TEMA RCB-8 Flexible Shell Elements (Bellows)

[RonJeremy]

Hello. Here is a question about the formulas used in TEMA 8th edition for the design of expansion bellows (called FSE). Actually, I doubt if anybody knows the definitive answer - this is more of a heads-up to my fellow engineers that there is yet another problem in TEMA. I've been wanting to submit the query to TEMA, but their website has been down about 6 months: I'll have to use snail-mail.

I'll try to keep this short, but if you want to know more, let me know.

If the FSE is about the same thickness as the shell to which it attached you will get a factor C2 which is around about 1.0. Depending on whether C2 is less than 1.0 or greater than 1.0, you have to use a different set of formulas to calculate C4:C8 and e. Look at the attached graphs: there is no convergence around C2 = 1.0.

I have a FSE where the spring rate is 2.2 million pounds per inch and the stress is 173 ksi if you take the FSE to be 18 mm, but if you change the thickness to 18.00005 mm (therefore C2 < 1), the spring rate drops to 150000 lb/inch and the stress drops to 43 psi. So a tiny change in the thickness of the FSE results in monumental changes to the final results. By the way: 1) there is nothing wrong with my maths, 2) it doesn't matter whether you use pound-inch or Newton-meters, the results come out the same.

 

[nickelkid]

Why are using the 8th edition? The 9th has been out for almost a year.

 

[RonJeremy]

Because that is the project requirement, of course! In an EPC contract the contractual documents are frozen at an agreed date, for purely practical reasons. Since this project was sanctioned about a couple of years ago, some of the documents are not bang up to date. That cannot be helped. I'm sure it would be a great idea to buy the 9th ed. but I don't think our accountants would let me, and we cannot wait for the delivery. I was rather hoping when I wrote the thread that someone had come across this problem before and could give a concise and helpful reply.

Anyway, to put aside nitpicking about which edition to use: what is the answer? Has 9th ed. put the error right?

 

[nickelkid]

My understanding is that the 9th edition TEMA RCB-8 FSE was "completely rewritten" to address numerous problems.

Changes highlighted in a webinar presented on

http://www.paulin.com

are:

1) The 9th edition TEMA RCB-8 FSE guidelines will generally result in lower stiffnesses of from 1-to-2 times for the brief survey given.

2) The 9th edition TEMA RCB-8 FSE guidelines will generally result in lower stresses of from 1-to-2 times for displacement based stresses and 1-to-6 times for shell side pressure stresses.

3) Programs using the 8th Edition of TEMA for FSE’s may be too conservative and can show “no solution” results, where solutions using FSE’s exist.

4) VIII-I UHX-17 permits higher allowables but requires a plastic evaluation of the FSE. Kj=J=0 can be used to simulate this condition for other exchanger components.

5) The TEMA 9th edition software will calculate the plastic stiffness for the user given the plastic displacement of interest.

6) Guidelines are given for squirm where multiple FSE’s are used.

7) Simplified FSE sizing steps were provided.

8) Methods for finding the design displacement “d” for use in the 9th edition of TEMA RCB-8 are given for UHX and TEMA methods.