Corrosion in Deminerelized water process

[Asadee]

pipe all line : Austenitic ss 304 and welding (weld decay)

process : raw water(lake,river) >>> Activated carbon >>> cation exchanger >>> anion exchanger >>> storage

found pitting corrosion on pipe surface : before activated carbon , after activated carbon and before cation exchager only.

why after that not found ?
what cation exchanger did ?
how to fix or other grade ?

sorry for my English.
thank you very much.

 

[EdStainless]

Are you injecting chlorine to kill microbes?
If not I am guessing that MIC is your problem.
And yes you would need a better alloy, probably 2205 would be the best option.
But we would need full water analysis to really know.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Agree with Ed. If MIC, change alloy. 316 will prove no better than 304. Depending on Temperature and Chloride content, 2205 may not work and a super-duplex may be required.
Consider change to HDPE for inlet piping.

 

[EdStainless]

I agree Stan, using non-metallic pipe for the intake section is a very good option.
You could run this up to your first ion exchange bed.
After ion exchange the Cl should be very low (I hope) and 2205 is a good low risk option.


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P.E. Metallurgy, Plymouth Tube

 

[Asadee]

thanks.
i'm guessing not is MIC because not found Biofilm in pipe and found corrosion around the pipe.
process : raw water(lake,river) >>> sand filter >>> Activated carbon >>> cation exchanger >>> anion exchanger >>> storage
(i'm sorry)
acttivated carbon can absorb some Cl. but after Activated carbon found corrosion (may be efficiency of activated carbon)
and after cation exchanger not found because Cl loss for corrosion at after activated carbon. after cation exchanger Cl Very low was not enough for corrosion.
(i'm guessing)

 

[bimr]

If the chloride concentration is high, the pitting may be attributed to the chlorides. When the chloride concentration exceed 200 mg/L, 316L would be preferred. Manufacturers often recommend a chloride ceiling for Type 316L of 500 mg/L.

You should have lined pipe starting at the cation unit, so obviously there would not be corrosion after the cation unit.

Normally, water from a lake would not have a high chloride concentration.

 

[EdStainless]

So are you killing the micro-organisms or just assuming that since they aren't forming thick film that there are none?
If this is 316, and you are finding pits that are not associated just with welds, then either you have high Cl or MIC, or you are depositing specs of carbon into the pipes and then driving galvanic corrosion at those locations.

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P.E. Metallurgy, Plymouth Tube