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COMSATS Institute of Information Technology
Defence Road, Off Raiwind Road, Lahore, Pakistan
CorrosionOccurrence in Major Environments
Presented by
GROUP 7
Hafiz Annus MehmoodCIIT/SP10-BEC-015/LHR
Mohammad AbubakarCIIT/SP10-BEC-015/LHR
Noaman AhmedCIIT/SP10-BEC-015/LHR
Saim KhanCIIT/SP10-BEC-015/LHR
Corrosion
• It is the gradual destruction of a metal due to its reaction with the environment
• The main reaction is oxidation of the metal
• The environment usually contains elements and conditions which cause corrosion
• Most common include• Presence of oxygen
• Acid content in atmosphere (Acid rain)
• High temperature
Classification of Environmentin terms of corrosion
• Three main classes exist• Natural environment
• The atmosphere
• The marine areas
• Organic environment
• Inorganic environment
Natural EnvironmentAtmosphere
• The atmosphere can be further classified into three classes i.e., rural, industrial and marine – but this classification is impractical
• Variations in humidity, temperature, rainfall, wind, and pollutants inhibit this classification
Natural EnvironmentAtmosphere
• Degree of corrosion due to atmosphere depends upon• Type of corrosive agent
• Amount of corrosive agent
• Most common is SO2 gas, produced by industries burning high-sulfur coal
• In the presence of moisture and oxygen, SO2 forms sulfurous and sulfuric acids, which are highly corrosive to all metals except the compatible combination with lead
Natural EnvironmentAtmosphere
• Chloride (in air), usually present more in marine environments, are the second common source of atmospheric corrosion
• Some solid particles, including dust, tend to be hygroscopic and hold moisture against the metal surface
Natural EnvironmentAcid Rain
• Acid rain is a rain or any other form of precipitation that is unusually acidic
• It possesses elevated levels of hydrogen ions (low pH)
• Acid rain is caused by• Volcanic Activity
• Lightning
• Combustion of fossil fuels
• Automobile exhaust
• Industrial effluents
Natural EnvironmentAcid Rain
• Acid rain usually contains dilute acid
• Long term exposure to acid rain can cause severe corrosion in metals
• Acid rain also damages biological life
Organic EnvironmentOrganic Acids
• Effect of formic acid (HCOOH) is considerable
• It is considered the most corrosive carboxylic acid
• It has applications in dyeing, finishing, textiles and paper industry
Organic EnvironmentOrganic Acids
• Type 304 stainless steel is used for storing the acid
• Alloy 20 is used for higher temperatures
• Alloy C nickel alloys and titanium are also excellent storage materials
Organic EnvironmentSewage and Waste Water
• Few metals can withstand chlorides, sulfates, H2S and bacteria present in municipal sewage
• NH4+ , Cr3+ , and Fe3+ are damaging because their salts hydrolyze to create acids
Organic EnvironmentSewage and Waste Water• Austenitic S.S (GRADES: 304, 316, 316L) are able to
withstand chloride concentrations up to 400 ppm in municipal sewage for oxidation temperatures of 175 to 315 degree Celsius without pitting or cracking
• At higher chloride contents of about 5000 ppm, titanium performs very well
• Nonmetallics such as cement, fiber-glass reinforced plastics and HDPE withstand waste-water better than metals
Inorganic EnvironmentSulfuric Acid
• Sulfuric acid is considered the most important industrial chemical
• It’s used in making fertilizers, chemicals, paints, in petroleum refining, and other industries
• The concentrated acid has a concentration of 95-98%
Inorganic EnvironmentSulfuric Acid
• Steel is most common material for H2SO4 storage and transport of conc. of 70% or higher but near room temperature
• A film of FeSO4 forms to protect the steel
• But as the temperature increases, the film begins to dissolve
• Chemical lead (containing 0.01% Ag) corrodes at less than 0.1 mm/y at 100 degrees Celsius for all H2SO4 concentrations up to 70%
Inorganic EnvironmentAlkalies
• Alakli refers to hydroxides and carbonates of alkali metals (Li, Na, K etc.) and the NH4+ ion
• An alkali is any strong base that produces OH- ions in water
• KOH, NaOH, NH4OH are susceptible to cause corrosion at industrial level
Inorganic EnvironmentAlkalies
• Nickel alloys are compatible with caustic solutions and are used in caustic production plants
• Nickel, however, is unsuitable to NH4OH even in conc. as low as 1%
• S.S handles NH4OH solutions readily
Inorganic EnvironmentAlkalies
• Iron and carbon steels can handle caustic up to about 70% at 80 degrees Celsius
• Magnesium is suitable for any conc. of alkali at room temperature
Compatible Metal-Enivronment Combinations