Degradation Mechanisms and Corrosion Mechanisms

Published: July 25, 2018 By: Paul Cripps

There are several degradation mechanisms for components in the oil and gas field. Among them are:

  1. Corrosion
  2. Wear
  3. Catastrophic/unforeseen overload
  4. Fatigue

Among the corrosion mechanisms, NACE (Basic Corrosion Course) has identified 9 basic forms of corrosion that affect metals and alloys:

  1. General Corrosion
  2. Pitting Corrosion
  3. Crevice Corrosion
  4. Inter-granular Corrosion
  5. Fretting Corrosion
  6. Stress Corrosion Cracking
  7. Filiform Corrosion
  8. Hydrogen Embrittlement
  9. Galvanic Corrosion

For refineries API 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, is useful. API 571 identifies damage mechanisms that fall under one or more of than 9 forms of corrosion. The mechanisms are grouped as:

  1. Mechanical and Metallurgical Failure Mechanisms – 20
  2. Uniform (General) Corrosion Types – 24
  3. High Temperature Corrosion – 7
  4. Environment Assisted Cracking – 15

Within the typical refining process units (e.g. crude unit, amine treating) API 571 indicates a total of 66 damage mechanisms are possible. API 571 also reviews the mechanisms possible in each type of refining process unit. Although API 571 reviews fixed equipment, its concepts may be extended to piping and rotating equipment.

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