Anode Myths part1.

[Chewbacka]

If you want to see anodes making power then you could do worse than getting one of these -

https://www.amazon.co.uk/4M-2749-Lemon-Clock/dp/B0065FYTT2/ref=sr_1_2?keywords=Lemon+clock&qid=1568881217&s=kids&sr=1-2

 

and it’s a good excuse for a G&T with a slice of lemon

 

 

Edited September 19, 2019 by Chewbacka

[Machpoint005]

16 hours ago, Chewbacka said:

Like all batteries it supplies power, just in this case not very much power at all.

 

No, the circuit supplies energy. The anode does not supply power.

If you are going to hide behind technical concepts you really need to use your terms accurately.

Just like the OP fails to do.

[Chris and PJ]

7 minutes ago, Machpoint005 said:

 

No, the circuit supplies energy. The anode does not supply power.

If you are going to hide behind technical concepts you really need to use your terms accurately.

Just like the OP fails to do.

Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.

[Chris and PJ]

9 minutes ago, Chris and PJ said:

Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.

The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow, so (negatively charged) electrons flow out the anode into the outside circuit

[Machpoint005]

15 minutes ago, Chris and PJ said:

Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.

 

Your original use of the term "power" was still inaccurate though. I notice you didn't use the term at all in this quoted post.

 

The highlighted text here is dimensionally inconsistent. You have [M]  [A]^-1  [T]^-1 on the one hand, and [M]  [A]^-1 on the other.

[Chewbacka]

27 minutes ago, Machpoint005 said:

 

No, the circuit supplies energy. The anode does not supply power.

If you are going to hide behind technical concepts you really need to use your terms accurately.

Just like the OP fails to do.

Power is amps multiplied by volts.  A cell (often incorrectly called a battery, which is 2 or more cells wired together) consist of an anode and a cathode immersed in an electrolyte.  There is a potential difference between the anode and cathode and if you connect a load between the anode and cathode a current will flow.

 Assuming that the load is appropriately sized there will be a potential difference (voltage) across the load and a current (Amps) will flow.

So the power supplied by the cell to the load can be calculated.

[Machpoint005]

2 minutes ago, Chewbacka said:

Power is amps multiplied by volts.  A cell (often incorrectly called a battery, which is 2 or more cells wired together) consist of an anode and a cathode immersed in an electrolyte.  There is a potential difference between the anode and cathode and if you connect a load between the anode and cathode a current will flow.

 Assuming that the load is appropriately sized there will be a potential difference (voltage) across the load and a current (Amps) will flow.

So the power supplied by the cell to the load can be calculated.

 

I don't dispute this. Please don't patronise me with second-form physics.

 

The OP was implying the anode was a power source, which it isn't, any more than the steel hull or the electrolyte is. You only have current flow, and therefore energy transfer, when there is a circuit. 

 

 

22 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...

"sacrificial anode supplying power"

[Chris and PJ]

On ‎17‎/‎09‎/‎2019 at 21:12, Chris and PJ said:

Again any electrically changing of the corrosion potential of your hull can simply be measured with an ag/agcl half cell. Non functioning galvanic isolators being just one cause. Of course the best isolation is achieved by the air gap within an isolating transformer.

My view on galvanic isolators is that all the circuit diagrams, that I have looked at of how they work tells me that most types rely on the voltage drop of diodes which is fine.

My problem with the  use of diodes is this application is the fact that %90 of diode failure modes result in a short circuit within the diode.

So if they fail, they no longer offer a voltage drop and just conduct like a piece of wire.

 

One thing about diodes is that they don't like high current spikes even of 1000 thousandths of a second. And tend to eventually fail over time if repeated spikes are sent through them.

Most ac appliances that contain transformers, especially microwave ovens, upon shut down snub any back EMF`s down to earth through `y` configured capacitors.

These high voltage, very high current spikes, of very short duration are normally absorbed by the earth and are unnoticed.

 

Its just a thought and somewhere in this forum a qualified electronic guy will be able to confirm or dismiss this.

[Chris and PJ]

28 minutes ago, Machpoint005 said:

 

I don't dispute this. Please don't patronise me with second-form physics.

 

The OP was implying the anode was a power source, which it isn't, any more than the steel hull or the electrolyte is. You only have current flow, and therefore energy transfer, when there is a circuit. 

 

 

"sacrificial anode supplying power"

I strongly advise to go look at:

https://www.matcor.com/impressed-current-cathodic-protection/

 

Anything else I say could be considered patronising

[Chris and PJ]

3 hours ago, Chewbacka said:

If you want to see anodes making power then you could do worse than getting one of these -

https://www.amazon.co.uk/4M-2749-Lemon-Clock/dp/B0065FYTT2/ref=sr_1_2?keywords=Lemon+clock&qid=1568881217&s=kids&sr=1-2

 

and it’s a good excuse for a G&T with a slice of lemon

 

 

Should there be a heath warning regarding possible electrocution if you are earthed and your lips touch the lemon. Perhaps this is why cocktail sticks are non conductive 

[Chewbacka]

44 minutes ago, Machpoint005 said:

 

I don't dispute this. Please don't patronise me with second-form physics.

 

But you told me I was wrong to say you could get power from a corrosion cell, at least we are agreed you do.  I shall say no more.

[WotEver]

11 minutes ago, Chris and PJ said:

I strongly advise to go look at:

https://www.matcor.com/impressed-current-cathodic-protection/

I’ve scanned it and don’t believe there’s anything in that which isn’t already understood on these boards. I also note that at no point do they refer to ‘power’. 

[yabasayo]

1 hour ago, Chris and PJ said:

Anode current rating – all anodes have a current rating based on how long they can be expected to operate at a given current rating.  All anodes have some defined expected life based on current output and time – so many Amp-Hours of service life.  For example a magnesium anode may have an expected consumption rate of 17 lb/Amp-year (7.8 kg/amp) so if a 17 lb anode is operated at 0.1 amps it would have a life of 10 years.

Not an exact science. Erosion rate of the anode is not linear and depends on its surface area and condition. The anode would be far less effective when it reaches year 10 of your example than it was when new. For those reasons anodes should be replaced when they have lost around 60% of their mass.

Edited September 19, 2019 by yabasayo

[Guest]

Not aimed at anybody in particular: Had hoped to learn a little from this thread, but looks like it will descend into the usual hair splitting. Pity.

Edited September 19, 2019 by Guest

[Chris and PJ]

17 minutes ago, WotEver said:

I’ve scanned it and don’t believe there’s anything in that which isn’t already understood on these boards. I also note that at no point do they refer to ‘power’. 

Copied from the site that you obviously did not read:

Basic Types of Cathodic Protection

There are two basic types of CP systems: galvanic (or sacrificial) and impressed current. Galvanic anode systems (also termed sacrificial anodes systems) use a metal that is naturally more negative than the metal being protected and thus when the two metals are connected electrically to each other, current flows from the metal that is more electrically negative to the metal that is more electrically positive. This current flow results in a rapid consumption of the anode, hence the common term “sacrificial anode” is often used to describe these anode systems. Typical galvanic anodes include magnesium, zinc and aluminum as each of these are more electrically negative than carbon steel or other steels.

Impressed current anode systems are different than galvanic (sacrificial) systems because they utilize an external DC power supply to create the electrical current flow. The use of an external power supply enables an impressed current system to generate significantly higher current output with fewer, longer lasting anodes than any sacrificial anode system.

 

And from the same site:

Impressed current cathodic protection systems have the benefit of using an external power supply to drive current. This makes it possible to protect virtually any structure, regardless of size or current requirements using long life anodes and enough appropriately sized power supplies.

 

 

PERHAPS THE POWER YOU ARE THINKING ABOUT DOES IS NOT MEASURED IN WATTS (AMPS X VOLTS)

PERHAPS YOU THINK CURRENT CAN FLOW IN A CIRCUIT WITHOUT A POTENTIAL DIFFERENCE (VOLTS)

 

ANODES SUPPLY CURRENT. TO SUPPLY CURRENT HAS TO BE A POTENTIAL DIFFERENCE

ANODES ARE ELECTRICALLY MORE NEGATIVE THAN THE MORE POSITIVE CATHODE HULL SO THERE IS A POTENTIAL DIFFERENCE. THEY ARE CONECTED TOGETHER SO CURRENT FLOWS 

CURRENT = AMPS POTENTIAL DIFFERENCE= VOLTS 

AMPS TIMES VOLTS = WATTS

WATTS IS THE MEASUREMENT OF POWER

 

I politely suggest that you do not understand that an anode is electrically more negative  of say-1 volt than a cathode of say -0.5volt making a 0.5 volt potential difference or that current flows from the more negative to the more positive

 

If you get a bunch of magnesium anodes put them in a bucket water with a piece of steel and connect a 3v torch bulb between the anodes and the piece of steel  it will light. Power to do this comes from the magnesium anode.

 

 

[Chris and PJ]

32 minutes ago, yabasayo said:

Not an exact science. Erosion rate of the anode is not linear and depends on its surface area and condition. The anode would be far less effective when it reaches year 10 of your example than it was when new. For those reasons anodes should be replaced when they have lost around 60% of their mass.

It is an exact science. Anodes of MIL-A-21412A  by specification are designed to work in a linear fashion, for a known time to a set loss of original weight and surface area. Oil platform anodes are designed to last for the design life of the platform because they are stupendously expensive to replace 

If you mean that Narrowboat anodes systems have not being designed to last for the design lifetime of the hull or take into account the varying water types or environmental conditions or no real compliance testing of anodes because they are cheap to replace. You are absolutely correct

 

My example is from an industry that requires the highest standards

31 minutes ago, catweasel said:

Not aimed at anybody in particular: Had hoped to learn a little from this thread, but looks like it will descend into the usual hair splitting. Pity.

I entirely agree with you.

[WotEver]

28 minutes ago, Chris and PJ said:

Copied from the site that you obviously did not read:

Oh, and now insults! Thank you for your kind words. 

 

You have copied and pasted a large chunk of what I’ve already read and I repeat, at no point does it mention the ‘power’ of an anode as you did in a previous post. It explains in baby language that the PD of an anode-hull circuit must be impressed if it cannot be achieved simply by selection of the anode type, depending on the circumstances of the boat wrt the electrolyte it’s sitting in. Obviously, the resultant circuit will use power as does any circuit but an anode does not itself possess power as you suggested earlier in this thread, it merely forms part of a circuit, either galvanic or impressed, which will result in energy being expended. 

[WotEver]

56 minutes ago, Chris and PJ said:

If you get a bunch of magnesium anodes put them in a bucket water with a piece of steel and connect a 3v torch bulb between the anodes and the piece of steel  it will light. Power to do this comes from the magnesium anode.

That’s like saying a piece of lead is ‘powerful’ because if you put it into some H2SO4 with a piece of lead dioxide it’ll power a motor. 

[Chris and PJ]

4 minutes ago, WotEver said:

That’s like saying a piece of lead is ‘powerful’ because if you put it into some H2SO4 with a piece of lead dioxide it’ll power a motor. 

 

5 minutes ago, WotEver said:

That’s like saying a piece of lead is ‘powerful’ because if you put it into some H2SO4 with a piece of lead dioxide it’ll power a motor. 

Please explain how an anode works

Please explain why external power supplies are necessary in impressed current systems used to directly replace sacrificial anodes to get exactly the same result.

[WotEver]

2 minutes ago, Chris and PJ said:

 

Please explain how an anode works

Please explain why external power supplies are necessary in impressed current systems used to directly replace sacrificial anodes to get exactly the same result.

See post #67. I’m not going to write it again if you don’t understand. 

[Machpoint005]

1 hour ago, WotEver said:

See post #67. I’m not going to write it again if you don’t understand. 

 

I'm glad (but not surprised) that you know what I'm on about! It's still no good, though: he will not admit that his original use of the term "power" was simply incorrect. He just thinks we don't get it.

 

Apparently it is splitting hairs to insist on the correct use of technical terms in a technical post.

 

 

[ditchcrawler]

I often wondered about impressed current protection, we use to use it offshore to protect pipelines, the jackets were covered in blood great anodes

[Machpoint005]

Didn't the blood wash off?

[WotEver]

7 minutes ago, Machpoint005 said:

Didn't the blood wash off?

Nope, it was impressed into the material...

10 minutes ago, ditchcrawler said:

I often wondered about impressed current protection, we use to use it offshore to protect pipelines, the jackets were covered in blood great anodes

Simply put, if the galvanic action of the anode is insufficient on its own then you give it a little help with a power supply.

 

Knowing what size and type (not power) of anode to use, and exactly what voltage needs to be applied to it is a science. 

[Chris and PJ]

16 minutes ago, WotEver said:

Nope, it was impressed into the material...

Simply put, if the galvanic action of the anode is insufficient on its own then you give it a little help with a power supply.

 

Knowing what size and type (not power) of anode to use, and exactly what voltage needs to be applied to it is a science. 

be interesting for us all to hear how you get anything other than power from a power supply to correct an anode that is insufficient.

As someone who has designed and installed both Sacrificial and Impressed current offshore corrosion protection systems for more than  40 years may I ask what your technical background is?

again anode output can simply be described in KW hours