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Corrosion of passive metals

Corrosion of passive metals. Jacek Banaś. University of Science and Technology (AGH-UST) Faculty of Foundry Engineering Department of Chemistry and Corrosion of Metals. Wagner definition of passivation.

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Corrosion of passive metals

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  1. Corrosion of passive metals Jacek Banaś University of Science and Technology (AGH-UST) Faculty of Foundry Engineering Department of Chemistry and Corrosion of Metals

  2. Wagner definition of passivation Metal is passive when its corrosion in course of chemical or electrochemical reaction is lower at higher affinity of reaction than at lower affinity of chemical or electrochemical process C. Wagner: Corrosion Science 5, 751 (1965)

  3. Mechanism of passivation in aqueous solutions dissolution passivation intermediate

  4. Mechanism of iron passivation in aqueous solutions Cyclic voltamperometric curve of iron polarization in neutral environment W.J. Lorenz, K. E. Heusler in Corrosion Mechanisms ed. Marcel Dekker Inc. N. York 1987

  5. Sponateous passivation active state (corrosion) Ic < ip passive state (protection by oxide film) Ic > ip Effect of oxidant concentration on spontaneous passivation of metal

  6. Effect of chemical composition on passive behaviour of the alloy Stationary polarization curves of Fe-Si alloys in 1M H2SO4 Stationary polarization curves of austenitic Fe-Cr-Ni alloys in 1M H2SO4 Effect of chromium on the structure of passive film on Fe-Cr alloys in neutral aqueous solutions J.Kruger in Passivity of Metals, ed.by Electroche. Soc. Inc. Princetown ,N. Jersey 1978 Model of passive film on pure chromium

  7. Effect of chemical composition on passive behaviour of the alloy

  8. Corrosion of passive alloys Crevice corrosion Stress corrosion Pitting corrosion Corrosion-erosion degradation Inergranular corrosion

  9. Pitting corrosion Mechanism of pitting corrosion in chloride containing media Pitting corrosion of iron in atmosphere polluted with SO2

  10. Pitting corrosion Pitting corrosion of Ti in CH3OH-LiCl solutions Pitting corrosion of Fe-18%Cr alloy in CH3OH-H2SO4 solutions Corrosion of heat exchanger (carbon steel) in water

  11. Inergranular corrosion Inergranular corrosion of NIROSTA 2202steel (22%Cr,6%Ni,3%Mo) in 93.5 wt.% H2SO4 (1000C)

  12. Stress corrosion cracking Crack velocity: • Ds. – surface self diffusion coeficient • L – diffusion length • – elastic surface stress at the crack tip a3 – volumen of vacancy Surface mobility model of Stress corrosion cracking (SCC) according to Galvele J.R. Galvele, Corrosion Science 27,1 (1987)

  13. Hydrogen embrittlement Hydrogen absorption HadHLattice  Crack initiation  Crack propagation    Anomalous structure Segregation of Mn and P Inclusions (elongated MnS) Corrosion (H++eHad)    • Low content of S and P • Spheroidization of inclusions • Heat treatment • Rolling conditions • Alloy components • Coatings • Inhibitors

  14. The effect of H2S on hydrogen embrittlement HIC – hydrogen induced cracking, occurs in low- and high-strength steels even without external stress. Crack propagation proceeds paralell to surface. SSCC – sulphide stress corrosion cracking, occurs in high-strength steels. Crack propagation proceeds perpendicular to surface.

  15. The effect of H2S on hydrogen embrittlement HIC, mikrocracs parallel to pipe surface  Nucleation of cracks • HISCC, mikrocracs perpendicular to pipe surface Nucleation of cracks HIC and HISCC of pipelines after 10 years exploitation in natural gas containing 4.5% H2S.

  16. Hydrogen embrittlement Mechanism of hydrogen embrittlement by stress iduced hydride formation.

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