Minimum/Maximu pressure in a vessel

[auba]

Hi all,

1) can anybody tell me what minimum/maximum pressures in a vessel is treated by ASME SEC VIII.

2) what is the minimum pressure in a vessel to call it as a "pressure vessel"...

Thanks

 

[chaulklate]

To the best of my knowledge, there is no maximum pressure limit defined by the code.

Minimum pressure limits are defined in Paragraph U-1(c)(2)(h) as 15 psi. But it also has exceptions relative to service and diameter. I suggest reading U-1 in it's entirety for clarity.

 

[auba]

Hi friend,

thanks for help....but in U-1 it says:

==============================================
(h) vessels having an internal or external
operating pressure (see 3-2) not exceeding 15 psi
(100 kPa) with no limitation on size [see UG-28(f)];
=============================================

?) what is meant by "(see 3-2)" here...

?) and it is normal practice that in almost all of cases (where vessels are above ground) we take external pressure as 15 psi or rather 14.7 psi; atomospheric case.... so is not it strange that this point will bring our vessel beyond ASME SEC VIII scope..

Thanks

 

[pleckner]

Any vessel with a design (or Maximum Allowable Working Pressure, MAWP) of 15 psig or higher falls within the ASME scope. Note the use of "g" in psig.

If your vessel is designed for anything less than 15 psig, it does NOT fall within ASME Section VIII sope but may then fall within the various API standards, API 2000, API 650, API 620, etc.

 

[JoeTank]

auba,
Are you saying that your practice is to design an aboveground vessel for a full vacuum of 15 psi? Just for the record, at 15 psig, the vessel would not fall within pressure limits of the ASME Code, unless you chose to do so. The design pressures in ASME are psig, not psia.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[pleckner]

Need to clarify my previous post. To be a pressure vessel, the INTERNAL design pressure would actaully be anything GREATER than 15 psig (we typically make sure that we specifiy nothing greater than 14.9 psig so there is no question or interpretation). And if the INTERNAL pressure is anything greater than 15 psig, then it falls within ASME Section VIII scope. But if the internal pressure is only a vacuum consideration, then it does not necessarily fall within the scope.

 

[chaulklate]

3-2 refers to Appendix 3, paragraph 2.

I'm not sure what you mean by your second question.

 

[auba]

Hi friends,

i am cleared now for external pressure case as said in UG-28(f)

==============================================

Vessels intended for service under external working
pressures of 15 psi (0.1 MPa) and less [see U-1(c)(2)(h)]
may be stamped with the Code Symbol denoting compliance
with the rules for external pressure provided all the
applicable rules of this Division are satisfied. When the
Code Symbol is to be applied, the user or his designated
agent shall specify the required maximum allowable
external working pressure.16 The vessel shall be designed
and stamped with the maximum allowable external working
pressure.
==============================================

SO EXTERNAL PREWSSURE OF 15 PSIG FALLS WITHING ASME SCOPE.. HOWEVER FOR INTERNAL PRESSURE I MUST GO ABOVE 15 PSIG IN ORDER TO BE WITHIN ASME SCOPE..

i hope i am right?????

Thanks...

 

[pleckner]

Yes, your internal design pressure must be ANYTHING greater than 15 psig to fall within the Section VIII scope.

 

[auba]

Hi friend,

so if my pressure vessel internal pressure is below 15 psig then to design it which code i should use...

i mean what about pd5500 ot BS codes....

Thanks

 

[davsy]

Where is this vessel destined to be installed, surely if you are not installing it in Europe then you do not need to look at British codes. A previous reply mentioned that the vessel may fall under one of the API codes.

If you are in Europe then the internal pressure at which it falls into the PED (i.e is classed as a pressure vessel) is 0.5 Barg (not 15 psig like ASME)

 

[auba]

Hi friend,

my vessel will be underground and will be placed in canada...

my vessel is actually having 3 psi of internal pressure..

still confusing whether to use asme codes or not..

Thanks

 

[waskillywabbit]

auba,

I don't see why you are still confused. Several folks have laid it out there pretty plain...DESIGNED for under 15 psig and you are outside the bounds of ASME XIII div 1. I think the part you need to decide is determining the DESIGN pressure, not the OPERATING pressure, which I assume from your comments to be "3 psi". Being underground you are going to have to account for the external loading of the soil etc.

Good luck.

Brian

 

[chaulklate]

The usual rule of thumb for vessels less than design pressure of 15 psig is to design, test, and inspect as per ASME Section VIII, but not to "register" it. Also, as it is going in Canada, be sure to refer to CSA B51-03, the Canadian vessel code.

 

[jte]

auba-

Even if your vessel has a design internal pressure of 3 psig, you may, at your option, design, fabricate, and stamp it per VIII-1. That's made perfectly clear in the code:

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

So, yes, while a vessel with strictly an external pressure design condition equal to or less than 15 psig is excluded from the scope, you may still stamp it. This is commonly done, though usually the MAWP (internal) is greater than 15 psig.

On the other hand, if you choose, you may design and fabricate to VIII-1, but not U stamp the vessel. Or perhaps API-620 (I don't have it handy so can't check the scope).

As mentioned in previous posts, check (i.e. in writing!) with the jurisdiction in which the vessle will be installed before you commit to any particular code or standard.

jt

 

[panduru]

From a practical point of view, it appears that it may be better to design the vessel to withstand 15 psi internal, and 15 psi external pressure; though the operating pressure may fall between these two values.

In such a case, there is no doubt a little over-design, but Code compliance will not be an issue. This is not too uneconomical in general.

In fact, this stems from an observation of a majority of client specifications.

 

[CaptainKidd]

Where is the 15 psig measurement taken? Do you have to take static head into account? We're looking at building a tank that'll be either atmospheric or very slightly positive pressure in the vapor space. The bottom might approach 15 psi when full. If that's a concern, we'll go wider and shorter then.

Thanks.

 

[panduru]

@CaptainKidd:

I would take everything into account, including static head, yes.

"...might approach 15 psi..." apparently, you are talking about the operating pressure. There's every reason to consider 15 + 1.5 psi for the design then.

As for the L/D, there are several other factors to consider such as piping and nearby equipment.

 

[pleckner]

Per ASME, Section VIII, Division 1, Section UG-98, you the specifier are only take into account the top of the vessel in its normal operating position. When the vessel is designed by the manufacturer, they must take into account the maximum liquid density and height so that they can account for these in determining the necessary thickness of metal at the vessel's bottom.

 

[JoeTank]

CaptainKidd,
The 15 psi is considerted at the top of the vessel/tank in it's normal operating position. In the case of a tank with an open vent or gas pressure not exceeding 15 psi, the tank would not fall under the rules of ASME. FYI... API Standard 620 covers tanks upto 15 psi design pressures.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com