COMSATS Institute of Information Technology

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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