Microbiological Induced Corrosion

[Yobbo]

Hi,

I also got the MIC diagnosis on a CuNi 90-10 piped heat exchanger, that cools hot air down with raw water from a nearby canal. The expert tells me there's little one can do. Killing the bacteria off with chlorine dosage is not allowed any more due to environmental regulations. The second best would be to periodically clean the inside of the pipes. From the material analysis it resulted that the chosen material CuNi seems to be less resistant against the organisms. He recommended us to step back to the former material Al-Brass. That seems to be able to form a better passivation layer that might ward off the attack. The problem could be avoided with titanium pipes.

The reason for my reaction is:

1. to share this experience with others
2. to find out if there are proven preventive measures other than using chemicals. I am also interested in proven cleaning methods. We apply hard plastic rotating brushes, but it is very hard to determine whether the biological slime is properly being removed by that.


Any other suggestions or tips ( pipe material ) are welcome!

Awaiting your reply,

Karel

 

[metengr]

Regarding material for MIC exposure, I would strongly consider Seacure for this heat exchanger. Your only other alternative is to go with Titanium. I have seen brass heat exchanger tubing suffer from dezincification under silting conditions.

 

[EdStainless]

While 90-10 has good corrosion resistance the two worst things for it are SRB (sulfate reducing bacteria) or alternating clean water and dirty water.
I have recently seen 90-10 pit in some very clean water, that only saw dirty water with bacteria a couple of days a month.

If you go back to Al brass all you will do is spread the corrosion out.

You probably can't go to Ti because of the risk of vibration.

We see people using SEA-CURE or AL-6XN (the latter if they have a lot of money). They can both stand up to MIC, stagnant water, and they have the stiffness to let you use thin walls and still have vibration resistance.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[davefitz]

Typically the copper alloy tubes have a low design water velocity, which allows the MIC to attach to the wall . If you switched to Seacure or an appropriate SS you can increase the design water velocity to over 7 fps, and thus avoid attachement of the MIC to the tube surface. Also would need to drain the HX dry during idle periods, and would likely need to change the circ water pump to address the new flow requirements.