3. Wet Corrosion
4. Electrode Potential
5. Corrosion Rate
7. Forms of Corrosion
8. Uniform Corrosion
9. Crevice Corrosion
11. Intergranular Corrosion
atmosphere corrosion takes place in the grain boundary region and may lead to failure In the welded stainless steel component, the problem of sensitization and corrosion is faced by material near the weldment. It is called as weld decay. It can be avoided by use of low carbon grade (e.g. AISI 304L) steels or stabilized (e.g.AISI 316) steels or giving heat temperament called as solutionising after welding.
12. Selective Leaching
13. Erosion Corrosion
14. Stress Corrosion
15. Prevention of Corrosion
Proper selection of material.
• Separation of corrosive environment from component surface.
• Altering the corrosive environment.
• Use of electrical current.
• Use of galvanic couple.
• Altering the characteristic of material by heat treatment.
16. Material Selection
17. Design for Corrosion Resistances
• In assembly dissimilar alloy parts are separated electrically by using rubber gasket.
• Excessive turbulence should be avoided by providing round elbow in piping.
• Proper drains should be provided in water storage.
• If galvanic corrosion cannot be avoided, anodic area should be large than cathodic area.
• Vibration level should be reduced.
• Retention of air in the electrolyte should be avoided.
18. Application of Heat Treatment
19. Alteration of Environment
20. Cathodic and Anodic Protection
2) Use of sacrificial Anode.
(a) Underground pipe and (b) Domestic water heater.
• Domestic and industrial water heater.
• Elevated water storage tank
• Underground pipes
21. Use of Inhibitors
used in closed spaces such as during packing or storage of metal components.
2) Most of the inhibitors are toxic
3) Some of the Inhibitors can not be used in the industry dealing with food products
4) Most of the inhibitors loose their effectiveness with changes in environment intensity and temperature.
5) Inhibitors may become ineffective if stored for a long period.
6) Inhibitors cannot be recycled or reused. They should therefore, be selected keeping in view their effectiveness as well as their economy in use.
22. Use of Surface Coatings
2) Inorganic coatings and
3) Organic coatings.
for metalising of steel. Metals with high melting points can be deposited with plasma jet spraying. Various tanks, vessels, bridge shuffles and fabricated iron and steel products are metallised.
familiar. Zinc rich paints (i.e. Zinc powder is added to paints) are also suitable in marine applications.
23. Corrosion Testing and Monitoring
• Ultrasonic Testing
• Eddy Current Testing
• Coupon Testing
• Electrical Resistance Measurement
• Galvanic Probes
• Chemical Analysis
• Electrochemical Potential Measurements
Various corrosion-testing methods are
• lntergranular Corrosion Resistance tests for Stainless Steels
• Pitting corrosion Resistance test
• Salt Spray test
• AC Impedence test
• Linear Polarisation Resistance test
• Stress Corrosion Cracking resistance test
• Atmospheric corrosion test
• Immersion corrosion test
24. Corrosion-monitoring Methods
at different locations of the pipeline.