Variant of reverse flange design

[mechengineer]

Hi dear PV experts,

Due to the small channel ID of 465 mm, we need to use a variation of the reverse flange design. Can ASME VIII-1, Appendix 2-13 for Reverse Flanges be applied to this variant?
If anyone has experience designing this type of reverse flange variation, I would appreciate your insights. I believe this variant may be more effective than Fig. 2-13.1, as it appears to experience less internal pressure bending.

Thanks.

 

[SnTMan]

Well, I don't believe you can fairly call this a "reverse flange". It is more a variation on a Sketch 2-4 intergral flange to my eye.

Design of a similar desigh was discussed in this post https://www.eng-tips.com/threads/as...ell-boundary-permissible.524846/#post-9039665

Why not just design a flange that fits clearly within the Rules? Why make life hard on yourself?

 

[mechengineer]

@SnTMan ,

My requst is in beteewn reverse flange and studding flange to minimize the flange size and weight. FPSO project, it is very critical space limit. I will try to go to studding flange if there is not calculation reference for my request. It is not possible to install the removable partition plate if using the reverse flange (flange ID is too small).

 

[TGS4]

Studding flanges carry their own issues. My recommendation would be to use sparingly.

 

[r6155]

Install the studs and never remove them. A pleasing design to me.

 

[SnTMan]

Speaking from possibly imprecise memory here:

TEMA Type W, packed floating head exchangers use a similar flange design at the floating tubesheet because the clearance between the packing flange and floating tubesheet is necessarily small. These units are of course moderate pressure and temperature.

When designing one of these I would treat the flange as having a B dimension equal to the shell ID, 465 units in the OP's case. g0, g1, h. A, C etc. were set accordingly. There are no particular computational difficulties presented by the the gasket ID or even G being smaller than B. Of course the hub shape factors and resultant stresses are not correct, but better for computational purposes to neglect metal that is actually there than the other way around. LOL

Probably catch a bunch of flak over this, so be it

OP: 40 thousand PSI? Really? Sec VIII, Div 1 may not be appropriate.

Regards,

Mike

 

[mechengineer]

@SnTMan ,
Because of the different shape of flanges, some simplifications of geometry shape can be made to cater to the exised formula, that may be acceptable or derive the formula by hand-calculation.
Yes, DP=247 MPa. Design by VIII-2. Appendix-2 is appliclbe for VIII-2. It may remove to VIII-2 in future, like tube sheet calculation UHX.

 

[SnTMan]

Well, best of luck with your gasketed joints

 

[mechengineer]

@TG4,
Yes, ASME VIII does not provie studding flange calculation. Currently, <Pressure Vessel Design mannual> 4th Ed. by Moss has been used for studding flange design.

I’m happy to see you here again. Let me take this opportunity to share the current status on heat exchanger flange design by using ASME Appendix-2 and PCC-1 App-O.

When using the m and y values of the gasket to determine the required bolt area in ASME VIII-1, Appendix-2, and the required gasket stresses (Sgmin-s and Sgmin-o) to determine the required bolt area in PCC-1 Appendix-O, the results differ. The higher of the two values will be used as the basis for the design bolt area. However, the code does not provide values for Sgmin-s and Sgmin-o, unlike the m and y values which are provided. Currently, Sgmin-s is set to 140 MPa and Sgmin-o to 97 MPa (for most gasket types, such as SWG, Kammprofile, metal jacket gaskets, etc.) as per API 660 Table 3, which is widely used in design practice.

This, of course, raises the design requirements for flanges. However, no one dares to directly use the Sgmin-s and Sgmin-o values provided by the gasket vendor, as the code does not offer them.

It would be greatly appreciated if you could appeal to the ASME Flange Design Committee to improve the flange design rules, ideally unifying them under a single guideline/design rule, whether it’s Appendix-2, Appendix-O, or another approach (such as leak rate considerations).

The current situation in heat exchanger girth flange design is as follows:

The design process is very complex, leading to higher engineering costs.

The required bolt area and flange size have increased due to the use of Appendix-O and API 660, leading to an estimated 20% increase in flange material costs.

P.S. with my 40 years design experience, I have not seen any design issue for the girth flange design for vessel/heat exchanger as per ASME VIII-1 Appendix-2.

Thanks.

 

[mechengineer]

@SnTMan , RTJ metal ring gasket used.

 

[r6155]

@ (OP)
On your drawing, DP = 274 MPa.
On your publication, DP = 247 MPa (35,825 psi).
Both DP values are incorrect based on the thickness of your drawing.
You say, "ASME VIII does not provide stud flange calculations.". Incorrect.

 

[TGS4]

FYI - in the 2025 Edition of VIII-1, Appendix 2 will be "removed", with reference to VIII-2 4.16. No new methods will be introduced in VIII-2 in the 2025 Edition. However, the SWG-BFJ is working on implementing alternative rules for the 2027 Edition (fingers crossed).