NACE CP2 Study Guide

1. oxidation: loss of electrons, positive charge atoms (anode) 2. reduction: gain of electrons, negative charged atoms (cathode) 3. forms of corrosion: uniform, crevice, galvanic (dissimilar metals) if two metals have to be couple then best to couple metals close together in the galvanic series, pitting, intergranular, selective leaching (dezincification, graphitization), velocity phenomena, environmental cracking (corrosion fatigue, hydrogen embrittlement, SCC (Carbonates/bicarbonates) 4. High PH: Low hydrogen, alkaline, easy polarization 5. Low PH: high hydrogen, acidic, harder to polarize 6. High oxygen/High Hydrogen concentration: harder to polarize, work at the cathode only, called cathodic depolarizers. 7. factors affecting corrosion: A. anything that affects polarization. (temp. etc...) B. concentration cells (oxygen, temp, etc.) In an oxygen concentration cell, what is the anode? (i.e. the area with more or less oxygen?) In a metal ion cell, which2 / 24 area is the anode (i.e. the area with the greater of lower concentration)? C. Anaerobic bacteria (MIC) Absence of oxygen, depolarizer 8. polarization: a. corrosion current reduces with polarization b. polarization increases with CP current applied c. Occurs at surface of both anode and cathode. 9. shielding: a. shorted casings b. proximity of other structures c. reinforced concrete 10. amphoteric materials: corrode at low and high pH 11. on potential: native + polarization + IR drop 12. polarized potential (off): native + polarization 13. kirchoff's laws: a. voltage (series circuits) b. current (parallel circuits) 14. faraday's law: W=KIT relates weight loss of metal in a corrosion cell with time and current flow. 15. rate of corrosion: directly proportional to current flow 16. cathodic protection limitations: -shielding issues -attenuation3 / 24 -interference