Skirt Allowable Stress in PVE Lite 2

[mechengineer]

The Skirt Allowable Stress.
I have another unpleasant experience with PVE lite and the support team working recently.
The case number is 00196823. If you are interested, please go to PPM Smart Community (you shall be a listened PVE Lite user). This may help you to understand what the after-sale service provided by PVE Lite support team is currently.
Please allow me simply to state the case 00196823 here and welcome all to comment.
Subject (revised): The skirt allowable stress shall be in accordance with AISC or equivalent, not ASME pressure vessel code.
The answered from the development engineer:
I agree that the allowable skirt stress could be based on design rules from AISC or equivalent. However, to the best of my knowledge, the general expectation from the vast majority of users, Notified Bodies etc. is to use the ASME or Code based computed allowable stress.
I replied:
PVE is to selectively treat customer requests according to the size the customer (the majority of users). There is discrimination against small companies.
For engineering design and technical issues, the requirements from major customers go beyond the engineering design principles themselves.
This approach discards the respect for those users from small companies and also goes against engineering design principles and professional ethics.
The Manager of Support team:
Requested the justification from a published document, interpretation based on research, adopted in practice etc.
I replied:
I showed up the Pressure Vessel Handbook (10th Ed) Eugene F. Megyesy that indicate the skirt allowable stress shall be for structural purpose.
And I asked the manager, what is the justification that PVE Lite uses the pressure vessel code allowable stress for the skirt? Any reliable justification from a published document, interpretation based on research (have had no answer till now from the support team)
The Manager of Support team:
He requested me to explain the allowable request of the Pressure Vessel Handbook and said that I think this case is done and requires no further discussion unless more data is provided or found.
I replied:
I really don’t understand what are the ‘more data’ you’re required. As you required, I already showed you the Pressure Vessel Handbook (10th Ed) Eugene F. Megyesy that state to use structural allowable stress for the skirt design, which is the published and widely used in the industry. Even if I don’t think that is necessary because that is a normal sense that structure design shall be as per a structural code and pressure vessel design as per pressure vessel code.
The manager of support team:
PV Elite Support and Dev are not in the capacity to change what is accepted in the industry.
I replied,
You are like saying that all errors/mistakes in PVE Lite are accepted in industry because PVE Lite has used in industry. The material allowable stresses shall be from the relative design codes rather than the vast majority of users, Notified Bodies.
The manager of support team,
If you wish to use AISC you will have to do a separate analysis. If you have evidence that this becomes accepted in industry we'd be happy to consider.
I replied,
I think that you may not know about the G-2 Supports Consideration in the code. You have been doing nothing on the study and research for it since the customer revealed this mistake to you. And instead of that, you keep asking customer to do this for you for free. You are extracting your customers' labor and technical resources for your business software for free. You are too much to request the customer to give you an evidence that this becomes accepted in industry. But also you have no any evidence that the skirt allowable stress used in PVE Lite accepted in industry except the software has used in industry.
Note: the case already closed by the namager without any further reply. PVE Lite has still used pressure vessel code allowable stress for the skirt.
PS: ASME Sec VIII Div 1 - Nonmandatory Appendix -G
G-2 SUPPORTS CONSIDERATIONS
The details of supports should conform to good structural practice, bearing in mind the following items (see Manual for Steel Construction, latest edition, by the American Institute of Steel Construction).
The skirt support design and allowable stress shall be as per AISC that confirmed by Appendix-G.

 

[mechengineer]

@saplanti,
Thanks for your leaving.
But in the end, I would like to advise you: don't self-righteously say to someone in the forum that he/she have no knowlegde, no experience, need training, reading some book, such nonsence words. It only shows you being vulgar, arrogant. It doesn't hurt much, but extremely insulting. If you can't give help just leave.

 

[r6155]

@ mechengineer
Example:
skirt d= 48” H= 240” (two shell sections), bottom head SA-516-70 (Sallow 20000 psi)
Please, can you tell us?
1) skirt material and Sallow in tension and compression.
2) Joint E= ? for head -skirt weld
3) Joint E= ? for skirt-skirt weld

Thank you
Regards

 

[mechengineer]

r6155.
Thank you for your persistence. But what your concern is exceed the point I would like to talk here. I have had the satisfied resolution is that the skirt support design and allowable stress shall be as per AISC that has confirmed by ASME VIII-1 Appendix-G. I have no others need furhter to discuss. If you like, you may make a new post in the forum.
Thanks for your understanding.

 

[david339933]

Shall be per AISC is a bit of a stretch...let's not forget App. G is non-mandatory. Prudent thing to do is use the more conservative value.

 

[r6155]

@ mechengineer
Exactly this answer is what I expected from you. Regrettable.
It's a waste of time for me.
Good luck.

 

[dig1]

mechengineer,

My intention is not to be disrespectful as this thread has become somewhat contentious, so please do not take any of my comments in that manner.

I do not disagree that AISC can be used for the skirt design. However, Non-mandatory Appendix G uses the word "should" and not "shall". It also provides a other recommendations in G-2 and G-5; which I know you are aware of.

I'm sure you are aware that if you elect to use AISC you will need to use all the provisions including Chapter B to determine slender/non-slender and compact/non-compact, Chapter C for stability and determine P-Δ and P-δ effects as necessary, chapters D (tension), E (compression elements), F (flexural elements), and H (combined forces).

Obviously, these requirements will result in a large cost for the software providers in terms of programing, quality control/verification, etc. If most of their client base uses another method I can respect that decision and it is not unconservative.

In ASME PTB-4-2021 "ASME Section VIII, Division 1, Example Problem Manual", Example 4.15.2 "Vertical Vessel, Skirt Design" does not use AISC but rather the Div. 2 methodology.

You could take the results from PVElite and write a simple spreadsheet and use the methodology you want.

This next statement applies to anyone working in the United States where ASCE 7 is used and seismic design is involved. Your analysis must include the requirements of 15.7 and please note 15.7.3 that deals with the over-strength factor. A few years ago we were involved in a project where Compress was used (we use both PVElite and Compress) and the over-strength factor was not included. I don't know if this has been updated (I do not believe it has been) but we have always done these calculations in spreadsheet outside of the software to be sure we know we are in compliance with the buidling code (ASCE is adopted in IBC) which has to be followed where adopted and may result in "thicker" designs than ASME requires.

BR,

 

[mechengineer]

@6155,
You might not waste your time if you were carfully in the dicussion and read the last sentence in my original post. Especially that would save people time reading your comments and replies.
Regards,

 

[mechengineer]

@dig1,
Most of the controversy was the attitude of the words said to others, not the technology itself. Therefore, I believe you will not be involved in such a controversy.
1. Client shall not care about your cost. Thus, as the software user will not be able to accept such reason that said it's very costly to make a program. In another way, users can do the calculation manually to replace where he/she think PVE Lite is incorrect.
2. Design engineer (manufacturer) is fully responsible for the design correctness. Software is just a tool. Thus, we can't accommodate software bugs and incorporate them into your design. If the design exceeds your technical area you shall seek a professional to help or PE in a relative area to review. A practical example, since PV Elite cannot properly design the lifting lugs ( a flat type) for tall towers with a heavyweight. We calculated the lifting lug manually and obtained structural/civil PE approval.
BTW, I found this mistake in PV Elite was when I considered disaster (blast) load. So-called "Conservative", "industry practice" is untenable in technical.
Loading conditions, theories of failure and modes of failure are completely different between the pressure vessel and the structural beam. Thus the allowable stress for pressure vessels and the allowable stress for a structural beam is different concepts. It is not simply to say “conservative”.
As for “industry practice” or “good engineering practice”, normally that is for those cases which are not included in industry codes and have no ready formula. But the skirt is not.
Thanks.

 

[mechengineer]

@dig1,
Step 3 (Example 4.15.2) – Check the allowable stress acceptance criteria.
At the weak point, based on von Mises Stress to calculate the combined stress, which is the same method as AISC to obtain the combined stress. But I have a different opinion on using code allowable by ASME PTB-4. The code allowable stress is for the primary general membrane stress at the whole cross section area of the cylinder, but the maximum combined stress is only at one point of the skirt. So, of course it is greatly conservative in value. But to apply the allowable stress of the primary general membrane stress to a cantilever beam design is definitely incorrect. It's dissonant and irrelevant. Thus it should use the relative allowable stress from ADS (AISC).
Step 4 (Example 4.15.2) - Check the allowable compressive stress per UG-23(b).
The same is true for the allowable compressive stress. The code allowable compressive stress applies to the buckling of a cylinder under external pressure (radial stress). But the skirt as the cantilever beam is under the bending compressive stress (due to wind & seismic loads) and weight compressive stress (axis compressive stress). It should be no such buckling problem like a cylinder under an external pressure. It is just check the combined stress of bending, sheear and weight stresses at the weak point of the skirt. ADS gives the combined allowable stress and the allowable stress of buckling of a column under axial loading (if it is required).
You are a civil engineer. I think you should know better than I, pressure vessel engineer do how to design a simple cantilever beam (like the skirt of a column). Please correct me if what I said is incorrect.
BTW, I think that we shall be in compliance with code, ASME VIII-1, Appendix-G as first priority rather than ASME PTB-4, Example 4.15.2 if any conflict.

Thanks.

 

[mechengineer]

@david339933,
If you always are lucky and every client, user and manufacturer you have accept it, it's ok. But I don't think that's prudence, it's probably just "lucky". But i feel it seems like a very far-fetched argument.