Pitting corrosion on 316 in chlorinated RO water heater
Pitting corrosion on 316 in chlorinated RO water heater
(OP)
Looking for information on corrosivity (crevice & pitting) on 316SS plate heat exchanger being used to heat RO permeate water.
The permeate has been hardened by addition of lime (about 30ppm hardness & 90ppm alk, pH 8), but has up to 2ppm free chlorine from hypo addition. Temp is 55-65 degC.
Look forward to seeing if anybody has documented data.
Cheers
The permeate has been hardened by addition of lime (about 30ppm hardness & 90ppm alk, pH 8), but has up to 2ppm free chlorine from hypo addition. Temp is 55-65 degC.
Look forward to seeing if anybody has documented data.
Cheers





RE: Pitting corrosion on 316 in chlorinated RO water heater
RE: Pitting corrosion on 316 in chlorinated RO water heater
My concern is that I have 2ppm of free chlorine, not just chlorides.
There does not seem to be any literature that sites the effect of the free chlorine on pitting.
There are references to it in chlorination of sea water for scum removal/control in offshore rig water circuits, but not for clean, soft water. This water is used in food industry application, hence the hypo dosing.
RE: Pitting corrosion on 316 in chlorinated RO water heater
If you have continuous flow then I wouldn't be too worried.
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Plymouth Tube
RE: Pitting corrosion on 316 in chlorinated RO water heater
The flow is quite high rate, not sure what the o2 content. Though I thought that crevice corrosion would be worse if it was high o2 content. WShat mechanism are you thinking for that reasoning?
Recent HX maintenance has shown extensive crevice corrosion between plates after 6 months operation & we are looking for a fix (without changing the plates for Ti). This is a food contact application.
RE: Pitting corrosion on 316 in chlorinated RO water heater
If you have had 316 crevice plates, then you may need to move to a better alloy. Can you get 2205 plates?
You might also look into the gaskets. It could be the type of elastomer that they used.
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Plymouth Tube
RE: Pitting corrosion on 316 in chlorinated RO water heater
There is also some pitting in some of the 316SS pipe lines where pipes were not properly flushed before service (pitting in bottom 1/2 of pipe only).
As to gaskets, they are nitrile and they have seen degradation in that the are loosing their filler, so rubbing black on your hands. How do you think the elastomer may be affecting the crevice corrosion?
RE: Pitting corrosion on 316 in chlorinated RO water heater
They should be perfectly intact. 65C in water should have zero effect on the rubber.
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Plymouth Tube
RE: Pitting corrosion on 316 in chlorinated RO water heater