Erosion corrosion is the accelerated deterioration of a metal due to the combined effects of corrosion and mechanical erosion from solid or liquid particles in fluid flow. It occurs when a corrosive fluid carrying solid particles flows rapidly across a metal surface. This damages protective surface films and removes metal, leading to deeper corrosion. Common examples include erosion corrosion in pipes, valves, pumps and heat exchangers exposed to fluids. Prevention methods include design modifications to reduce turbulence, filtering solids, using more erosion-resistant materials, coatings, cathodic protection, and altering the environment.

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2. Erosion Corrosion

3. Presented to:
Sir Nadeem Ahmed
Presented by:
Sania Aslam MME-12-26
Asia Abbas MME-12-27
Arif Ali MME-12-01
Sarmad Saeed MME-12-02

4.  Removal of material from the surface by the action of
solid or liquid particles.
It occurs due to:
 High velocity of solid or liquid particles.
 Abrupt changes in the fluid flow.
 Large amount of entrained solid or liquid particles.
Erosion

5.  Destruction or deterioration of a material by its
environment.
 Occurs due to chemical or electrochemical action.
 It is a reverse process of extraction.
 In extraction metal is extracted from ore mostly oxide
e.g. iron oxide.
 In corrosion, iron is converted to oxide.
Corrosion

6.  Accelerated or increase in the rate of deterioration on
a metal because of relative movement b/w corrosive
fluid & metal surface.
 Relative movement is quite rapid so mechanical wear
effects are involved.
 Metal is removed from the surface either:
• In the form of solid corrosion products.
• In the form of dissolved ion.
Erosion Corrosion

7. Remember the distinction between erosion-corrosion
and erosion:
 Erosion is the straightforward wearing away by the
mechanical abrasion caused by suspended particles
e.g., sand-blasting, erosion of turbine blades by
droplets.
 Erosion-corrosion also involves a corrosive
environment.
 The metal undergoes a chemical reaction.
Contd……….

8.  Many metals & alloys are susceptible to erosion corrosion
e.g. aluminum, lead, stainless steels, carbon steels
 All types of equipment exposed to fluid are susceptible to
this type of corrosion e.g. piping systems, elbows, tees,
valves, pumps, blowers.
 Also centrifuges, propellers, impellers, agitators, heat
exchangers tubing
 Measuring devices like orifices, turbine blades, ducts & all
those equipments which are some way or the other
exposed to fluids.
Examples

9. Appearance
 It appears in the form of
grooves, gullies, waves,
rounded holes & valleys.
 They typically show a
directional pattern.
 This is figure showing
erosion corrosion of
condenser tube wall by
water flow.

10.  Many types of corrosive media could cause erosion
corrosion.
 Gases, aqueous solutions, organic systems & liquid
metals are some common corrosive media that
causes this type of corrosion.
Corrosive Media

11.  These are specially developed layers on the surface of
metals which can protect the metal from corrosion.
 Such films develop due to the action of different
environment on metals e.g. Al₂O₃ film developed on Al
metal protect it from corrosion.
 There are two types of such films:
• Relatively thick porous diffusion barriers, formed on
carbon steel (red rust) & copper (cuprous oxide).
• The thin invisible passive film on SS, Ni & Ti etc.
Surface films

12.  Diffusion barrier is formed by ionic dissolution
followed by precipitation.
 It is more easily damaged & can be corroded.
 Passive films are formed by direct oxidation & can
withstand much more sever conditions.
Contd……..

13.  Exact mechanism of erosion corrosion is less
understood but it is believed it occurs due to:
• Turbulent flow.
• Impact of suspended solid particles.
• Liquid droplets in gas flow.
• Impact of gas bubbles in aqueous flow.
Mechanism

14.  Turbulent flow is one of the major cause behind the
occurrence of erosion corrosion.
 It causes agitation of the liquid at the metal surface.
 It results in more contact b/w metal & environment
i.e. fluid.
 It is mostly confined to few inches at tubing inlet.
Why??????
Contd……

15. Contd..….
 Solid particles entrained in
liquid flow damage both types
of surface films explained
above.
 Such particles can erode the
metal as well & contribute to
metal loss.
 This happens due to high
impact of solid particles on the
object through which fluid is
passing.
 It is the figure of erosion
corrosion of 100 mm dia pipe
by sand slurry.

16.  Liquid droplet can cause erosion corrosion due to
exposure of solid to repeated impact by droplets.
 It generates impulsive & destructive contact pressure.
 It is a problem with low pressure turbines & also rain
erosion of aircrafts.
 Erosion corrosion of copper alloy heat exchanger is
due to local damage of film by air bubbles.
 Nitrogen bubbles can also do the same damage.
Contd…….

17.  Flow velocity plays an important role in erosion corrosion.
 At high velocities corrosion rates may be high or low.
 Corrosion rate of steel may be high at high velocity as it may
provide O₂, CO₂, H₂S in contact with metal surface.
 It may decrease corrosion rate & improve effectiveness of
inhibitors by providing chemicals to the metal surface at higher
rate e.g. less Sodium Nitrate is required to protect steel from tap
water at high velocity.
 It can decrease attack by preventing deposition of silt & dirt on
metal surface.
 Suspended solid will damage the surface protection at high
velocity.
Effect of flow velocity

18. Contd….

19.  Chemical composition, corrosion resistance &
hardness can affect this type of corrosion.
 Composition tells us metal’s corrosion resistance..
How?????
 Soft metals can easily be eroded by the action of fluid
or other reagents favoring erosion corrosion.
 Hardness is best criteria to control the wear.
Nature of metal & Alloy

20. Methods are used to prevent erosion corrosion.
1. Design
2. Alteration of Environment
3. Coatings
4. Cathodic Protection
5. Better material
Preventive Methods

21. 1. Design
• Design involves change the shape, geometry of part.
• Design of inlets & outlets should be streamlined to
prevent turbulence.
• It also involves redesigning the flow of the fluid to
ensure there is less turbulence.
Preventive Methods

22. 2. Alteration of Environment
• Settling & filtration to remove solid particles.
• Temperature of environment should be reduced.
3. Coatings
• Coatings are utilized but they are not much effective.
• Welded overlays & hard facing are applied at times.
• Repair of attacked areas is done by welding.
Contd…..

23. 4. Cathodic Protection
• Helps to reduce attack.
• Not much used in erosion corrosion.
• Steel plates are used on condenser head for Cathodic
protection.
• Zinc plugs are used for water pumps.
5. Better material
• Use that material which is more corrosion resistant than
the previous one.
• It is an economical solution of erosion corrosion.
Contd….