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Anode Myths part1.


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2 hours ago, Chris and PJ said:

Then tell me what is considered to be the most common corrosion cause steel hulls.

 

1        Is it connection to shore power?

2        Is it something faulty electrical on board?

3        The boat next door?

4        Anodes not working / insufficient?

5        Stray currents

or something else

 

I will then tell you how I would test for it in simple steps if it was my boat.

 

I don’t think we know with any certainty. There are perhaps 25,000 steel hulled narrowboats out there generally of anything up to 50 years old and the evidence suggests that by far and away the majority of them live happily with a low-tech bitumen blacking and no treatment of the baseplate which is made of thicker steel to compensate.

 

Therefore general corrosion through oxidisation in either air or water isn’t a major concern although some folk do seem to live in fear of sinking slowly in 3’ of water.

 

Occasionally boats suffer pitting and this can apparently happen quickly. I think the general thought is that this is induced corrosion due to stray currents be that of the boat itself or of other boats moored nearby.

 

I doubt many folks here think too much about the effectiveness of their anodes, it’s just custom to fit them to bow and stern swims and some boats have them amidships too.

 

Microbially induced corrosion has afflicted one member’s boat here recently but this seems to be a relatively new occurrence on canals.

 

Many folk blame corrosion on the steel citing quality and/or origin. I have made many posts trying to dissuade them of this notion.

 

Bear in mind there are a good number of boats - mine included - that have never been attached to shore supply and use 12v DC only and for many years that was the case with almost all boats. I have anodes largely because that’s the way things are done and they were fitted when I bought it. I will admit to being something of a sceptic, particularly when it comes to those at the bow. I have a vague hope those at the stern are helping stop migration of tin from the bronze propellor although I doubt they were provided with that purpose in mind.

 

JP

Edited by Captain Pegg
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6 hours ago, Chris and PJ said:

Trouble is as soon a you say something simple like:

`An anode is just a power supply` your faced with a whole lot of derision.

 

'An anode is just a power supply'

I have not spent decades in the field of anode technology and so that Is not a simple statement to me.

I welcome the expertise I find on this forum and I am sure you could be a valuable asset but I would suggest that a long treatise on your specialised subject is just gobbledygook to me and I suspect many others.

However a clear and simple explanation in the manner eloquently outlined by Captain Pegg in post 117 May well be of benefit to myself and others. 

As for the derision part of your statement I have highlighted above I think what you may see as derision is in my view not derision but requests for clarification. Some of the request for clarification have come from experts in their field that I have come to respect over the years and are far more qualified than me to ask the questions. 

The only things you need to know about this site is it can be a valuable resource but respect has to be, particularly in technically matters, earned it cannot be demanded. 

I would suggest that you may have taken the wrong tack with your post original post. It does come across as someone saying I'm brilliant, you are not therefore you must respect and admire me. What you need to know is that it is I who decides who I respect, who knows long term it may very well be that I include you in that list, only time will tell. 

Edited by reg
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33 minutes ago, reg said:

I would suggest that you may have taken the wrong tack with your post original post. It does come across as someone saying I'm brilliant, you are not therefore you must respect and admire me.

 

I too suspected the OP might 'know his stuff', but on balance probably not. Or at best he is unable to explain things in layman's terms to non-experts in his subject.

 

In particular his dismissal of dimensional analysis as nit picking suggests he is a bit of a bull in a china shop. And his habit of responding to requests to explain specific points by linking to an external website rather than actually explaining, suggests he is not going to be much help to boaters like me wanting to learn and understand anodes and protection.

 

 

 

 

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22 hours ago, Captain Pegg said:

I don’t think we know with any certainty. There are perhaps 25,000 steel hulled narrowboats out there generally of anything up to 50 years old and the evidence suggests that by far and away the majority of them live happily with a low-tech bitumen blacking and no treatment of the baseplate which is made of thicker steel to compensate.

 

Therefore general corrosion through oxidisation in either air or water isn’t a major concern although some folk do seem to live in fear of sinking slowly in 3’ of water.

 

 

Why does a beer can that is about 0.4 mm thick last for years without rusting through but  my boat which is 8mm thick need blacking every couple of years?

 

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11 minutes ago, ditchcrawler said:

Why does a beer can that is about 0.4 mm thick last for years without rusting through but  my boat which is 8mm thick need blacking every couple of years?

 

<Jamaican accent on>

 

Cos the beer can  is made of pig iron.

 

<Jamaican accent off>

Edited by rusty69
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Just now, ditchcrawler said:

Why does a beer can that is about 0.4 mm thick last for years without rusting through but  my boat which is 8mm thick need blacking every couple of years?

 

Beer can is made of aluminium. Probably.

 

The question works with cars though, they are made with very thin gauge steel compared to a boat but have far more scientific coating systems. They probably don’t last as long but most probably do far more work and in a harsher environment than the average boat. As I’ve said many times on corrosion related subjects the natural rate of corrosion of steel is very slow. The factors that speed it up are what we are interested in.

 

JP

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1 hour ago, ditchcrawler said:

Why does a beer can that is about 0.4 mm thick last for years without rusting through but  my boat which is 8mm thick need blacking every couple of years?

 

Because it is plastic coated on the inside.

 

or because it has tiny little anodes inside?

Edited by Chewbacka
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On 23/09/2019 at 21:11, Captain Pegg said:

 

The question works with cars though, they are made with very thin gauge steel compared to a boat but have far more scientific coating systems. They probably don’t last as long but most probably do far more work and in a harsher environment than the average boat. 

 

40-50 years ago cars rusted through pretty quickly. Now they last for years. Is that purely down to the coating systems used?

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9 minutes ago, David Mack said:

 

40-50 years ago cars rusted through pretty quickly. Now they last for years. Is that purely down to the coating systems used?

As nothing else has changed (they still drive around on tarmac in moist air) what else could it be?

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2 hours ago, WotEver said:

As nothing else has changed (they still drive around on tarmac in moist air) what else could it be?

Understanding the causes, designing out water traps, plastic liners, use of adhesives, avoiding dissimilar metal issues, etc, might have contributed a bit. There may also have been just a tiny bit of quality control improvement.

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3 hours ago, Sea Dog said:

Understanding the causes, designing out water traps, plastic liners, use of adhesives, avoiding dissimilar metal issues, etc, might have contributed a bit. There may also have been just a tiny bit of quality control improvement.

Most catastrophic rust was from the inside coming through the panel or structural  box section to the outside, so very difficult to treat.  Modern steel car bodies get dunked in a phosphate bath and then an e-coat bath before painting which coats all the inner surfaces with a very resistant coating.  External panels are often Zn coated as well to reduce surface rusting, so a lot more technology.

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I convened a group of engineering experts to discuss anodes yesterday. One of my colleagues not only possesses a superb engineering brain but also happens to be a material scientist by training and once worked as a consultant testing narrowboat hulls for insurance companies amongst other things. Conclusions;-

 

- the basic premise of Chris & PJ (as per their opening sentences) is correct

 

- a hull in water will have a potential that while not true earth is likely to be very close

 

- fitting anodes will have the effect of earthing the hull

 

- if your anodes aren’t being eaten away over a year or two then you probably don’t have much to worry about

 

- using industry standard technology (half cells have a history in checking steel reinforcement within concrete) is probably unnecessary in relation to the likelihood of problems and the level of associated risk

 

- there was sceptism that the capacity of the power supplies to which narrowboats are routinely connected are sufficient to cause major damage in isolation through stray current

 

- as an aside in relation to the above it was suggested that If stray current is present it is probably better to have the entire hull uncoated rather than have damaged areas in the coating to concentrate the stray current

 

- one answer to “Is the anode a power supply?” was “No. It’s the cathode.”!

 

- the only serious galvanic corrosion my colleague ever witnessed on a narrowboat was where someone had used brass or bronze weights as ballast and cast concrete around them in a wet environment.

 

In summary then a group of independent experts concludes the narrowboat world uses anodes in a proportional way but if you suspect you have problems - or are just a born worrier - the scientific approach as per this thread is appropriate.

 

JP

 

Edited by Captain Pegg
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16 hours ago, Machpoint005 said:

I would think paint technology has come on quite a bit too.

 

 

I suspect this is only that half of it. Actually painting the concealed surfaces instead of just spaying the finished bodyshell was the step change, so rust was delayed from getting a grip on the inside surfaces. Mini sills, Triumph Spitfire outriggers etc being prime examples of rot from no protection internally. 

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1 hour ago, Captain Pegg said:

 

- one answer to “Is the anode a power supply?” was “No. It’s the cathode.”!

Thanks for your work on this. Just for clarity to someone who's has only a rudementary understanding on this subject could you please clarify whether or not this was said in jest? 

If not then how does the statement stand up? 

 

Edited by reg
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5 hours ago, reg said:

Thanks for your work on this. Just for clarity to someone who's has only a rudementary understanding on this subject could you please clarify whether or not this was said in jest? 

If not then how does the statement stand up? 

 

It’s inclusion in the post above was intended to be light hearted. The comment itself was a serious answer and was given in respect of the fact that electrons flow from cathode to anode. This business about the use of the term ‘power’ above is something of a red herring. It doesn’t change anything significant. Power is a term that is more often than not incorrectly used in a strict scientific sense and I think the people I asked recognised I’d asked a slightly odd question but endeavoured to interpret what I meant and answer it logically. I very much doubt the folk who got excited about it have never conflated the terms ‘mass’ and ‘weight’ and their respective SI (derived) units of kg and N. If you don’t follow the argument that’s to your advantage; you don’t need to worry about it.

 

JP

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36 minutes ago, Captain Pegg said:

It’s inclusion in the post above was intended to be light hearted

Which is very much how I read it, however I thought it necessary to have that pointed out to have absolute clarity on the matter. 

The problem with the op's initial assertion that 'An anode is just a power supply' and his steadfast defence of that assertion left me in a position of wondering how much of the rest of his post was incorrect and therefore whether it had any validity at all.

Now that the op's fundemental error has been identified and cleared up it appears that the original post may have some value after all. Hopefully he sees this whole process as being a submission of a draft document for review. 

Personally I wouldn't mind seeing a redrafted post with ambiguities and clutter removed. 

 

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3 minutes ago, reg said:

Which is very much how I read it, however I thought it necessary to have that pointed out to have absolute clarity on the matter. 

The problem with the op's initial assertion that 'An anode is just a power supply' and his steadfast defence of that assertion left me in a position of wondering how much of the rest of his post was incorrect and therefore whether it had any validity at all.

Now that the op's fundemental error has been identified and cleared up it appears that the original post may have some value after all. Hopefully he sees this whole process as being a submission of a draft document for review. 

Personally I wouldn't mind seeing a redrafted post with ambiguities and clutter removed. 

 

In my view one needs to have an Anode, Cathode and electrolyte making a corrosion cell before it can be called a power supply.  An anode on it's own is just a lump of metal.

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8 minutes ago, Chewbacka said:

In my view one needs to have an Anode, Cathode and electrolyte making a corrosion cell before it can be called a power supply.  An anode on it's own is just a lump of metal.

Indeed. As per my observation that by OP’s criteria a lump of lead was “very powerful” because it could power a motor (if it was in some acid along with a lump of lead oxide).

Edited by WotEver
Lead, not less, you stupid autocorrect...
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13 minutes ago, Chewbacka said:

In my view one needs to have an Anode, Cathode and electrolyte making a corrosion cell before it can be called a power supply.  An anode on it's own is just a lump of metal.

Exactly. But I think I understand what Chris and PJ meant. You already own a big lump of metal that you float in water. It is the act of attaching an anode to the boat (cos let’s face you don’t buy a boat to attach to an anode) that creates the ‘power source’.

 

JP

Edited by Captain Pegg
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1 hour ago, reg said:

Now that the op's fundemental error has been identified and cleared up it appears that the original post may have some value after all.

Apart from his assertion that an impressed anode system can prevent MIC. Nothing I’ve read about MIC has suggested that galvanic action has any relevance to it. 

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55 minutes ago, WotEver said:

Apart from his assertion that an impressed anode system can prevent MIC. Nothing I’ve read about MIC has suggested that galvanic action has any relevance to it. 

It stops mussels attaching themselves as I have witnessed at work when it stopped working all the strainers on the sea water pumps filled wit mussels in a very short time

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