VIII-1 Appendix 2 Nonsense 1

I'm about 80% through writing a spreadsheet to run flange calculations per Appendix 2 and I now have to program 44 different LONG equations in for the "flange constants". C, C1, C2, C3, ... C34 etc. What kind of nonsense is this? Why didn't they just combine all of these factors into a few factors empirically?

I've also noticed that when you run these calc's that the flange stress can increase as you increase the hub angle (say, beyond 12 degrees). Does that make ANY sense?

Are there any plans to eliminate this from the code?

 

[kstaylor]

Christine74,

I will attempt to answer your questions in reverse order.

4. Are there any plans to eliminate this from the Code?

There is a special working group within the ASME VIII-1 Code Committee that is developing a revised flange design method. The Pressure Vessel Research Council is sponsoring this work and the new method is referred to as the PVRC method. Details of this new method have been published in several journals over the last few years. The new method is based on selection of a leakage criteria for the flanged joint in question. New gasket factors have been developed to replace the current m & y numbers. Incidentally, the new method fell out of an effort to validate the existing m & y numbers that was started more than 10 years ago.

I suspect that when the PVRC method is added to the Code it will first appear as a non-mandatory appendix. It may exist as a non-mandatory appendix for several years before it is given mandatory status.

3. Does increased flange stress with increasing flange hub angle make any sense?

I assume that you are talking about longitudinal hub stress increasing as the hub angle increases. This does make sense if you think about what is happening physically as the angle increases. As the hub angle increases the hub effectively gets shorter. This results in the transition from the flange ring to the straight cylinder (i.e. pipe) being shortened up. In effect you are increasing the “notch sharpness” of this transition. Increased notch sharpness results in increased or higher concentrated stresses. So, yes, it does make sense that a shorter hub or larger hub angle will result in higher flange stress.

2. Why can’t they combine all the factors into just a few?
1. What kind of nonsense are the 44 flange constants?

I’ll combine both these questions in a single answer. Appendix 2 attempts to establish rules for flange design for many different types of flanges (integral w/ hub, integral w/o hub, slip-on, socketweld, screwed, split ring, etc. etc.). Each of these different types has different geometries, necessitating different factors. With all the different combinations of geometries and types, plus some of them being able to be analyzed as either loose or integral, you wind up with a lot of factors. Now if you are only calculating one type of flange, say tapered hub type flanges like a weld neck flange, you can program just the actual formulas needed for that type. If you want a more general program/spreadsheet you will need them all.

I gather from your post that programming your spreadsheet is your first effort at flange design or analysis. If this is error please forgive me. I would strongly recommend that you make several calculations by hand before attempting to develop a computer solution, even a spreadsheet. You will learn much about the nuances of flange design that just running a computer solution will not give you.

If you want to understand the flange design rules better I would direct you to some important papers that detail the development of the ASME Code rules for flanges. These are as follows:

- E.O. Waters, D.B. Rossheim, D.B. Wesstrom, & F.S.G. Williams, “Development of General Formulas for Bolted Flanges,” Taylor Forge & Pipe Works, Chicago, IL, 1937.

- E.O. Waters, D.B. Wesstrom, & D.B. Rossheim, “Formulas for Stresses in Bolted Flanged Connections”, ASME Transactions, 1937. Also see associated discussion. Article available in Pressure Vessel & Piping Design, Collected Papers 1927 – 1959 by ASME, recently reprinted.

- D.B. Rossheim & S.E. Bergh, “Effect of Internal Pressure on Stresses and Strains in Bolted-Flanged Connections”, ASME Transactions, 1951. Also available in Collected Papers 1927 – 1959.

Other important publications on flange design or analysis are:

- Bulletin 502, “Modern Flange Design”, 7th edition, originally published by the Taylor Forge Co. (now out of print). Copies may be found in technical book stores (e.g. Brown Books in Houston) or used bookstores. In another thread someone indicated they have posted a copy on the web in PDF format.

- “Process Equipment Design”, L.E. Brownell & E.H. Young, John Wiley & Sons, NY, NY, 1959, Chapter 12, Design of Flanges (recently reprinted and available on Amazon.com).

 

[TD2K]

Just to pop in here, the Taylor Forge "Modern Flange Design, Bulletin 502" can be downloaded in PDF format at

http://briefcase.yahoo.com/testdog2000

in the eng-tips folder.

 

[mgp]

Christine74

Check this thread
thread378-19042
in the Piping & fluid mechanics engineering Forum

I made a spreadsheet including the factors, dimensional databases and so on, which you might find useful.

Send me a mail and I'll drop you a copy

Regards
Mogens
mgp@kabelnettet.dk

 

[rkchalla]

TD2K
I looked in the yahoo address that you have given and did not find the pdf file. Can you post it again.
Thanks
Rama

 

[TD2K]

This is very annoying.

Yahoo has recently changed the terms and conditions and non-Yahoo users now no longer see any files there (as opposed to the 'can not enter' message you might expect).

To get access, go to Yahoo and sign up for a free email account. Then, go to

http://briefcase.yahoo.com/testdog2000

and the files are visible.