ASME Section VIII Div 1 Nozzle Loads 8

[RVAmeche]

I'm working on a project involving a stainless steel ASME vessel rated for 120 psig designed to Section VIII Div 1. While doing the piping design, we identified high forces/moments on this 3" nozzle due to relief forces.

We sent the loads to the vessel vendor to try to confirm the nozzle is okay and/or propose reinforcement, but they basically said they can't run the numbers. They further stated the maximum bending moment this flange can withstand is approximately 19 ft-lbs, limited by the Class 150 flange and governed by MAWP reduction due to external load in their software. He said it'd need to be a Class 900 flange for the moments we were showing.

I'm not an ASME pressure vessel code guy but the 19 ft-lb response seems absurdly low to me. We're pursuing FEA analysis and preliminary results seem to be indicating a minor repad will be needed due to stresses at the head connection, but no concerns about the flange itself. Does this make sense and Div 1 is just absurdly conservative in this regard? It feels like we're missing something.

 

[Heaviside1925]

OP,
I am curious what your FEA spits out.
I will say, if your firm is specifying vessels built to Div 1, you or someone at your firm should at least know how to work through at a minimum the first 100 pages of the BPVC. If you don't have a copy, there are, abiet illegal, copies online, or the best is to ask your firm to buy one or a license. Once you know how to work through it, you will be able to do a much better job at specifying vessels and avoid the pitfalls you are dealing with now. It is not necessarily hard to work through but can be time consuming the first few times, that said, it's not just a bunch of random, thou shall and thou shall not, it's a prescriptive code, so follow it through, do the calcs and in most cases its fairly clear. Think of the time you have spent on here and now doing FEA and still don't have a clear answer, whereas you could spend a couple hours (or less) working through the code and would know for sure if the vendor made a mistake or not. I think it's clear that most posters are here are pointing you to BPVC code sections, why, because that's the only way you can answer your question.

 

[Rob VE]

Like TGS4 (Mechanical) mentioned, UG-44(b) is very conservative. Code case 2901-1 describes a much more accurate values of Fm. most software however will not yet have the option to use this option. likely you or your vessel supplier will have to write your own file.
Note, CC2901-1 is added in supplement 4 of current asme code cases.

 

[FPPE]

2) Do NOT use the UG-44(b) Fm values - instead, use the Code Case 2901-1 Fm values. That will greatly assist you.

TGS4, I have few questions regarding the above quote:

[ol 1]
[li]Is verification according to UG-44(b) mandatory even if the word "may" is used?[/li]
[li]If used, can the parameters of the new edition 2023 code case 2901 be used as an alternative even if ASME Code has its own parameters in Table UG-44-1?[/li]
[li]I was trying to access the Code Case and, failing, emailed ASME who responded with "In order to be able to access the Members-only pages of C&S Connect you must be a committee member". Why can't Code Cases be accessed in a public way?[/li]
[/ol]

Thank you in advance

 

[TGS4]

FPPE
1. That is between you and your AI. The prior interpretation says that external loads must be accounted for in the design and UG-44(b) provides one way to accomplish that.
2. Yes - the Code Case specifically calls out that the values are an alternate to the existing UG-44(b) rules.
3. The Code Case was issued in Supplement 4. Check with your electronic Code provider (Accuris/Techstreet/other). Failing that, please contact me offline.

 

[FPPE]

TGS4, thank you very much, I have found Supplement 4 in our Techstreet package.
Best Regards

 

[RVAmeche]

FYI the FEA analysis came back and we were able to get away with a big repad to satisfy the external loads we were seeing. The FEA did show that unreinforced nozzle allowable loads for this nozzle were very low.

Thanks again for all the insights.