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.

 

[saplanti]

PV integral parts are given in the code, the remaining is under structural code. However, the stress may be limited by the buckling of the structural plate. Consider this requirement as well.
I hope this is sufficient.

 

[NRP99]

4.15.2.5 Vessel support systems composed of structural steel shapes shall be designed in accordance with a recognized code or standard that cover structural design (e.g., Specification for Structural Steel Buildings published by the American Institute of Steel Construction). If the support is at a temperature above ambient due to vessel operation and the recognized code or standard does not provide allowable stresses at temperatures above ambient conditions, then the allowable stress, yield strength, and ultimate tensile strength, as applicable, shall be determined from Annex 3-A and Annex 3-D using a material with a similar minimum specified yield strength and ultimate tensile strength.

Although Sec VIII div 2 allows to use AISC code for support arrangement of structural steel shapes, skirt design is complex due to local and thermal stresses issue.

4.15.2.2 Unless otherwise defined in this paragraph, if a stress analysis of the vessel and support attachment configuration is performed, the stress results in the vessel and in the support within the scope of this Division shall satisfy the acceptance criteria in Part 5.

If stress analysis (whether PV Elite or detailed FEA I think) is performed then the Part 5 requirements of code allowable stresses apply.

Logically, I think you are correct that for structural components attached to vessel can be designed using AISC allowable. The code requirements are not clear which makes people to have different interpretations. Check whether code interpretation is available or raise one. If the interpretation exist and allows to use AISC then you can refer that to PV Elite support.

For Skirt to vessel junction FE analyses I have done, I used ASME allowable. PV Elite support is correct in their own way to accept code and not a book approach which may be widely used (and logically correct) but cannot stand for code requirement.

Edit:

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).

Even Sec VIII Div 1 allows to use structural code but subject to some requirements given below this para which requires to perform detailed calculation or stress analysis. This leads us to ASME allowable.

 

[saplanti]

In case an elevated temperature involved in the pressure vessel, some companies use kind of temperature gradient, and extend the same material used for shell/head on skirt to acceptable level of temperature for the structural steel application, and use structural steel from that level.

This thermal gradient is to be used in the analysis for the selection of allowable stresses of the integral extended part as well.

From Lisega papers this thermal gradient (temperature reduction from source)is about 2 degC/mm if uninsulated. Companies have their own formula for it.

 

[mechengineer]

@saplanti & NRP99, Please note that the case talked about the skirt (non-pressure part) allowable stress only, not shell or head (pressure part) analysis where located the skirt.

 

[saplanti]

Yes I talked about the skirt. You did not mention about a design temperature but if it has elevated temperature you may have to use pressure vessel material for certain level as I explained in my previous post.

 

[mechengineer]

@NPR99, thanks for your input.
The case is a normal skirt design without thermal analysis required. It's a simple catilever beam under wind/seismic/weight loads. No FEA is required.
I don't think ASME Pressure Vessel Codes needs to provide the non pressure parts or stuctural components design guidance. The code analysis related those supports (non-pressure part) is only to obtain the reaction force on the pressure vessel for the local stress analysis on the pressure parts (shell), not the non-pressure part (supports) it'sself. You must clearly divide the way to analyze non-pressure part (by AISC)and pressure part (by ASME VIII-1 & 2).

 

[saplanti]

If you see there is an inconsistency in the analysis you may directly write to Hexagon/Coade for the issue. I believe they will be happy to answer your question.

Or you may check the user guide of the software to see the application method on skirts.

 

[mechengineer]

NRP99, Please advise more, the contact detail of Hexagon/Coade. Do you think that will be the better way than using PPM Smart Community?

 

[NRP99]

mechengineer
No. When it comes to ASME (stamp) vessel, code must provide minimum guidelines whether its structural/pressure part (which is already in place). Otherwise if it is completely left for interpretation, there will be chaos/mess. Yes, there are some requirements which appears unclear. For which, you are suggested to raise interpretation.

 

[mechengineer]

@NRP99, Code already gives the guidance as the post by you
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).
I don't think it is necessary to raise interpretation.

 

[r6155]

What CODE is used for skirt inspection?
Does anyone take NDE into account for butt welds and fillet welds on the skirt?
Calculations without considering inspections is future scrap.

Regards

 

[david339933]

I See Megyesy stating to use the Stress Value of the head or skirt, whichever is less.
Skirts still fall under the Code...Welding(UW-5), calculations(UG-22), MDMT.(UCS-66)
That being said, Skirt material does not have to conform to any specifications permitted by the Code....Code being Sec. VIII Div.1.(UG-4)

 

[mechengineer]

@r6155,
In general, a pressure vessel manufactuirer may use ASME pressure vessel code to inspect the structure components on the vessel, like lifting lug, suports and so on because they may not have experience to inspect it as per structural code.
The lifting lug is the typical sample that use AISC (allowables) and inspection as per ASME code (100% UT and PT)that approved by strictural P.E without any issue in may projects I did at manufacturer companies. ASME pressure vessel code inspection requirement may be mostly higher than the sturcture.
To respond you, please note that the skirt weld have no RT requirement normally and the skirt is full pentration weld. But I don't think the inspection method will affect you how to determine the allowable stress of the skirt. The topic discussed here is that the skirt allowable stress shall be in accordance with AISC or equivalent, not ASME pressure vessel code.

 

[r6155]

@ mechengineer
1) Any material selected should be compatible with the vessel material in terms of weld ability. If shell is SA 516-70 is not allowable to use a skirt SA-283 Gr C when high wind force (or seismic) , or when lifting the pressure vessel during installing.
2) Weld joint E= 0,55
3) Since this is a very important structural part the allowable stresses used are the same of pressure parts.
4) UT is frecuently used for weld skirt to head.

See Bednar Handbook and Denis Moss Manual.

Regards

 

[r6155]

More information in
PIP VESV1002 COMPLETE REVISION
Design and Fabrication Specification for Vessels January 2019
ASME Code Section VIII, Divisions 1 and 2

Regards

 

[mechengineer]

@r6155,
I disagree it totally.
Is it your own opinion? Please show where it is if it is mentioned in Bednar Handbook, Denis Moss Manual or relative codes as you recommened to see.
How do you judge the importance and unimportance for structural components? What is the basis in behiand, such as design codes or enven if the client specification? But I do think the design allowable stress should not be determined in this way what you want. The Code Appendix-G gives the guidance for the vessel support: '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 AISC allowable stress shall use for the skirt design, there's no question about it.
The skirt as a canlever beam under the weight and bending loads and the pressure vessel under the internal/external pressure loads. The loads and failure modes are completely different. It's an incredible idea to exchange the allowable stresses so confusingly. I think you may need to go through how to derive/determine allowable stress and consideration for both AISC and ASME pressure vessel code. They are totally different.
May I know E=0.55 what is for in the skirt thickness design? There is no the weld joint efficient E in the skirt thickness calculation formula at all. I think that you don't even know how to calculate the skirt thickness. And you take wrongly the skirt (non-pressure part) to the bottom head (pressure part) weld joint as the pressure vessel lap joint weld (E=0.55).Your wrong opinion may come from not knowing how to calculate skirt wall thicknesses and assuming that pressure vessel rules apply to structural members (skirt). It may happen when pressure vessel engineers know nothing about a relatively simple structural design.

 

[mechengineer]

@r6155,
Nothing help to the topic of the skirt allowable stress except let me know you know the above what you list here are.
Thanks.

 

[r6155]

@ mechengineer
You are confused.
You are very comfortable, take a look yourself. You need a comprehensive reading on pressure vessels.
You use the calculation programs without having previous experience in calculations by hand.
Calculations cannot be made without knowledge of welding, inspection and NDE. You need training on this.
You are very comfortable doing computer calculations, but you are not progressing as a pressure vessel engineer.
Sorry.

Regards

 

[GD2]

I am not sure what PVE Lite takes into account while designing a vessel skirt but what I know is that Sec VIII Div 1 doesn't provide a great deal of guidance. Isn't the procedure in Sec VIII Div 2 Para 4.3.10 applies to skirt design? This section provides the rules for supplemental net axial force and bending moment allowable at the base of the skirt. Table 4.1.2 gives the Design Load Case Combinations with allowable stress. Once you determine the governing load case (usually from Axial Weight Force, Appurtenance Live Load, Bending Moment from Appurtenance, Earthquake and Wind loads, check if it qualifies the allowable stress, S at design temperature for the skirt material of construction per Sec II Part D.

GDD
Canada