austenitic SS tube wall reduction for TTS expansion joint

[lganga]

Vendors for tube expansion tools, say that the required tube wall reduction for SS tube is about 5% and no more than 7% in CS
I suppose it has relation with the hardenability of the austenitic Stainless Steel during deformation and the consequence of plastic deformation in the tubesheet hole
But maybe there are some others variables that I am not considering.
can you help me to get more about the limit of 5% wall reduction in austenitic SS tubes (like 316L).
Thanks
Luis

 

[metengr]

Tube wall reduction is based on tube material, tubesheet material and service conditions - pressure and temperature. The percent wall reduction seems reasonable for austenitic stainless steel, for carbon steel I have seen tube wall reduction range from 8% to 12%. The actual wall reduction for your application should be based on a tube to tubesheet mock-up with pull out test results.

What more do you need to understand?

 

[lganga]

metengr
Thanks for your answer,.
The problem is that we have a vendor that wants to send us a new U tube heat exchanger with a failed tube (plugged).
But I am sure that one tube failed , is like an emerging part of an Iceberg. May i will have 2/3 parts of problems at future.
I told them to do RCFA to that tube and after that, to check all the tubes (boroscopy-ECT-Helium test) as a way to have a diagnosis of the equipment .
Is a 2 gooves tube sheet hole and seal welded. Both sides ot the tube sheet are 316 claded.They have expanded, the 1.6 mm wall thickness at 8%. So I suspect, that those guys have overexpanded the tube wall in all the equipment.To replace the tube (that was my first answer to vendor) means to take off 10% of the equipment tubes (U tube arrangement). So to take those tubes off, will be worst, because of the scratch on the tube hole.I want to request for a new tube bundle
I will appreciate any other comments.
Luis

 

[metengr]

Luis
The 8% wall reduction may still be acceptable. As I mentioned it is application specific and no one tube wall reduction can be used across the board.

You are correct in having an RCFA of the tube but make sure you don't throw out a good tube bundle for a sake of having one plugged tube. There could be other reasons than to blame the tube roll.

 

[EdStainless]

1. Tube wall thinning is not the correct criteria to be trying to control. When they did the mock up they should have recorded actual hole sizes and tube sizes before and after rolling, as well as the rolling torque. Then when they did the push out testing they could determine a rolling torque that gave good strength and was in a safe wall reduction range.
2. It is not uncommon to see high pressure feedwater heaters (large u-tube HX) go into service with a few plugged tubes. Between variations in handling, installation, rolling, and welding it is not unusual for a few tubes to not be correct in some way. Better to just weld plugs into them and move on.

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