Calculation required for ASME B16.5 flange that is machined

[customgeo]

Our customer has request a pressure vessel with an altered B16.5 Flange. They need 2 counterbored holes drilled radially through the outside diameter of the flange, between the bolt holes, similar to an oriface flange. Are there code calculations to verify, i.e. area replacement, or min. wall thickness? Thanks for your help.

 

[CodeRef]

Consultation with your AIA of record is necessary.
I had a similar issue where this came up but the question was dismissed because it was decided to end the Code boundary at a nozzle stub, so as to have the owner/user connect the piping to the vessel under the governing piping code upon installation of the vessel. So, this issue never did get answered for me. However I am curious as to the correct answer here.

In my opinion, it should not be very difficult. I do not know why VIII-1 does not recognize B16.36 (Orifice Flanges) because it is an ASME/ANSI Standard. VIII-1 does not restrict Manufacturer's Standards, yet only because B16.36 is not addressed in Table U-3 or UG-44, it is implied that it is not acceptable for use. It may be resolved easily with your AIA. Hopefully someone else has come across this issue and had it resolved.


There are three kinds of people in this world; those who can count and those who can't.

 

[customgeo]

I spoke with our AIA and he said you can't alter the flange. In his opinion to use the altered flange you must design per appendix 2.

I'm in the process of confirming this from those higher up the ladder.

 

[CodeRef]

How do you design for orifice holes per Appendix 2?

I had a shop that had to address holes for guide pins in their Appendix 2 flange for which they could not provide any calculations. (guide pins to guide the floating tube sheet into the flanged channel/head.) The answer was addressed by a proof test which was required for the channel inlet/outlet nozzles that did not comply with UG-37. We just addressed both issues and the alternative design for each issue was resolved by a single proof test.

IMHO, I would go the route of UG-11 and try to get the AIA to recognize the ASME/ANSI Standard.

There are three kinds of people in this world; those who can count and those who can't.

 

[dcasto]

Just buy orifice flanges, or do you larger holes?

 

[prex]

Your AIA is correct on the principle, after all it is not their duty to have a practical sense (though that would always help).
Personally I would follow this way of reasoning:
-App.2 calculations are based onto a ring beam model, and the strength of a ring beam is governed by the section modulus of the rectangular section about its neutral axis at mid thickness (bt²/6, b=flange ring width, t=flange thickness)
-App.2 does not require to deduct bolt holes from the section modulus, and the reduction of the modulus is proportional to the ratio of hole diameter to b (so that it may be not really negligible)
-a radial hole at mid thickness will also reduce the section modulus, this reduction may be easily calculated and will be quite negligible: the section modulus of a rectangular section changes by only 12.5% when the hole has a diameter that's half the depth t
-hence the reduction in flange strength due to the radial hole is much less than the reduction due to bolt holes, and if bolt holes are acceptable...

prex

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[proinwv2]

prex

While I would like to agree with your logic, I have a problem.

First, how many small, radial, holes would be acceptable? Even though the code ignores the existence of the bolt holes, it is not a "correct" assumption. Several have shown that the area of highest stress is usually at the id, near the bottom (adjacent the flange). This is where the holes penetrate the boundary.

Conservative assumptions in the code, local compression at bolts, and stress redistributions in ductile materials keep us out of trouble.

I am sure that many have experienced the inadequacy of Appendix 2.

Paul Ostand

http://www.ostand.com

 

[unclesyd]

We have numerous flanges that are components of our polymer transfer system that have radial holes drilled in the flange proper to allow for either a thermowell or pressure tap. The flanges are CL 2500 and the system has a design pressure of 3000 pounds @ 700 F. These holes were drilled about 30 years ago with the full blessing of our AI, after he consulted with the home office.

Calculations at the time showed, as stated above, that the effect of the holes/holes was negligible when it comes to meeting the requirements of Appendix II, resisting hydrostatic end force and gasket seating.

 

[bk834]

As a follow up to one of the previous posters, I was told today that our AI would not approve the use of an orifice flange meter run in BEP because the ASME B16.36 standard is not referenced within the ASME B31.1 code. I have worked for two previous companies where orifice flanges have been supplied in metering runs for both ASME Section I and BEP applications. I cannot remember the basis for approval of these applications by our AIA and I do not like using anecdotal evidence (ie. "we have always done this") to support my position. I would appreciate any additional enlightenment on the topic that anyone can offer.