Title: Opening Area Method VIII-1 UG-37 and Pressure Area Method VIII-2 part 4.5 1

[mechengineer]

Hello everyone,

Whether it allows to use VIII-2 part 4.5 instead of VIII-1 UG-37 by code?
My understanding is that should be no problem for the re-pad with full penetration & full UT or the integrally reinforced opening with full UT (no cyclic load).
The case is that DP=23 bar, DT=80 deg. C, material: SA516Gr70, SA106B, shell ID=1150, 12" nozzle CL300. Re-pad is not allowed as sour service (DP=10 bar only). If use VIII-2, part 4.5 the reinforcement area is sufficient with sch.120 and the shell thickness of 15.88 mm, but if as per UG-37 the nozzle has to use a forging neck (40 mm thk.) for this nozzle even LWN (35 mm thk.) can't be used.
I prefer to use VIII-2 part 4.5 or Appendix 1-10 of ASME VIII-1 for this nozzle. However code does not clearly indicate allows to use VIII-2 part 4.5 instead of VIII-1 UG-37 and moved Appendix 1-10 of ASME VIII-1 to VIII-2 part 4.5, which give a impression that seems Appendix 1-10 is not applicable for ASME VIII-1 PV design. This feedback is from is a lot of engineers and clients.
Welcome to share your idea here. Thank you.

 

[r6155]

Something may be wrong. Check UG-37 and UG-45. Is this nozzle on head or cylindrical shell?

Regards
r6155

 

[SnTMan]

I don't believe you can go to a Div 2 (or another alternative calculation) just because you don't like the way the Div 1 calculation comes out.

Only written backup I can find is U-1(3), second to last sentence. I'd be surprised if there were not interpretations on the subject.

Regards,

Mike



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

 

[TGS4]

See Code Case 2695. Or U-2(g).

 

[SnTMan]

Yes, but is that not all one way, or all the other? Or can you pick and chose? This is Div1, that is Div 2, etc?

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

 

[SnTMan]

Huh, from the Codeware website: "Beginning with COMPRESS 2018, Code Case 2695 may now be activated for individual nozzles. This provides more flexibility in your designs as the parent component and other nozzles located on the parent component may now remain under Division 1 design."

I guess you can pick and chose. Yee

http://www :)

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

 

[TGS4]

Yup - it's fairly a la carte.

Wait until you see how we have changed/fixed U-2(g), added another Appendix, all to effectively incorporate CC2695 into VIII-1.

 

[SnTMan]

By the time you reach a certain age, you know change is bad. It's been demonstrated over and over...

I miss the old days



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

 

[TGS4]

Of all of the changes that I have seen, this upcoming one will be for the better (or at least will be less worse). It shouldn't be painful to get used to the change, and it closed a number of very bad loopholes.

 

[mechengineer]

Hi, thanks for all.
Our wishes are good, the theory is good and code is correct, but not practical.
The user’s thinking is very simple, the thickness is thicker and safer. If you want to reduce the thickness by Code case, the user will advise you ‘don’t use code case, don’t use VIII-2….’ In such cases, you have only one choice that is ‘You pay money, I will do what you want’. A lot of manufacturer are going this way. As an engineer I know that the safety factor is 3.5 for VIII-1, 3 for class 1 of VIII-2 and 2.4 for class 2 of VIII-2 (it’s like playing a safety factors game, just a joke), for opening reinforcement it can use code case 2695 instead of UG-37 ......, but the user will ask you why you make your design so complex we haven’t kwon before? We can’t expect a user to understand Code even code case in deep. There is only way to resolve such issue is to make Code simple, easy practicable. Otherwise code case 2695 and VIII-2 will lose a lot of application opportunities.

 

[TGS4]

Your "understanding" of this quantity that you term "safety factor" is multiply not correct. First, there is no such thing as a safety factor. Instead, there are design margins against failure modes. And these are different, even within the same Division. In all of three Codes that you listed, the margin against yield is 1.5. And the margin against buckling is also the same - approximately 2.0. And once you're in the creep regime, the margins are also the same.

The calculation methods are what are different. The calcs in Division 1 are simplified and somewhere between a little and a lot conservative. The calculations in Division 2 are much more modern, and as s result have less excess.

I strongly encourage use of the Division 2 calculations, regardless of whether you're using Division 2 or coming to it through Code Case 2695. Changes coming in the 2019 Edition of Division 1 will greatly simplify going back and forth from the calculations in Division 2.

 

[mechengineer]

TGS4, To make your strongly encorage to become an action, the best way is to recommend ASME VIII commettee to use the method of opening reinforcement in VIII-2 to replace UG-37 and put UG-37 into Appendix of VIII-1. Further more, combine VIII-1 & VIII-2 into one ASME VIII which shall be possible in technical. Otherwise, all design methods in VIII-2 will be not widely used if one desigm with two ways, VIII-1 & Viii-2. My personal opinion.

 

[TGS4]

mechengineer thank you for your feedback. Unfortunately, all of these activities take volunteer time and effort, of which there seems to be precious little. My personal preference it to take methodologies that are effectively obsolete in VIII-1 and delete them from VIII-1 and replace them with a reference to VIII-2. If we do that for long enough, eventually there will be a groundswell of voices from the industry begging to combine VIII-1 with VIII-2 (effectively delete VIII-1 and replace with VIII-2). However, until that groundswell of voices appear, the voices that the Code volunteers are hearing is what is leading the Code in its current direction.

(This is the part of the conversation where I encourage you and all others to get involved in the ASME Code Committees. They are simply volunteer groups of engineers who want to get involved and do what they think is the right thing. It doesn't get more "grassroots" than this - but only if enough people get involved)

 

[DriveMeNuts]

I think of Div 1 as the "pressure vessels for dummies" code.
It is conservative when compared to PD 5500 and EN 13445-3 or Div 2 even after taking into account the different NDT requirements.

Div 1 should have any relevant parts incorporated into Div 2 and what remains should be deleted or transferred into a code case.

 

[mechengineer]

TGS4, thank you for sharing the information. What you indicated here may be a part of the reason, but it is too weak to change the direction. I remembered what you said before is ‘there are political issues’. This may be a real reason.
I will use 'design margin' rather than 'safety factor' and thank you for correction.

 

[r6155]

I like the term "Ignorance coefficient".

Regards
r6155