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

21. Compatible Metal-Enivronment Combinations