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Pitting Crevice Corrosion - Pitting Pitting and crevice...

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1 1 Pitting and crevice corrosion 2 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements Various forms of corrosion ± passivity ± galvanic corrosion ± pitting/crevice corrosion ± cracking ± erosion corrosion ± corrosion environments Corrosion mitigation Pitting Pitting corrosion is a localized form of corrosion by which cavities or "holes" are produced in the material. Pitting is considered to be more dangerous than uniform corrosion damage because it is more difficult to detect, predict and design against. image source: Corrosion Doctors , www.corrosion-doctors.org 3 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements Various forms of corrosion ± passivity ± galvanic corrosion ± pitting/crevice corrosion ± cracking ± erosion corrosion ± corrosion environments Corrosion mitigation A pit general attack (small pits) deep pit (anode) intact (cathode) An aluminum A92519 specimen exposed to a 3,5% NaCl solution for seven days. The width of the picture is approximately 1 mm. image source: Corrosion Doctors , www.corrosion-doctors.org 4 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements Various forms of corrosion ± passivity ± galvanic corrosion ± pitting/crevice corrosion ± cracking ± erosion corrosion ± corrosion environments Corrosion mitigation Causes of pitting Localized chemical or mechanical damage to the protective oxide film. Low dissolved oxygen concentrations and high concentrations of chloride (as in seawater) Localized damage to, or poor application of, a protective coating The presence of non-uniformities in the metal structure of the component, e.g. inclusions.
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2 5 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements Various forms of corrosion ± passivity ± galvanic corrosion ± pitting/crevice corrosion ± cracking ± erosion corrosion ± corrosion environments Corrosion mitigation Passive metals pit Pitting corrosion on a stainless steel bar exposed to an alkaline solution loaded with chlorides. image source: Prof. Dr. H. Böhni, www.ibwk.baum.ethz.ch 6 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements Various forms of corrosion ± passivity ± galvanic corrosion ± pitting/crevice corrosion ± cracking ± erosion corrosion ± corrosion environments Corrosion mitigation Morphology of pitting narrow/deep pits elliptical pits shallow pits mesa attack image source: Corrosion Doctors , www.corrosion-doctors.org 7 Introduction Electrochemical thermodynamics Electrochemical kinetics Corrosion rate measurements
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  • Spring '10
  • Prof.Sulis
  • erosion corrosion corrosion, corrosion pitting/crevice corrosion, corrosion corrosion environments, passivity galvanic corrosion

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