Duplex tubes expanded in 316 tubesheet

[motorjoost]

We have new air-cooler bundles, with Duplex tubes expanded in 316 headerboxes.
The tubes have been expanded in accordance with API 660.

Principle of the connection is plastic deformartion of the tubes into the grooves of the tubesheets.
As the yield strength of duplex is 2,5x yield strenght of 316, I doubt if the connection is sufficient and leak tight.
(hydrotest has been performed without problems).

Does anyone have experience with this situation?

Kind regards,
Joost

 

[metengr]

As long as a tube rolling or other form of tube expansion procedure was written and qualified via pull out testing (using a tubesheet mock-up to verify tube wall reduction), I see no problems.

 

[vpl]

Motorjoost

What I understand from your post is that you're questioning whether performing a plastic deformation of the tubes into the grooves of the tubesheets in accordance with API 660 will lead to problems with leakage in the future.

I don't deal with the petroleum standards such as API so I don't know how that applies; however, the concept of using tube expansion is valid and, as metengr said, as long as you used a qualified test procedure, you should be ok.

As you say the hydro was performed without problems, what is underlying your concern about the application? Do you have really high vibration in the tubes? Have you seen problems before?

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[motorjoost]

Thanks for your answers so far.

Herewith some more information:

The expanded connention has not been qualified by means of pull-out test.

A hydrotest test does not necessary mean the connection is leak-tight.
for example:
A tube-bundle can pass a hydrotest @ 30 barg, however the same bundle can leak at a helium leaktest @ 0,3 barg.
(note: a helium leak-test has also not been performed)

Joost

 

[SnTMan]

motorjoost, you are right to be concerned about this joint.

If available you might look at ASME Sec VIII, Div 1, Appendix A. API 660 may have something similar, I am not familiar with it.

Without looking up the numbers I believe Appendix A would require qualification testing due to the difference in yield strengths between the tubes and tubesheets.

Regards,

Mike

 

[metengr]

motorjoost;
Here is what you should do; use the same conditions for tube expansion in the field and with a mock-up perform a pull out test. You will know right away if the roll expansion was too light. Roll joint strength relies on frictional force between the tubesheet hole and the roll expanded tube.

You cannot simply use mechanical property data to base your evaluation. A pull out test is definitive.

 

[weeeds]

We would do a Helium Leak Test by putting the tube side under vacuum, introducing Helium from the outside, and checking for leaks using a mass spec.
Best test available.

 

[unclesyd]

Weeeds
That method is well and good but it is sometimes hard to located the actual leak as there are several welds in close proximity. I think a better way is to pressurize the
shell with He and N and use a sniffer probe. Prior to the I would use a leak detector fluid and check for and fix any leaks. If any are found leaking fix them before checking
with the probe.

Even if a pull-out test shows some deficiency in the joint as is I think the bundle can and should be made workable.

The link to Hydra Pro has a list of papers/articles that you could get through a library or the Linda Hall Library. Also on the Hydro Pro site they have a method for the future of presetting the tubes prior to mechanical rolling or hydro expansion or welding.

To All:
How difficult would it be to seal weld the tubes?

Have you considered hydraulic expansion?

What is the tube and tube hole size information and how many grooves?

what are the operating conditions?

http://www.hpro.com/papers.php

http://www.lindahall.org/

 

[motorjoost]

All,

Thanks for your help!

ASME VIII div.1 appendix A specifies indeed exactly the tests that need to be performed in these kind of situations.

Kind regards,

Joost