Corrosion and its occurence in major environments
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This document discusses corrosion that occurs in major environments. It describes the classification of environments into natural (atmosphere, marine), organic, and inorganic. Specific corrosion issues are outlined for the atmosphere (SO2, chlorides, acid rain), organic acids like formic acid, sewage/waste water, sulfuric acid, and alkalies. Compatible metal combinations are mentioned for some environments like nickel alloys for caustic solutions, stainless steel for NH4OH, and magnesium for alkalies.
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Corrosion and its occurence in major environments
- 1. COMSATS Institute of Information Technology Defence Road, Off Raiwind Road, Lahore, Pakistan
- 2. Corrosion Occurrence in Major Environments
- 3. Presented by GROUP 7 Hafiz Annus Mehmood CIIT/SP10-BEC-015/LHR Mohammad Abubakar CIIT/SP10-BEC-015/LHR Noaman Ahmed CIIT/SP10-BEC-015/LHR Saim Khan CIIT/SP10-BEC-015/LHR
- 4. 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
- 5. Classification of Environment in terms of corrosion • Three main classes exist • Natural environment • The atmosphere • The marine areas • Organic environment • Inorganic environment
- 6. Natural Environment Atmosphere • 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
- 7. Natural Environment Atmosphere • 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
- 8. Natural Environment Atmosphere • 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
- 9. Natural Environment Acid 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
- 11. Natural Environment Acid 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
- 12. Organic Environment Organic 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
- 13. Organic Environment Organic 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
- 14. Organic Environment Sewage 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
- 15. Organic Environment Sewage 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
- 16. Inorganic Environment Sulfuric 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%
- 17. Inorganic Environment Sulfuric 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%
- 18. Inorganic Environment Alkalies • 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
- 19. Inorganic Environment Alkalies • 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
- 20. Inorganic Environment Alkalies • 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
Editor's Notes
- Alloy B – A nickel-molybdenum alloy with outstanding resistance to hydrochloric and sulfuric acids in the as-welded condition and excellent thermal stability.