Causes of Corrosion

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. 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

Reference

  1. Staehle, R.W., "Understanding Situation-Dependent Strength: a Fundamental Objective in Assessing the History of Stress Corrosion Cracking," Proceedings of Environment-Induced Cracking of Metals, M.B. Ives and R. Gangloff, Eds., National Association of Corrosion Engineers, Houston, TX, 1989, pp. 561-612.


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