How to stop crevice corrosion?

[jt11791]

My boat has 4 dorade vents that all show crevice corrosion like the photo. I have treated with rust stain remover, which cleans them up temporarily, but the rust always returns and it is getting worse. Any ideas on how to stop it?

[rbk]

Not sure how this is crevice corrosion. Looks like normal corrosion, clean up with your choice of cleaner, stainless steel inst as stainless as most think. Also may be lower grade of stainless.

[sailormed]

By the look of it it is caused by the fabrication of this model of vent.
There seems to be a crevice caused by the bending of the metal.
I do not see a solution to this problem, sorry.

[rbk]

Lol it does appear to be a crevice caused by corrosion...

[sailormed]

Very linear corrosion, nature doesn’t like straight lines .....

[Corrosion-Eng]

Please send detailed photo. I will be able to determine if the cause is Marine Electrolysis.

[rbk]

Originally Posted by Corrosion-Eng

Please send detailed photo. I will be able to determine if the cause is Marine Electrolysis.

Looks like all the hair has already been removed...

[jt11791]

It seems my original photo link died. The corrosion seems to be at a welded joint.

[Corrosion-Eng]

Hi,
The corrosion, rust colored, is created by air carried low level current (stray current). Chrome plating would normally stop that stray current creating rust. The chrome has insufficient depth to stop rust forming. Re plating or coating with anything that stops air would stop the rust from forming. Such as a good quality paint or coating. No water based paints.


Detail at: Search for marine electrolysis, click Conquer marine corrosion CAUSE

[Jim Cate]

The corrosion, rust colored, is created by air carried low level current (stray current).

Say what???

"Air carried low level current"... please, some elaboration of this rather novel concept as applied to a s/s cowl vent mounted on a non conductive fiberglass substrate.

I am far from convinced that painting stainless steel is a useful means of stopping such corrosion, nor that it would be an attractive solution to the OP.

And for the OP: one possible approach is to passivate the weld area... something that good welders do routinely. One can buy "pickling paste" at welding shops, or use citric acid, usually sourced from home brew equipment vendors, or phosphoric acid. Returning the surface of the s/s weld area to a passive state should retard the corrosion.

Jim

[sailorchic34]

Originally Posted by jt11791

It seems my original photo link died. The corrosion seems to be at a welded joint.

!not sure if that's a weld joint or just Chrome plated Steel. If it really is a weld this was non ss welding rod. Was this made in China. either way it's not stainless. Get some phosphoric acid from the hardware store and coat all the Rusty bits. That will passivate the rust. Then have a little West epoxy to fill in the cracks and crevices. Then paint with the color of your choice.

It's not stray current. it's probably just cheap material. it would not be the first time I saw stainless steel parts welded with non stainless rod from China.

[Wotname]

Originally Posted by Jim Cate

Say what???

"Air carried low level current"... please, some elaboration of this rather novel concept as applied to a s/s cowl vent mounted on a non conductive fiberglass substrate.

.......
Jim

Jim, you gotta look at the big picture and not cherry pick the words. The full description was "air carried low level current (stray current)". The stray current is what gives meaning to the phrase - you gotta know your electrical theory to understand what is happening.

You see real (or proper) current is the current that runs around metal wire and it is kept there by the insulation on the wire but at the terminals of the wire, most folk don't cover them with the right stuff. Some even leave them exposed to the air and this is where the current strays off from the wire. It is called stray current and it then travels around wherever the air carries it. Of course it is low level unless there is a significant thermal updraft that carries it higher.

I'm not sure but I think that if enough of it is carried aloft, it stays there until it rains which washes it out and back to the ground - we call it lightning

By keeping a weather eye on the covering of the electrical terminals, you can stop it straying into the air and causing problems for other nearby boaters.

Simple really

[Uncle Bob]

Originally Posted by Wotname

Jim, you gotta look at the big picture and not cherry pick the words. The full description was "air carried low level current (stray current)". The stray current is what gives meaning to the phrase - you gotta know your electrical theory to understand what is happening.

You see real (or proper) current is the current that runs around metal wire and it is kept there by the insulation on the wire but at the terminals of the wire, most folk don't cover them with the right stuff. Some even leave them exposed to the air and this is where the current strays off from the wire. It is called stray current and it then travels around wherever the air carries it. Of course it is low level unless there is a significant thermal updraft that carries it higher.

I'm not sure but I think that if enough of it is carried aloft, it stays there until it rains which washes it out and back to the ground - we call it lightning

By keeping a weather eye on the covering of the electrical terminals, you can stop it straying into the air and causing problems for other nearby boaters.

Simple really

[redsky49]

Could the deck mounted flange be constructed of a material other than stainless steel?
It looks like a casting, plated bronze perhaps??

[sailorchic34]

Originally Posted by Wotname

Jim, you gotta look at the big picture and not cherry pick the words. The full description was "air carried low level current (stray current)". The stray current is what gives meaning to the phrase - you gotta know your electrical theory to understand what is happening.

You see real (or proper) current is the current that runs around metal wire and it is kept there by the insulation on the wire but at the terminals of the wire, most folk don't cover them with the right stuff. Some even leave them exposed to the air and this is where the current strays off from the wire. It is called stray current and it then travels around wherever the air carries it. Of course it is low level unless there is a significant thermal updraft that carries it higher.

I'm not sure but I think that if enough of it is carried aloft, it stays there until it rains which washes it out and back to the ground - we call it lightning

By keeping a weather eye on the covering of the electrical terminals, you can stop it straying into the air and causing problems for other nearby boaters.

Simple really

A lovely discription. Wish i had thought of it....