we know a lot about loss of due to corrosion and prevention of corrosion. a lot of information you can know in this slide

1. LOSS OF CORROSION AND
PREVENTION OF CORROSION
GROUP 4
MD. AL FAHAD ID: 2161381002
MD. MASUM RANA ID: 2161381006
BATCH : 11TH (REGULAR)

2. CORROSION CYCLE

3. FACTS ABOUT CORROSION
 Corrosion is a natural process.
 Corrosion is an electrochemical process.
 Corrosion leads to tremendous loss. It can’t be eliminated completely.
However, its extent can be minimized.
 Corrosion is exactly the reverse of extraction of metals and also known as
weeping of metals.

4. LOSS OF CORROSION
 Every year almost all country of the world face a large amount of economic
loss due to corrosion .
 The overall economic loss due to corrosion may be divided into two
classes,
 Direct loss
 Indirect loss

5. DIRECT LOSS
 Cost of replacing corroded parts of the articles and machinery including
labour cost.
 Cost of repairing the structure, where prevention of rusting is prime
object.
 The capital cost involved in modifying the metal by alloy
 Cost of galvanizing or nicel plating of steel
 Cost of addition of corrosion inhibitors to water or any other environment
 Use of dehumidifying storage room for metal, metallic apparatus,
equipment's etc.

6. INDIRECT LOS DUE TO CORROSION
 Its can not be measured in term of cost of metal and materials
 Losses con not be replace by money
 A few example of indirect loss are,

7. SHUTDOWN OF THE INDUSTRY
 The replacement of corroded part in many industry may cost an
appreciable amount of money or per year which considered as direct loss
 During repairing , the industries are to be shutdown which may cost huge
amount of money in production loss.
 Replacement of corroded boiler or condenser tube of a power plant may
require a lot of money per year for power purchased from interconnected
electric system to supply customers while the boiler is down.

8. LOSS OF PRODUCT
 Oil gas water etc. may be leak out through corroded pipe system.
 Through a corroded radiator antifreeze liquid may also leak out which may
cause a serious accident.
 In addition to these the total production of an industry is reduce due to
corrosion of its machinery.

9. LOSS OF EFFICIENCY
 Boiler may occur by decreasing heat transfer capacity through the
accumulation of corroder products.
 The pipeline for water supply may also be clogged by the deposition of
rust which required increase pumping capacity.
 Internal combustion of automobile engine
 Loss of critical dimension of piston ring and cylinders

10. CONTAMINATION OF THE PRODUCT
 Corroded product do not have mechanical strength.
 The possibility of adulteration of the product with the substance is very
high.
 Example soap industry, copper salt mixed with raw materials accelerates
the rapidity of soap and shortens the time for which the soap is to be
stored before sale. A small amount of copper picked up by corrosion of
copper piping.
 Load equipment is no recommended to use in pharmaceutical, food,
beverage industry because of toxic property of lead and its corroded
product
 For the same reason lead pipe are not safe for transporting soft water for
drinking purpose.

11. OVER DESIGN
 Over design is a common phenomenon that incurs huge amount of loss.
 In the designing of unde ground pipeline, water tanks, reaction vessel,
boiler, condenser tube, marine structure, etc.
 the young engineers designer usually do many times heavier than that is
required for normal operation pressure applied stress in order to ensure
safety of life.
 This is due to lack of information about the corrosion rate, name of
environment quality of materials method of corrosion control etc.
 Example :over design is always common in the under ground oil pipes.

12. PREVENTION OF CORROSION
 THE HUGE ANNUAL LOSS DUE TO CORROSION IS A NATIONAL WASTE
AND SHOULD BE MINIMIZED
 MATERIALS ALREADY EXIST WHICH, IF PROPERLY USED, CAN
ELIMINATE 80 % OF CORROSION LOSS
 PROPER UNDERSTANDING OF THE BASICS OF CORROSION AND
INCORPORATION IN THE INITIAL DESIGN OF METALLIC
STRUCTURES IS ESSENTIAL

13. Factors that affect the rate of
corrosion
Temperature Oxygen
Humidity Chemical Salts
Chemicals and airborne gases

14. How to avoid (or control) Corrosion?
 Material Selection! Remember – environment key. Look at
potential pH diagrams!!!
 Eliminate any one of the 4 requirements for corrosion!
 Galvanic - Avoid using dissimilar metals.
 Or close together as possible
 Or electrically isolate one from the other
 Or MAKE ANODE BIG!!!
 Pitting/Crevice: Watch for stagnate water/ electrolyte.
 Use gaskets
 Use good welding practices
 Intergranular – watch grain size, environment, temperature,
etc.. Careful with Stainless Steels and AL.

15. Methods To Control Corrosion
 Design of structures
 Material selection
 Cathodic Protection
 Reduce the activity of the cathode and or electrolyte. (Polarization)
 Protection of the Anode. (Passivation)
 Alteration of environment
 Inhibitors
 Protective Coatings

16. DESIGN OF STRUCTURE
 Avoid sharp corners
 Complete draining of vessels
 Avoid sudden changes in section
 Avoid contact between dissimilar metals
 Weld rather than rivet
 Easy replacement of vulnerable parts
 Avoid excessive mechanical stress

17. MATERIAL SELECTION
 Metallic : [metal and alloy]
 Nonmetallic : [rubbers (natural and synthetic), plastics, ceramics, carbon
and graphite, and wood]

18. IMPROVEMENTS OF MATERIALS
 Purification of metals: Al , Zr
 Making more noble, e.g. Pt in Ti
 Passivating, e.g. Cr in steel
 Inhibiting, e.g. As & Sb in brass
 Scavenging, e.g. Ti & Nb in S.S
 Improving other properties

19. Material Selection - Galvanic Series
[Seawater at 77⁰ F.]
 Magnesium
 Zinc
 Aluminum
 Mild Steel
 Cast Iron
 Copper
 Stainless Steel
 Gold
 Platinum

20. CATHODIC PROTECTION
 Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making it
work as a cathode of an electrochemical cell. This is achieved by placing in contact with the
metal to be protected another more easily corroded metal to act as the anode of the
electrochemical cell. Cathodic protection systems are most commonly used to protect steel, water
or fuel pipelines and storage tanks, steel pier piles, ships, offshore oil platforms and onshore oil
well casings.
 Types of CP:
 sacrificial anodes (zinc, magnesium or aluminum): The sacrificial anodes are more active
(more negative potential) than the metal of the structure they’re designed to protect. The
anode pushes the potential of the steel structure more negative and therefore the driving
force for corrosion halts. The anode continues to corrode until it requires replacement,
 Impressed current CP: done for large structures (pipes, offshore platforms, etc.) where a
galvanic (or sacrificial) anode can not economically deliver enough current.
 Galvanized steel (see previous slide): again, steel is coated with zinc and if the zinc coating
is scratched and steel exposed, the surrounding areas of zinc coating form a galvanic cell
with the exposed steel and protects in from corroding. The zinc coating acts as a sacrificial
anode.

21. POLARIZATION
 This is an effect which reduces the actual chemical potential driving of the
cell. If the thermodynamic force driving the ion into solution is reduced, this
is polarization.
 Easy example. By lowering the electrolyte temperature, we find that it is
usually less corrosive. Diffusion of ions is slowed.
 Inhibitors are chemicals which slow corrosion. Some of them do this by
promoting the polarization of the cathode.

22. PASSIVATION OF THE ANODE
 We have two examples already. Stainless and aluminum.
 A thin oxide layer forms on the surface and isolates the metal from the environment.
 Zn, Mg, Cu and Ti are also capable of passivation under normal conditions of operation.
 Steel will also passivate in the presence of an alkaline environment, such as rebar in
concrete.
 Corrosion inhibitors. Some of these, such as the chromates, are capable of coating a steel
and passivating it.
 Coatings, paints, etc.

23. Environment factors affecting
corrosion
 Dust particles and man-made pollution – CO, NO, methane, etc.
 Temperature – high T & high humidity accelerates corrosion.
 Rainfall – excess washes corrosive materials and debris but scarce may leave
water droplets.
 Proximity to sea
 Air pollution – NaCl, SO2, sulfurous acid, etc.
 Humidity – cause condensation

24. INHIBITORS
 Inhibitors are materials that may be injected into the system . They plate out
on the surface and inhibit the formation of corrosion cells. They are
commonly used in pipelines and other vessels that will contain materials that
are corrosive.
 Some metals, such as gold and platinum, corrode very slowly or not at all.
Choosing a corrosion resistant material can reduce the rate of corrosion.

25. THANK YOU