Microbiologically Induced Corrosion
API 570 STUDY GUIDE
MODULE 2 : PART 10
API 571 : Clause 4.3.8 : Microbiologically Induced Corrosion (MIC)
Description of Damage:
* Caused by living organisms such as bacteria, algae or fungi
* Often associated with the presence of tubercles or slimy organic substances
Affected Materials
Most common materials of construction including,
Carbon and low alloy steels,
300 series SS,
400 Series SS,
Aluminium,
Copper,
Some nickel base alloys.
Critical Factors
- Where water is present there is chance of MIC
- Water if stagnant, low flow are MIC promoting conditions
- MIC is not only with water, organisms can 'eat' inorganic and organic substances and can live. The conditions such as lack of oxygen, dark or light, high salinity, pH range of 0 to 12 , temperatures from -17 deg C to 113 deg c can also be conditions in which these microbiological organisms can survive.
- Organisms can live in sulfur, ammonia, H2S, hydrocarbons and organic acids.
- All organisms require a source of carbon, nitrogen and phosphorous for growth.
Affected Units or Equipment
- Where water is stagnant, 1) Fire water system 2) piping system or equipment where hydrotest water is not drained properly.
- Where there is low flow conditions of water, water cooled heatexchanger
- Bottom of storage tanks.
- Piping in contact with some soils
Appearance or Morphology of Damage
- Localized pitting under deposits or tubercles that shield the organisms
- Cup-shaped pits within pits in carbon steel
- Subsurface cavities in SS
Prevention/Mitigation
- Treat water with biocides for avoiding microbes which need water for survival
- Proper application of biocides can control but cannot eliminate MIC
- Drain hydrotest water or treat that water with biocide.
- Maintain coatings inside tanks.
- Wrapping and cathodically protecting underground structures
- If MIC is identified, complete removal of organisms are needed which can be with the combination of blasting, pigging, chemical cleaning and biocide treatment
- Biocides: Cl, Bromine, Ozone, Ultraviolet light or proprietary compounds
Inspection and monitoring
- Foul smelling of water is a sign of microbes in water
- Loss of duty of heat exchanger or loss in heat exchanger efficiency is a sign of fouling and potential MIC damage
- Monitor water treatment
- Special probes have been designed which can detect fouling which may precede or coincide with MIC
- In Cooling water systems, treated water is analysed by measuring biocide residual, microbe counts and visual appearance.
Related Mechanisms
* Cooling Water Corrosion
QUESTIONS
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