Corrosion Factors

A point of view proposed by Professor Staehle is that all engineering materials are reactive chemically and that the strength of materials depends totally upon the extent to which environments influence the reactivity and subsequent degradation of these materials.

Factors influencing corrosion reactions

In order to define the strength of an engineering material for a corrosion based design it is essential to define the nature of the environments affecting the material over time.

• Material Factor

  • Bulk chemical composition

  • Microstructure

  • Grain boundary composition

  • Surface condition

• Environment Factor

  • Nominal environment definition

    • type

    • chemistry

    • concentration

    • phase

    • conductivity

  • Local environment definition

    • velocity

    • thin layer wetting

    • wetting and drying cycles

    • heat transfer boiling

    • wear and fretting

    • deposits

• Stress Factor

  • Stress definition

    • mean stress

    • maximum stress

    • minimum stress

    • constant load/constant strain

    • strain rate

    • plane stress/plane strain

    • modes I, II, II

    • biaxial

    • cyclic frequency

    • wave shape

  • Sources of stress

    • intentional

    • residual

    • corrosion wedging

    • thermal cycling

• Geometry Factor

  • Discontinuities which intensify stress

  • Generation of galvanic potentials

  • Chemical crevices

  • Settling of solids

  • Restricted geometries leading to concentration cells

• Temperature Factor

• Time Factor

  • Changes in GB chemistry

  • Changes in microstructure

  • Changes in surface deposits, chemistry or/and heat transfer resistance

  • Development of surface defects, pitting or/and erosion

  • Development of occluded cells