Cold-Reforming of UNS 39274 (duplex) Tubes

[Peter113]

Hello to all,
we have a multitube heat exchanger (minimum center to center diameter: 14") with tube bundle according to UNS 39274 (superduplex) cold formed and solution annealing(U-bends and 12"). The tubesheet layout is square pitch (1") and the U-Bends have been formed according to triangular layout (15/16"). Due to long delivery date of new forged tubesheet (UNS 39750) or new tubes, we would like to repair the U-Bends safely. Herebelow you have sime more detailed information:
- Maximum radial displacement: 1.5" (opening and closing the bend).
- Total length oh tube bundle: 240"
- Distance between the U-Bends tangent line and the first baffle: 1"
- BWG: 16
- Tube OD: 3/4"

Our major concern is the first baffle because this is the most deformed region because the radial displacement of the tube is 1.5" in 1" distance (i.e, 56º). Our idea is to perform necesssary and realistic non-destructive/destructive to assure the integrity of the tube: For example, we have proposed the following:
- Thickness, ovality, visual inspection, diameters, eddy current testing,. Which is your opinion?

From a metallurgical point of view, we could have any problem with the tube based on the above information. Would be necessary to perform again the solution annealing? Would you recommend to perform any non-destructive examination or any other?

Thanks for your support and awaiting for your reply.
Regards
Peter

 

[EdStainless]

I don't see any problems with reforming the ubends. I would suggest that you NOT try to reanneal the bends. There is very little risk of CSCC with this alloy and there is a very real chance of messing up the properties by not heating or cooling correctly.

If you had asked me I would have suggested that you not anneal the bends in the first place.

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Plymouth Tube

 

[captsmith]

we take used tube bundles and rebuild them our selves to save money. I not an engineer but I've found that unless you have to anneal the tube to make the bend don't. we use 3/8 type k copper and have a 1 inch bend for the inner row and have problems with the bender crushing the pipe while bending, to overcome this we anneal just the area to be bent and then fill the pipe with packed sand and bend, between the softened metal and the sand filling the void it makes a nice bend and we have not had problems with service life.

 

[mcguire]

The heat affected zone near the annealed zone will probably have sigma making it both brittle and less corrosion resistant. Heat treating super duplex is dangerous.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/