Boiler Pressures

[macmet]

Are listed boiler pressures always given as gauge pressures? That would seem to make sense to me and I've seen them listed as psig before. However, I've notitced that most of the time pressure is given as just 'psi'. Can i assume that that is psig?

 

[rmw]

Typically, boiler pressures are given as gage pressure. It would be cumbersome to have to do the mental math everytime one looked at an operating gage that wasn't delineated in PSIA in order to arrive at the real operating pressure.

rmw

 

[macmet]

That is sort of what I figured. It would be helpful of spec sheets would specify though... or at least comforting to know for sure and not have to make an assumption.

 

[rmw]

If you are looking at a heat balance on the other hand, expect to see PSIA. If spec sheets are generated from the heat balance, then they might be also.

I thought your question pertained to the guages that the operators used day in, day out for operation.

rmw

 

[macmet]

I was asking about boiler spec sheets. I have quotes on a couple and a few just say 'psi'. I assumed it was gauge since that would be displayed on the actual pressure gauges (like you said) but wanted to know if this is standard notation or if I have to ask each vendor.

 

[rmw]

Do you have any clues? Typically boiler pressures run in whole numbers, using old school numbers, 100psi, 1200psi, 1800psi, 3500psi, etc. If you have any that are 115, 1215, 1815, etc, then they are probably absolute numbers.

rmw

 

[macmet]

This particular one is operating at 160psi with design pressure of 200psi.

I'm fairly certain it's gauge pressure.

 

[NickDubya]

I find it best not to assume anything and query the matter with the supplier, after all you're not the one who neglected to use the correct units in the literature so you shouldn't feel like you 'should' know the answer. The penalty for not checking will be far greater than the occasional twinge of uncertainty you might feel.

The most annoying thing for me is to have to divide the old fashioned pressures mentioned by 14.5 to arrive at a meaningful number ;-)

 

[racookpe1978]

I was going to rather blithely and somewhat smugly ask if it really mattered - but that's wrong. Really wrong - now that I think about it.

Sure. At a boiler pressure of 1200 psi - does it matter if the rating/design criteria is 1200 psig (which is almost certainly the case) or 1215 psia? No, not really.

But you are down lower - much lower. And 15 psi difference on a 160 psix boiler IS a big deal: almost 10% of the working pressure!

Yes. Track down the definition specifically. That 15 psi difference matters on relief valve settings, and it matters in this case on the design spec's.