On February 10, 2021, The Electrochemical Society hosted Dr. Reza Javaherdashti’s live webinar, “Microbiologically Influenced Corrosion: Tips, Myths, Skills.” Dr. Javaherdashti is General Manager at Eninco Engineering B.V., The Netherlands. Below are Dr. Javaherdashti’s responses to questions asked in the Q&A session following his talk.
Dr. Javaherdashti has taught more than 5000 hours about electrochemical corrosion, corrosion management, and microbial corrosion to various industries worldwide. In this webinar, he discussed and explained the most important theoretical and practical aspects of microbiologically influenced corrosion (MIC) and microbiologically influenced deterioration (MID) mechanisms and how industry practitioners can recognize them.
View Dr. Javaherdashti’s Webinar
NOTE: Registration is required to view the webinar.
ECS thanks Hiden Analytical, the generous sponsor of Dr. Javaherdashti’s webinar.
Q&A
Q1. What is the proof that bacteria consume electrons and that it is not a reaction of their metabolic products with metal?
The proof is based on research that first started in 2008 regarding the mechanism of electron transfer between SRB (sulfate-reducing bacteria) and a metallic substrate. For more information, please see Reza Javaherdashti and Farzaneh Akvan. Failure Modes, Effects and Causes of Microbiologically Influenced Corrosion: Advanced Perspectives and Analysis
Q2. Would you explain oxygen evolution (during polarization tests) and why some metals show that and not others (e.g., Cr and Ta)?
Generally speaking, oxygen evolution is just one of the existing cathodic reactions based on the current chemistry and oxygen availability.
Q3. Can MIC be responsible for hydrogen-initiated corrosion or HIC?
Definitely, Clostridia that can produce ample amounts of hydrogen have been addressed as one of the culprits to HIC when they are available and active.
Q4. Could you advise on the impact, if any, of MIC on highly corrosion-resistant alloys such as 25Cr super-duplex stainless steel? The impact of biocides is known to degrade over time. Is this topic covered in any of your books?
Your question has two parts:
4.1. I have shown in my research (Reza Javaherdashti, MIC and Cracking of Mild and Stainless Steels, PhD Thesis) that SAF 2205 (22% Cr) was very susceptible to premature failure during SSRT (slow strain rate testing) tests where iron-reducing bacteria were present.
4.2. I think the so-called “effect weakening” is not unique to biocides; all chemicals, including corrosion inhibitors, do suffer from the same weakness. However, if you meant something like an adaptation of bacteria to biocides, it is a myth that I don’t really accept. Please see these books:
- Reza Javaherdashti and Farzaneh Akvan, Failure Modes, Effects and Causes of Microbiologically Influenced Corrosion: Advanced Perspectives and Analysis
- Reza Javaherdashti, Microbiologically influenced corrosion—an engineering insight
Q5. Is microbial corrosion an issue in de-ionized water systems?
De-ionized waters are supposed to be ion-less; therefore it is not supposed to be a problem. However, under real-life situations, they may start to become a corrosive fluid, then the MIC likelihood would also exist.
Q6. Will controlled UV Radiation exposure limit or reduce the risk of MIC?
It can be up to 99.9%, but don’t forget that there are proven cases where UV lamps have been themselves covered with biofilm. See: Reza Javaherdashti, Microbiologically influenced corrosion—an engineering insight
Q7. Can we expect bacteria, etc., in produced water?
The general rule is that the water must contain necessary ions and nutrients as well as appropriate pH and temperature range, so that all these will support bacterial growth and activity.
Q8. What is your opinion on SRB vs. APB vs. IRB in a sessile and planktonic interaction in a pipeline and reservoir?
I can say that acid-producing bacteria (APB) includes aerobic sulphur-oxidizing bacteria and anaerobic Clostridia, among others. Your question is based on the assumption that each bacterial group can do a specific activity that contributes to corrosion; this is not true. Methane-producing bacteria that can contribute to corrosion mainly by cathodic depolarization can also reduce ferric to ferrous ions, such as IRB (iron-reducing bacteria). Also, in addition to SRB, some other CRB (corrosion-reducing bacteria) can contribute to corrosion to ETT mechanism.
Q9. How does welding increase the probability of MIC?
Thermal welding (in which heat is used to melt the metal) induced high entropy can be assumed as the dragging force for establishing a gradient of alloys from the bulk to the grain boundaries as well as HAZ (heat-affected zone). This concentration of alloying elements can serve as a “self-service restaurant” to planktonic and then sessile CRB.
Q10. What are the main types of bacteria we can experience in oil and gas and utility services? Is their combinational effect always synergistic and accelerating, or they may negate each other’s effect?
10.1 It is a really a tough question, especially given that not all CRB and CRA (corrosion-related archaea) are known yet! However, my “personal choices” are SRB, IRB, SOB, IOB, Clostridia.
10.2 So far the research shows that the combinational effect of CRB on corrosion is much more effective in increasing it than single type cultures.
Q11. Please explain the exopolysaccharide produced by the microbes/biofilms.
As the name also suggests, it is generated out of the cell “exo,” and it has a polysaccharide “polymeric” structure. They mainly help build the biofilm—I don’t like the term biofilm as it is a wrong term; I suggested temenos instead—and assist planktonic bacteria attach themselves to the surfaces to achieve nutrients that are on the surface. EPS (exopolysaccharide) acts as an “anchor” to the planktonic bacteria and as a “glue” to the sessile bacteria.
Q12. Is the IRB mechanism or their influence (accelerated) if we surpass a certain flow rate inside the pipe?
Having a relatively high flow rate (above 1.5 m/s or 5 ft/s) is a necessary condition to avoid MIC; however it is not enough measure. This means that by just increasing the flow rate, one can’t decrease the risk of MIC.
Q13. What is the most important group of corrosion-related microorganisms?
It is really not that easy to answer this question. However, see 10.1 for my choices.
Q14. Why could DGGE (denaturing gradient gel electrophoresis) not detect methanogens?
Please read:
Chatterjee I, Shukla V, Chauhan D, Geissler BLM, Keller-Schultz C, and Keasler VV. Molecular microbial monitoring: using next-generation DNA sequencing for oilfield biocorrosion diagnostics, Paper No. 14124, 15th Middle East Corrosion Conference& Exhibition, Manama, Kingdom of Bahrain. February 2e5, 2014.
Q15. Could ozone be used for destroying massive biofilm?
Ozone and UV are also beneficial, but their effectiveness ranges are too limited. Read this paper for more information: Reza Javaherdashti, Microbiologically influenced corrosion—an engineering insight
Q16. IF the ICCP system fails in ships, how can MIC be prevented for bronze propellers? Also, how to avoid barnacle, etc., growth in standing waters?
16.1: CP (cathodic protection) including ICCP (impressed current cathodic protection) is just one of the five options that can be applied against corrosion in general and MIC. Based on the system in question and real working conditions, the most feasible corrosion management to control/protect against MIC can be applicable.
16.2: One way would be the application of protective coatings that, due to their properties, will not allow biofilm (temenos) formation. Smart coatings with proper features in this context are becoming more and more important.
Q17. Corrosion in drinking water is recently in the news with EPA’s revisions to the Lead and Copper Rule. Are there any comments on if the rule will effectively address MIC?
Definitely! We must not forget that biofilm (temenos) formation could be one of the main reasons that would allow concentration of microorganisms, including pathogenic bacteria and accumulation of toxic metals, and to promote the likelihood of MIC. Also, prevention/control of corrosion could significantly affect the leaching out of metals, including metals such as, but not limited to, Cu and Pb (polished brass).
Q18. Please explain about MIC in the biofuels storage tanks. How much is possible to happen?
These fuels are highly likely to develop the best environment to form the necessary nutrients for bacterial growth. Also, the water phase formed can efficiently act as the necessary electrolyte and the medium through which biochemical reactions necessary to keep the bacteria alive can be performed. Therefore, biofuel storage tanks could be quite vulnerable to corrosion and particularly MIC. Several options may be available to control and prevent MIC, and by using these options, the corrosive effects of CRB/CRA that can develop in the fuel will be minimized.
