Stray- Current Corrosion, or Galvanic Corrosion, or?????...Help

[CharlieJ]

The damage exhibited by the photos does not appear to be caused by stray current, also known as electrolytic corrosion and is generally caused by the victim vessel.
Stray current corrosion is generally a DC phenomenon, it is very destructive to the affected underwater component and generally very fast in its manifestation: days and weeks.
Galvanic corrosion is a slow, low voltage process that takes months and years to manifest itself. An everyday example is the shaft anode on a propulsion shaft.

A high quality bonding system includes:
>> Electrical connection to each u/w component
>> Using AWG 8 stranded wire
>> With each connection <1 Ω resistance
>> Final connection to the hull (plate) anode

One of the benefits of a high quality bonding system is that it all but eliminates the possibility of stray current corrosion of the underwater metal components. With the u/w components all bonded together, they are all at the same electrical potential so current cannot flow. Touch a B+ to a well bonded boat's u/w component and...no corrosion will occur.

Continuity Testing: Most DMMs that mesure continuity will indicate continuity when the resistance is < 100 to 200 Ω. That just isn't good enough in corrosion mitigation. While the boat is out of the water, make up some long test leads and check for resistance between your u/w components. All should be <1Ω; correct all that are not.

With the exception of the strut, it appears that you have a paint system failure, as BoatPoker postulates. Insulate the metal components from the copper based paint by applying Interlux 2000/3000 to a properly prepared u/w component and I believe your problem will resolve.

The strut appears to be under-protected by the plate anode and can be corrected by correctly bonding it as discussed above.

BTW, "electrolysis" is the dissociation of water into its constituent parts and has nothing to do with marine corrosion.

For what its worth, I am an ABYC Corrosion Technician and a former ABYC Certification Instructor.

PM me if you have any questions.

[Neptune's Gear]

Have you changed your anode size, type or location lately? This looks like paint blasting due to over protection? The half cell test will tell you....

[foggysail]

Originally Posted by Neptune's Gear

Have you changed your anode size, type or location lately? This looks like paint blasting due to over protection? The half cell test will tell you....

Would you explain how a half cell will tell if over protected

[CharlieJ]

Over protection requires an excellent bonding system connected to the hull anode

[Wood]

Originally Posted by foggysail

Would you explain how a half cell will tell if over protected

Assuming aluminum anodes on fiberglass hull 1/2 cell should read -1050 mv or so. Over protection would show > -1200mv or thereabouts.



You can check specs for steel hulls / or different anodes on places like boatzincs.com

[Wotname]

A reminder the OP initially posted about 15 months ago, let's hope he has resolved the issue by now .

[fstbttms]

Originally Posted by CharlieJ

Stray current corrosion is generally a DC phenomenon, it is very destructive to the affected underwater component and generally very fast in its manifestation: days and weeks.

This damage took place in a matter of weeks. The cause? Broken insulation on a 12-volt bilge pump wire.

[fstbttms]

Originally Posted by Corrosion-Eng

Use an insulation tester or my instrument.

Virtually every post you've made in this forum is a blatant advertisement for your service or product. I suggest you familiarize yourself with the forum rules:

Marine Service Providers may not use any section of the forum to discuss their products or services unless answering a direct question and even in this case may not quote prices or post links, images, videos or contact details in support of that response.

[foggysail]

Originally Posted by Wood

Assuming aluminum anodes on fiberglass hull 1/2 cell should read -1050 mv or so. Over protection would show > -1200mv or thereabouts.



You can check specs for steel hulls / or different anodes on places like boatzincs.com

Weelll, OK but the max voltage for aluminum is -1.1v. But I get the idea. What troubled me was that adding additional anodes is the same as adding batteries in parallel so the terminal voltage does not change but the current capacity obviously would increase. So it makes sense at least to me that an anode's current is not only determined by the resistance of the solution and the voltage between the anode and the metal under test. It is also because the anode will have a maximum current determined by its surface area.

Greater area, greater current so there would be less voltage dropped in the internal resistance of the anode proper.

Conclusion--- I agree with you!

[Warren Drifter]

SeaBis electrolysis elimination system is a pretty good gadget to have connected all the time to monitor if and when there is stray DC current. Mine works very well and helps when tracking down suspicious DC equipment.

The device has a built-in AC alarm. As I am never connected to AC shore power, it is only an added unused feature. But whenever the solar panels belt out any higher than 13.8 volts DC, that AC alarm light starts flashing intermittently along with the battery negative side of the monitor and sometimes the positive side as well. If I turn off the solar panels or wait til sundown so their output is below 13.8 volts DC, all goes back to normal.

The seller suggested my solar panels are producing too much AC voltage. I am wondering if anyone out there has the same experience.

[boatpoker]

Originally Posted by Warren Drifter

SeaBis electrolysis elimination system is a pretty good gadget to have connected all the time to monitor if and when there is stray DC current. Mine works very well and helps when tracking down suspicious DC equipment.

The device has a built-in AC alarm. As I am never connected to AC shore power, it is only an added unused feature. But whenever the solar panels belt out any higher than 13.8 volts DC, that AC alarm light starts flashing intermittently along with the battery negative side of the monitor and sometimes the positive side as well. If I turn off the solar panels or wait til sundown so their output is below 13.8 volts DC, all goes back to normal.

The seller suggested my solar panels are producing too much AC voltage. I am wondering if anyone out there has the same experience.

I had never heard of this system so I had to look it up. As a Certified Marine Corrosion Analyst I have never seen so much snake oil, absolute BS and complete misuderstanding of stray current and electrolytic corrosion in one place. My dock neighbour & buddy (retired two years ago as president of IEEE) just had a look at it together and had a good laugh.

It would literally take me all night to go through the BS on that site one point at a time. Let me just suggest you hire a real Certified Marine Corrosion Analyst before falling for that nonsense.

One tidbit I will offer ... Anyone who uses the term "electrolysis" in relation to electrolytic or stray current corrosion clearly does not understand what the word means. No marine corrosion professional trained in thses matters would use that word as it is a different process altogether.

I'm sure there are some who will argue this point but this is so stupid I will not be replying.

[senormechanico]

Ya gotta get rid of those AC solar panels.

Get some DC panels !!

>sarcasm<

[foggysail]

Originally Posted by Warren Drifter

SeaBis electrolysis elimination system is a pretty good gadget to have connected all the time to monitor if and when there is stray DC current. Mine works very well and helps when tracking down suspicious DC equipment.

The device has a built-in AC alarm. As I am never connected to AC shore power, it is only an added unused feature. But whenever the solar panels belt out any higher than 13.8 volts DC, that AC alarm light starts flashing intermittently along with the battery negative side of the monitor and sometimes the positive side as well. If I turn off the solar panels or wait til sundown so their output is below 13.8 volts DC, all goes back to normal.

The seller suggested my solar panels are producing too much AC voltage. I am wondering if anyone out there has the same experience.

Did the seller suggest what the AC voltage frequency might be produced by your DC solar panels

[Corrosion-Eng]

Hi Warren,
I am the designer with 2 degrees in corrosion cause elimination and 45 years commercial experience.

The solar cell is generating excessive AC when at full power. If allowed to do so persistently that AC must damage batteries and electronics. This is typical of solar cells from China, at this time. I suggest you contact the manufacturer via the supplier. Mean while avoid excessive use. Keep use to just enough to supply you adequate power.

Glen Bishop of SeaBis.

[skipmac]

Well it has been 30 years since I got a degree in electrical engineering that focused on IC design and fabrication and only a couple of classes touched on solar cells but from all I know about them it is would be completely impossible to produce AC directly from a solar cell. Maybe fluctuating DC (especially if you could get the sun to strobe) but AC, no way.

Again maybe you could get pulsating DC or maybe even some AC from a poorly made or malfunctioning controller but the cell itself, don't think so.

PS Boatpoker. Very impressed that your neighbor is a former president of IEEE.