent piping design engineer demonstrates his value to the organization. A competent piping design isn’t all derived form a book, it is many books plus experience.
Although there are some recognized specific guidelines by various organizations like the API and others the selection of flange facing is usually based on a company standard such as you have. You depend on the piping system designer to make exception to the plant guidelines for specific applications. These exceptions are normally based on experience, materials engineers, and the process engineers.
In our piping guidelines, specific for every fluid on site, calls out every aspect of a piping system for that fluid. This is the minimum requirement for any piping system and the piping designer is allowed to change the recommended components to the plus side as he sees fit. One can never go under the recommendations without a formal CID procedure.
We have as general rule that RTJ flanges on anything above 500°F, mainly on the steam side, with Class 300 RTJ flanges as the minimum though Class 600 or higher is preferred.
When I mention that design dictates the flange face and gasket one specific example is in our jacketed polymer system where we use raised face Class 2500 flanges, Spiral wound gaskets on the process, 2200 psig @ 600°F and RTJ's Class 300 on all the Therminol Vapor lines, 600°F @ 20 psig, heating media. All flanges in the Therminol system are RTJ’s, no exception.
We use raise face flanges with Spiral Wound gaskets on 24" hot gas lines, 1250°F @ 250 psig and in the same building the generated steam, 650 psig at 750°F uses RTJs’. Steam to the Turbine, 650 psig @ 750°F uses spiral wound gaskets after the Upside Down Valve, startup valve, and RTJs’ back to the source.
We started many years ago to standardize on gasket but we still end up with a myriad of gasket types and styles. Trying to stay with standard flanges no matter what the type is essential if you want improve both the construction and maintenance costs.
If you are working with bolted joints you need to keep an open mind as you will learn something everyday, some good and some bad.
