Corrosion and its Types, Prevention Got this power point presentation from the other department.

1. TYPES OF CORROSION AND ITS
PREVENTION By Group 3 :
Jerelyn Polo
Daniela Revira
Carmela Kayle Braga
Jhulian Rodree Saria
Arth Peter Joseph Caguitla

2. What is corrosion?
Corrosion is the term usually applied to the deterioration of metals by
an electrochemical process or slow and continuous eating away of
metals by the action of environment is called corrosion. Corrosion
causes damage to buildings, bridges, ships and cars.

3. TYPES OF CORROSION

4. 1. Uniform Corrosion
• This corrosion is also called general corrosion
• Effect produced by most direct chemical
attacks
• This is common form of corrosion
• This type of corrosion is first seen as a general
dulling of the surface and, if allowed to
continue; the surface becomes rough

5. How to prevent uniform corrosion?
• Use thicker materials for corrosion allowance
• Use paints or metallic coatings such as
plating, galvanizing or anodizing
• Use corrosion inhibitors of modifying the
environment

6. 2. Galvanic Corrosion
• Also called as "dissimilar metal corrosion"
• Takes place when two metals are in
physical contact with each other and are
immersed in a conducting fluid
• Corrosion damage induced when two
dissimilar material are coupled in a
corrosive electrolyte

8. Ways to preventing Galvanic Corrosion
• Galvanic corrosion can be avoided by selecting the appropriate contacting metals
and by minimizing the potential difference between the metals.
• One of the most effective ways of breaking the electrical path in the
electrochemical cell is to place a non-conductive material between the contact
points of the coupling metals. Galvanic corrosion occurs because electrons are
allowed to flow from the anode to the cathode, producing a galvanic current in
the system. Insulation material blocks the flow of electrons, thus preventing
oxidation and reduction reactions from occurring. One of the most effective ways
of breaking the electrical path in the electrochemical cell is to place a non-
conductive material between the contact points of the coupling metals. Galvanic
corrosion occurs because electrons are allowed to flow from the anode to the
cathode, producing a galvanic current in the system. Insulation material blocks
the flow of electrons, thus preventing oxidation and reduction reactions from
occurring.

9. 3. Differential Aeration
Corrosion
• This type of corrosion takes
place when a metal is
unevenly exposed to different
oxygen/air concentrations
• The part which is exposed to
less oxygen
undergoes corrosion

10. 4. Pitting Corrosion
• Pitting corrosion is a localized form of
corrosive attack that produces holes or
small pits in a metal
• The bulk of the surface remains unattached
• Pitting is often found in situations where
resistance against general corrosion is
conferred by passive surface films.
• Pitting attack induced by microbial activity,
such as sulfate reducing bacteria (SRB) also
deserved special mention.

11. Ways of preventing Pitting Corrosion
Preventing pitting corrosion starts early. First and
foremost, choosing the right metal during the design
of an asset makes a big difference. The risk of pitting
corrosion is greatly reduced when the ways materials
react in different environments are understood ahead
of time. Higher-alloy metals resist corrosion more
strongly than do low-alloy materials.

12. 5. Stress Corrosion
• This type of corrosion is observed in
fabricated articles which are subjected to
various mechanical operation
• Here mechanical operations refers bending,
hammering and annealing
• This corrosion is usually unpredictable is
nature

13. Ways of preventing Stress
Corrosion
1. Selection and
control of materials
2. control of stress
3. control of
environment

14. 6. Corrosion Fatigue
• Corrosion Fatigue is a special case of stress corrosion caused
by the combined effects of cyclic stress and corrosion
• Control of corrosion fatigue can be accomplished by either
lowering the cyclic stress or corrosion control

15. Ways to prevent Corrosion Fatigue
• Reducing the fatigue by minimizing vibration and pressure
fluctuation
• Reducing the corrosion by using high performance alloys
resistant to corrosion fatigue
• Reducing the corrosion by using coating and inhibitors to
delay the initiation of corrosion fatigue cracks

16. 7. Crevice Corrosion
• Crevice corrosion is a localized form of corrosion usually
associated with the a stagnant solution on the micro-
environmental level.
• Such as stagnant microenvironments tend to occur in
crevices (shielded area) such as those formed under
gaskets, washers, insulation material, fastener heads, surface
deposits, disbonded coatings, threads, lap joints and clamps.

18. Ways of preventing Crevice Corrosion
• Eliminate small gaps which might trap electrolyte and lead to
stagnation
• Keep electrolyte flowing freely or at high enough rates to prevent
stagnation

19. 8. Intergranular Corrosion
• Intergranular corrosion refers to preferential (localized)
corrosion along grain boundaries
• Or immediately adjacent to grain the boundaries, while the
bulk of the grains remains largely unaffected
• This form of corrosion is usually associated with chemical
segregation effects (impurities have a tendency to be
enriched at grain boundaries) or specific phases precipitated
on the grain boundariesKeep electrolyte flowing freely or at
high enough rates to prevent stagnation

20. Ways of preventing Intergranular Corrosion
• Use low carbon (e.g. 3041) 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

21. 9. Microbiological Corrosion
• Caused by microbes like bacteria, algae, fungi and etc.
• These microbes can be aerobic or anaerobic
• Aerobic bacteria decrease the concentration of oxygen in the
medium in contact with metal surface
• The main product of corrosion is anaerobic corrosion is iron
sulphide

23. Ways to prevent Microbiological Corrosion
• Regular mechanical cleaning if possible
• Chemical treatment with biocides to control the
populationof bacteria
• Complete drainage and dry-storage

24. 10. Filiform Corrosion
• Occurs under painted or plated surfaces when moisture
permeates the coating.
• Filiform corrosion is also known as "underfilm corrosion" or
"filamentary corrosion"
• Filiform corrosion can be visually recognized without using
a microscopy

25. Prevention methods for Filiform Corrosion
• Filiform Corrosion can be prevented in the following
methods:
• Control the relative humidity
• Use brittle coatings.

26. WAYS OF CORROSION PREVENTION
You can prevent corrosion by selecting the
right:
- Metal Type
- Protective Coating
- Environmental Measures
- Sacrificial Coatings
- Corrosion Inhibitors
- Design Modification

27. METAL TYPE - One simple way to prevent
corrosion is to use a corrosion resistant metal
such as aluminum or stainless steel. Depending
on the application, these metals can be used to
reduce the need for additional corrosion
protection
WAYS OF CORROSION PREVENTION

28. •PROTECTIVE COATINGS - The application of a
paint coating is a cost-effective way of
preventing corrosion. Paint coatings act as a
barrier to prevent the transfer of
electrochemical charge from the corrosive
solution to the metal underneath.
WAYS OF CORROSION PREVENTION

29. ENVIRONMENTAL MEASURES
Corrosion is caused by a chemical reaction between the metal and
gases in the surrounding environment. By taking measures to control
the environment, these unwanted reactions can be minimized. This
can be as simple as reducing exposure to rain or seawater, or more
complex measures, such as controlling the amounts of sulfur, chlorine,
or oxygen in the surrounding environment. An example of this would
be would be treating the water in water boilers with softeners to
adjust hardness, alkalinity, or oxygen content.
WAYS OF CORROSION PREVENTION

30. •SACRIFICIAL COATINGS involves coating the
metal with an additional metal type that is
more likely to oxidize; hence the term
“sacrificial coating.” There are two main
techniques for achieving sacrificial coating:
cathodic protection and anodic protection.
WAYS OF CORROSION PREVENTION

31. SACRIFICIAL COATINGS involves coating the
metal with an additional metal type that is
more likely to oxidize; hence the term
“sacrificial coating.” There are two main
techniques for achieving sacrificial coating:
cathodic protection and anodic protection.
WAYS OF CORROSION PREVENTION

32. •CATHODIC PROTECTION the most common
example of cathodic protection is the coating of
iron alloy steel with zinc, a process known as
galvanizing. Zinc is a more active metal than
steel, and when it starts to corrode it oxides
which inhibits the corrosion of the steel.
WAYS OF CORROSION PREVENTION

33. ANODIC PROTECTION involves coating the iron alloy
steel with a less active metal, such as tin. Tin will not
corrode, so the steel will be protected as long as the
tin coating is in place. This method is known as anodic
protection because it makes the steel the anode of an
electrochemical cell.
WAYS OF CORROSION PREVENTION

34. •CORROSION INHIBITORS - are chemicals that
react with the surface of the metal or the
surrounding gases to suppress the
electrochemical reactions leading to corrosion.
They work by being applied to the surface of a
metal where they form a protective film.
WAYS OF CORROSION PREVENTION
WAYS OF CORROSION PREVENTION

35. PASSIVATION - In passivation, a light coat of a
protective material, such as metal oxide,
creates a protective layer over the metal
which acts as a barrier against corrosion.
WAYS OF CORROSION PREVENTION

36. • DESIGN MODIFICATION - can help reduce corrosion
and improve the durability of any existing protective
anti-corrosive coatings. Ideally, designs should avoid
trapping dust and water, encourage movement of air,
and avoid open crevices. Ensuring the metal is
accessible for regular maintenance will also increase
longevity.
WAYS OF CORROSION PREVENTION

37. THANK YOU!!!!