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Old 15-12-2020, 21:32   #1
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anode in heat exchanger - mistake?

I'm worried that my ignorance of the subtleties of anodes might be leading me to improper treatment of my heat exchanger.

My Fischer Panda generator heat exchanger sprung a leak. Turned out the outlet nipple was poorly soldered/braised, and it was leaking at the joint. No substantial corrosion visible, except on that outlet nipple. After getting a $900 quote from Fischer Panda for a new exchanger, I opted to take it to a local radiator shop instead. The greybeard working there told me it was likely cupronickel. I asked if he knew why there wasn't an anode, and he said he could add a threaded port for a pencil anode. He did, and I fitted a small pencil anode. All was good, no leaks, happy generator.

Six months later while doing routine maintenance on the generator, I checked the anode. I half expected it to be un-touched, since the manufacturer deemed one unnecessary. Instead, 2/3 was gone, and the remainder crumbled to a paste between my fingers. .

My questions:

1) My experience with prop/hull/saildrive anodes is that though they disappear, the remainder stays hard. It unnerved me that this was so soft. It made me worry that chunks of anode paste might clog up the tubes. Why is the zinc so soft here, but stays hard with external anodes?

2) Is there any chance I'm doing more harm than good with this anode?

3) Any ideas why the OEM wouldn't deem an anode necessary on an expensive part like this in contact with sea-water? Do cupronickel heat exchangers typically have anodes?

Any anode gurus out there, I'd love your thoughts! Thanks!
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Old 15-12-2020, 23:46   #2
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Re: anode in heat exchanger - mistake?

It’s doing it’s job. Better the zinc than the heat exchanger. My heat exchanger came with a zinc.

Consider changing it more frequently.
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Old 16-12-2020, 00:03   #3
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Re: anode in heat exchanger - mistake?

Does yours ever have that soft crumbly texture?
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Old 16-12-2020, 00:46   #4
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Re: anode in heat exchanger - mistake?

The following is just dockside hearsay but one I have heard often - take it with a grain salt (or zinc ).

Cupronickel is fairly inert in seawater and AFAIK, Yanmar uses it for some of their heat exchangers and when they do, they do not fit anodes. However bronze heat exchangers do usually have anodes.

If the anode is disappearing, then it is working and protecting something. It is unlikely you will be harming anything.

I have found anodes go 'soft' (or crumbly) in cast iron raw water cooled Yanmars.
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Old 16-12-2020, 04:22   #5
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Re: anode in heat exchanger - mistake?

Our pencil anode goes soft and pasty as well. If left it does cause mild clogging of the tubes. In our case this clogging is remedied with some CLR poured down the anode hole.

I’ve also started replacing the anode every quarter to mitigate the paste problem.
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Old 16-12-2020, 04:53   #6
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Re: anode in heat exchanger - mistake?

Just for reference our Onan generator had a pencil anode with recommended change every 500 hrs. it was soft and pasty too at changeover time.
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Old 16-12-2020, 08:29   #7
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Re: anode in heat exchanger - mistake?

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Originally Posted by ohthetrees View Post
Does yours ever have that soft crumbly texture?
Only if I wait too long to swap them out. I wouldn't want a sacrificial anode more than 50% decayed. Based on your description, I'd be swapping every 3 months and see how that goes.
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Old 16-12-2020, 08:46   #8
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Re: anode in heat exchanger - mistake?

My new CuNi heat exchanger (new from Lenco) came with a zinc which does erode over time.

While I am NOT an electrochemist, I suspect that adding the zinc actually causes the zinc to erode. This creates the galvanic circuit between the zinc and CuNi.

Is the zinc REALLY necessary? Don't really know, but if it erodes it IS doing its job.

As an anecdote, I also have a salt-water cooled CuNi oil cooler, also from Lenco. It does NOT have a zinc. It's been in use for 5 years with no apparent corrosion issues.
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Old 16-12-2020, 10:45   #9
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Re: anode in heat exchanger - mistake?

To the OP, i doubt any particles of Zn would permanently block yr system since where-ever they end up in the circuit they will eventually dissolve but i agree w the others that if your pencil anode is showing consumption then it is doing its job. Definitely continue rather than dump the idea. If you are concerned with mushy Zn blocking the tubes then just change the anode more often. It is a matter of time between changes, not the number of hours of the running of yr genset. Best to aim for max 50% anode consumption between changes.
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Old 16-12-2020, 11:12   #10
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Re: anode in heat exchanger - mistake?

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Originally Posted by jamhass View Post

While I am NOT an electrochemist, I suspect that adding the zinc actually causes the zinc to erode. This creates the galvanic circuit between the zinc and CuNi.
This gets at the nut of the thing. Would there be a circuit without the zinc? I have a jefa rudder and they strongly warn that it should not be bonded to a zinc. It should be electrically isolated. Maybe similar thing here.
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Old 16-12-2020, 11:15   #11
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Re: anode in heat exchanger - mistake?

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Originally Posted by SaltyMetals View Post
To the OP, i doubt any particles of Zn would permanently block yr system since where-ever they end up in the circuit they will eventually dissolve but i agree w the others that if your pencil anode is showing consumption then it is doing its job. Definitely continue rather than dump the idea. If you are concerned with mushy Zn blocking the tubes then just change the anode more often. It is a matter of time between changes, not the number of hours of the running of yr genset. Best to aim for max 50% anode consumption between changes.
Andrew
Thanks. My gut is telling me that the zinc might or might not be necessary, but I can’t see how it would do any harm assuming that any zinc paste clogging the tubes dissolves itself rapidly enough.
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Old 16-12-2020, 11:25   #12
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Re: anode in heat exchanger - mistake?

It seems to me that if all the various bits of engine and generator are connected together (i.e. grounded) and some of them are in contact with seawater, the electrical current generated by dissimilar metals will cause all anodes to erode away. I may be wrong, but I would think that the rate of erosion of each anode would depend on how many were in the system. In other words, if you already have an anode in your engine heat exchanger, it will protect that and also the generator. If you add one to the generator, then my simple-minded guess is that each would then erode only half as fast. However, this assumes that there is a conductive path through the water. This may not be true for either the engine or generator heat exchangers because of the raw water pumps, which may in effect isolate the two from each other, and also from the outside of the hull. (The water on the intake side of the pump has the rubber vanes between it and the exhaust side.) That may be why you need an anode in the heat exchanger to begin with! At any rate, having them can’t hurt anything and seems like a good idea. Does anyone else know more about this? I am always amazed at the mysteries of electrolysis.
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Old 16-12-2020, 11:32   #13
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Re: anode in heat exchanger - mistake?

Make your anode life a little easier wrap teflon tape around threads for a good seal. Add a touch of blue loktite to anode screwcap connection to minimize corroded zinc dislodging and having to extract.
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Old 16-12-2020, 11:38   #14
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Re: anode in heat exchanger - mistake?

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Originally Posted by toodoggone View Post
Make your anode life a little easier wrap teflon tape around threads for a good seal. Add a touch of blue loktite to anode screwcap connection to minimize corroded zinc dislodging and having to extract.
Then the anode would be isolated and do nothing. If you’re using standard pencils anode and base, bases are usually brass, adding this to the mix, not only is the zinc providing protection to the HX (somewhat) but also that brass base which is more susceptible to galvanic corrosion.
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Old 16-12-2020, 11:51   #15
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Re: anode in heat exchanger - mistake?

Quote:
Originally Posted by toodoggone View Post
Make your anode life a little easier wrap teflon tape around threads for a good seal. Add a touch of blue loktite to anode screwcap connection to minimize corroded zinc dislodging and having to extract.
Teflon will electrically isolate the zinc, which means it won’t work at all. Just fyi, if you use similar techniques for your prop zincs, or anywhere else, I’d undo it right quick.
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