Classification | |
---|---|
Temperature | Corrosion at high temperature, Corrosion at low temperature |
Environment | Atmospheric corrosion, seawater corrosion, soil corrosion, microbiologically influenced corrosion |
Types | 1. Uniform Corrosion (General Corrosion) 2. Galvanic Corrosion (Two-metal corrosion) 3. Intergranular Corrosion 4. Crevice Corrosion 5. Pitting 6. Erosion Corrosion 7. Stress Corrosion 8. Selective Leaching 9. Hydrogen Damage |
Uniform | Galvanic | Intergranular | Crevice | Pitting |
---|---|---|---|---|
Classification | Cause | Preventive Measure |
---|---|---|
Galvanic Corrosion |
It is caused by the potential difference between two contacted metals | · Use neighbored metals from galvanic series: Reduction of potential difference · Make big and thick metal · Coating · Use more corrosive metal than two metals (Sacrificial Anode) |
Intergranular Corrosion |
When performing the heat treatment under the sensitive temperature range between 450°C and 850°C for austenite, Cr23C6 carbide is educed to intergranular. It causes lack of Cr around intergranular and corrosion and erodes the passive film and corrosion | · Solution heat treatment: Educed carbide is fully solidified at high temperature · Reduction of carbon content : Less than 0.03% (304 L) · Add the stabilizer: Ti, Nb (347, 321) |
Pitting | · Effect of CI ion : The passive film is partly destroyed according to the action of CI and its area is liquefied first · Effect of temperature : Reaction with CI is accelerated at higher temperature · Effect of extraneous matter : The extraneous matter on the product surface increases CI density |
· Prevent the CI ion and adhesion · Surface treatment (grinding) · Heat treatment to welded part · Use steel that is strong to CI: Add Mo (316, 316L) |