Economizer and BFW piping design pressure

[coold]

I am designing piping for two fire-tube boilers (58MW each) that are directly coupled to a single furnace without dampers. There is no way to heat one boiler without heating the other.

First question:
The shutoff valves for the single line that feeds both boilers are located upstream of two economizers which act in series (no valves between economizers and boilers). Is this allowed?
Or do I need to locate BFW shutoff valves at the entrance to each boiler?

Second question:
If answer to the first question is yes, what design pressure do I use for the BFW and economizers?
The boilers MAWP = 7200kPag.(1044 psig)
The pump deadhead pressure = 11100kPag.(1610 psig)

I assume that from the final shutoff valve to the first econ header, the design pressure would be the lesser of 7200kPag*1.25 or 7200kPag+225psig (= 8750kPag), and from the first econ header through to the boilers would be 7200kPag.

 

[davefitz]

You first need to explain what boiler code is mandated, or what legal jurisdiction the boilers will operate in .

ASME section I and B31.1 explain the required design presure for those components and the required valve configuration for multiple boilers in parallel.