medium pressure steam

Tony Conner

... "medium" pressure at 80 PSIG - if it falls under one of the pressure piping codes, then it's classed as "pressure piping". For things like steam & compressed air, if the safety valve lifts at anything over 15 PSIG - then it's probably pressure piping. Medium sounds like an ASHRAE designation, and I don't know of any jurisdiction that uses ASHRAE for pressure piping code requirements. It's more for operational things, like sizing lines at a given pressure for a particular load. I'm assuming that 80 is the operating pressure, but the code (the applicable one is probably the ASME B31.1 Power Piping Code) will base the requirements on the safety valve set pressure. There is a specific section on "boiler external piping" (blowdown, feedwater, etc) that has more stringent requirements than the rest of the code. My code book is at the shop, but I believe if the safety valve setting is over 100 PSIG, then most or all of the boiler external piping needs to be a minimum sch 80 seamless if it's threaded. For the blowdown piping (at least), I believe it specifies ONLY steel fittings - and goes on to identify all the ones that are NOT permitted - cast iron, malleable iron, galvanized, bronze, etc.

B31.1 is a big, tedious (and I mean REALLY tedious) book to go through, and there are things that are judgement calls like corrosion/erosion allowances. Those are left to the designer. My guess is that unless you've got a lot of time to commit to this exersize (and a customer willing to pay for it), I'd just go with what the inspector wants. In the end, it may not be as much overkill as you think.

SteveB

steam for dry cleaner

I am quoting a medium pressure steam job (80PSI). I'm very familiar with the layout needed, but was told by a boiler inspector that all the piping needs to be done with forged steel fittings. I have done a few other jobs and only used standard sched 40 pipe and black malleable fittings. Naturally the forged parts cost way more and I don't want to cost my customer any more than needed. Does anyone know? What reference is used? I'm sure it's ASME but what book do I need? Thanks in advance for any help.