Copper-Nickel Tubesheet 4

[Fred190]

Hello all,

Our company is about to receive a project for marine application condensers. We are at the R&D stage but can't figure out the best way to seal the tubes and tubesheet joints. Here are the information about the tube and tubesheets,
Copper-Nickel tubesheet (SB-171 70600) with two grooves inside holes
Copper Nickel tubes, 3/4"OD
The tubesheet has been designed per ASME VIII. Pressure is around 400PSI. The diameter is relatively small from 6" to 14".
Tubes are expanded by rolling. But apparently it does not seal tubes to tubesheet. re-expansion and changing the diameter of the holes did not help either. It looks to me that CuNi is too soft to be used as the tubesheet and with every expansion, the holes get deformed and a few leaks show up. Does anyone have any experience with CuNi tubesheet? Is it even possible to use it or we have to go for clad material? Or we have to weld?

Thank you.
Fred

 

Copper-Nickel Alloys - Properties and Applications (12007)
Copper-Nickel Alloy Fabrication


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[SnTMan]

I am pretty sure the joints can be welded. Have also done Al-Br TS w/ Cu-Ni tubes, also welded, but welding is a little difficult.

Monel can also be used for seawater services.

I'd look at changing TS material if you want to avoid welding.

Regards,

Mike

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

 

[MJCronin]

Have you explored TIG welded joints ?..... Can they be done with your application ?

Can you post drawings of the tubesheet showing tube spacing etc ?

Welded Cu-Ni joints have been successful in the past...

See page 15 of this document

https://www.copper.org/applications/marine/cuni/pdf/pub139.pdf

MJCronin
Sr. Process Engineer

 

[Fred190]

@SnTMan,
We had a couple of meetings today and as a result I know that there are other companies who roll the 90/10CuNi tube inside 90/10CuNi tubesheet and it works properly. Also, I learnt that folks use clad for thick tubesheets, probably because of the cost.

@MJCronin,
The welding is possible and we had someone here to check it. But the final estimated cost would be way too high that definitely we won't be competitive.
I will post the pitch size of the tubes to give you an idea of tube spacing.

Although, the fabrication team is following the recommendations of the expander company, but we think that the expander has been set-up improperly. At this moment, we have to figure out a way to keep the final expanded tubes perfectly round.

I will post the results if it worked out. Meanwhile, if someone has any suggestion, I would be happy to hear.

Thank you guys.

 

[SnTMan]

Fred190, you are reaming the tubeholes, correct? And grooving or otherwise enhancing the finish?

Sometimes accurately-sized (tight-fitting) mandrels are placed in tubes adjacent to the one being expanded. Helps, but not a lot. Tedious also.

Regards,

Mike



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

 

[EdStainless]

The trick is that the plate for the tube sheets is made to a higher strength than the tubes (which should be dead soft).
You need to be very careful with the expansion.
Roller expand, well lubricated, testing, and using very good rolling torque control.
You will find if you roll a series of tests at different torque values that the joint strength will gradually increase, and then start falling off.
There are lots of details involved in getting this correct.
You need to make sure that you don't roll too near either face of the tubesheet.
Seal welding is possible, but it takes great care to get correct in CuNi

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Fred190]

@EdStainless,
Yes, indeed what you mentioned is the trick. We could get them passed by doing precise expansion, inside out pattern over the tubesheet. Larger ligament and smaller holes would help, too.

 

[r6155]

Try with test block as per Appendix A in ASME VIII Div.1

Regards
r6155