PECM Issue 29 2017 | Page 106

interView QuestiOn and answer On ‘MicrObiOLOGicaLLy infLuenced cOrrOsiOn’ icrobiologically Influenced Corrosion (MIC) can be addressed as an electrochemical corrosion in which the role of micro- and macro-organisms is undeniable. Between 20 to 40% of the economic loss of corrosion is due to MIC. In Canada, 50 % of external corrosion cases of gas pipelines are attributed to MIC. Being electrochemical in nature means that MIC can be treated by conventional ways of controlling corrosion: coating, CP, use of chemicals, materials selection and design. Being microbial in nature, however, adds more into these measures as well as if they can be applied with 100% success: the chemical used are called biocides (other than inhibiters), Not all coatings are resistant to MIC, CP may or may not control MIC and all known engineering materials (except Titanium and its alloys) have been reported to be vulnerable to MIC. If MIC happens in non-metals (such as concrete or composites), it is more technical to address it as MID (Microbiologically influenced deterioration).MIC can be operate as a pre-commissioning factor in increasing the risk of corrosion in M 106 PECM Issue 29 common practices such as hydrostatic test or during inspection practices such as intelligent pigging. There are two groups of methods to be used for the recognition of MIC: Culture-dependent and culture-independent. Both groups have serious drawbacks in addition to their undeniable advantages. Likewise, there are four ways to treat MIC: physical (use of coating)/mechanical (pigging, scrubbing) - Chemical (use of biocides), electrical (CP) and microbiological (Bacteria against bacteria). All these treatment methods also have their own intrinsic limitation and disadvantages. 1. W HAT IS MICROBIOLOGICALLY INFLUENCED CORROSION (MIC) AND HOW HAS IT ATTRACTED ATTENTION OVER THE PAST DECADES ? Microbiologically influenced corrosion (MIC), or as Europeans mostly prefer to say microbiologically induced corrosion is an electrochemical process in nature where micro-organ isms (such as bacteria and Archaea) and macro-organisms (such Barnacles) are capable of affecting the severity of corrosion by initiation, acceleration and sometimes deceleration it. Due to its very high costs, both economic and ecologic, the interest in MIC always shows an ever-increasing trend. 2. W HAT ARE THE KEY TECHNOLOGIES AVAILABLE IN MARKET TODAY IN TERMS OF MONITORING AND DETECTING MIC? Culture-dependent methods such as MPN (most probable number) and serial dilution as well as simple absence/presence cultures are available. However, these methods all have the drawback that about 99% of bacteria are not culturable. Recently, culture- dependent methods that rely on molecular microbiology methods, such as PCR, DGGE, ATPG2 and the like have been developed. While Culture-independent methods do have accuracy advantage over their culture-dependent methods, they also suffer from serious limitations. In addition, unlike culture-dependent methods that are the base for all field tests such as but not limited to BART, culture-independent methods y have not been “Field-friendly”…yet!