Microbial corrosion, also called
bacterial corrosion,
bio-corrosion,
microbiologically-influenced corrosion, or
microbially-induced corrosion (
MIC), is
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
caused or promoted by
microorganismA microorganism or microbe is an organism that is microscopic...
s, usually chemoautotrophs. It can apply to both metals and non-metallic materials.
Bacteria
Some
sulfate-reducing bacteriaSulfate-reducing bacteria comprise several groups of bacteria that use sulfate as an oxidizing agent, reducing it to sulfide. Most sulfate-reducing bacteria can also use other oxidized sulfur compounds such as sulfite and thiosulfate, or elemental sulfur. This type of metabolism is called...
produce
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
, which can cause sulfide stress cracking.
AcidithiobacillusAcidithiobacillus is a genus of proteobacteria. The members of this genus used to belong to Thiobacillus, before they were reclassified in the year 2000....
bacteria produce
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
;
Acidothiobacillus thiooxidans frequently damages
sewerA sanitary sewer is a type of underground carriage system, , for transporting sewage from houses or industry to treatment or disposal...
pipes.
Ferrobacillus ferrooxidans directly oxidizes
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
to
iron oxideIron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides.-Oxides:* FeO, iron oxide, * Fe3O4, iron oxide,...
s and iron hydroxides; the
rusticleA rusticle is a formation of rust similar to an icicle or stalactite in appearance that occurs underwater when wrought iron oxidizes. They may be familiar from underwater photographs of shipwrecks....
s forming on
RMS TitanicThe RMS Titanic was an Olympic-class passenger liner owned by British shipping company White Star Line and built at the Harland and Wolff shipyard in Belfast, United Kingdom...
wreck are caused by bacterial activity. Other bacteria produce various
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
s, both organic and mineral, or
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula NH
3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers...
.
In presence of oxygen,
aerobic bacteriaAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. -Types:*Obligate aerobes require oxygen for aerobic cellular respiration...
like
Thiobacillus thiooxidans,
Thiobacillus thioparus, and
Thiobacillus concretivorus, all three widely present in the environment, are the common corrosion-causing factors resulting in
biogenic sulfide corrosionBiogenic Sulfide Corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is oxidized in the presence of moisture to form sulfuric acid that...
.
Without presence of oxygen,
anaerobic bacteriaAn anaerobic organism or anaerobe is any organism that does not require oxygen for growth and may even die in its presence. There are three types: obligate anaerobes, which cannot use oxygen for growth and are even harmed by it; aerotolerant organisms, which cannot use oxygen for growth, but...
, especially
Desulfovibrio and
Desulfotomaculum, are common.
Desulfovibrio salixigens requires at least 2.5% concentration of
sodium chlorideSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
, but
D. vulgaris and
D. desulfuricans can grow in both fresh and salt water.
D. africanus is another common corrosion-causing microorganism. The
Desulfotomaculum genus comprises sulfate-reducing spore-forming bacteria;
Dtm. orientis and
Dtm. nigrificans are involved in corrosion processes. Sulfate-reducers require reducing environment; the electrode potential of at least -100 mV is required for them to thrive. However, even a small amount of produced hydrogen sulfide can achieve this shift, so the growth, once started, tends to accelerate.
Layers of anaerobic bacteria can exist in the inner parts of the corrosion deposits, while the outer parts are inhabited by aerobic bacteria.
Some bacteria are able to utilize
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
formed during cathodic corrosion processes.
Bacterial colonies and deposits can form
concentration cellA Concentration cell is an electrochemical cell that has two equivalent half-cells of the same material differing only in concentrations. One can calculate the potential developed by such a cell using the Nernst Equation...
s, causing and enhancing galvanic corrosion.
http://httd.njuct.edu.cn/MatWeb/corrosie/c_bio.htm
Bacterial corrosion may appear in form of
pitting corrosionPitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the lack of oxygen around a small area. This area becomes anodic while the area with excess of oxygen becomes cathodic,...
, for example in pipelines of the oil and gas industry. Anaerobic corrosion is evident as layers of metal sulfides and hydrogen sulfide smell. On
cast ironCast iron usually refers to grey iron, but also identifies a large group of ferrous alloys, which solidify with a eutectic. The colour of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due to its carbide impurities which...
, a graphitic corrosion
selective leachingSelective leaching, also called dealloying, demetalification, parting and selective corrosion, is a corrosion type in some solid solution alloys, when in suitable conditions a component of the alloys is preferentially leached from the material. The less noble metal is removed from the alloy by...
may be the result, with iron being consumed by the bacteria, leaving
graphiteThe mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek γραφειν : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead...
matrix with low mechanical strength in place.
Various
corrosion inhibitorA corrosion inhibitor is a chemical compound that, when added to a fluid or gas, decreases the corrosion rate of a metal or an alloy.The effectiveness, or corrosion inhibition efficiency, of a corrosion inhibitor is a function of many factors like: fluid composition, quantity of water, flow regime......
s can be used to combat microbial corrosion. Formulae based on
benzalkonium chlorideBenzalkonium chloride, also known as alkyldimethylbenzylammonium chloride and ADBAC, is a mixture of alkylbenzyldimethylammonium chlorides of various even-numbered alkyl chain lengths. This product is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group...
are common in oilfield industry.
Microbial corrosion can also apply to
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
s,
concreteConcrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, aggregate , water, and chemical admixtures...
, and many other materials. One such example are
Nylon-eating bacteriaNylon-eating bacteria are a strain of Flavobacterium that is capable of digesting certain byproducts of nylon 6 manufacture. This strain of Flavobacterium, Sp...
.
Aviation fuel
Hydrocarbon utilizing microorganisms, mostly
Cladosporium resinae and
Pseudomonas aeruginosaPseudomonas aeruginosa is a common bacterium which can cause disease in animals and humans. It is found in soil, water, skin flora and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also with little oxygen, and has thus colonised many natural and...
, colloquially known as "HUM bugs", are commonly present in
jet fuelJet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw colored. The most common fuels are Jet A and Jet A-1 which are produced to an internationally standardized set of specifications...
. They live in the water-fuel interface of the water droplets, form dark black/brown/green, gel-like mats, and cause microbial corrosion to plastic and rubber parts of the aircraft fuel system by consuming them, and to the metal parts by the means of their acidic metabolic products. They are also incorrectly called
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in...
due to their appearance.
FSIIFuel System Icing Inhibitor is an additive to aviation fuels that prevents the formation of ice in fuel lines. FSII is sometimes referred to by the registered, genericized trademark Prist. Jet fuel can contain a small amount of dissolved water that does not appear in particulate form...
, which is added to the fuel, acts as a growth retardant for them. There are about 250 kinds of bacteria that can live in jet fuel, but fewer than a dozen are meaningfully harmful.
Recent events
In response to increased awareness of the nature and danger of microbial corrosion, a two-day international
symposiumSymposium originally referred to a drinking party but has since come to refer to any academic conference, or a style of university class characterized by an openly discursive format, rather than a lecture and question–answer format...
was held in
Perth, Western AustraliaPerth is the capital and largest city of the Australian state of Western Australia. With a population of 1,650,000 , Perth ranks fourth amongst the nation's cities, with a growth rate consistently above the national average....
in February 2007. The symposium, originally proposed by Dr.Reza Javaherdashti, was sponsored by EXTRIN Consultants and Curtin University of Technology, as well as other local industries.It attracted speakers and attendees from as far as
ArgentinaArgentina, officially the Argentine Republic , is the second largest country in South America, constituted as a federation of 23 provinces and an autonomous city, Buenos Aires. It is the eighth largest country in the world by land area and the largest among Spanish-speaking nations, though Mexico,...
,
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
,
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
, the UK and the US in addition to Australian representatives. The symposium primarily focussed on the identification of Microbial Corrosion in marine,
miningMining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, vein or seam. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash...
and
industrialAn industry is the manufacturing of a good or service within a category. Although industry is a broad term for any kind of economic production, in economics and urban planning industry is a synonym for the secondary sector, which is a type of economic activity involved in the manufacturing of raw...
environments and the best course of action to remove and prevent further attacks.
Further reading
Kobrin, G., "A Practical Manual on Microbiologically Influenced Corrosion", NACE, Houston, Texas, USA, 1993.
Heitz,E., Flemming HC., Sand, W., "Microbially Influenced Corrosion of Materials", Springer, Berlin, Heidelberg, 1996.
Videla, H., "Manual of Biocorrosion", CRC Press, 1996.
Javaherdashti, R., "Microbiologically Influenced Corrosion-An Engineering Insight", Springer, UK, 2008.