ASME Section VIII Div. 1 Vessel Stamp 1

[foxymophandlpapa]

This is a question regarding the specified MAEWP on the vessel's stamp. We would prefer that our vessel's MAEWP says "FV" but the tank vendor refuses, saying code requires them to put an actual number.

Currently, they are showing "15 psi". First, I find "psi" as a very gray area, especially on a vessel stamp. This "psi" indicates a differential pressure to me, which negates a reference point. I would prefer this to show "15 psig" or "0 psia". Unfortunately, their stamps are fabricated already with "psi" so a change can't be shown there. Is this common on most vessel stamps?

What is the best, and most typical way to specify full vacuum on a tank stamp?

 

[jte]

foxy-

I’d suggest that you have your supplier read VIII Div. 1 Appendix 3-2 full vacuum (FV) and UHX-19.1. They can then perhaps explain why they still think “FV” is not code legal.

jt

 

[foxymophandlpapa]

Thanks JT. I definitely agree with the definition explanation. Obviously if ASME will define FV, then I'm sure they would accept it on their vessel.

As for UHX-19.1, unfortunately thats for heat exchangers and they could deem that not applicable since this is a 50 L vessel. All the same though - governed by ASME Sec. VIII.

But have you heard of NOT being able to use FV on a vessel stamp? I've scanned over Sec. VIII for about an hour now and see no limitations on it. Nor do I see guidance on exactly how a vessel should be stamped (numbers, decimals, etc.).

 

[jte]

foxy-

The point of the UHX reference is that it provides an example on how to comply with the UG-116 stamping requirements. The beauty is, one of the examples uses "FV" as the external pressure.

jt

 

[jte]

Taking things a step further... from Interpretations Volume 57:

Question (3): If a Manufacturer chooses to indicate an external pressure rating of “Full Vacuum” on a Section VIII, Division 1 pressure vessel, is it the intent to allow the use of the abbreviation “FV”?
Reply (3): Yes.

Enjoy!

jt

 

[foxymophandlpapa]

Thats perfect JT. Can you post a link to that volume?

 

[jte]

Sorry, but no, you'll have to purchase your own copy. It was published with the 2007 code. If you have an IHS subscription, you probably have Interpretations included and should be able to get it from there. In any case, your fabricator better have 'em.

I forgot to mention the Subject of the Interpretation: UG-116, Required Marking for External Pressure

jt

 

[foxymophandlpapa]

Thanks, we have an IHS subscription. Is it listed under "Interpretations Volume 57"?

 

[foxymophandlpapa]

I found it, thanks for all the help JT.

 

[jte]

You bet. Let us know how it goes with the reluctant fab shop!

jt

 

[doct9960]

foxymophandlpapa,

This is a question regarding the specified MAEWP on the vessel's stamp. We would prefer that our vessel's MAEWP says "FV" but the tank vendor refuses, saying code requires them to put an actual number.

Currently, they are showing "15 psi". First, I find "psi" as a very gray area, especially on a vessel stamp. This "psi" indicates a differential pressure to me, which negates a reference point. I would prefer this to show "15 psig" or "0 psia". Unfortunately, their stamps are fabricated already with "psi" so a change can't be shown there. Is this common on most vessel stamps?

Yes, they are common and acceptable. In the ASME vessel world, the unit "psi" indicated on design pressure, MAWP or MAEWP always meant gage pressure. If your preference is "psig" or "FV" (in the case of external pressure), it needs to be stipulated on the purchase order or marked up on the vendor's drawing submittals. Most vendors don't usually proceed with fabrication without drawing approvals from the client.

If the vessel is still in the vendor's shop and you still prefer to change the MAEWP from "15 psi" to "FV", they can still change it, but don't be surprised if there is a cost or schedule impact. If the vessel is already shipped, forget about it because the vessel will require a stamp "R" for the nameplate replacement.

 

[jamesl]

If you read UG-116 and Figure UG-118, you will see the standard unit for MAEWP on nameplate is psi, not psig.
Full Vacuum is defined as 15 psi external pressure in Appendix 3. Fabricators use 15 psi as MAEWP on nameplates all the time. 15 psi or FV are both acceptable.

 

[CodeRef]

doc is correct from various interpretations found in the ASME Codes. A good example is the following interpretation regarding a subsea system and how "coincident pressure" and "differential pressure" is determined.

Interpretation: (B31.3) 16-14
Subject: ASME B31.3a-1996 Addenda, Para. 304.1.1, Pressure Design of Components
Date Issued: November 10, 1997
File: B31-97-029
Question: For subsea production systems where ASME B31.3 is required, can
the internal design gage pressure, P, in paras. 304.1.1 and 304.1.2 be
interpreted as coincident internal design gage pressure minus external
gage pressure?
Reply: Yes; however, when the coincident external gage pressure is
greater than the internal gage pressure, the design shall be in accordance
with para. 304.1.3.

The below interpretation is an example of the various interpretations in the ASME Codes. This one is specific to ASME Section I

Interpretation: I-83-33
Subject: Section I, PG-27.3, psia vs. psig
Date Issued: February 15, 1983
File: BC82-608
Question (1): Paragraph PG-21 states that the term maximum
allowable working pressure refers to gage pressure, "except when noted
otherwise in the calculation formula of PG-27.2." The latter contains no
advice regarding gage vs. absolute pressure. Where is this note to be
found?
Reply (1): The advice "except when noted otherwise in the calculation
formula of PG-27.2" was applicable to an earlier edition of the Code, but
is no longer valid. The Committee will delete this reference in future
editions of the Code.
Question (2): Are the terms for pressure used in PG-27.2 expressed in
terms of psia or psig?
Reply (2): Psig.

FAQ731-376