Pitting Corrosion_Rahul
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Pitting corrosion is a localized form of corrosion that leads to the formation of small cavities or holes in the material. It occurs when small areas become active (anodic) while the surrounding areas remain passive (cathodic). This creates galvanic cells that drive the corrosion process. Pitting corrosion initiates at defects on the material surface and then propagates in an autocatalytic manner. It is most common in alloys protected by a passive film when exposed to environments containing chlorides, oxygen, and stagnant conditions. Proper material selection, surface finishing, controlling environmental factors like pH and chloride levels, and using protective coatings or cathodic protection can help prevent pitting corrosion.
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There are several types of corrosion that can occur:
1. Uniform and galvanic corrosion which results from direct chemical attack or from dissimilar metals in contact being exposed to an electrolyte.
2. Erosion corrosion caused by abrasive fluid flow removing a metal's protective surface film.
3. Crevice and pitting corrosion which are localized forms of corrosion occurring in cracks, crevices or defects in a metal surface.
4. Intergranular corrosion which attacks grain boundaries in metals or alloys.
5. Other forms include exfoliation, selective leaching, stress corrosion cracking, waterline corrosion affecting ship hulls, soil corrosion depending on soil conditions, and microbiologically influenced corrosion caused byCorrosion.pptx
Corrosion.pptxSneha10D
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Corrosion is an electrochemical process where a metal oxidizes and dissolves into its environment. There are several types of corrosion including uniform corrosion, galvanic corrosion, pitting corrosion, and crevice corrosion. Uniform corrosion proceeds uniformly over the entire metal surface. Galvanic corrosion occurs when two dissimilar metals are electrically coupled in a corrosive electrolyte. Pitting and crevice corrosion are localized forms of attack that can cause perforation. Cathodic protection is a technique to control the corrosion of a metal by making it the cathode of an electrochemical cell.Corrosion 
Corrosion Dipal Prajapati
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This document discusses various types and theories of corrosion. It begins by introducing corrosion as the chemical reaction between a metal and its environment that causes the metal to deteriorate. It then describes three main theories of corrosion: the acid theory, dry/chemical theory, and galvanic/electrochemical theory. The rest of the document details eight specific types of corrosion including uniform, pitting, intergranular, exfoliation, stress, crevice, galvanic, and erosion corrosion. It provides examples and explanations for each type.
I/II SEM BE, VTU, ENGINEERING CHEMISTRY , Module 2
I/II SEM BE, VTU, ENGINEERING CHEMISTRY , Module 2rashmi m rashmi
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1. The document discusses various types of corrosion including dry corrosion, wet corrosion, differential metal corrosion, differential aeration corrosion, pitting corrosion, stress corrosion, and water line corrosion.
2. It explains the electrochemical theory of corrosion and factors that affect the rate of corrosion such as the nature of the metal, corrosion product, potential difference, anodic/cathodic areas, pH, temperature, and conductivity.
3. Methods of corrosion control discussed are anodizing, phosphating, galvanization, and tinning which involve coating metals with protective layers to prevent corrosion. Anodizing forms a protective aluminum oxide layer while galvanization coats iron with zinc and tinning coats iron with tin.Factors affecting and prevention_Corrosion (1).ppt
Factors affecting and prevention_Corrosion (1).pptToranSahu18
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Corrosion Corrosion bahut jyada corrosion Corrosion engineering
Corrosion engineeringAtul Shinde
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Corrosion is the spontaneous reaction between a material like steel and its environment that degrades the material over time. For ships, corrosion poses a major problem as it can compromise the structural integrity of the vessel. There are two main methods to prevent corrosion - cathodic protection, which makes the structure negative to corrosion, and coatings, which act as a barrier between the steel and environment. Effective coatings must adhere well to the steel, be impermeable to water and oxygen, and have a thickness and pigmentation that limits penetration over the life of the coating.Pitting Corrosion_Rahul
- 1. Presentation on Pitting Corrosion Prepared by- RAHUL DEO SONAR Jr. Metallurgist 1 Metallurgy Dept.- Dammam Lab-KSA
- 2. INDEX Definition of Pitting Corrosion Mechanism Common Environments of Pitting Corrosion Prevention 2
- 3. Definition It is a form of entirely localized corrosion. Leads to formation of cavities or holes in the material. Considered to be the most dangerous and insidious type of corrosion. Rate of corrosion is higher than uniform corrosion because of large cathode/anode ratio. Difficult to detect and measure. Its is autocatalytic in nature. Occurs usually in the direction of gravity. Fig.1: Pitting corrosion on a Stainless Steel surface 3
- 4. Mechanism of Pitting Corrosion Principle: Metal oxidation results in localized acidity that is maintained by the continuously undergoing cathodic & anodic half-reactions, this acidity breaks the passive layer, which creates a potential gradient and electromigration of anions will start in the pit . Three stages of pitting corrosion:  Initiation of pit.  Propagation of pit (at this point autocatalytic in nature).  Perforation or Termination of pit. 4
- 5. Let us take the figure below, we are having a passivating metal in contact with sea water(oxygen rich). The reaction taking place will be: M ïƒ M2+ +2e- …...........................anodic O2 + 2H2O + 4e- ïƒ 4OH- ………...cathodic  Here the oxygen rich fluid in contact with metal becomes cathodic and the bottom part becomes anodic.  Metal at the pit will be ionized to release e- and form M2+.  This e- will travel to the top of the pit & reacts with O2 & H2O to form hydroxide ions(OH-).  Now the M2+ ions will react with OH- ions to form rust.  More anodic dissolution takes place in the pit so we will have more M2+ ion concentration & promotes pits.  Deeper the pit lesser the oxygen content and higher will be the pitting corrosion rate. 5
- 6. Common environments of pitting corrosion  Occurs in alloys that are protected by passivating film like stainless steel, Al alloys.  Materials having poor surface finish may undergo this corrosion.  Presence of dirt on surface.  Stagnant water conditions favour pitting(low velocity). Cholride environment. Oxidizing metal ions with chlorides are aggressive pitters. Prevention  Proper material selection(e.g. SS316 with Mo) will have higher resistance to pitting.  Controlling oxygen level.  Cathodic & Anodic protection.  Good surface finish required.  Agitation of stagnant fluids. Controlling the pH, chloride concentration and temperature. 6
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