Corrosion is the deterioration of metals due to chemical or electrochemical reaction with their environment. It is a major problem worldwide that impacts safety, health, and the environment. There are many types of corrosion including uniform corrosion, pitting corrosion, stress corrosion, galvanic corrosion, and erosion corrosion. Corrosion can be prevented through various methods like using corrosion inhibitors, coatings like painting, and selecting corrosion resistant materials. The document discusses the causes, mechanisms, types, and prevention methods of corrosion in detail.

1. Corrosion and its Prevention
By
Mr Pankaj Sharma

2. Introduction
• Corrosion is natural phenomenon which attacks
metal by chemical, electrochemical actionconverts
metal into metallic compound , suchasan oxide ,
hydroxide or sulphate.
• Destruction or deterioration and consequent loss of
solid metallic materials , starting at its surface due to
chemical or electro chemical attack, by their
environment.
• Corrosion is major problem worldwide in all
industrial sectors.
• Itimpacts on safety , health and environmental
issues.

3. Corrosion cycle

4. Causes ofCorrosion
• Pure or noble metals suchasgold, silver,platinum,
aluminum , copper do not corrode since they are
chemically uncombined in their natural state.
• Following conditions must exist beforecorrosion.
i)Presenceof metal that will corrode (anode)
ii) Presenceof cathode
iii)Presenceof conductive liquid(electrolyte)
iv)Electrical contact between
anode andcathode
• Elimination of any one ofthese
condition will reduce or stop
corrosion.

5. CorrosionTriangle

6. Classification ofCorrosion
• on the basis ofworking
temperature
i) Low temperature Corrosion
ii) High temperature Corrosion
• on the basis ofworking
environments
i) Dry or ChemicalCorrosion
ii) Wet or
Electrochemical
Corrosion

7. i) Dry or ChemicalCorrosion
• It occurs when oxygenin air reacts with metal ,
without presence ofliquid.
• It is very sensitive totemperature
• Rateof dry corrosion varies from metal to metal ,
asaresult of mechanismsinvolved.
• Oxide layer on steel & iron is knownasrust.

8. • In aluminum , copper oxide layer formed due to
reaction with atmospheric oxygen ,stops further
corrosion.
• As oxide layer formed , prevents further contact of
oxygen asfilm is non porous.
• Thisstopping is known asPassivations.
• Active Corrosion- steel, CI,Mg.

9. ii) Wet or ElectrochemicalCorrosion
• Itis electrochemical phenomenon , which occurs
in galvaniccell.
• Particularly when two metals are in contact with
aliquid , liquid containing salt and electric
potential is formed between themetals.
• in some cases in single metal , when comes in
contact with liquid or electrolyte , a anode and
cathode areasare created.
• When anode area starts corroding withrespect
to cathode areas, is termed aswetcorrosion.

11. Mechanism ofCorrosion
• Electrochemical reaction – transfer ofelectrons
• Electrochemical corrosion cell- Electrical circuit andits
associated chemical reaction are called
electrochemical corrosioncell.

12. i) Anode- Oxidation occurs, metal dissolution takesplace
& production ofelectrons
ii) Cathode – electrons are consumed & reduction
reactions occurs
iii) Metal Path – movement of electronfrom
anode to cathode
iv) Electrolyte- ionic currentflows

13. Anodic & cathodic reactions in corrosioncell
2 
Fe  Fe  2e O  2H O  4e
 4OH 
2 2
AtAnode-Oxidation At Cathode-reduction

14. • Typeof Metal
• Heat treatment & Graindirection
• Presenceof dissimilar metal
• Anode & cathode surfacearea
• Temperature
• presence of electrolyte
• Availability of oxygen
• time of exposure to corrosiveenvironment
Factors Influencing Corrosion

15. Types of corrosion
1.Pitting Corrosion- Aluminum, Mg alloys, Cualloy.

17. Mechanism of pittingCorrosion
• Factorsinfluencing pitting Corrosion
1.Alloying elements
2.Surface finish
3.Heat treatment

18. 2.Stress corrosion & seasoncracking
• It is combined action of corrosive environment
and mechanical stresseswhich often due to poor
design or poor maintenancepractice.
• Stresscorrosion cracking (SCC)is intergranular
cracking of metal causedby stress& corrosion.

19. stress corrosion crackingprocess

20. Mechanism of stress corrosioncracking
Transgranular cracking inS
C
C

21. Control or Prevention ofSCC
1. Control of stress level andHardness.
2. Avoid chemical corrosion that causesS
S
C
3. Control of temperature
4. Modification in design , that will reduce SCC

22. 3.Cavitation Corrosion
• Protective films are removed from metal
surface during fluid flow.
• Low pressure development due to
discontinuity in flow path , causes vapour
bubbles to form in fluid steam.
• Due to collapsing of bubbles shock
waves produced and removes protective
film from metalsurface

23. Cavitation corrosion on pumpimpeller

24. Cavitation damage in pumpimpeller
Control of cavitation Corrosion-
1. Careful material selection i.e. high alloy steelscontaining
Ni, Cr,W
2. Useof soft rubber coating , it absorbs cavitationenergy
3. Smooth Surfacefinish

25. 4.Hydrogen Embrittlement
• Hydrogen blisters results from hydrogen atoms ,
formed during sulfide corrosion process on steel.
• Hydrogen atom
combines to form
hydrogen molecule.
Hydrogen blisters on steelsurface

26. Mechanism of hydrogenblistering
3Fe  4H2 O  Fe3O4  4H2

27. 5.Inter Granular Corrosion
• Form of corrosion where boundaries of grainof
metal are more susceptible to corrosion than
inside grain.
•Difference in Corrosion
potential between grain
and grain boundary.
e.g. CuAl2in Al alloys,
Cr23C6in stainlesssteel.
Inter granular corrosion in Austenitic stainless steel

28. sensitization
• Formation of chromium carbide precipitants
(Cr23C6) at grain boundary occurs when stainless
steel of type 300 are heated to atemperatureof
400 to 9000Cin rolling mill or fabrication or
welding.

29. Prevention of IntergranularCorrosion
Knife LineAttack (KLA)
• Use of low grade stainless steel (304 L, 316L grades)
due to which less carbon will be available for
precipitation of chromiumcarbide.
• Use of stabilized grade of stainless steel (321, 322
grade) titanium
• Useof post weldtreatment.

30. 6.Crevice Corrosion
• Localized attack that occursin restricted areas,
gaskets,flanges, fasteners, lap joints.
• Occursbetween two metal plassets.

31. Prevention of crevicecorrosion
• Avoid crevice during fabrication i.e. smooth
weld.
• avoid solution get into crevice i.e.apply
greaseto nuts andbolts.
• routine cleaning
• Apply external coating.

32. 7.Erosion corrosion
• It results from loss of film under high velocity or high
turbulent fluid flow.
• Corrosion reaction which is accelerated by relative
movement between corrosive fluid and metalsurface.
• High Turbulence intensity
• impact velocity , angle, relative densitybetween
particle and fluid,
particle size.

33. Impingement corrosion
erosion corrosionof
condenser tube

34. control of erosioncorrosion
• selection of resistant materials- highwear
resistance , high hardness
• Decreasing flow velocity
• minimizing the turbulence

35. 8.General or UniformCorrosion
• It is attack over entire exposed surface or large areaof
metal .
• Metal loss is distributed uniformly acrossexposed
surface.
Manholecover

36. 9.Galvanic Corrosion
• It occurs when two metals , with different compositions
are connected in presence of electrolyte.
• Current will flow from anode to cathode.
• Rateof galvanic corrosion depends on differencein
electrolytic potentials.

37. control of Galvaniccorrosion
• selection of metals that are close togetherin
galvanic series.
• Insulate metal from eachother
• Painting of both metals

38. Corrosion Prevention Methods

39. 1.Active corrosionprotection
• T
oinfluence reactions which proceed during
corrosion.
• e.g.Addition of inhibitors to aggressivemedium.
2.Passive corrosion protection
• Bymechanically isolating packagecontents from
aggressivecorrosive agents by using protective
layers , films, coatings.
• Thismethod neither changesability of package
contents to corrode nor aggressivenessof
corrosive agent.

40. 3.Permanent corrosionprotection
• T
oprovide protection at the place of use.
• e.g. stable oxide layer (nonporous film)forming
metals
4.Temporary Corrosion protection
• Stressesoccurring during transport, handling,
storage are much greater than those occuringat
place of use.
• e.g. extreme variation in temperature which
results in condensation during transportation.

41. 5.Corrosion Inhibitors
• Chemicals that react with metallic surface&
givescertain level of protection.
• inhibitors haschemical bonding with base
metal , it is more adherent tobasemetal , due
to which corrosion reactionstopped.

42. Use ofcoatings
1. Hot dipping-

43. 2.Metal spraying

44. 3.Electroplating

45. Low and High temperature corrosion
Creepfailure, oxidation, High
temperature hydrogen attack

46. 46