Effects of corrosion and damage mechanisms

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.

Damage Mechanisms

  • 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.

Preventing Corrosion and Damage

  • 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.