Effects of corrosion and damage mechanisms

Effects of Corrosion

Corrosion refers to the destructive and gradual process that transforms metals and alloys back into their native state.
Common types of corrosion include uniform attack, galvanic or two-metal corrosion, crevice corrosion, pitting, intergranular, selective leaching, stress corrosion cracking, and erosion corrosion.
Rust is the most common and visible form of corrosion, which usually affects iron and steel. Other metals can also corrode but may not form such obvious markings.
Corrosion occurs due to the chemical reaction between a metal and its environment, resulting in the formation of metal oxides or salts.
It leads to material degradation reducing the load-carrying capability and leading to premature failure of the material.
Corrosion can cause significant economic loss due to the damage of structures and the requirement for replacement or maintenance.
Critical industries like aviation, automotive, oil, and gas must continually monitor and mitigate corrosion to ensure safety.

Mechanical Damage: Can occur due to forces like tension, compression, shear, torsion, and bending. This can lead to deformation or fractures.
Wear: This is caused by the removal, displacement or deformation of material from surfaces in relative motion. Types include adhesive wear, abrasive wear, surface fatigue, and fretting wear.
Fatigue: Occurs due to repeated loading and unloading cycles. Micro-cracks initiate and propagate, leading to failure if the material is subjected to cyclic stresses over a period of time.
Creep: It’s a time-dependent deformation under constant stress, typically at high temperatures. Leads to elongation or rupture of the material.
Embrittlement: Process that reduces a material’s ductility, making it brittle. Chemical reactions, often involving hydrogen or heat treatment, cause the crystalline structure of the material to change, promoting crack formation.

Material selection is important to prevent corrosion. Corrosion-resistant materials should be used, especially in harsh environments.
Protective coatings or paint prevent direct contact of the metal with the corroding environment.
Cathodic protection is a technique used to prevent corrosion in which the material is made a cathode in an electrochemical cell.
Regular maintenance and inspection to detect damage early and take corrective action.
Design items to minimise stress concentration, reduce operating stresses, and avoid damaging vibratory stresses. Opt for good quality control in manufacture to avoid defects.
Use of lubricants reduces wear by providing a protective layer between surfaces in relative motion.
Control operating temperature to avoid problems related to high-temperature damage mechanisms like creep and embrittlement.