Galvanizing and cathodic protection

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In summary: The corrosion protection provided by galvanizing depends on the presence of an anode and a current running through the metal. You can achieve corrosion protection by using a sacrificial anode or by using an impressed current. However, galvanizing is not always effective in preventing galvanic contact with soil.
  • #1
peachy
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okay, I'm having an argument at home, we're all 2nd year engineers and have different views on the galvanizing process.

the way i see it is metals are dipped in zinc (anode) and are connected to the metal (cathode). a reaction takes place which provides cathodic protection to the metal if the galvanized coating happens to become chipped or scratched because the zinc is more electronegative than the steel.

the other two got taught (or understand from the teaching) that cathodic protection only takes place with an electic current running through the metals. as far as they're concerned galvanizing only protects steel by covering it, much like painting, to cathodically protect it you need to have the metals connected to a dc power source

any clear opinions/knowledge?? i would appreciate some proof of either theory too if possible

thanks
 
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  • #2
It's been I while since i took my corrosion course, but I think you can achieve CP either by using a sacrificial anode (like zinc) or by using an "impressed current" - so you're both right. When you use a sacrificial anode, you reduce the rate of dissolution of the protected metal by making it a cathode.

I'm sure there are useful resources on the web.
 
  • #3
yeah, I've since come to that conclusion but nowhere on the internet specifies 100% that there is no need for electric current to provide the cathodic protection. i need some hardcore evidence to prove my point...
 
  • #4
Any corrosion book should have that.

Read : http://www.erps.com.au/the_rust_reaction.html [Broken]

Try googling "sacrificial anode"...
 
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  • #5
Do you think conducting or contact grease like the kind for wire to spark plug connections would work on the cathodic protection? Is there another type of grease or product that would not wash or melt away?
 
  • #6
hongkongphooey said:
Do you think conducting or contact grease like the kind for wire to spark plug connections would work on the cathodic protection? Is there another type of grease or product that would not wash or melt away?

Buried piping is often coated with bitumus to prevent galvonic contact with soil. It is not extremely effective. Cathodic protection is still needed.
 

What is galvanizing?

Galvanizing is a process of coating iron or steel with a layer of zinc to protect it from corrosion.

How does galvanizing protect against corrosion?

When zinc is applied to iron or steel, it forms a protective layer that acts as a barrier against corrosive elements in the environment. This layer also sacrifices itself to protect the underlying metal, extending its lifespan.

What is cathodic protection?

Cathodic protection is a technique used to prevent corrosion on metal surfaces by making it the cathode of an electrochemical cell. This is done by connecting the metal to a more easily corroded metal, such as zinc, which acts as an anode and sacrifices itself to protect the metal.

How is galvanizing different from cathodic protection?

Galvanizing is a type of cathodic protection where the metal is coated with zinc to prevent corrosion. However, cathodic protection can also be achieved by using sacrificial anodes or impressed current systems, where an external current is applied to the metal to protect it from corrosion.

What are the common applications of galvanizing and cathodic protection?

Galvanizing and cathodic protection are commonly used in industries such as construction, transportation, oil and gas, and marine. They are used to protect metal structures, pipelines, and equipment from corrosion and extend their lifespan.

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