Aluminum anode degradation in cooling water

[kevlar49]

I have noticed that aluminum anodes (not sure if they were indium alloyed, but they should have been that or mercury) have decomposed in cooling water service (couldn't find out what temperature) and started to plugging the exchanger.

Does anyone know why that would happen? I am aware that aluminum anodes will start to lose current capacity and possibly passivate at higher temperatures, but why would it decompose?

 

[EdStainless]

The sludge is mostly aluminum oxide. It is from rapid degradation of the electrodes. I am going to guess that this water has high conductivity and low flow rate. This stuff should be flushed through the system with normal flows. You may need to look at anode alloys with lower potentials to reduce consumption rates.

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Plymouth Tube

 

[kevlar49]

Thanks Ed. Is there a certain anode spec that I should follow (e.g. ASTM, MIL) to avoid this problem?

 

[SMF1964]

You're dealing with general corrosion of aluminum in cooling water environments. Your sludge is a mixture hydrated aluminum oxide/aluminum hydroxide and is typical of exposure of aluminum to, as EdStainless pointed out, high conductivity stagnant water.