"Pitting corrosion in exchanger Cooper tube"

Question:

"This week we've have a great problem that has caused a shutdown plant. A failure in an cooler with spiral cooper tubes. After inspecting the tubes we have found that copper tubes were attacked by pitting corrosion. The fluid in shellside ( in contact with the external surface of the tube ) is Octane and residual Chlorine ( we can see a green waste in shellside and over tubes so we suspect chlorine is present. So my question is, Could the chlorine waste cause pitting corrosion in this Copper tubes? This cooler is about ten years old. presence of HCl is in the O.D.of the tubes. We are looking for another tubes material more HCl pitting resistant than Copper. We are thinking in Hastelloy or Titanium, the problem is in this case the cost of this materials. My question is: Which type of material do you recommend in HCl service? (I suppose it depends on Tª and concentration, at this moment I don´t know these data because we are analysing the shellside fluid )."

Answer:

I responding to your post, I am assuming that the pitting corrosion was originating from the O.D. If chlorine was present in the O.D. fluid and water was also present, either intentionally or due to ingress from contamination, dilute, aqueous hydrochloric acid (HCL) could be present on the shellside. While copper is somewhat resistant to HCL, its resistance depends on concentration and temperature. You may want to investigate this possibility. You are correct. The appropriate exchanger tube selection will depend on the process temperature and concentration of hydrochloric acid (HCL) on the shellside. (Plus the ability to manufacture spiral tubes from altenate alloys!).

 

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