Pressure vessel nozzle boss 2

[mariolucas75]

Dear All,

Pressure vessel nozzle thickness is calculated with ASME VIII UG-45 "nozzle neck thickness".
However my question is - how is it calculated a nozzle boss thickness - which is a much more thick?
And hypothetical question - actually down to what thickness it can deteriorate - until it gets the thickness of neck (where the flange is welded ) ?

Thks a lot

 

[SnTMan]

mariolucas75, not sure what a "nozzle boss" is, but I assume your construction is similar to Fig. UW-16.1 (g).

The required thickness is determined per UG-37 reinforcement calculations, taking any corrosion allowance into account.

Minimum thickness is per UG-45 rules, again taking any corrosion allowance into account.

If the UG-37 thickness exceeds the UG-45 thickness, you are good to go, if not the UG-45 thickness governs.

If a pipe neck is attached to your boss, UG-45 must be met for it as well.

The boss and neck can "deteriorate" untill the relevant rules are no longer met.

Regards,

Mike

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

 

[mariolucas75]

SnTMan yes exactly I meant the Fig. UW-16.1 (g)
Actually one of the vendor had notation that thick thing as a "nozzle boss"
The UG-37 that you recommended refers to "REINFORCEMENT REQUIRED FOR OPENINGS IN SHELLS AND FORMED HEADS"
However i am interested how the thickness is calculated of the portion that I marked in red in attached screenshot.
May be I miss something in your explanation ?

 

[SnTMan]

mariolucas75 that thicknecss is determined from UG-37 calculations. It contributes to opening reinforcent as Area A2. see Fig. UG-37.1. Used to avoid large, thick pads or when integral reinforcemnt is required.

Pipe neck thickness is per UG-27 & UG-45.

Your nozzle boss is called a "heavy bore" in my part of the world

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

 

[mariolucas75]

Dear SnTMan,

Further to previous explanations i posted my question in attached PDf file ("Extract from ASME VIII), would you be so kind and advise me please...

Thank you so much ...

 

[Maslov]

Yes, the thickness t[sub]n[/sub] is the thickness of the nozzle in the reinforcement zone, which in most cases will be the "barrel" thickness you have labeled on UW16.1(g) in the pdf. Just make sure it remains that thickness throughout the height of the reinforcement zone (else you will have to get creative with area calculations).

t[sub]n[/sub] must be equal to or greater than that prescribed by UG-27 & UG-45. There is no direct formula for t[sub]n[/sub] in UG-37.

Rather, you usually assume a nozzle thickness, do the calculations per UG-37, and if your reinforcement area is not larger than the required area you can try a thicker nozzle (larger t[sub]n[/sub]) or add a repad (introduce a t[sub]e[/sub]).

If you really wanted, you could reverse the area calculations of UG-37 and solve for t[sub]n[/sub], or even set up a spreadsheet and do what-if analysis to determine it that way, but heavy bore (HB) and variable body connection (FVC) nozzles have standard sizes, so just pick a size and do the area calcs.

 

[mariolucas75]

Dear Maslov,

Thank you very much....

I still struggle with the following: i do have a "heavy barrel nozzle"... and that barrel or whatever it is externally badly corroded .... and i want to figure out that thick nozzle barrel which in fact is an integral reinforcement to what extent may corrode not to compromise it reinforcement service ? In other words down to what thickness this "heavy barrel nozzle" wall may reduce ?

 

[Maslov]

In that case, you will need to reverse UG-37 to calculate a minimum t[sub]n[/sub]. That will give your minimum thickness for reinforcement.

I suggest: calculate your required area A and subtract the non-nozzle reinforcement areas (A[sub]1/3/4/5[/sub]). That will leave you with your minimum A[sub]2[/sub], which will give you a minimum t[sub]n[/sub].

 

[mariolucas75]

Dear Maslov,

Thank you very much .... i will have a look on this....

 

[mariolucas75]

Dear Maslov,

Can you advise me any software for such heavy barrel nozzle and in general pressure vessel calculations?

Regards

 

[SnTMan]

mariolucas75 -- Maslov has it right.

Any number of software available often with free trial. You'd have to see what meets your needs.

For this one calculation it is not too difficult to set up a spreadsheet.


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

 

[TomRob142]

Hi this is a relatively similar subject to a query that I have, @SnTMan perhaps you can add your thoughts? I have a vendor that has completed prelim nozzle calcs for a vessel I am procuring, and we have some 'heavy bore', or as I call them self-reinforced, large bore nozzles for access manways (we have gone with the heavy bore nozzle design due to a DEP requirements for H2S duty).

The vendor calcs include the increased bore thickness in the A2 area calculation, section of the code (UG-37.1) requires the use of t[sub]n[/sub] and t[sub]rn[/sub] for this area calculation. However, should t[sub]n[/sub] be used as the thickness of the thickened section, or the thin section (where it is welded to the flange etc). Figure UG-40(e-1) gives a tn measurement across the thinnest part of the nozzle, to be used where the thickened section is relatively short compared to the thickness of section. In my case we have a relatively short thickened section of almost 140mm thick, but only a 13mm thickness where it reduces down...so t[sub]n[/sub] used has a large impact on the A2 calc.

I think the intent of the area replacement calc is to take credit for any thickness within the limits of reinforcement, whether they are in the A2 (pipe outside the vessel) or A5 (area available in the element), however the equation for A2 in UG37.1 gives this t[sub]n[/sub] a 'bigger impact' on the result as it calculates A2 as the smaller of

5(t[sub]n[/sub]-t[sub]rn[/sub])*f[sub]r2[/sub]*t
2(t[sub]n[/sub]-t[sub]rn[/sub])*(2.5t[sub]n[/sub]+te)f[sub]r2[/sub]

Whereas the A5 calc is just the straight area of the element. The vendor has used compress which calculates it as part of A2. I have checked on PVelite and it calcs it as part of A5...

 

[SnTMan]

TomRob142, I am not familiar with Compress, but PVElite (as I recall, haven't run it in a log time) determines tn as per Fig UG-40 (e), so whether the thicknened wall is considered in A2 or A5 depends on the distance L per Note 3).

Now, in Fig UG-40 (e), I take issue with the definition of tx, as this seems to contradict the plain language of UG-40(c)(1).

The common practice, when I was working was to insure L was at least 2 1/2 x t, corrroded shell thickness, thereby treating the thickened neck as part of A2. For a radial nozzle, L was measured from the nozzle centerline, longitudinal plane.

I suppose it is possible in some classes of work that, even with a heavy bore type nozzle that it could fall under UG-40(c)(2), but I never saw one.

As to your situation I don't have an easy answer. I suppose you are going to have to look at the actual dimensions and relevant parts of UG-40 to determine which of the two calculations is correct.

EDIT: I suppose that if the shell thickness was sufficiently thicker than the thickened part of the neck that (c)(2) could apply.

Regards,

Mike

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