Galvanizing and cathodic protection

peachy

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

Gokul43201

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.

peachy

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...

Gokul43201

Any corrosion book should have that.

Read : http://www.erps.com.au/the_rust_reaction.html

Try googling "sacrificial anode"...

hongkongphooey

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?

Enginator

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