Corrosion can occurs in every point of location in steam boiler. Each location of occurrence, corrosion can be caused by some reasons depend on type of corrosion. The following below is the classification of corrosions in steam boiler based on reason for occurrence:
1. Inter granular Corrosion
Inter granular corrosion occurs in the metal of chromium which may be starved by formation of chromium carbide so chromium oxide as its protective layer is not produced.
2. Fatigue Corrosion
Fating corrosion is caused by stress which working cyclic and fluctuating.
3. Pitting Corrosion
Reason of occurrence this corrosion is the presence of pitting because of electrochemical reaction which can break protective oxide layer
4. Caustic Attack
Caustic attack is caused by high concentration PH which can break protective layer of iron oxide.
5. Acid Attack
Acid attack is caused by low concentration PH in the water wall tubes which can accelerate occurrence of corrosion.
6. Stress Corrosion
Stress corrosion commonly occurs because of combination of stress, environment and material.
7. Galvanic Corrosion
Electric potential will be generated on two dissimilar material such section superheater and reheater tubes and cause particle of metal move from one to other (anode to cathode).