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[Alfreedo]

I'm working in an ethylene plant that has a vessel that takes filtered quench water with boiler feedwater makeup level control and uses a series of high pressure steam fed reboilers to boil the quench / bfw mixture to generate a lower pressure steam which is mixed with the ethane cracking furnace feed.  In this plant, the main vessel, all the reboilers and superheater are built to ASME Section VIII and the overpressure protection system is also all compliant with Section VIII code.  To me, this system looks like a classic unfired boiler and while the code says the vessels themselves can be built to section VIII, I believe the overpressure protection system must be built to Section I (no block valves unless they are Section I compliant switching valves, 3% overpressure rules, etc...).  The low pressure steam runs at about 800 kPag.   Am I out to lunch?  We are possibly replacing one of the switching valves.  The vendor is saying that they have to be Section I because its on steam service period.  I don't think that is necessarily the case if the steam PSV wasn't part of a boiler system, but in this case, I believe this to be an unfired boiler which should have Section 1 compliant OPP.    Am I out to lunch? Anyone have any experience with these?