The Basic Introduction of Corrosion and its Types are considered in this presentation .In the next Presentation i will complete Wear and its Types.

1. PRESENTATION ON BASIC INTRODUCTION OF
CORROSION AND TRIBOLOGICAL WEAR
CENTRE FOR ADVANCED STUDIES,AKTU,
LUCKNOW
PRESENTED BY
SHUBHAM KUMAR SINGH
UNDER THE GUIDANCE OF
Dr. GOPAL JI

2. CORROSION
• Corrosion is the detreoration of the metal as a result
of chemical reaction between it and the surrounding
environment.
• It is an oxidation process. It causes loss of metal.
• The responsible factors for the corrosion of a metal
composition of the metal , the environmental
chemicals , temperature and design.
• Example – Formation of rust on the surface of Iron
etc.

3. Heavy rust on the links of a chain
Formation of green films on the
surface of copper
Examples -

4. TYPES OF CORROSION
• Uniform or General attack corrosion
• Galvanic orTwo metal corrosion
• Pitting corrosion
• Intergranular
• Selective leaching or Parting
• Erosion corrosion
• Stress corrosion Cracking
• Crevice Corrosion

5. GENERAL ATTACK CORROSION
• It is also known as
uniform corrosion.It is
caused by chemical or
Electro chemical
reaction that results in
the detreoration of the
entire exposed surface
of a metal.
• Ultimately, the metal
deteriorates to the point
of Faliure.

6. Uniform corrosion can be prevented by-
• Use thicker materials for corrosion
allowance.
• Use paints or metallic coatings such as
plating , galvanizing or anoding.
• Use corrosion inhibitors or modifying the
environment.
• Cathodic protection and Anodic protection.

7. GALVANIC CORROSION
• Galvanic corrosion ( bimetallic corrosion ) is an
electrochemical process in which one metal corrodes
preferentially to another when both metals are in electrical
contact in the presence of electrolyte.
• A Galvanic couple forms between the two metals where,
one metal becomes the anode and other is cathode .
• Three conditions must exist forGalvanic corrosion-
1. Electrochemically dissimilar metals must be present.
2. The metals must be in electrical contact .
3. The metals must be exposed to an electrolyte.

8. PREVENTION OF GALVANIC CORROSION -
• Select metal/alloys as close together as possible
present in the Galvanic series.
• Avoid unaffordable area effect of a small anode and
large cathode.
• Insulate dissimilar metals where as practical.
• Apply coatings with cautions. Paint the cathode (or
both) and keep the coatings in good repair on the
anode.
• Avoid threaded joints for materials far part in the
galvanic series.

9. PITTING CORROSION
• Pitting corrosion is a localized form of corrosion by
which cavities or "holes" are produced in the material.
• Pitting is considered to be more dangerous than uniform
corrosion damage because it is more difficult to detect,
predict and design against corrosion products often
cover the pits.
• Pitting corrosion can produce pits with their mouth open
(uncovered) or covered with a semi-permeable
membrane of corrosion products.
• Pits can be either hemispherical or cup-shaped.

10. TYPES OF PITTING CORROSION -
Trough Pits:-
Narrow, deep Shallow, wide
Elliptical Vertical grain attack

11. Sideway Pits:-
Subsurface
Undercutting Horizontal grain attack

12. PREVENTION OF PITTING CORROSION-
• Proper selection of materials with known resistance to
the service environment.
• Control pH, chloride concentration and temperature.
• Cathodic protection and/or Anodic Protection.
• Use higher alloys (ASTM G48) for increased resistance
to pitting corrosion.

13. INTERGRANULAR CORROSION
• Intergranular corrosion (IGC), also known as intergranular
attack (IGA), is a form of corrosion where the boundaries
of crystallites of the material are more susceptible to
corrosion than their insides
Microscope view of a
polished cross section of a
material attacked by
intergranular corrosion

14. PREVENTION OF INTERGRANULAR
CORROSION-
• Use low carbon (e.g. 304L, 316L) grade of stainless
steels.
• Use stabilized grades alloyed with titanium (for
example type 321) or niobium (for example type
347).Titanium and niobium are strong carbide-
formers.They react with the carbon to form the
corresponding carbides thereby preventing
chromium depletion.
• Use post-weld heat treatment.

15. SELECTIVE LEACHING OR PARTING
CORROSION
• It is also called Dealloying or Graphitic corrosion.
• Dealloying is the selective corrosion of one or more
components of a solid solution alloy.
• Common dealloying examples are decarburization,
decobaltification, denickelification, dezincification,
and graphitic corrosion.
• Decarburization is the selective loss of carbon from
the surface layer of a carbon-containing alloy due to
reaction with one or more chemical substances in a
medium that contacts the surface.

16. Graphitic Corrosion in Iron Pipes andValves

17. PREVENTION OF GRAPHITIC CORROSION-
• Select metals/alloys that are more resistant
to dealloying. For example, inhibited brass is more
resistant to dezincification than alpha brass, ductile
iron is more resistant to graphitic corrosion than
gray cast iron.
• Control the environment to minimize the selective
leaching.
• Use sacrificial anode cathodic protection or
impressed current cathodic protection.

18. EROSION CORROSION
• Erosion corrosion is an acceleration in the rate of
corrosion attack in metal due to the relative motion of a
corrosive fluid and a metal surface.The increased
turbulence caused by pitting on the internal surfaces of a
tube can result in rapidly increasing erosion rates and
eventually a leak.
• Erosion Corrosion refers to the combined action
involving erosion and corrosion in the presence of a
moving corrosive fluid or a metal component moving
through the fluid, leading to accelerated loss of metal.
• For example, burrs left at cut tube ends can upset smooth
water flow, cause localized turbulence and high flow
velocities, resulting in erosion corrosion.

19. PREVENTION OF EROSION CORROSION-
• Streamline the piping to reduce turbulence.
• Control fluid velocity.
• Using more resistant materials.
• Using corrosion inhibitors or cathodic protection
to minimize erosion corrosion.

20. STRESS CORROSION
• Stress-corrosion cracking (SCC) is a cracking process
that requires the simultaneous action of a corrodent
and sustained tensile stress.
• This excludes corrosion-reduced sections that fail by
fast fracture.
• Stress corrosion cracking (SCC) is the cracking induced
from the combined influence of tensile stress and a
corrosive environment.
• The impact of SCC on a material usually falls between
dry cracking and the fatigue threshold of that material.

21. PREVENTION OF STRESS CORROSION
CRACKING-
• Avoid the chemical species that causes SCC.
• Control of hardness and stress level (residual or load).
• Introduce compressive stress by shot-peening for
example.
• Use of materials known not to crack in the specified
environment.
• Control operating temperature and/or the
electrochemical potential of the alloy.

22. CREVICE CORROSION
• Crevice Corrosion refers to the localized attack on a
metal surface at, or immediately adjacent to, the gap or
crevice between two joining surfaces.
• The gap or crevice can be formed between two metals
or a metal and non-metallic material.
• Outside the gap or without the gap, both metals are
resistant to corrosion.
Crevice corrosion in Iron material

23. PREVENTION OF CREVICE CORROSION-
• Use welded butt joints instead of riveted or bolted joints
in new equipment.
• Eliminate crevices in existing lap joints by continuous
welding or soldering.
• Avoid creating stagnant conditions and ensure complete
drainage in vessels.
• Use solid, non-absorbent gaskets such asTeflon.
• Use higher alloys (ASTM G48) for increased resistance to
crevice corrosion.