Vacuum vessel
Vacuum vessel
(OP)
Hello,
I am designing a 42" diameter pressure vessel that will be used for vacuum service. Internal pressure will be -13.75 psi. Spec'ing a tank head for internal positive pressure is pretty straightforward, but what about external pressure? Where can I find a good write-up about this? Currently I don't have access to ASME code, I imagine I'll be directed to section 8 division 1. Maybe there's something online? Thanks!
I am designing a 42" diameter pressure vessel that will be used for vacuum service. Internal pressure will be -13.75 psi. Spec'ing a tank head for internal positive pressure is pretty straightforward, but what about external pressure? Where can I find a good write-up about this? Currently I don't have access to ASME code, I imagine I'll be directed to section 8 division 1. Maybe there's something online? Thanks!





RE: Vacuum vessel
Joe Tank
RE: Vacuum vessel
A vessel operating below a pressure 15 psi does NOT come under the purview of the ASME VIII-1 Code. Your pressure vessel is most likely to come under the purview of API 620/650. PLease specify the exact design pressures and temperatures [both internal and external].
-jehan
RE: Vacuum vessel
ASME code covers vessels operating above 15 psig and at "significant" vacuum conditions
API-650 covers "atmospheric storage tanks" up to +2.5 psig and at slight vacuum conditions (that they refuse to define)
API-620 covers storage tanks" above +2.5 psig to ~ 14.5 psig and at sliht vacuum conditions (that they refuse to define). API-620 also covers higher temperatures
In my opinion, the rules of ASME-VII apply to this "-13.75 psi" case. Banu should define minimum MAWP in psia
Now, whether or not the vessel can be designed, fabricated, inspected and certified is another matter..
Where will this component be installed ?....Iran ?
-MJC
RE: Vacuum vessel
RE: Vacuum vessel
Regards,
Mike
RE: Vacuum vessel
Sorry, but my views differ from your above reply.
Based on the above clause, my interpretation is that the pressure vessel decribed in Plasmech's 1st post cannot be qualified as as a Div 1 vessel.
Regarding API-650, these tanks are designed either to operate under atmospheric pressure only (vented to atmosphere) or under internal pressures not exceeding weight of roof plates. Higher pressures upto 18 kPA are allowed provided tank conforms to design as per Appendix F of API-650.
Be advised; API standards, have upper temperature limitations.
For API-620, these tanks are designed for a maximum positive pressure of 15 psig and a vacuum (not able to quantify this value right now; been a hard workday today
Irrespective of my above opinion, now that Plasmech has mentioned that the contents are "pelletized" changes the nature of his theread all together.
In my opinion, since this is a bulk product (granular/ powder) dealt with, API standards 620/650 and ASME codes VIII-1 will not suffice. If Plasmech intends to design storage vessel for "pelletized" contents then it is strongly recommended that a standard like DIN 1055 Part 6 pertainnng to design of silos and bins be employed in the desingn.
BULK SOLIDS (POWDERS/ GRANULES, ETC) EXERT LOADS WHICH ARE DIFFERENT IN NATURE (AND HIGHER IN MAGNITUDE) THAN THOSE EXERTED BY A EQUIVALENT LIQUID STATIC HEAD.
Hope this helps. Please give in your views.
regards,
jehan
RE: Vacuum vessel
Aother thing I need is a detailed drawing of an ASME semi-ellipsoidal tank head, .211 min. Is this online somewhere? Also material selection, what is the strongest readily available commonly used carbon steel material? I don't deal in this stuff so it's all new to me, bear with me! Thanks again.
RE: Vacuum vessel
You are splitting hairs.....
"-13.75 psig" is nearly the same as "15 psig external presure.
Use the rules of ASME VIII, they are much closer to apply than the rules of API-650 or 620.
I would design the component for FV and be done with it.
my opinion only
-MJC
RE: Vacuum vessel
I agree with you that a vessel for vacuum service only, not exceeding 15 psi external, is out of scope of VIII-1, as you point out in your quote. However...
...you chose to selectively quote the code, and I don't understand why. The full quote is below:
U-1(c)(2) Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:
I added the bold. So, please provide further explaination as to why you feel that this container cannot receive a VIII-1 U stamp.
For lack of other codes or standards available to design to 13 psi external, I'd go with MJCronin's suggestion, design it to full vacuum and some nominal (say 5 psi) internal MAWP and be done with it.
Now, whether or not to actually stamp the vessel is more dependent on local jurisdictional issues - there may be an advantage to not stamping the container from a repair / maintenance perspective.
RE: Vacuum vessel
I concur with your logic regarding the qualification as per Code but........ my viewpoint is that by simply incrementing the design conditions to "fit" into the Code would be a way a kind of over design. The economic aspect too needs to be looked into. Is it feasible to rate this vessel as per ASME VIII-1 and then bear the additional cost of the increased engineering/ documentation? Is the time, effort and documentation really worth the "simplicity" of the vessel? We frequently joke amongst ourselves when we encounter the design of a small vessel that the equipment weight will be <100 kgf and the accompanying ASME documentation will be 50 kgf
ASME VIII-1 Code will allow many types of vessels falling under the "grey-areas"/ "battery-limits" of it's scope (example clauses U-2g, 1-5g, 1-8e).
Ok, the "vessel " under the current discussion might be small and maybe the minimum thickness would be adequate in this case.... but the documentation/ inspection etc ?
In addition, as I have previously highlighted in my earlier post,
Bulk solids exert a myraid of loads- switch pressures, filling and discahrging pressures (to name a few as per the DIN 1055 part 6 standard).
Hoping to hear from your end on this issue.
-jehan
RE: Vacuum vessel
MJCronin- You are brutally honest in saying that I am splitting my hairs on this one. I could'nt agree with you more on this
Plasmech- Can you give more info regarding the nature of the contents being stored and where this vessel is intented to be installed?
Thank you all.
Regards,
jehan
RE: Vacuum vessel
RE: Vacuum vessel
Reverting to your original post, you sense it correctly that a container subjected to full vacuum or near full vacuum is considered a pressure vessel and should be designed accordingly. There are many free, unregistered "design software" on the net, most likely not updated for long time, therefore useless and are not supported by the latest edition of any pressure vessel code (ASME, JIS, EN, AS, IS etc..). You won't be able to get design approval, registration or certification either based on those calculations. I doubt it that any decent fabricator will accept a dubious design and fabricate / guarantee the vessel for you. You'll be better off to pay an experienced designer who can guarantee the design and register it with the authorities, including a formal third party design verification, perhaps later an independent third party inspection on your behalf.
Unless you do that, you might have the surprise of someone knocking at your door to take you away...
Cheers,
gr2vessels
RE: Vacuum vessel
Just to be very explicit so we're sure we understand each other: I believe that the vessel as proposed, at ~0.9*FV can be designed and stamped as a VIII-1 vessel. Set some nominal MAWP, perhaps 5 psi, and also place the 13.75 psi on the nameplate and U-1A form. It is code legal. You are not obliged to bump up either the internal nor external pressure to put a U stamp on. Part of my point is that even "FV", or 15 psi, does not exceed the 15 psi limit, thus even a FV vessel may be excluded from the scope. But at the purchaser's option, it may be included provided all of the other conditions are met.
Local jurisdictional issues may be more complicated and/or ornery and are out of scope of this thread - so there!
plasmech
There is a publication out there titled something like Useful Information for the Design of Steel Silos I think published by AISI. Might be useful for you. I think I have a copy in the office; I'll look for it tomorrow to verify title and publisher.
jt
RE: Vacuum vessel
Not that this should EVER happen especially since I will likely consult someone with a LOT of experience on this vessel, but if something like this were to implode and someone was standing right next to it, what could happen? Are we talking simply scaring someone half to death or are we talking major shock wave that could be a fatality? Like I originally said, vacuum is a whole lot different than positive pressure, which is easy to predict...
RE: Vacuum vessel
a small diameter like this is relatively easy as long as the shell does not get too long. Length of straight shell is much more subceptable to external forces than a formed head.
if you want, I can fax you the formula, but the tables and long formula may be tougher.
don't forget to check openings for reinforcement for external pressure separately from internal.
and Yes, I would not hesitate to apply Sect VIII Div 1 to this vessel.
RE: Vacuum vessel
vesselfab-
Out of curiosity, have you ever seen a case where you've designed a vessel for which vacuum conditions governed over internal pressure for opening reinforcement? I don't doubt it could happen (it's covered in Div. 1, though simplistically, after all), but I have a hard time dreaming up a case where it would happen in real life.
jt
RE: Vacuum vessel
and tolerances for external pressure vessel are much tighter for roundness to resist it.
RE: Vacuum vessel
It can happen, and needs to be checked out.
Regards,
Mike
RE: Vacuum vessel
Like I said, just a rule of thumb.
Mike