Applicability of Sec. VIII, Div. 1, App. A to Tube End Seal Welding

[bam8888]

This question pertains to seal welding of tube-to-tubesheet joints per ASME Sec. VIII, Div. 1.

Does anyone know if App. A is required for seal welded tubes, since they are not covered by UW-20?

In my particular case, I have 2205 Duplex Tubes seal welded to SA-516-70N Tubesheets (Fixed TS exchanger). The problem I am having is that if I follow App. A, A-2 for definition of Fy, it states that qualification testing is required when tubesheet-to-tube yield stress ratio falls below 0.6. In my case at the specified operating temp's, Fy=0.44. We will not be performing any qualification testing, so this violates App. A requirements.

I know app. A is listed as non-mandatory, but our latest design software continues to tack app. A onto the end of the UHX tubesheet calcs.
I just want to be sure there is no reference in the code that invokes App. A for seal welding so that I can ignore the Fy ratio requirement.

Any help on this is greatly appreciated.

 

[gr2vessels]

bam8888,
Tube-to-tubesheet joint seal welded only is not in accordance with the ASME VIII-1. Hence the tubes must be expanded in the tubesheet (refer Table A-2). If it is expanded and the Fy is less than 0.6, you have to perform qualification tests as per the code (refer A-3 and A-4) and use Fr in Table A-2. Otherwise you cannot prove/calculate the stresses in the shell, tubesheet and tubes, particularly when large temperature differential is experienced between the shell and the tubes.
Cheers,
gr2vessels

 

[bam8888]

Sorry, I forgot to mention the tubes will be roll expanded after welding. Thanks for the help. Guess we have no way out of this one without the qualification testing.

 

[SnTMan]

bam8888, a little more to the story: Apx A is of interest only if you need to calculate an allowable tube-TS joint load, which you do for a fixed TS exchanger.

The reason for limitations on Fy are because, such as in your case, with a high tube yield and low TS yield the tubesheet can be yielded while the tube is not. No seal. Also as tubes are rolled, previously rolled tubes can be loosened. This is why qualification is required.

Of course, Apx A is, as you point out, non-mandatory. You could take your chances

Regards,

Mike