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Common Types of Metal Corrosion Hydrogen Embrittlement Atomic hydrogen can diffuse or become adsorbed into steel. It then reacts with carbon to form methane or microscopic gas formations which weaken and detract from ductility. Usually this happens at high temperature under conditions where FRP is ordinarily notconsidered. The same type of mechanism of attack is associated at lower temperatures with various forms of galvanic or stress induced corrosion. Quite often hydrogen embrittlement can be a problem for steel which has been electroplated or pickled, especially when done improperly or inefficiently. Some of these matters are receiving more attention due to future considerations of hydrogen in fuel cell and other energy applications. Sulfate Reducing Bacteria and Microbially Induced Corrosion (MIC) Colonies of microorganisms, especially aerobic and anaerobic bacteria contribute greatly to corrosion of steel through a wide variety of galvanic and depositional mechanisms. Usually the corrosion is manifested in the form of pitting or sulfide induced stress cracking. Perhaps the most significant type of such corrosion involves sulfate -reducing bacteria (SRB), which metabolize sulfates to produce sulfuric acid or hydrogen sulfide. Such bacteria are prolific in water (including seawater), mud, soil, sludge, and other organic matter. L: These bacteria are a major reason why underground steel storage tanks are corroded, and this has lead to widespread use of FRP as an alternative or as an external protective barrier to steel. Various manifestations of MIC are seen far -and wide, including industrial environments which inadvertently serve as warm or nutrient -rich cultures for biological growth. FRP is unaffected by many of the mechanisms associated with MIC. Apart from sulfate reducing bacteria, other forms of microbial corrosion which affect metals include acid producing bacteria, slime forming organisms, denitrifying bacteria which generate ammonia, and other corrosion associated with various species of algae and fungi. It is expected that biologically induced corrosion will receive increased attention as more applications and technologies evolve in the field of energy production associated with biomass and renewable resources. Processing will include such things as aerobic and anaerobic digestion, fermentation, enzymatic hydrolysis and conversion of cellulose, lignin, or polysaccharides to sugars, which in turn may be converted to ethanol. Carbon and stainless steels are not the only metals affected by MIC. Also routinely corroded are copper and various alloys as well as concrete. The most common example of which involves sewage and waste treatment applications in the presence of the thiobacillus bacteria, which oxidizes 1-12S to sulfuric acid. FRP has a long history of successful use in these environments.