Tube to tube sheet joint

[Nagaprasanna]

Dear Experts,
We have fixed tube sheet type heat exchanger in Ammonia plant. Due to corrosion, leak was observed in tube to tube sheet joints. Tube to tube sheet joint is expanded (double grooves) with seal weld. We intent to replace the tube bundle with SS tubes & SS overlaid Carbon steel tube sheet. Can we have the same tube to tube sheet joint (Expansion with seal weld) design?

Design Parameters
Shell Side
Design Pressure:23 Kg/cm2(g)
Design Temperature:70 Deg C
Fluid:Ammonia
Joint Efficiency:0.85
Tube Side
Design Pressure:6 Kg/cm2(g)
Design Temperature:50 Deg C
Fluid: Cooling Water
Joint Efficiency:0.85

Thank you

With Best Regards,
Prasanna

 

[gr2vessels]

What ammonia, is it liquid ammonia, Aqua Ammonia or what? What cooling water, how corrosive is. How much dissolved oxygen is in the water?
You seem to have an interstitial corrosion problem, perhaps stress corrosion cracking of the seal weld of your tubes. You need to stop the 'ammonia' penetrating the gap between the tube and tubehole. One way is to over expand the tubes past the tubesheet about 3 mm or so (I assume you will overlay the shell side of the tubesheet).
I don't see much of use of the seal weld once you prevented the ammonia entering the mentioned gap, but if you do, be careful to not overheat the tubes and generate differential thermal expansion of the tube and tubesheet, resulting in loss of tube expansion in grooves.