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Corrosion basics for kiteboarders

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Bille
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Re: Corrosion basics for kiteboarders

Postby Bille » Mon Jun 24, 2019 12:53 pm

plummet wrote:
Mon Jun 24, 2019 8:18 am
Ok, what is Intergranular corrosion?
...
You research complicated stuff ; then make it simple enough for a Dumb-Ass like me
to understand ! :thumb:

Are you a teacher, by trade ?

Bille

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Re: Corrosion basics for kiteboarders

Postby plummet » Mon Jun 24, 2019 6:01 pm

Bille wrote:
Mon Jun 24, 2019 12:53 pm
plummet wrote:
Mon Jun 24, 2019 8:18 am
Ok, what is Intergranular corrosion?
...
You research complicated stuff ; then make it simple enough for a Dumb-Ass like me
to understand ! :thumb:

Are you a teacher, by trade ?

Bille

Yeah, trying to absorb the mechanisms of corrosion does make your brain hurt! No, I am not a teacher. Engineering is my game. In a previous job, part of my role was to develop and present technical training sessions for engineers and technicians. So I do have a good 11 years of technical training experience. Corrosion basics was one of those training sessions.

plummet
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Re: Corrosion basics for kiteboarders

Postby plummet » Mon Jun 24, 2019 6:21 pm

Here's a good read on galvanic corrosion with carbon fiber.

https://www.corrosionpedia.com/galvanic ... ers/2/1556

plummet
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Re: Corrosion basics for kiteboarders

Postby plummet » Sat Jul 06, 2019 7:05 pm

Ok now you have had time to absorb Galvanic, pitting, crevice and intergranular corrosion. Lets attack a few more types.

What is MIC?

Mic stands for microbial induced corrosion.

Essentially when microbes attached together to form a bacterial colony on the metal surface they can create the conditions that lead to pitting corrosion.
You end up with a localized anodic zone created by the bacteria. Chemical reactions of the bacterial can also accelerate the corrosion process.


F1.large.jpg
If you want more detail watch this vid.



plummet
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Re: Corrosion basics for kiteboarders

Postby plummet » Sat Jul 06, 2019 7:54 pm

What is SCC?

SCC stands for Stress Corrosion Cracking.

When you combine a susceptible material, corrosive environment and stress/strain you have the conditions for SCC.

Stainless steels are a susceptible material, Saltwater is a corrosive environment that could enable SCC. Typically SCC occurs over 55 Deg C. However it is possible at lower temps if the environment and stress are sufficient.

Now you add tensile stress. This could be stress or stain caused by the parts use or manufacturing stresses like welding, forming etc.

SCC typically starts with stress/strain breaking the passive oxide layer at the crack tip exposing active material to the corrosive environment and corrosion starts. If the stress is above a threshold level then the crack will continue to propagate exposing more active material leading to more corrosion.

Interestingly the SCC occurs well below the yield strength of the material. So parts can fail well below the designers safety margins. What is yield strength you ask? Yeild strength where a material goes from elastic deformation to plastic deformation. IE bend it and it bounces back = elastic deformation, bend it and it stays bent = plastic deformation.
scc Tri-Round.jpg



Perhaps my failed stainless widget has failed due to stress corrosion cracking? or a combination of SCC and IGC?
IMG_0827.JPG

plummet
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Re: Corrosion basics for kiteboarders

Postby plummet » Sat Jul 06, 2019 8:17 pm

What are the corrosion controls for MIC

Clean and lubricate your gear, make sure there is no build up of foreign material that could lead to a colony of bacteria.

SCC?

Wash down your gear and don't leave salty damp gear in a hot car for hours on end. Remember that corrosion takes place faster when the temperature increases. For SCC it may not occur at ocean temps. However if then stuff your gear into the car and leave it there in the heat of the summer you could take the parts into the danger zone for scc.


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