CORROSION_CATHODIC_PROTECTI.PPT - DEFINITION CORROSION IS THE DETERIORATION OF A MATERIAL DUE INTERACTION WITH ITS ENVIRONMENT OR LOSS OF USEFUL

CORROSION_CATHODIC_PROTECTI.PPT - DEFINITION CORROSION IS...

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DEFINITION CORROSION IS THE DETERIORATION OF A MATERIAL DUE INTERACTION WITH ITS ENVIRONMENT. OR LOSS OF USEFUL PROPERTIES OF A MATERIAL AS A RESULT OF CHEMICAL OR ELECTROCHEMICAL REACTION WITH ITS ENVIRONMENT.
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CORROSION IN SEA WATER CORROSION REACTION AT ANODE Fe = Fe ++ + 2e - (anodic reactions) Fe ++ ION FORMED AT ANODE COMBINES WITH (OH) ION ALREADY PRESENT IN SEA WATER AND PRODUCES FERROUS HYDOXIDE Fe ++ + 2(OH) - = 2Fe(OH) 2 FERROUS HYDROXIDE GETS OXIDISED BY DISSOLVED OXYGEN TO THE FERRIC HYDROXIDE TO FORM RUST 2Fe(OH) 2 + H 2 O + ½ O2 = 2Fe(OH) 3
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CORROSION IN SEA WATER CORROSION REACTION AT CATHODE ELECTRONS GENERATED FORM ANODIC SITES ARE TAKEN UP EITHER BY HYDORGEN ION OR BY OXYGEN. 2H + + 2e = H 2 O2 + H2O + 4e = 4(OH)
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PROPER SELECTION OF MATERIAL AND GOOD DESIGN REDUCES COSTS OF CORROSION. IN ADDITION GOOD MAINTENANCE PROGRAMME REDUCES COSTS OF CORROSION. MARINE ENVIRONMENTS ARE MORE AGGRESSIVE THAN MOST INLAND ENVIRONMENT.
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MARINE ENVIRONMENTS (a) MARINE ATMOSPHERE (b) SPLASH ZONE (c) AREAS IMMERSED DURING HIGH TIDE (d) AREAS BETWEEN HIGH TIDE AND LOW TIDE. (e) SEA WATER (f) MUD AND (g) COASTAL AREAS
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HARMFUL EFFECTS BAD APPEARANCE MAINTENANCE AND OPERATING COSTS PLANT SHUTDOWNS CONTAMINATION OF PRODUCT LOSS OF VALUABLE PRODUCT EFFECTS ON SAFETY AND RELIABILITY
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FORMS OF CORROSION UNIFORM OR GENERAL CORROSION GALVANIC OR TWO METAL CORROSION CREVICE CORROSION PITTING INTER GRANULAR CORROSION SELECTIVE LEACHING OR PARTING EROSION CORROSION, AND STRESS CORROSION.
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UNIFORM SURFACE CORROSION ALL EXPOSED ATOMS OF THE EXPOSED SURFACE OF THE METAL ARE ATTACKED AT THE SAME RATE. IN PRACTICE SUCH TYPE OF CORROSION REARELY OCCURS. IF THE SURFACE OR ENVIRNMENTS ARE NOT UNIFORM,THE CORROSION DOES NOT REMAIN UNIFORM BUT BECOMES CONCETRATED AT THE PLACE CAUSING PITTING.
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GALVANIC OR TWO-METAL CORROSION . A POTENTIAL DIFFERENCE USUALLY EXISTS BETWEEN TWO DIS-SIMILAR METALS WHEN THEY ARE IMMERSED IN A CORROSIVE OR CONDUCTING SOLUTION (ELECTROLYTE). IF THESE DIS-SIMILAR METALS ARE PLACED IN CONTACT (ELECTRICALLY CONNECTED), THIS POTENTIAL DIFFERENCE PRODUCES ELECTRON FLOW BETWEEN THEM.
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BASIC REQUIREMENTS FOR BIMETALLIC CORROSION PRESENCE OF AN ELECTROLYTE. ELECTRICAL CONNECTIONS BETWEEN THE METALS. DIFFERENCE IN POTENTIAL BETWEEN THE TWO METALS.
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GALVANIC SERIES . PLATINUM, GOLD, GRAPHITE, TITANIUM AUSTENITIC STAINLESS STEELS (PASSIVE) NICKEL AND HIGH NICKEL ALLOYS (PASSIVE) MONEL, BRONZE, GUNMETAL, 70/30 CUPRO NICKELS, COPPER-NICKEL IRON ALLOYS COPPER, ADMIRALTY BRASS, 70/30 BRASSES ICKEL AND HIGH NICKEL ALLOYS (ACTIVE) Cont….
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NAVAL BRASS, 60/40 BRASS, HIGH-TENSILE BRASS LEAD, TIN AUSTENITIC STAINLESS STEEL (ACTIVE) HIGH NICKEL CAST IRON .
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  • Fall '17
  • d.p singh
  • Tide, magnesium alloys

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