Q:
What are the effects of Erosion Corrosion?



A:
  • Two effects result in more rapid and severe attack. Two
    special subsets are cavitation and fretting corrosion. All
    types of corrosive media can generate erosion corrosion,
    e.g., gases, aqueous solutions, organics, liquid metals
    -- any of these with suspended solids.

  • An example of horseshoe-shaped depressions
    on the internal surface of a brass heat exchanger
    tube caused by erosion-corrosion is shown below.





  • Following is a schematic of erosion-corrosion
    of a condenser tube.






  • Important Features: Velocity (presence of
    critical velocity for increased attack), turbulence (causes
    impingement or localized attack), galvanic cell action may
    be greatly accelerated, metal mechanical properties, heat
    treatment may increase/decrease resistance. An illustration
    of cavitation is shown below.

  • Cast steel feed water-pump impeller severely damaged by
    cavitation. Note how damage is confined to the outer edges
    of impeller where vane speed was maximum.