Pitting and Crevice corrosion

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Hi all,
I am trying to understand how the process of either crevice or pitting corrosion works (I believe they are quite the same)
I understood the part of how they start and what enhances them or how they can be prevented, but I can't understand an actual scenario.
Say for example we have stainless steel in a water solution;
  1. From which elements and to which elements do the electrons travel?
  2. With which elements does the water react? -> and does it always change to hydrogen and hydroxide?
  3. How does hydrogen increase the acidity?
  4. Why does the steel where the corrosion take place always become the anode?
I would really appreciate it if someone could explain this to me!

Thanks a lot!
 
Last edited:
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I am actually in my final year of the degree (mechanical engineering) however materials was never my strong point :sorry:
I did read that information before and I also watched a number of videos on pitting/crevice corrosion, however I couldn't find a suitable example explanation.

A summary of what I know (will focus on Crevice):
  • the fact that the crevice needs to be big enough for the corrodent to enter but small enough to remain stagnant,
  • the fact that crevices trap pollutants, moisture, and excludes oxygen (not entirely sure about the oxygen however to be honest, since it is required for corrosion to take place)
  • the oxide layer formed between the metal and oxygen to stop electron flow
  • this layer can be broken by mechanical means like scratching
  • and in order for crevice corrosion to take place 2 factors are important:
    1. drop in potential into the crevice
    2. and the chemical composition of electrolyte
As you can see what I know (assuming it is correct) is only the theoretical aspect, I don't know how it would actually happen.
 

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