Acid Resistance of Cast Iron 2

[jpuy]

Hi, i'm new to this forum. need help...

We are unable to run our Sewage Treatment Plan Lifting Station at the moment due to high salinity/acidity content of water. (ie. Water TDS (total dissolved solids) = 5000ppm due to groundwater seepage).

We are afraid that pump impeller (cast iron) will not resist too high acid water content. (damaging impellers too quickly)

Any suggestions? (we are trying to lower TDS of water to 2,000ppm)

Thank you.

 

[arunmrao]

You can provide a coating of rubber on the impeller just to be safe.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[swall]

What is the pH? How long do you expect this condition to persist?

 

[EdStainless]

There are some alloy cast iron grades that are used for very bad waters, even seawater.
The only problem with using rubber coating is if there is H2S present (often is in sewage) then it will likely attack the rubber.
This would not preclude the use of a different coating.
There are many epoxy based coating systems. While they are more susceptible to impact damage than rubber is they have much better chemical resistance. If you go this route get references from the coater and call them to ask how it has held up. You are always better off coating the parts prior to any exposure.
Surface preparation is 99% of a coating job.

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Plymouth Tube

 

[mw1st]

I'm not sure if it is feasible in your case and you may not have time, and foundry close by willing to to the job. In our city we replaced those impeller for sewage treatment with stainless steel. We use the original impeller as a pattern and casted it in 316 SS.

 

[jpuy]

Thank you for all your valuable information.

@ swall, We have not obtain pH value. We concentrated on the TDS level only.

At the moment, we are trying to locate the source of seepage in the network and apply chemical blasting method to seal it.

Any opinion?

 

[cloa]

I assume it is grey cast iron.

 

[quark]

There is no relationship between TDS and pH. You can maintain 5000 ppm TDS water at perfectly neutral condition. The first question, as swall already asked, is what is the pH?

Reducing TDS will not guarantee you of increase in pH.

 

[blacksmith37]

High silicon (like 10% as I remember) cast iron can handle very corrosive conditions. It has been around forever so there must be information available.

 

[IRstuff]

Alternately, if this is a continuing issue, you would need to have a neutralizer, i.e., something adds alkalinity back into the water to crank up the pH. We used to do that with our semiconductor lab, to ensure that the acidic effluent didn't attack the sewer pipes.

Supposedly, some jurisdictions like to have the sewage flow to be a bit on the alkaline side



TTFN

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[arunmrao]

blacksmith37,higher grades of silicon can handle acid attacks well. Unfortunately they render the metal brittle,annd in extreme cases special handling. as the application is for a pump impeller,it is not advisable to use higher silicon grades,rather use some protective coating instead.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[blacksmith37]

Oppps, I thought they were looking for pipe and impellers. For only an impeller, spend a little money; C 276, 625, etc.