propensity to standardize on 150 psig / 150 F nameplate design
propensity to standardize on 150 psig / 150 F nameplate design
(OP)
I have run into a situation where some little pressure vessels (vendor supplied) in warm water service are nameplate-rated to 150 psig / 150 F. The trouble is, the water might sometimes be closer to 180 F (i.e., "hot", as opposed to "warm").
What is, in my opinion, a disproportionately large controversy has erupted over this, both for cases where existing vessels in service nameplated to 150 / 150 "...cannot possibly under any acceptable circumstance..." be exposed to 150 / 180, and for new vessels of the same make and model now having to be re-designed and re-registered with the associated impacts on delivery and cost.
I don't have an issue with doing what needs doing in order to stay within nameplate constraints and fully meeting Code, even if it means buying new little vessels that won't be available until 5 months from now. My question is more along the lines of this...
When I read ASME Section II Part D Sub-Part A Table 1-A for the materials in question, the allowable stress values in tension are the same at 200 F as they are at 150 F. If so, and if there are no other weaker, limiting components to be concerned about, why would vendors standardize on 150 / 150 as opposed to 150 / 200 on the nameplate rating? There must be a reason they do it that I don't know about.
Am I missing something obvious here?
What is, in my opinion, a disproportionately large controversy has erupted over this, both for cases where existing vessels in service nameplated to 150 / 150 "...cannot possibly under any acceptable circumstance..." be exposed to 150 / 180, and for new vessels of the same make and model now having to be re-designed and re-registered with the associated impacts on delivery and cost.
I don't have an issue with doing what needs doing in order to stay within nameplate constraints and fully meeting Code, even if it means buying new little vessels that won't be available until 5 months from now. My question is more along the lines of this...
When I read ASME Section II Part D Sub-Part A Table 1-A for the materials in question, the allowable stress values in tension are the same at 200 F as they are at 150 F. If so, and if there are no other weaker, limiting components to be concerned about, why would vendors standardize on 150 / 150 as opposed to 150 / 200 on the nameplate rating? There must be a reason they do it that I don't know about.
Am I missing something obvious here?
Regards,
SNORGY.





RE: propensity to standardize on 150 psig / 150 F nameplate design
RE: propensity to standardize on 150 psig / 150 F nameplate design
It's actually the vessel vendor that appears to have standardized on 150 / 150, not us. I just would like to know why.
The relief valve is outside of vendor scope of design and supply (i.e., it is in our scope of design and supply), so that's not the problem.
I am just curious why a vendor would standardize on a nameplate for 150 / 150, when it seems to me that for no extra effort, cost or complication, it could be 150 / 180.
Regards,
SNORGY.
RE: propensity to standardize on 150 psig / 150 F nameplate design
RE: propensity to standardize on 150 psig / 150 F nameplate design
RE: propensity to standardize on 150 psig / 150 F nameplate design
Agreed that this doesn't make any sense...
RE: propensity to standardize on 150 psig / 150 F nameplate design
From an engineering standpoint I've never designed anything made of steel that was rated at 150F that I wouldn't be perfectly happy rating at 200F with the same materials and the same manufacturing processes.
David
RE: propensity to standardize on 150 psig / 150 F nameplate design
its an easy job.
RE: propensity to standardize on 150 psig / 150 F nameplate design
I was looking to see if I could find something in the Code(s), in one of the design equations or clauses that are not common knowledge to non-specialists like me, where the temperature would have an effect on some factor or other that would change the design. At a rather high level, I rationalized (thus far) that if the Code allowables were the same, what would change in the equations that would make 150 F OK and 200 F not OK?
It was a "mixed signals" phenomenon. We were being asked to buy something standard "...exactly like one of these...", and subsequently we bought "...exactly one of those...", which diverted our attention away from the scrtuiny of minutiae in any detailed bid evaluation. We ended up with "hot water, warm filter, oops, D'OH!".
A nameplate for 150 / 200, as opposed to 150 / 150, would have saved a lot of what I consider to be needless uproar. It's not an HF filter in an alkylation plant.
To me, it's like zdas04 stated, in not so many words: once upon a time, somebody knew the reason, and nobody has questioned it since.
Regards,
SNORGY.
RE: propensity to standardize on 150 psig / 150 F nameplate design
A little calculating showed that this particular Hx could have been rated at 200 psig & Full Vac, at a MAWT of 400°F. That's a LOT of temp & pressure to leave "laying on the table" when ordering a new vessel.
RE: propensity to standardize on 150 psig / 150 F nameplate design
These are in Canada, requiring CRN registration.
If a new nameplate is required, then it also requires new design registration (by Vendor), which costs them time and money.
Maybe I am reckless, but I would just be inclined to take them "as is" and accept that they will sometimes see hot water.
Regards,
SNORGY.
RE: propensity to standardize on 150 psig / 150 F nameplate design
Not quite what I said. I said that when the designation was created, it almost certainly had a sound reason. Over time processes and materials have changed and the reason (which has been lost in time) may make zero sense today, but since no one currently alive knows what it was it just stays.
David
RE: propensity to standardize on 150 psig / 150 F nameplate design
Regards,
SNORGY.
RE: propensity to standardize on 150 psig / 150 F nameplate design
Not a likely situation however, but it was fun to throw it on the pile!
Clients always specify exactly what they need for the process and often don't realize what they are missing.
Some of my clients have wanted to restrict operations from leaving the reservation.
Was the original process for the vessels sensitive to evaporation above 150F? (regardless of safety would >150 have damaged the product or process in the vessel?)
Another possible reason is that insulation may not be required by some other standard (like OSHA) if the Design Temperature is less than.....
So the reasons for doing something odd like that are varied and sometimes don't make any sense structurally, but make lots of sense organizationally.