Microbiologically Influenced Corrosion Investigation in Fire-fighting System of Fajr Petrochemical Company

Microbiologically influenced corrosion is a major cause of industrial system failures. In the present study, for investigation of microbiologically influenced corrosion in fire-fighting system of Fajr petrochemical company, a variety of methods, including microbial cultivation, X-Ray diffraction, corrosion morphology and inspection of selected points of lines were employed. Different groups of corrosion-causing bacteria were observed in fire-fighting system. Sulfate reducing bacterial count in different parts of the system such as outlet of raw water tank and one hydrant were 103 and 104 per ml, respectively. Also producing bacterial count in some system parts such as outlet of raw water tank was 104 per ml. Heterotrophic bacteria were distributed throughout the system and their count in one hydrant reached 4 × 105 per ml. Furthermore, different groups of bacteria were observed in corrosion product deposits. Sulfate reducing and heterotrophic bacterial count were 104 and 5 × 105 per gram of deposits, respectively. Iron bacteria were also detected in corrosion products. Additionally, analysis of corrosion product deposits using XRD technique demonstrated the presence of Fe2O3, FeO(OH) and FeS. In addition, a variety of pit structures with different shapes, particularly pear-shaped pit, were observed. Pipelines inspection obviously proved formation of discrete deposits, including nodules and tubercles. These results indicated that microbiologically influenced corrosion occurred in fire-fighting system of this industrial unit. Thus, monitoring and mitigation of microbiologically influenced corrosion in fire-fighting systems must be fully considered.