Galvanic Corrosion on Anion Feed Pump

[cremesti]

Dear Colleagues,

We recently opened the feed pump that pumps decationized water (pH about 4) from the strong cation exchanger to the anion exchanger and we noticed that the impeller which is made from cast iron is eroded away significantly at the suction side and there is also erosion on the discharge side. The shaft is made from SS and the SS nut on it is 50% gone. The pump casing which is also made from cast iron is eroded/pitted. The most interesting observation is that the impeller is covered with a graphite like substance.

How do you explain these facts? if it is galvanic corrosion why is the cast iron AND the SS nut eroded? same question if it is low pH corrosion? and what is this graphite like substance? is the C which is in the cast iron leaching out as graphite?

I would appreciate any insights.

Best regards from Poland

rami

 

[bimr]

Decationized water is basically a weak mixture of sulfuric and hydrochloric acids. There are not many materials that will stand up to those acids.

You need a lined pump, like the demineralizer piping is supposed to be. Polypropylene or saran lined.