In one of our projects we have to use in-line pressure balanced expansion joints as the line is connected directly between the reactor bottom nozzle and pump top nozzle. This is a process requirement and we have cyclic operation of the line with following conditions :
Op. / Des. Pressure = 3.5 / 26.8 barg
Op. / Des. Temp. = 130 / 250 Deg. C
No. of cycles = 26500 ( Op. case )
7000 ( Des. case )
Since our design code is ASME B 31.3 the no. of cycles were defined as ASME cycles in the requisition.
Vendors are coming back with calculations telling that they can give these cycles as per EJMA but not as per ASME.
Is it possible to accept the allowed no. of cycles as per EJMA instead of ASME? What are the issued involved?
In the past also the merits and demerits of ASME v/s EJMA cycles were posed to vendors in general but without any conclusive answers.
Appreciate detailed replies.

Regards.

Rajesh,

The vendor typically gives you allowable displacements for specific no. of cycles with correction factor for different no. of cycles.

I presume the no. of cycles you have referred to are the no. of cycles the pipe will be subjected to i.e 26500 .

Now coming to your problem, your pipe and bellow will be subjected to same no. of cycles. I am against using the term ASME Cycles as B31.3 only tells you what will be your allowable stress range for a specific no. of cycles.

If EJMA is not giving any allowable displacement for the specified no. of cycles and your vendor is unable to come out with data for allowable displacement for the specified no. of cycles, then in my opinion talk to process group regarding the possibility of reduction in the no. of cycles , but frankly speaking I don't think that 26500 can come down drastically low.

If your system will actually be subjected to that many no. of cycles then B31.3 will only give you the stress range, it is silent about bellows life. Your vendor has to come out with solution to provide you with allowables for the computed displacement at the specified no. of cycles.

You cannot design bellows and the connected piping for different cycles as they are integral.

Anindya Bhattacharya

B31.3 Appendix X (Metallic Bellows Expansion Joints) has the following statement immediately following the title: "Design requirements of Appendix X are dependent on and compatible with EJMA standards."

You imply that there is a difference between EJMA cycles and ASME cycles. What is you basis for this assumption?

Without digging any deeper to confirm, I believe EJMA & B31.3 calculate fatigue stress the same way but they use different fatigue curves to evaluate those stresses.

And then there's always ASME VIII Div. 1 Appendix 26. We have it in CodeCalc.

Dear Aninda and Dave,
Thanks for your replies.
Actually there is a difference between the ASME and EJMA allowed no. of cycles and they are not compatible.Even the calculation softwares have both the options, to design as per EJMA or B-31.3 This comes due to the difference in the summation of stresses for the computation of stress range in EJMA and B-31.3. e.g. for the expansion joints in question , for the same design parameters the allowed no. of cycles according to vendor calculations are :
2337265 ( EJMA ) and 16397 ( ASME )
You can see there is a huge difference between the two values. This difference was known to us but normally the no. of cycles encountered for bellows was low so we never faced a problem before.
Coming back to my earlier post.
For piping designed as per B-31.3, can we ignore Appendix-X and specify cycles purely as per EJMA? Would it be considered as a change in design code?

Dear Rajesh,

Two things :
1) As Dave mentioned Appendix X is dependent on and compatible with EJMA standards.
2) Appendix X tells ( X 302.1.3)that the curves are for use only with the EJMA equations.

So there is a confusion.I agree that you have shown a case where the allowables differ widely between the two standards, but as I mentioned previously there is no separate ASME allowable as ASME allowable is inseparable from EJMA by point 2).

If there is a difference it mounts to an oxymoron and we need to go deep because it violates the basic statement" dependent on and compatible" as per Appendix X


Anindya Bhattacharya

Dear Rajesh,

I revisited the EJMA requirements and found that you are correct, the EJMA and ASME requirements differ although the total stress range equations per Meridional stress should be as per EJMA ( paragraph X 302.1.3 ).The difference lies in the curve fitting equation and the constants used.

Coming to your question as to whether we can avoid Appendix X, since the "requirements are dependent on and compatible with EJMA standards" as per Appendix X , which unfortunately is proving to be an oxymoron in your case, you can go as per EJMA design.In my opinion this is nota violation of code rule.

Although EJMA defines fatigue life only in terms of meridional stress and since your case is pretty complicated, you can check for the hoop stress effects ( if they are high ) with Modified Goodman diagram.This is implied in EJMA.

Anindya Bhattacharya

If the vendor can't satisfy your requirements based on ASME cycles, then they can't satisfy your design, period!

You'll need to sign up for a free ID, but if you check out MDP16 here

http://www.pathwayb.com/index.html

Go to LITERATURE on the side bar, TECHNICAL PAPERS, MATERIAL DATA PAPERS, and choose MDP16, you will find a write up on the difference between ASME and EJMA cycles.

Basically, ASME cycles are designed to insure that the design will survive the number of cycles specified. If you call for EJMA cycles, they are based on a fatigue curve fit that goes through the failure points, meaning some failure occur above the level, and some occur below. If you specify EJMA cycles, you need to specify a higher number to give a safety factor.

Essentially, if you need 26500 ASME cycles (which you do, if that is how many cycles your system must undergo), then you would need to specify somehing like 50000 EJMA cycles to get a design to do what you need.

Now that's that is out of the way, I think you're going to have a very hard time getting an expansion joint designed to handle that kind of cycle life. I'm guessing that your number is to be the cycles for a 20 year design life.

What you are probably going to have to do is discuss with your client what the planned interval is between shutdowns and see if you can get the joint designed for that cycle life, with plans to replace the joint as part of the planned shutdown work.

Thanks Edward,

MDP16 is quite informative and gives a clear idea about the differences in ASME and EJMA cycle life.

Rajesh,

You can also through the the book: Process Piping: A complete guide to B31.3, Chapter 18, by Charles Becht. This chapter contains an elaborate discussion on the same topic. Thanks for raising such an important subject for discussion in this forum.

Anindya Bhattacharya