Expanded Only Tube to Tubesheet Allowable Loads

[meltedEng]

Hello,

For reference this question is related to ASME BPVC VIII Div 1, appendix A. This is where we started.

I'm trying to justify the allowable load and the joint design on an expanded only enhanced TTS joint (type i per Table A-2). Normally we only work in welded only using A-2 with A-3 testing, but currently we are working with some unweldable alloys for corrosion.

We created some QW-193 style mock-ups and push-out tests per A-1(e)(3)(-d). We could apply A-2 (with fr from A-3) to get L(max) as we normally do for welded, which gives an acceptable allowable load of 2000 lbs for at operating temperature push-out. Our application only requires 400 lbs.

A-1(e)(3)(-d) requires A-5 to be satisfied, which by inspection requires an fr of 1. This would give us an allowable load of 5000 lbs. We only need an fr of ~0.2 for this application. Rolling this material to reach an fr of 1 is ill advised.

Essentially we don't need to handle the loads that appendix A seems to be designing for. We are considering disregarding A-5 as it appears to be wanting us to highly over engineer. Our push-out at temp gave us the 2000 lbs allowable, and we're comfortable with that.

Is there another industry standard or reference for determining the allowable load on this joint type at operating temperature? If anyone has some insight or reference into the justification of A-5, that would be appreciated.

 

[SnTMan]

meltedEng , your references to the various parts of Appendix A are confusing to me (no A-1(a)(1)(d) for example). Why are you not just calculating Lmax per eqn (3) w/ fr = 0.7? Does your material combination fall under A-1(e)(3)? Tubesheet CTE equal or greater than the tube?

Failing all else, you have apparently established that your loads established by test exceed the design loads required. Appendix A is Non-Mandatory.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[meltedEng]

SnTMan/Mike, my mistake, it should be A-1(e)(3)(-d) (I edited the OP), you are correct, we must do the test.

Part 1 is that customer requires qualification of the joint. Part 2 is that we have evidence from another non-ASME job that the joint would not meet fr = 0.7, so we know we can't make that assumption in good faith. We have historically made that assumption on all other alloys and done a "full" expansion, but can not do a "full" expansion here.

I agree, it is non-mandatory, and we are planning to go ahead on the basis of eqn (3) with the fr from eqn (5). For fT, I took that as L(test)1/L(test)2 (coming out to 0.8). I don't believe the A-5 qualifier should apply. If we wanted to use fr(test) of 0.9 from Table A-2, it would make sense.

 

[SnTMan]

meltedEng, complicated subject, hard to navigate thru without exact design data.

It appears to me that under A-1(e)(3)(-d) a joint is qualified for a proposed operating temperature per A-5 eqns (6) & (7) without establishing a value for fr, and in turn Lmax. Establishing an operating temperature under A-1(e)(3)(-b) is complicated by the interface pressure factors Po, Pt and may not be practicable. Also apparently does not yield a value for fr.

So to then establish a value for fr one would apparently need to revert to A-4 eqn (5). How to resolve with A-5? L(test) and L2(test) presumably represent the same test data so one could conclude that fr = 1.0, but it's kind of a circular argument if you ask me.

At any rate, it sounds as if you have established an acceptable allowable load by test, and if both you and the client are happy with it I see no reason not to proceed.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand