Appendix 2: Reverse Flange Design - Dimension C is close to B (=B') 1

[sxz]

Hi,
I have a reverse flange design, I am concerned that the circumferential stress 1 in the g1 area is larger than that in the g0 area due to the area reduction by the bolt hole, see the attached sketch. I think the ratio of g1/g0 should be greater than 2, then the circumferential stress 1 should be equal to the circumferential stress 0. Please advise if we need to make g1/g0 >2.
Thanks.

http://files.engineering.com/getfil...Reduction_Due_to_Bolt_Hole_Circumferentia.pdf

 

[XL83NL]

Attachment missing

 

[sxz]

Attached the sketch. Thanks.

 

[prex]

Why are you defining it as a reverse flange? IMO it is a regular direct flange.
Also IMO, you don't need to deduct the bolt hole in evaluating stresses, this is not required by App.2.
Consider also, aside from normative considerations, that the ring flange behavior of this flange is very limited, due to the relatively small lever arm of bolt location to wall location: bending stresses per App.2 should be low.

prex
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[sxz]

Prex,
Thank you for your response.
1) Appendix 2, 2-13 is applied for Reverse Flange.
2) St1 and St2 (tangential stress is used in Appendix 2) contain the moment M0, St1 and St2 are under the allowable stress limits. But if we use the basic formula for the ring flange, St = PR/t, t should be the effective thickness by deducting the bolt hole diameter, St will be more than the allowable stress, Sfa. The integral ring flange is part of vessel shell.

 

[prex]

This is NOT a reverse flange, as the bolt circle is outside, not inside vessel wall mid line.
And BTW t is flange thickness in axial, not radial, direction

prex
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[sxz]

Prex,

Thanks for your time and valuable input.
I agree on the first one, not a reverse flange.
For the second question: The ring flange is part of vessel shell. If we use the basic stress formula for the ring, Circumferential stress = PR/t, t (ring thickness in radial direction) should be the effective(or remaining) thickness by deducting the bolt hole diameter, the circumferential stress in the ring will be more than the allowable stress. The required thickness is 6", the remaining thickness is 4" (=9"-5"). There are over 20 bolt holes (5" in diameter).
Can we say the ring wall thickness in radial direction is not adequate?

 

[prex]

Yes, sorry, you are right. IMO you need the required shell thickness on the inside of the bolt holes, you can't count on the material on the outside to satisfy the minimum thickness requirement.

prex
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[r6155]

The bolt hole is filled with the bolt, hence the bolt is part of the shell thickness.

Regards
r6155

 

[prex]

r6155, what you state might be true for compressive stresses, but certainly not for tension; anyway it is not permitted by code. One could always, however, follow the detailed analysis route...

prex
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[r6155]

prex, please see Pressure Vessel Design Manual by Dennis Moss 4th edition pag 517 Studded Flange Detail and you can see (under figure) the text "Assume this material does not exist and analyze the flange as an ordinary weld neck flange"

Regards
r6155

 

[sxz]

Prex,

I got another question, regarding the depth of tapped hole for the stud, can we use the formula: 0.75d (Sb/Sa) from UG-43(g)?

R6155,

Thanks for your input, but I don't have the design manual, 4th edition, I have one in 3rd edition.

 

[r6155]

Prex
1)Is very easy to imagine an welding neck flange in your scheme, or
2)Buy the 4th edition of design manual and charge the cost to the project.

Regards
r6155

 

[sxz]

R6155,
The current design of body flange on shell side is a ring type, bolt hole in the ring, that makes me worrisome. The body flange is not a weld neck type.

 

[r6155]

sxz
See attached sketch

Regards
r6155

 

[prex]

r6155
your figure is not applicable to the present case, as the bolt holes, as in all ordinary situations, are outside the continuation of the outer diameter of shell. As a consequence the shell thickness is maintened intact up to the flange face, as in all ordinary ring flanges. In the present situation the bolt holes are much closer to the inner shell face, and IMO the minimum required shell thickness need be maintained between the bolt holes and the inner shell face.

sxz
I think you can use UG-43(g)

prex
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[r6155]

prex
I believe that you do not have design manual 4th edition by Dennis Moss.

Regards
r6155