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Showing posts from September, 2017

Boiler Corrosion

Galvanic Corrosion
Can occur due to Oxygen attack or contact of two dissimilar metals in an electrolyte (eg: Copper + Steel).

Oxygen Attack (Pitting Corrosion)
At the Anode:

Metal goes into solution               Fe ⟶ Fe2+ + 2 e-OXIDATION

At the Cathode:

Oxygen is reduced           ½ O2 + H2O + 2 e- ⟶ 2 OH- REDUCTION

The variables pH, temperature and the concentration of oxygen affect the rate of corrosion.
To avoid this alkaline conditions are maintained in the boiler.
Oxygen reacts with iron to give ferric oxide (rust) Fe2O3 which will not protect the metal from further attack and metal is continuously dissolved.

4Fe + 3O2 → 2 Fe2O3 Hematite (ferric oxide)

Oxygen corrosion is usually observed as localized pitting on a metal surface. (Pitting Corrosion)

This form of corrosion can be reduced by: reducing the level of oxygen as far as possible using mechanical means which include deaeration and/or judicious heating, coupled with good feed-system design (Cascade Tank)

by ensuring that t…

Boiler Scale Formation