Erosion corrosion is a corrosion reaction which is accelerated by the relative move-ment between a corrosive fluid and the metal surface. This causes a removal, or erosion, of the protective surface (oxide) layer (i.e., passive film). This removal is followed by a complete (though somewhat localized) de-passivation. The presence of entrained solids in the fluid (together with high flow velocities) will enhance the de-passivation process. The attack increases with increasing velocity, and varies with the smoothness of the metal surface, degree of turbulence and presence of particles. This is also sometimes called ‘Flow Accelerated Corrosion’ for obvious reasons.
Key Properties of Erosion Corrosion
- Is caused by corrosive media flowing against a weak oxide layer:
- 1. Media attacks weakly adhered oxide layer
- 2. Oxide layer is worn off by flow velocity. Followed by creation of a new ox-ide layer.
- 3. Attack is progressive and repetitive. Surface roughness increases and flow becomes more turbulent. Increasing rate of oxide removal.
- Process may be accelerated by presence of entrained solids and increasing flow velocity.
Where does it occur?
- Pump casings
- Valves
- Elbows
- Piping systems
- Heat exchangers
How to Control Erosion Corrosion?
Erosion Corrosion may be controlled in a variety of ways, including:
- Reduce flow velocity
- Improve equipment design
- Use erosion-resistant materials
- Apply protective coatings
Source: Chesterton ARC Manuals
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