Materials Performance

DEC 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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40 DECEMBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 12 CHEMICAL TREATMENT M Microbiologically influenced corro- sion (MIC) is a special type of corro- sion that is very difficult to identify. Its occurrence is often known only after a consequence. MIC can cause pipe- line leaks, particularly in nonpiggable pipeline sections. Also, portions of storage tank bottoms are more prone to this type of corrosion. MIC often causes pitting, due to the concentra- tion of many generations of bacteria at one point in a structure. Special ex- pertise and experience are required to monitor and prevent MIC. This ar- ticle discusses the practical chal- lenges associated with monitoring and preventing MIC. Microbiologically influenced corrosion (MIC) is a major corrosion mechanism with failures beyond expectation levels in many cases. MIC develops as follows: • Chemical adsorption of organics • Bacterial epiphytes adhere to sub- merged surfaces • Colonization of other microorgan- isms • Entrapment of particles, dead cells, and chelation of heavy metals from water The main types of bacteria that can cause MIC are: • S ul fat e - re du c i n g b a c t er i a ( SRB ) , w hi ch pro du c e hydrogen sul f i d e (H 2 S) • A c i d - p r o d u c i n g b a c t e r i a ( A P B ) , which produce organic acids (acetic acid, succinic acid, etc.) and inor- ganic acids (sulfuric acid [H 2 SO 4 ]) • Slime formers • Iron bacteria, which commonly plug water systems and produce slimy precipitates of hydrated ferric oxide (Fe 2 O 3 ) Even in an aerobic environment, these bacteria can create anaerobic conditions with the help of slime-forming bacteria. Anaerobic conditions allow the production of gases such as H 2 S, which cause severe corrosion. Because bacteria can concen- trate at one point for many generations, MIC causes pitting. Although there are many methods to count bacteria, all will give probable bacteria counts only. Nor- mally, only a few varieties of bacteria are identified, and their effects are severe; how- ever, there are wide varieties of bacteria that affect the atmosphere inside pipelines and contribute indirectly to corrosion. MIC Monitoring Obtaining the bacteria count in pro- duced water from a pipeline is most impor- tant when assessing MIC. Both planktonic and sessile bacteria counts should be mea- sured for SRB and general anaerobic bacte- Practical Challenges in Monitoring and Preventing Microbiologically Influenced Corrosion Ta T a L. n . m ur T hy, GSPC, Ltd., Andhra Pradesh, India

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