ASME PBVC VIII. Div 1, U-1(c)(2)(f), Pressurized Air in a Vessel Containing Water 3

[fruiz79]

Hello, I was trying to interpre U-1(c)(2)(f), and I found the following interpretation issue by ASME:

Subject Description: Introduction, U-1(c)(2)(f), Pressurized Air in a Vessel Containing Water
Date Issued: 11/06/2009
Record Number: 09-771
Interpretation Number : VIII-1-10-11

Question(s) and Reply(ies):
Question: Paragraph U-1(c)(2)(f) recognizes that a vessel may
be designed with a constant mass of air that serves as a
cushion of pressurized air. When water enters the pressure
vessel, the air pressure so created is directly related to the
increase in water volume and the associated decrease in air
volume in the vessel. Is a pressure vessel containing water
with a design pressure of less than 300 psi (2 MPa) and a
design temperature of less than 210ºF (99°C) and is designed
to be pressurized by air from an external source a class of
vessel that is not included in the Scope of ASME Section
VIII, Division 1 per U-l(c)(2)(f)?

Reply: No.

I would like to know, why was the answer to the question negative?, if clearly, They are talking about a hydropneumatic tank that fall into the exceptions of scope of ASME BPVC VIII, per U-l(c)(2)(f)

 

[TGS4]

it is not wise to ask "why" any particular answer is given for an inquiry. The inquiry answer is the inquiry answer. Leave it at that. The Code volunteers do not provide rationale for these answers. If you really want that, then you need attend the Code Committee meetings when these items are discussed.

Note that, unless the same volunteer answered a similar question now (11 years later), I cannot guarantee that the answer would be the same (and it might depend on if those Code paragraphs have changed or are going to change).

 

[SnTMan]

fruiz79, can't say that I actually know, but:

Perhaps that the vessel in question is "designed to be pressurized by air from an external source", rather than simply containing air as a cushion.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[david339933]

it is not wise to ask "why" any particular answer is given for an inquiry

So the ASME gods say...so shall it be!.....then why are there so many revised interpretations for the same Code Edition/Addenda. There are many interpretations that are followed by an 'R'....nobody is infallible.

 

[david339933]

Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1989 Edition), UG-116(e) and UW-12(d)
Date Issued: 07/09/1990
Record Number: BC90-418
Interpretation Number : VIII-1-89-210
Question(s) and Reply(ies):
Question: Which of the marking requirements under UG-116(e) in Section VIII, Division 1 apply for a vessel that consists of seamless ellipsoidal or torispherical heads when the vessel joints are spot radiographed and after the circumferential seams attaching the heads are separately spot radiographed per UW-11(a)(5)(b)?

Reply: "RT-3".

 

[david339933]

Standard Designation: BPV Section VIII Div 1
Edition/Addenda:
Para./Fig./Table No:
Subject Description: Section VIII, Division 1 (1989 Edition), UG-116(e) and UW-12(d)
Date Issued: 06/17/1991
Record Number: BC90-418*
Interpretation Number : VIII-1-89-210R
Question(s) and Reply(ies):
Question: Which of the marking requirements under UG-116(e) apply for a vessel that consists of seamless ellipsoidal or torispherical heads when the vessel joints are spot radiographed and after the circumferential seams attaching the heads are separately spot radiographed per UW-11(a)(5)(b)?

Reply: RT-4.

 

[XL83NL]

I understand your point David, but if you'd join a Code committee and understand and actually experience how Code changes are achieved, questions are addressed and inquiries handled, you'd be amazed at how elegantly TGS4 has provided valuable feedback.

Huub

 

[david339933]

Understood...and by no means am I trying to take away from the hard/great work the committee members do. My point is that there are instances where the wrong answer has been given and subsequently revised. To not question an answer IMO goes against the spirit of the Code and the industry in general.

 

[XL83NL]

No doubt about that. It’s always good to question an answer, and vice versa.
However in this circumstance, answering such a question would (probably) one person his or hers view on this point, and not address the committee’s point of view. Such an answer could then have adverse effects.

Huub

 

[marty007]

fruiz79, can't say that I actually know, but:

Perhaps that the vessel in question is "designed to be pressurized by air from an external source", rather than simply containing air as a cushion.

Regards,

Mike

I think this is what the interpretation boils down to. You can think about it in terms of stored energy inside the vessel.

If the air quantity is limited to acting like a cushion, then the stored energy is relatively minor. For a cushioned vessel that can fill with water pressure to 300psi, the volume of air when the vessel is at 300psi is reduced to 14.7/300 ~ 5% of the vessel volume.

If on the other hand you have a vessel that includes an air line that can pressurize the vessel to 300psi, then you can imagine a situation where the entire vessel is filled with air to 300psi. In this case if there is a failure the air could expand to roughly 300/14.7 ~ 20 times the vessel volume. This would be a much larger explosion.

Cheers,
Marty