Sailboat Owner's Guide to Corrosion - Galvanic and Stray Current Corrosion (Collier 6 & 7)

[Will Gilmore]

Welcome to Section 3 of our SBO Book club study of Everett Collier's book, 'The Boatowner's Guide to Corrosion".

We are reading and posting, in sections, as we work our way through the subject of corrosion in the marine environment. Each section will cover one or more chapters and be posted in its own thread. As the new threads are started, I will tag any interested participants and create a linked table of contents to make it easier to follow along and participate.

A rough outline of the sections to come are as follows. They may be edited and updated as the current of our discussion requires.

Sections

1. Sailboat Owner's Guide to Corrosion - Fundamentals (Collier 1-4)
2. Sailboat Owner's Guide to Corrosion - Self-Corrosion (Collier 5)
3. Sailboat Owner's Guide to Corrosion - Galvanic and Stray Current Corrosion (Collier 6 & 7)
4. Sailboat Owner's Guide to Corrosion - Metals Aboard (Collier 8 - 12)
5. Sailboat Owner's Guide to Corrosion - Protection (Collier 13 - 15)
6. Sailboat Owner's Guide to Corrosion - Hull and Motor (Collier 16 - 17)
7. Sailboat Owner's Guide to Corrosion - Electronics and Plumbing (Collier 18 - 19)
8. Sailboat Owner's Guide to Corrosion - Topsides (Collier 20 - 21)
9. Sailboat Owner's Guide to Corrosion - Resource

Let me know (@Will Gilmore) if you want your name added to this list. It will appear at the beginning of each new thread to let interested members know when the new thread has opened. You can then post something or click the [Watch] button to follow the thread.

Tagged participants:
@Will Gilmore
@DArcy
@mermike
@jssailem
@dlochner
@dLj
@JamesG161
@ontherocks83
@rgranger
@Mark Maulden
@Davidasailor26
@LeslieTroyer

I'll be happy to edit/update this list at any time.

Some basic rules for maintaining useful and topic focused discussion:
SBO is a public forum, and as such, anyone interested, is welcome to participate, ask questions and express their opinions. There are limitations to the form these expressions can take and the culture of participation. All the basic forum rules of decorum and good manners apply. As a participant in this series of discussions, we would ask that participants remain on topic and refrain from derogatory language or remarks. The express purpose of this series of threads will be to understand corrosion in the marine environment using Collier's book as a guide. We therefore, expect participants to make an honest effort to read and stay up on the material under discussion. We are a group of congenial sailors with a sense of humor that often can run astray. A playful comment on occasion is expected, but anyone of us will feel free to firmly redirect anyone back to the subject at hand if it looks like it is in danger of derailing the discussion. A moderator will be asked to intervene, edit out any inappropriate comments, and possible ban an offending participant, should the group find their continued presence a serious distraction. Posting in this thread will be considered agreement to these terms. Thank you so much for your understanding and cooperation. I look forward to being part of the amazing community that is developing around this subject. I know we will all have a great time.

-Will (Dragonfly)

 

[dLj]

Galvanic corrosion section? this should be fun!

dj

 

[dLj]

Looks like we just got moved.. Definitely a better place over here...

dj

 

[Will Gilmore]

Nice. All the links work too.

-Will (Dragonfly)

 

[jssailem]

Nice. We talked about this. “ When Phil gets back. “. He must be back.

Thank you @Phil Herring.

 

[dLj]

I just finished reading Chapter 6 - it's pretty short. In the section on stainless steel, he says there are three general classes, but really there are five: austenitic, ferritic, martensitic, duplex, and precipitation hardening stainless steels. He does get huge points where he talks about 18-8 being an imprecise term - YES! I think I have this conversation almost every day, certainly weekly... But that's a long story..

dj

 

[Will Gilmore]

Nice. We talked about this. “ When Phil gets back. “. He must be back.

Thank you @Phil Herring.

You can thank @Brian D. He's the one who saw the multiple threads with similar names and decided to move them to their own forum. Thanks Brian.
By the way, we also got Phil's blessing.

-Will (Dragonfly)

 

[Will Gilmore]

I just finished reading Chapter 6

I haven't gotten very far into chapter 6 yet. I do have a question, though.
I just wan't to make sure I'm clear on the difference between electrons being given up by an anode and ions. Ions are negatively charged atoms.

Collier talks about metal ions and hydroxyl ions. The hydroxyl ions form from the electrons flowing through the water and combining with dissolved oxygen? When the anode and the cathode are close together, they can cause damage to surrounding wood.

Am I reading this wrong? Why would this not cause damage or why would hydroxyl ions not form anywhere along the electron path from anode to cathode within the electrolyte and therefore still cause damage to the surrounding wood?

-Will (Dragonfly)

 

[Davidasailor26]

Ions are negatively charged atoms.

More precisely, ions are any charged atom or molecule. Fe+, OH-, Na+, etc.

When the anode and the cathode are close together, they can cause damage to surrounding wood.

I think his point was that the damage could be caused when the anode and cathode are not close together. In that case, the hydroxyl ions are formed at the cathode, and there’s no metal ions around from the anode to bond with. The free hydroxyl ions make a caustic basic solution around the cathode.

 

[dLj]

+1

Also, he was making the point that because the galvanic couple is driving the corrosion reaction faster than general corrosion would, there is a greater concentration of corrosion product(s) at the respective anode/cathode areas.

dj

 

[dLj]

@Will Gilmore - I'm thinking maybe you should set up the next section. I don't think there is a lot in this one to talk about. And if anyone has a question, they can just put it in down the road.

dj

 

[JamesG161]

I didn't buy the books so I remained quiet, but in a PM with Will suggested this was starting to get very broad.

Since we can't show the Language of Chemistry [Chemical Equations] in these chat type areas, it is most difficult to discuss.
Simple example of one side of an equilibrium chemical equation involving the Hydroxyl ion [OH-]

H+ + OH- ---> H2O

Check out the Equations section of this Link
Chemical reaction - Wikipedia

We make Paper in a chemical reaction from...

Wood + Hydroxyl ion [OH-] ---> Paper [if you control all aspects of the manufacturing process]

That was mentioned above like it was corrosion.

Jim...

 

[dLj]

I didn't buy the books so I remained quiet, but in a PM with Will suggested this was starting to get very broad.

Collier does go from simple to broad in the book. I'm wondering if somehow we can get you a copy of the book. I'd really love to hear your take on several things in it that I've been quiet on.

Since we can't show the Language of Chemistry [Chemical Equations] in these chat type areas, it is most difficult to discuss.

Why the heck can't you? I mean, I get it that with the interface, you can't just type them in, but you could pull them in from another source and put in images at least... Here's a simple example (random)

Simple example of one side of an equilibrium chemical equation involving the Hydroxyl ion [OH-]
H+ + OH- ---> H2O

We make Paper in a chemical reaction from...
Wood + Hydroxyl ion [OH-] ---> Paper [if you control all aspects of the manufacturing process]

See? You did it.. LOL

That was mentioned above like it was corrosion.

Jim...

He doesn't say it's corrosion of the wood, but rather the corrosion products cause the wood to deteriorate (probably my words, I'm not looking at the book).

I, for one, would most welcome you putting in the chemical equations.. Go for it!

dj

 

[Will Gilmore]

@Will Gilmore - I'm thinking maybe you should set up the next section. I don't think there is a lot in this one to talk about. And if anyone has a question, they can just put it in down the road.

dj

Ok. I've done a little quick browse of the next chapter, electrolytic corrosion and I propose to combine chapters 6 and 7 in this thread. I'll just edit the table of contents and thread title, if I can. How does everyone feel about that?

Really, there isn't much fundamentally new in chapter 6 and 7 looks like it is really starting to address the sailor's perspective, but the difference between galvanic corrosion and electrolytic corrosion is much smaller than their similarities.

-Will (Dragonfly)

 

[JamesG161]

C + 2Crap ----> Carbon DiCrapite. I did it!

Balancing a Chemical Equation was not so easy, if you don't understand Oxidation States, as Metals go to their stable chemical equilibrium oxidation state.

Then you have to consider the reaction rates, both forwards and reverse, to understand how fast to get there.

Equilibrium is where the Forward and Reverse rates are equal, at standard conditions.

Geezzzz really do we really want to go that broad?
______
If you understand this link, then you get A+.
Oxidation state - Wikipedia
But there is the key to corrosion and the chemical oxidation states for the elements and for metals on my boat.
____
Please note Helium's Oxidation state as "Happy" and the only one found free on Earth.
The other 2 "Happy" Inert gases are distilled from Air.

Jim...

PS: The Weather & Forecasting forum is keeping me and @jssailem well read and active on another Sailing subject.
PSS: I was in a plant that needed Pure Oxygen and got to see Liquefaction of Air and its distillation products. Argon was their money maker.

 

[dLj]

@JamesG161 I agree, we don't really need to go into the depths of redox equations unless in some aspect it helps understand some practical aspect. I think these threads are more to give a basic understanding of corrosion and hopefully provide some tools for better understanding.

@Will Gilmore please change the title from electrolytic corrosion to the correct term Collier is actually talking about which is Stray Current Corrosion.

I really should get through the rest of the book, as maybe we just need to get to something like, Practical Applications of Corrosion Science on Boats, or something like that....

dj

 

[Will Gilmore]

Ok. I know we've covered this electron flow vs current and really, I've had this stuff in a couple of college level electronics classes and I was at the top of my class, as well, but I'm confused by the scenarios Collier lays out with the bilge pump and on/off switch.
Collier says to always wire the switch on the positive (hot) side or current would always flow whether the switch was opened or closed.

Electrons come from the negative side (in this example, ground). When the positive side switch is closed, the circuit is practically complete. Elections move through the motor to the positive terminal. The motor runs. Open the switch, electrons stop flowing because the path is broken. The pump doesn't turn on.

Why is this not the case with the switch on the negative side? What is it about this that allows the motor to run when the switch is closer to the electron source but still seems to interrupt electrons that haven't yet even reached the motor?

Where is the electron source when the positive wire is referred to as hot?

-Will (Dragonfly)

 

[JamesG161]

Where is the electron source when the positive wire is referred to as hot?

The 12 volt positive source.

The difference is, if the motor windings are failing, you still have an electron flow from 12+ to the bilge water ground.
In my case, the grounded keel bolts are in the bilge water.
Jim...

 

[JamesG161]

The Load is the motor and a good example of potential...
Stray current corrosion.

Jim...

 

[Will Gilmore]

The 12 volt positive source.

Why are the electrons not coming from the negative side?

I think I see what you're saying. I misread Collier again and didn't realize he was saying, in case of a compromised system?

-Will (Dragonfly)