Mechanism behind stray current corrosion

[Alexander T.]

Hi, I am trying to understand stray current corrosion. I understand that stray current enters for instance a pipe at one place (cathode) and exits at another one(anode). I am struggling to understand why electrons leaving the pipe will cause corrosion.

Is it possible to get a good explanation on the mechanism behind stray current corrosion.

Thanks

 

[EdStainless]

In order for charge to stay balanced if electrons move in (current out) then metal ions must be moving out.
Just the opposite of electroplating.
It depends on a lot of conditions, current density, other materials, soil conditions (moisture and conductivity) so it can be difficult to predict.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

http://nptel.ac.in/courses/113108051/module3/lecture19.pdf

 

[Chumpes]

hello
solitary electrons do not exist in aqueous solution, they only exist in the metal...

electrons leaving the pipe surface to the electrolyte will be caught by an oxydizer (for example reduction of H+ to H2 : 2H+(electrolyte) + 2e-(bulk metal) = H2(electrolyte)). This surface area is a cathode (reduction of H+) and it is cathodically protected. the electric current on this surface area is going from the electrolyte to the surface, oposite to the flow of electrons.

current leaving a metal surface corresponds to the movement of positive metal ions leaving the metal surface to the electrolyte. this metal ions are Fe2+ and Fe3+ produced by corrosion reaction (oxydation) :
Fe(bulk metal) = Fe2+ (electrolyte) + 2e-(bulk metal)
this surface area is an anode and corrode faster (iron dissolution)

"WHERE ELECTRIC CURRENT GOES IN IT IS CP PROTECTED, WHEN ELECTRIC CURRENT GOES OUT IT CORRODES FASTER"