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Anode Myths part1.


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2 minutes ago, catweasel said:

A bit of an aside, but what are your thoughts on measuring the voltage within an engine to  "test" the corrosion control of the coolant? Lots of stuff about it on you tube but no real science expalined. BS?

If its a closed circuit cooling system the anti freeze contains probably nasty chemical inhibitors. If its an overboard system utilising canal water for cooling then the engine manufacturer should have avoided dissimilar metals and or fitted internal anodes. It would take considerable re-engineering to measure corrosion potentials

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17 minutes ago, blackrose said:

We had three mobile phones charging, two laptops, two battery chargers and several other appliances running at the same time but we still couldn't get my GI to go into conduction.

No you won’t. The rules were changed quite a number of years ago due in part to the proliferation of RCDs and GFCIs and the various electrical bodies around the world now tend to specify <85uA leakage to ground for any one device. The use of Y capacitors (or large bypass capacitors) as was common in the past is now frowned upon and in many countries is forbidden. 

 

Edit to add that many chargers are Class 2 anyway, so have no earth connection at all. 

Edited by WotEver
Add the last bit
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6 minutes ago, Chris and PJ said:

If its a closed circuit cooling system the anti freeze contains probably nasty chemical inhibitors. If its an overboard system utilising canal water for cooling then the engine manufacturer should have avoided dissimilar metals and or fitted internal anodes. It would take considerable re-engineering to measure corrosion potentials

Sorry should have said closed circuit.

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7 minutes ago, Chris and PJ said:

If its a closed circuit cooling system the anti freeze contains probably nasty chemical inhibitors. If its an overboard system utilising canal water for cooling then the engine manufacturer should have avoided dissimilar metals and or fitted internal anodes. It would take considerable re-engineering to measure corrosion potentials

I believe that Cat was referring to this:

https://www.familyhandyman.com/automotive/car-maintenance/coolant-testing-with-a-multimeter/

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15 minutes ago, WotEver said:

From a corrosion point of view I would say that if the inhibitor was worn out the coolant would become more acidic and a more accurate test would be a litmus paper test.

Reason being that the oxygen would in a closed system be depleted over time so the only corrosion mechanism would be hydrogen fueled causing the coolant ph to drop to acidic corrosive levels. But don't all engine manufactures quote replacement periods?

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6 minutes ago, Chris and PJ said:

From a corrosion point of view I would say that if the inhibitor was worn out the coolant would become more acidic and a more accurate test would be a litmus paper test.

Reason being that the oxygen would in a closed system be depleted over time so the only corrosion mechanism would be hydrogen fueled causing the coolant ph to drop to acidic corrosive levels. But don't all engine manufactures quote replacement periods?

Yes they normally do. It was just something that caught my interest really. I have done a litmus and it has shown alkaline. There are other things than corrosion protection of course! 
Sorry I overthink stuff :)

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13 hours ago, blackrose said:

 

Switch mode mains appliances can induce interference currents, but it takes a lot of RFI to force a decent spec GI into conduction.

 

About 12 years ago I did a test with ChrisW (remember him?) using his ossiloscope. We had three mobile phones charging, two laptops, two battery chargers and several other appliances running at the same time but we still couldn't get my GI to go into conduction. But if it's a concern then as you say, get an isolation transformer. Then there's absolutely no rub at all.

 

Modern phone chargers and other small devices with switch mode power supplies are not connected to earth. The earth pin on the plug isplastic and thus prevents any harmonic currents leaking to earth.

Edited by cuthound
Switch, not such mode power supplies.
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10 hours ago, Mike the Boilerman said:

 

I skimmed your post thanks, but didn't see any myths dealt with. 

 

 

 

 

I did wonder how the composition of the canal water might affect the performance of, or the need for, sacrificial anodes.

 

I'm no chemist, but just thinking about it logically, if the boat was floating in, say, hydrochloric acid, the hull would be getting thinner much more quickly, and the presence of an electric current would further accelerate the process, wouldn't it? . 

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7 minutes ago, Machpoint005 said:

 

I did wonder how the composition of the canal water might affect the performance of, or the need for, sacrificial anodes.

 

I'm no chemist, but just thinking about it logically, if the boat was floating in, say, hydrochloric acid, the hull would be getting thinner much more quickly, and the presence of an electric current would further accelerate the process, wouldn't it? . 

Water composition is critical, and as water becomes more conductive anode material changes otherwise the anode ‘effect’ is too strong and paint will start lifting.  So sequence is magnesium for fresh, then aluminium then zinc for sea water.

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2 hours ago, Machpoint005 said:

 

I did wonder how the composition of the canal water might affect the performance of, or the need for, sacrificial anodes.

 

I'm no chemist, but just thinking about it logically, if the boat was floating in, say, hydrochloric acid, the hull would be getting thinner much more quickly, and the presence of an electric current would further accelerate the process, wouldn't it? . 

Yes it would but if you made the hull more negative thus more cathodic only more positive more anodic elements would get thinner / consumed. Hence sacrificial anodes regardless of PH google Pourbaix diagram mild steel or iron

 

Of course the composition of canal water is relevant and if by measurement it is determined that a sacrificial anode of any practical surface area cant supply enough power to push the potential of the hull into the required -0.800 Volts cathodic protected zone then best practice indicates that additional power be added by means of an impressed current cathodic protection system. If that be the case its a question of cost effectiveness against the cost of loss. Magnesium anode of MIL-A-21412 spec are designed to work in drinking water canal water I something very different being loaded with cations and cations as can be seen a they collect on the brown tubercles attached to the canal pilings. 

 

Certainly reading this forum many are consuming anodes. Some are not. The question being why? Lots of good advice but no potential measurements!

Is it that some waters are more electrically conductive than others. Certainly off line marina waters that I have tested are considerably more active.

Is it that all anodes are not equal in effect due to construction and metallurgy? No one is measuring them! 

 

 

 

 

 

 

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I suspect the biggest driver of corrosion is bad shore power on both shore side and boat side.  Even a good boat in a ‘bad’ marina or next to a ‘bad’ boat is going to suffer.

 

If I was suffering serious corrosion of my hull, anodes would not be my first thing to look at, it would be leakage currents from the marina and adjacent boats.

Edited by Chewbacka
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11 minutes ago, Chewbacka said:

I suspect the biggest driver of corrosion is bad shore power on both shore side and boat side.  Even a good boat in a ‘bad’ marina or next to a ‘bad’ boat is going to suffer.

 

If I was suffering serious corrosion of my hull, anodes would not be my first thing to look at, it would be leakage currents from the marina and adjacent boats.

All of which can be determined in absolute terms, with no shadow of doubt by the use of half-cell.

I am happy to help anyone with the same concerns either in person or by loaning the equipment.

 

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3 hours ago, Chris and PJ said:

if by measurement it is determined that a sacrificial anode of any practical surface area cant supply enough power to push the potential of the hull into the required -0.800 Volts cathodic protected zone 

 

I'm sorry, but this is palpable nonsense. A sacrificial anode cannot provide any "power" whatsoever to anything.

Power is the rate of energy transfer.

 

 

 

 

Edited by Machpoint005
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7 minutes ago, Machpoint005 said:

 

I'm sorry, but this is palpable nonsense. A sacrificial anode cannot provide any "power" whatsoever to anything.

Power is the rate of energy transfer.

 

 

 

 

Thank you for your input

It will be added to Anode Myths part 2 as a Myth

In fact anodes are selected by their Voltage rating, Current capacity and design life

 

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1 hour ago, Machpoint005 said:

 

I'm sorry, but this is palpable nonsense. A sacrificial anode cannot provide any "power" whatsoever to anything.

Power is the rate of energy transfer.

 

 

 

 

The circuit comprising the anode (usually magnesium on fresh water), the cathode (boat metal) and the electrolyte (canal water) makes a battery.  Like all batteries it supplies power, just in this case not very much power at all.  If you were to disconnect the anode from the boat and put a current meter between the anode and boat you would measure a small current.  If your boat is lucky and the anodes last years, the current will be tiny.

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20 minutes ago, Chewbacka said:

The circuit comprising the anode (usually magnesium on fresh water), the cathode (boat metal) and the electrolyte (canal water) makes a battery.  Like all batteries it supplies power, just in this case not very much power at all.  If you were to disconnect the anode from the boat and put a current meter between the anode and boat you would measure a small current.  If your boat is lucky and the anodes last years, the current will be tiny.

Yes exactly

If a hull is correctly coated so no bare metal is exposed to the water no current will flow and the electrically connected sacrificial anode will not lose weight and the cathode will not corrode.

 

Remember that corrosion in metal occurs because of its direct contact with the water and mostly the action of the dissolved Oxygen in that water. Anodes offer a simple way of stopping this by making the metal too cathodic to corrode.

Magnesium sacrificial anodes are metallurgically designed to work in fresh water for long periods. Canal water mostly more conductive.

The voltage (potential difference) that causes an Fe atom to loose an electron to become a water soluble Fe ion (rust) is tiny  as is the current.  

 

 

 

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17 year old narrowboat, 2 pack coated when new, been blacked with bitumen over that regularly to cover scratches, spent most of its life in a basin without shore power for any of the boats, original 4 anodes still have perhaps one third remaining, hardly any hull corrosion. The basin also has a good through flow of water rather than being a stagnant side basin.

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18 minutes ago, PeterF said:

17 year old narrowboat, 2 pack coated when new, been blacked with bitumen over that regularly to cover scratches, spent most of its life in a basin without shore power for any of the boats, original 4 anodes still have perhaps one third remaining, hardly any hull corrosion. The basin also has a good through flow of water rather than being a stagnant side basin.

Sounds similar to our winter mooring. Our anodes seem to do 10 years or so (no shore power to any boats.)

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1 hour ago, PeterF said:

17 year old narrowboat, 2 pack coated when new, been blacked with bitumen over that regularly to cover scratches, spent most of its life in a basin without shore power for any of the boats, original 4 anodes still have perhaps one third remaining, hardly any hull corrosion. The basin also has a good through flow of water rather than being a stagnant side basin.

Is your base plate coated or bare metal?

Are your anodes being consumed equally

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