Great....just f***ing great.

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Carnot
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Re: Great....just f***ing great.

Post by Carnot » Thu Aug 23, 2018 3:12 pm

This is a case of electrochemical corrosion accelerated by the water. Just what was in the water? Was there a cleaning solution present, was it treated in any way (RO for instance)?

Obviously in the absence of any water solution the metals components were fine. When they were immersed in the ambient temperature water corrosion was rampant. It would appear that only the fittings (probes and element) were attacked not the shell of the kettle. That suggests that these were the anodes and suffered intense and rapid pitting corrosion. This is classical dissimilar metal type corrosion but it looks to have been catalysed by something - most likely something like a salt creating an electrolyte. An acid would do the same, but normally stainless is pretty resilient, though hydrochloric acid and stainless is not a good combination. My best guess is that this looks very much like chlorides and perhaps some crevice corrosion where the fittings enter the kettle.

I would seriously think about passivating the complete system. The easiest way would be via citric acid with a 4-10% solution. A would avoid using neat Starsan as this is a stiff solution of phosphoric acid and DDBSA. It will not passivate the surface. A few links with useful info.

http://www.ssina.com/corrosion/crevice-pitting.html

https://www.bssa.org.uk/topics.php?article=68

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LeeH
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Great....just f***ing great.

Post by LeeH » Thu Aug 23, 2018 9:00 pm

Just water, plain tap water passed through a standard 3 stage filter. Unless something got in from the build like solder flux?

Great advice on how to passivate, I will acquire some citric acid, fill the HLT and move it around the system. How long does it need to stand with the solution in?


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Carnot
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Re: Great....just f***ing great.

Post by Carnot » Fri Aug 24, 2018 9:41 pm

That is a bit tricky. As you have already cleaned up the system I would try something like a 6-8% solution by weight heated to about 50 deg C and left to soak for about 6 hours cooling naturally. Leave the vessels inside to avoid over-cooling by cold draughts. That should do the job. I assume the probes and the heating coils will be scrapped. Therefore replace all the probes and coils and then passivate. Let us know how you get along but this should set you up fine. Then store dry. I think you have learned a lesson the hard way; you will not be the first and you will not be the last. Put it down to experience.

Skittlebrau
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Re: Great....just f***ing great.

Post by Skittlebrau » Sat Sep 08, 2018 12:38 pm

:-x

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