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Thread: Galvanic corrosion

  1. #36
    Join Date
    Jul 2011
    Location
    Lindstrom, MN
    Posts
    2,267

    Default Re: Galvanic corrosion

    Quote Originally Posted by Chris mcm View Post
    I have tried to post images on WBF but without result. Any one interested may like to check out the Waitamata Woody's link https://waitematawoodys.com/2018/11/...oat-look-like/
    My mission is to save the wood rather than the metal that can be replaced.
    From Rankin Kennedy's Book "Electrical Installations" 1900 ish. I quote. but the result will be - chlorine, a gas at the anode , and hydrogen gas at the cathode . Common salt is sodium and chlorine combined. The question is what has become of the sodium? If we tested the solution we would find that it had become alkaline; in fact the sodium had parted from the chlorine and combined with the oxygen of the water to form caustic soda in solution. End of quote.
    OK This is water electrolysis and some say it does not occur below a voltage of about 1.3 volts?. It seems any voltage causes an increase of alkalinity of water and in the case of boats some water is trapped in the wet wood around the cathode. So I ask what is happening to these bonded boats as illustrated on the WW's site. If is not caustic soda,what is ruining these bonded boats, what is it? Pretty obvious to me. Any comments are welcome.
    Voltage and water:
    Water is a very complicated substance. It is a loose network of molecules that are linked by hydrogen bonds. Hydrogen bonds wander freely from molecule to molecule. This makes water a pretty malleable substance when it comes to pH. It takes 1.3V to make hydrogen gas, but hydrogen gas doesn't change the pH. Whatever voltage causes galvanic corrosion is generating ions at both the anode and cathode, and the ion concentration shifts pH. In pure water, the pH is 7, which means that there is an equal concentration(10-7mol) of H3O+ and OH-. As soon as you expose pure water to air, the pH drops to 6 because it picks up CO2 from the air. Point is that pH is easy to shift. When metal dissolves at the anode, the metal ions are positive (e.g. Zn++), and the water shifts to a higher OH- concentration to balance the charge. No hydrogen gas, just a reshuffling of the balance betweenH3O+ and OH-. I have to stop now because I hate inorganic chemistry (even if it did pay the bills for a few years) and I can't imagine that anyone else can stand any more.

    Pictures:
    1) You can upload a picture that is on your computer. Click the picture icon, select the From Computer tab, click select files, find the file, then click upload. When I click the picture icon, the select files box is blacked out. I have to click it, then allow Adobe Flash before I can use it.

    Capture.JPG


    2) You can use the URL of a file on the net. I use Firefox for browsing. Microsoft Edge works poorly on my laptop, and I haven't bothered with Chrome for a long time. Microsoft, in their typical invasive and privacy hostile way seems to have removed windows explorer during an 'automatic 'upgrade'. Having established my level of expertise in the blind leading the blind category... The following does not work in Edge. In Firefox, when you right click on an image, the two ways to copy the image address are 'Copy Image Location' and 'View Image Info'. The first one copies the URL directly, the second one opens a window with the address and some information about the image. 'View Image Info' also has a list of every image on the page, including ones you can't get addresses for directly.
    Capture.JPG
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  2. #37
    Join Date
    Nov 2004
    Location
    Port Townsend WA
    Posts
    11,893

    Default Re: Galvanic corrosion

    I am in full agreement with Chris mcm on the dangers of wood deterioration being caused by alkaline salts eating up a perfectly good hull. I learned this years ago from a friend, Ron Manning. Ron is a very knowedgeble marine electrition here on the West Coast of California. I had been concerned about current flow attacking the keel bolts of my Common Sense Sloop "Red Witch" and placed a small zinc torpedo on the ballast keel to protect the bronze rudder post and keel bolts. Within a few months blisters began to form under the bottom paint on the keel. These resembled acne on the skin of a teenager. Cutting into one of the blisters showed a collection of zinc crystals under the paint. This was a red flag and so I tried a detachable zinc in the water. This zinc was connected to the main standing backstay bolt just below the water line. In a few weeks, white caustic crystals showed up in the wood sorrounding the bolt. I immediately did away with the zinc and gave a call to Ron who came over and tested the potential of the hull. The test in proved to be that the hull was nearly nuetral showing only .02 of a microvolt proving that no zincs at all were needed for "Red Witch". After that, I quit using zincs on our H28 "Bright Star" as well and have checked her for potential also. I have seen several boats that were nearly ruined by the use of zincs that produced corrosive attack to the wood of the hull structure. Even so, I believe that a test of the hull's potential where it is tied up is an absolute must as some marinas have a lot of stray current action going on!
    Be safe! When in doubt, call in an expert! Sometimes they don't know either!
    Jay

  3. #38

    Default Re: Galvanic corrosion

    Thank you for your help. Breakaway kindly posted the images I had but missed the one showing how the subject vessel was bonded. Thank you MN Dave, Breakaway and Jay Greer for keeping this post running. I write like I am an expert, just because no one else has. I recognize the problem caused by Anodes and bonding on wooden boats and have witnessed the result. I need to find out exactly why this happens .If any one is interested I will share my findings on why this happens. Some will say "Get a life Chris" Actually, I find the research interesting.






    Quote Originally Posted by MN Dave View Post
    Voltage and water:
    Water is a very complicated substance. It is a loose network of molecules that are linked by hydrogen bonds. Hydrogen bonds wander freely from molecule to molecule. This makes water a pretty malleable substance when it comes to pH. It takes 1.3V to make hydrogen gas, but hydrogen gas doesn't change the pH. Whatever voltage causes galvanic corrosion is generating ions at both the anode and cathode, and the ion concentration shifts pH. In pure water, the pH is 7, which means that there is an equal concentration(10-7mol) of H3O+ and OH-. As soon as you expose pure water to air, the pH drops to 6 because it picks up CO2 from the air. Point is that pH is easy to shift. When metal dissolves at the anode, the metal ions are positive (e.g. Zn++), and the water shifts to a higher OH- concentration to balance the charge. No hydrogen gas, just a reshuffling of the balance betweenH3O+ and OH-. I have to stop now because I hate inorganic chemistry (even if it did pay the bills for a few years) and I can't imagine that anyone else can stand any more.

    Pictures:
    1) You can upload a picture that is on your computer. Click the picture icon, select the From Computer tab, click select files, find the file, then click upload. When I click the picture icon, the select files box is blacked out. I have to click it, then allow Adobe Flash before I can use it.

    Capture.JPG


    2) You can use the URL of a file on the net. I use Firefox for browsing. Microsoft Edge works poorly on my laptop, and I haven't bothered with Chrome for a long time. Microsoft, in their typical invasive and privacy hostile way seems to have removed windows explorer during an 'automatic 'upgrade'. Having established my level of expertise in the blind leading the blind category... The following does not work in Edge. In Firefox, when you right click on an image, the two ways to copy the image address are 'Copy Image Location' and 'View Image Info'. The first one copies the URL directly, the second one opens a window with the address and some information about the image. 'View Image Info' also has a list of every image on the page, including ones you can't get addresses for directly.
    Capture.JPG

  4. #39
    Join Date
    Nov 2004
    Location
    Port Townsend WA
    Posts
    11,893

    Default Re: Galvanic corrosion

    For those of you who read my posts, you should know that although I build and design boats, I am not very well versed in all the ins and outs of boats and electrical current flow problems. This dates back to the time when, at age three, I found a bobby pin on the floor of the dining room in my parent's home and began to probe a wall outlet with the wire pin. I remember a zapping sound and a bit of a flash! My mother told me that all I could say was "Bite, Bite!" I have had an aversion for things electric ever since that day!

    See Chris; you are not the only one who has had current problems!
    Jay

  5. #40
    Join Date
    Aug 2004
    Location
    Victoria BC, Canada
    Posts
    481

    Default Re: Galvanic corrosion

    Quote Originally Posted by Jay Greer View Post
    I am in full agreement with Chris mcm on the dangers of wood deterioration being caused by alkaline salts eating up a perfectly good hull. I learned this years ago from a friend, Ron Manning. Ron is a very knowedgeble marine electrition here on the West Coast of California. I had been concerned about current flow attacking the keel bolts of my Common Sense Sloop "Red Witch" and placed a small zinc torpedo on the ballast keel to protect the bronze rudder post and keel bolts. Within a few months blisters began to form under the bottom paint on the keel. These resembled acne on the skin of a teenager. Cutting into one of the blisters showed a collection of zinc crystals under the paint. This was a red flag and so I tried a detachable zinc in the water. This zinc was connected to the main standing backstay bolt just below the water line. In a few weeks, white caustic crystals showed up in the wood sorrounding the bolt. I immediately did away with the zinc and gave a call to Ron who came over and tested the potential of the hull. The test in proved to be that the hull was nearly nuetral showing only .02 of a microvolt proving that no zincs at all were needed for "Red Witch". After that, I quit using zincs on our H28 "Bright Star" as well and have checked her for potential also. I have seen several boats that were nearly ruined by the use of zincs that produced corrosive attack to the wood of the hull structure. Even so, I believe that a test of the hull's potential where it is tied up is an absolute must as some marinas have a lot of stray current action going on!
    Be safe! When in doubt, call in an expert! Sometimes they don't know either!
    Jay
    I've never heard of testing the potential of the hull (but there's a lot of things I've never heard of...). How do you go about it?

    Thanks,

    Jamie

  6. #41

    Default Re: Galvanic corrosion

    Hello Jay
    As you well know, I don't have a current problem as I don't bond or use anodes on the boat I look after. The 45 foot launch "Wirihana" was built in 1933 and belongs to the same family who had her built
    Any one interested in interested in the longevity of their wooden boat should search their back copies of wooden boat magazine.
    I recommend this issue to any wood boat owner. Number 93 has two articles by Ed McClave written in 1990! 28 years ago. In my view the best articles ever written about metal corrosion and it’s issues as applies to wooden boats. There are a total of about twenty pages written by Ed McClave. I suggest for about $5 you buy a digital copy of the magazine. https://www.woodenboatstore.com/prod...denboat_91-120
    Wooden Boat should supply it to Wooden Boat Forum and I am surprised it is not on the “OffCenterHarbor” site. On page 97 is a short paragraph “ Acids, Bases and Wood” That is the root of the problem! You have to read his 18 pages and more of information you will get no where else. It comes down to eliminating any electrical current in a wooden boat. Bonding and Anodes create a small but continuous electrical current that increases the alkalinity of entrapped sea water around bonded metal and destroys wooden boats. If you doubt me read Ed’s two articles in this super edition of Wooden Boat Magazine. Thank you Ed McClave.
    I have done my best to highlight the adverse results of Bonding and Anodes Wooden Boats in New Zealand.: http://waitematawoodys.com/2018/11/2...oat-look-like/ Sadly, I feel I am swimming against the tide. If I can save a few of our heritage boats from this scourge I will be happy.
    Cheers
    Chris


    Quote Originally Posted by Jay Greer View Post
    For those of you who read my posts, you should know that although I build and design boats, I am not very well versed in all the ins and outs of boats and electrical current flow problems. This dates back to the time when, at age three, I found a bobby pin on the floor of the dining room in my parent's home and began to probe a wall outlet with the wire pin. I remember a zapping sound and a bit of a flash! My mother told me that all I could say was "Bite, Bite!" I have had an aversion for things electric ever since that day!

    See Chris; you are not the only one who has had current problems!
    Jay
    Last edited by Chris mcm; 11-29-2018 at 05:38 AM.

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