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Name: Engr. Dr. Khursheed Mahmood Qualification: B.E.(Mechanical),NED,1974

Name: Engr. Dr. Khursheed Mahmood Qualification: B.E.(Mechanical),NED,1974 M.Sc.(Materials), UK,1978, Ph.D.(Matellurgical Engg.) UK,1988 Experience: More than 34 years of teaching &

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Name: Engr. Dr. Khursheed Mahmood Qualification: B.E.(Mechanical),NED,1974

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  1. Name: Engr. Dr. Khursheed Mahmood • Qualification: B.E.(Mechanical),NED,1974 • M.Sc.(Materials), UK,1978, Ph.D.(Matellurgical Engg.) UK,1988 • Experience: More than 34 years of teaching & • research at N.E.D. University of Engg. • & Technology, Karachi. • Present Status: Professor, Department of Materials Engineering NED University of Engineering & Technology,Karachi

  2. CORRODED Introduction to corrosion

  3. CORRSION IN PIPE LINES 31 March,2009

  4. CORROSION IN STRUCTURES

  5. CORROSION DUE TO VARIOUS ENVIRONMENTS

  6. CORROSION DUE TO HIGHER TEMPERATURS

  7. CORROSION • Corrosion is a universal and all time problem. • It causes deterioration in structures, machines, • metallic equipment, vessels, pipelines etc etc. • Once developed it grows very rapidly to capture • all equipment in its vicinity under its influence. • If due care and proper protection is not taken it • destroys every thing very rapidly.

  8. COST OF CORROSION • 20 % of the world ‘s steel production goes to • replace corroded steel. • In March 1969 the committee on corrosion • and protection formed by the UK Ministry of • Technology estimated the cost of corrosion at • £ 1.356 per annum which amounted to 3.5% • of their GNP. • It is generally accepted that cost of corrosion • amounts to similar proportion of the GNP in • all industrialized countries. • Here are some current facts and figures:-

  9. USA: 1.25% of GNP., 2002, an study estimated the cost of corrosion in USA to be $ 276 billion(3.1 % of GDP) UK: 3.5% of GNP (£ 136m,1969) India: estimated to be around $ 364 billion as of 2004. Sweden: 125% of GNP. West Germany: 3% (DM 6 billion, 1969) Any estimation of cost of corrosion for Pakistan can only be conjecture since no survey exists.

  10. Pakistan’s GNP for 2005 was estimated as $ 107.28 billion. 3.5% of GNP, the cost of corrosion well exceeds $3.5 billion . The recommendations that have arisen from such surveys in general were: 1.A need for better disemination of information On corrosion and protection 2. A need for greater educationin corrosion and Protection, and 3. An increased awareness of the hazards of corrosion.

  11. The above is especially pertinent to Pakistan where a lack of awareness about Corrosion and a low level of concern about its occurrence exists. • The cost of corrosion includes:- • That part of the maintenance cost arising from • corrosion damage. • The cost of inhibitors and other protective systems. • Consequential losses known to be caused by • Corrosion. • The cost of conservatism in design due to • uncertainties in operating conditions ,properties of • materials, etc. • The cost of technical effort devoted to corrosion

  12. Pakistan has been incurring a loss of about $ 3 • billion per annum on account of infra structure • and industrial corrosion and it needs a • comprehensive “national strategy” for corrosion • control. • This was stated by engineers and experts at a • local Conference on “Corrosion, Prevention and • Management” held in 2009. • It was told in the same conference that industrial • sector faces huge losses due to corrosion as the • replacement of costly machinery is an expensive • business. • It was also mentioned by a Sindh Minister in the • same conference that corrosion was a neglected • subject in the government quarters & there was • no plan for its prevention.

  13. The losses of corrosion can be minimized by • creating awareness among the society about its • damage and by using new technologies for • corrosion prevention. • Billions of rupees of public money are lost due to • corrosion in infrastructure facilities like water • supply and sewarage pipe line, bridges, etc. • An assessment report mentioned that about 3% of • GNP is lost every year in Pakistan due to corrosion • in industrial, infrastructure and house hold sectors. • In the year 2004-2005 the calculated extent of • loss was about $ 105.28 billion.

  14. Corrosion control is,therefore, necessary as it • enhances the cost of the projects. • Therefore, there is a need for th adoption of anti- • corrosion measures at the time of designing of • infrastructure projects. • Some of the measures adopted to protect metals • from corrosion may be through adequate concrete • cover and admixture , coatings and water roofing, • cathodic and anodic protection.

  15. In the limited time available it may not • be possible to cover a very vast area of • Corrosion control and Protection. • However, an under standing of the • fundamental principle s of corrosion • damage and its various types are now • presented as follows.

  16. Definition of Corrosion: “Corrosion is basically deterioration and degradation of Materials due to the interaction of variety of Environments.” Specifically speaking about metals it isdefined as: "AN ELECTRO-CHEMICAL REACTION BETWEEN A METAL AND ITS ENVIRONMENT THAT IS ELECTROLYTE ,IN WHICH METAL DETERIORATES AND LOSES ITS PROPERTIES".

  17. A CORROSION CELL • A Corrosion Cell, shown in figure 1, is develped. Causing deterioration of metals • . ANODE IS THE DEPLETING

  18. ANODE IS THE DEPLETING METAL • . • Anode – the metal that corrodes. • Cathode – the metallic part that is protected. • Electrolyte – the cell substance in which • electrons flow. • Metallic Path – path for flow of current out • side the cell.

  19. CORROSION TERMINOLOGIES • CATIONS: +vely charged ions of electrolyte. • ANIONS: - vely charged ions of electrolyte. • CONVENTIONAL CURRENT FLOW:- • Outside Cell : +ve to –ve(cathode to anode) • Inside Cell : -ve to +ve(anode to cathode) • ELECTRON FLOW is just opposite to conventional • current flow. • EXTERNAL CIRCUIT: cathode, anode, and metallic • path.

  20. CORROSION TERMINOLOGIES • POTENTIAL DIFFERNCE • - electromotive force between anode and cathode • measured in volts • RESISTIVITY OF ELECTROLYTE • – hindrance to flow of current by the electrolyte • measured as ohm-cm. • CONTACT RESISTANCE • - between Anode & Electrolyte to flow of current. • - between Cathode & Electrolyte to current flow.

  21. Basic Corrosion Mechanism • It comprises of only two reactions: • - Oxidation at Anode. • - Reduction at Cathode. • OXIDATION REACTION-removal of one or more electrons from anode metal. • REDUCTION REACTION-reaction of electron with hydrogen in the absence of oxygen or reaction of electrons with dissolved oxygen and breakdown of water into hydroxyle ions.

  22. OXIDATION REACTION M Mn++ n e- Where,  M = Metal involved n = Valence of corroding metal e = electrons Example: Fe  Fe++ + 2e-

  23. Reduction Reaction

  24. Cathodic Reaction O2 + 2H2O + 2 e- 4(OH)-

  25. CUMMULATIVE EFFECT Because there is no net gain or loss of electron, two atoms must dissolve to provide the four electrons required at the cathode. Therefore, the anodic and the cathodic reactions would be 2Fe 2Fe++ + 4e- (ANODIC) O2 + 2H2O + 4e- 4(OH-) (CATHODIC)

  26. OVERALL OXIDATION-REDUCTION REACTION 2Fe + O2 + 2H2O 2Fe++ + 4(OH-) After dissolution, ferrous ions (Fe++) generally oxidize to ferric ions (Fe+++); these will combine with hydroxide ions (OH)- formed at cathode to give a corrosion product called Rust {Fe(OH)3 or Fe203+ H2O}. The important point to remember is that anodic dissolution of metal occurs electrochemically, the insoluble corrosion products are formed by a secondary chemical reaction.

  27. COMPARISON OF A TYPICAL CORROSION CELL WITH THE PIPELINE CORROSION CELL

  28. THE SIMILIARITY • A typical corrosion cell is similar to a pipeline corrosion • cell. • The anodes and the cathodes are the portions, which • are actually developed on the pipeline due to varying • potential difference at different locations and due to • varying environment. • A potential difference is present in pipeline portions • due to electrolyte (soil) conditions. • The electrical path is in the form of pipeline itself. • The electrolyte is the soil containing the moisture in it.

  29. PROGRESS OF RUSTING • The anode and cathode are the localized areas on pipe and due to driving potential at that point electrons from anodic area of pipe go through the wet soil and gather at cathode area of pipe. • The free iron atoms, combine with OH ions in soil (containing moisture) to form Ferric Hydroxide in the form of rust. • The rust remains on the pipe and deteriorates it. While the electron at the cathode are taken by hydrogen ions to evolve the hydrogen gas. • So anodic areas in the pipe corrode while the cathode remains at its shape because it only gains electrons.

  30. Types of corrosion • Aqueous Corrosion • Dissimilar Metal Corrosion • Grain Boundary Corrosion • Inter-granular Corrosion • Selective Leaching • Microbiological Induced Corrosion • Crevice and Pitting Corrosion • Flow Induced Corrosion • Environmental Sensitive Cracking

  31. The aqueous or wet corrosion:- • This is a very common form of corrosion, also generally known as uniform corrosion. • Corrosion takes place in the presence of moisture or wet environments. • This form of corrosion is not of great concern and can be prevented or reduced by: • Proper materials, including coatings, inhibitors or • cathodic protection. • Most of the other forms of corrosion insidious in nature and are considerably more difficult to predict. • They are also localized as the attack is limited to specific areas or parts of a structure.

  32. Two metal corrosion • This form of corrosion is also known as galvanic corrosion. • The potential difference existing between two different metals in contact (galvanic coupling) is responsible for the electrons to flow from one to the other, thereby, causing metal loss or corrosion. • The less resistant metal becomes anodic and more resistant metal becomes cathodic.

  33. As an example, both steel and zinc corrode by themselves, but when they are coupled, Zn corrodes and the steel is protected. • The severity of the galvanic corrosion largely depends on the type and amount of moisture present e.g near the sea shore and inland location. • No galvanic corrosion when the metals are completely dry. • Severity of attack is more near the junction. • Unfavorable area ratio: LargeAc Aa

  34. PREVENTION • Avoide unfavorable area ratio • Insulate dissimilar metals (possibly completely) • Apply coatings • Add inhibitors • select combination closer together from galvanic series • Avoide threaded joints • Design for the use of readily replaceable anodic parts or make them thicker • Install a third metal which is anodic to both metals in the galvanic series.

  35. SACRIFICIAL ANODES

  36. ELECTROMOTIVE SERIES

  37. Types of Corrosion Cells in Pipelines • Several Types of Corrosion Cells are Developed • Dissimilar Metal Corrosion Cells. • Corrosion Cells due to Dissimilar Soils. • Differential Aeration Corrosion Cells. • New and Old Pipe Corrosion. • Mill Scale Corrosion.

  38. INTER GRANULAR CORROSION

  39. Corrosion Cell from two Dissimilar Metals A cell is produced if there is an electrical contact between two dissimilar metals on the same pipeline and there is a common contact between electrolyte (soil or water) and both metals.

  40. ELECTROMOTIVE FORCE OR ELECTRODE POTENTIAL • As a consequence, any two metals have • an electric potential between them. • The magnitude of the potential and • which metal should be anodic (corroded) and which should be cathodic, depends on the position of metals in the EMF series. Some of the EMF series of the metals were illustrated in the previous table:

  41. A PRACTICAL EXAMPLE • A dissimilar metal corrosion: • A buried pipeline is an example of two dissimilar metals. • i.e a plain steel section and a section of copper pipe. • Steel will be anodic and would corrode due to upper position in EMF series. • Yet another Example, (Figure on next slide) • Plain steel pipe and galvanized steel pipe with no electrical insulation between them. • In the table of emf series zinc is more active metal and would act as an anode and, therefore, it would corrode.

  42. Dissimilar Metal Corrosion Cell

  43. A CORROSION CELL DUE TO DISSIMILAR SOILS A corrosion cell has been established. The potential of electrolyte (soil "A“) is slightly different from the potential of the electrolyte (soil "B“).

  44. CORROSION DUE TO PARTIAL CONCRETING Even partially concrete buried pipe can develop a corrosion cell

  45. Small Pockets of Dissimilar Soils • Another special case in figure1(f) results in many special corrosion cells at the pipe surface which is not detected by potential measurements at the surface of the ground as shown in the figure. • These cells occur when the soil in the small area is totally different nature and each portion is of different composition as illustrated in the figure. • The local corrosion cells will develop at many small portions of pipe.

  46. Crevice & Pitting Corrosion • Crevice Corrosion: The attack occurs because a part of metal surface is in shielded or restricted environment, compared to the rest of the metal which is exposed to a large of electrolyte. • Crevice corrosion is very much associated with the geometry of structures, such as • in riveted plates, • In welded structures and • In threaded components

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