Failure Mechanism- Corrosion PDF

“Failure Mechanism- Corrosion” Mechanics of Materials-1 (MEC1003) Dr. Sithara P. Sreenilayam [email protected], Office: 336 Contents: MEC1003  Introduction (Week 1)  Revision and Basic Concepts (Week 2, 3)  Shear Force and Bending Moment –Analysis of Beams (Week4, 5, 6)  To...

“Failure Mechanism- Corrosion” Mechanics of Materials-1 (MEC1003) Dr. Sithara P. Sreenilayam [email protected], Office: 336 Contents: MEC1003  Introduction (Week 1)  Revision and Basic Concepts (Week 2, 3)  Shear Force and Bending Moment –Analysis of Beams (Week4, 5, 6)  Torsion (Week 7,8)  Creep (Week 9)  Failure Mechanism (Week 10, 11) -Corrosion Learning Outcomes At the end of this lecture, you should be able to:  To explain what corrosion is, including its electrochemical nature, and differentiate between various types of corrosion  Apply understanding of corrosion to real-world engineering challenges, such as selecting appropriate materials and protective measures for structures in corrosive environments. 3 Failure Mechanism- Corrosion Corrosion Background Process Environmental factors Common forms of corrosion Methods of corrosion control and prevention The Chemistry of Corrosion Oxidation is the loss of electrons Reduction is the gain in electrons These reactions are called REDOX reactions. Corrosion process therefore can be defined by two half- reactions useful as it includes all reactions in which electrons are exchanged and not restricted to those involving oxygen Example: Corrosion of iron (rusting) Failure Mechanism- Corrosion Most of the metals (except Pt, Au, Ag) exist in nature in the form of their ores; as oxides, chlorides, silicates, carbonates etc., have the natural tendency to go back to their combined states As a result, when pure metal is exposed to suitable environmental conditions the metal will tend to form stable compounds This is known generally as corrosion, a process of decay of metal by environmental attack. The process of corrosion is the reverse of metal extraction. Oxidation occurs in the presence of gaseous oxygen Corrosion is a similar electrochemical process which occurs generally, though not exclusively, in aqueous environments Failure Mechanism- Corrosion  The valuable metallic properties like conductivity, malleability , ductility etc., are lost due to corrosion.  The process of corrosion is very harmful and is responsible for the enormous wastage of metal in the form of its compounds.  Life span on the metallic parts of the machineries is reduced.  The failure of machinery takes place due to lose of useful properties of metals. Types of Corrosion and Factors Affecting Corrosion Rates Types of Corrosion Factors affecting Corrosion 1. Uniform Corrosion 1. Material Composition 2. Pitting Corrosion 2. Oxygen Concentration 3. Galvanic Corrosion 3. Humidity and 4. Crevice Corrosion Temperature 5. Intergranular Corrosion 4. pH of the environment 6. Stress Corrosion Cracking 5. Presence of salts irregular Corrosion Uniform Corrosion Pitting Corrosion Galvanic Corrosion irregular Corrosion Detection and Evaluation of Corrosion Ultrasonic Testing Visual inspection Visual inspection Radiography inspection Functional requirement of materials Why do metals corrode? Exposure to corrosive environment/ chemical medium Metal Energy Level Ore State/Time Why do metals corrode? Failure Mechanism- Corrosion Failure Mechanism- Corrosion  Physical Characteristics exposed area Large cathode: anode ratio - increased corrosion rate Large anode: cathode ratio - reduced corrosion rate time of exposure (more time, more corrosion) Environmental Characteristics acidic environment sulfur gas environment temperature (high temps, more corrosion) moisture (oxygenated moisture) Questions ? Thank you!