Rolling AL6XN Tubes into SS316 tubesheet
Rolling AL6XN Tubes into SS316 tubesheet
(OP)
Hi Guys,
I have a customer asking us to roll AL6XN tubes into a SS316 tubesheet. I am obviously suggesting that they go with the AL6XN tubesheets as well, but I am not familiar enough with AL6XN to know if it is even possible to roll AL6XN tubes into a SS316 tubesheet. I know that some materials cannot be rolled into others (ex. SS316 tubes into brass tubesheet) because of differences in strength and elasticity but what is the criteria in making this decision?
Please advise,
Allan
I have a customer asking us to roll AL6XN tubes into a SS316 tubesheet. I am obviously suggesting that they go with the AL6XN tubesheets as well, but I am not familiar enough with AL6XN to know if it is even possible to roll AL6XN tubes into a SS316 tubesheet. I know that some materials cannot be rolled into others (ex. SS316 tubes into brass tubesheet) because of differences in strength and elasticity but what is the criteria in making this decision?
Please advise,
Allan





RE: Rolling AL6XN Tubes into SS316 tubesheet
You will need to develop a tube rolling procedure (measurements before and after rolling to ensure proper tube wall reduction) between the AL6XN and 316 stainless steel and provide a mock-up to validate the tube rolling procedure.
RE: Rolling AL6XN Tubes into SS316 tubesheet
The problem of course is that the tubesheet potentially yields more than the tubes and you don't get a good joint. Rolling a given tube can loosen previously rolled tubes.
This could be an adequate joint or not, depending on the service. I'd kind of consider it a marginal choice for a rolled-only joint.
A mockup would perhaps be in order.
Regards,
Mike
RE: Rolling AL6XN Tubes into SS316 tubesheet
RE: Rolling AL6XN Tubes into SS316 tubesheet
Sntman, thanks for the info about Appendix A. At design temperature of 422F, the fy value is ~0.65 which is of course higher than 0.60. Therefore, we will advise our clients that it is acceptable to roll al6xn into ss316 but it is recommended to go al6xn also.
Thank You,
RE: Rolling AL6XN Tubes into SS316 tubesheet
Thanks again.
RE: Rolling AL6XN Tubes into SS316 tubesheet
Just asking because crevice corrosion of the 316 at the roll joint will be astronomical.
You really need a mock up and careful control of rolling torque, expansion alone is not a suitable control. With strong tubes and soft tubesheet there is no room for error (or re-rolling).
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P.E. Metallurgy, Plymouth Tube
RE: Rolling AL6XN Tubes into SS316 tubesheet
RE: Rolling AL6XN Tubes into SS316 tubesheet
Considering the design conditions (if this were a condenser application it would not matter), I would use a mock-up to demonstrate the effectivness of a rolled tube joint using the stated materials. If anything you can consider grooves in the tubesheet holes accepting the tubes to enhance leak tightness.
RE: Rolling AL6XN Tubes into SS316 tubesheet
RE: Rolling AL6XN Tubes into SS316 tubesheet
There is data reported on dissimilar metal crevice corrosion.
At the joint the 316L tubesheet will see faster attack than if there were 316L tubes in it.
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P.E. Metallurgy, Plymouth Tube
RE: Rolling AL6XN Tubes into SS316 tubesheet