2 What is Corrosion?Corrosion is the oxidation of a metal due to an ELECTROCHEMICAL reaction. The oxidizing agent is most often O2 (atmospheric corrosion) or H+ (chemical corrosion) or both.
3 Requirements for corrosion Active metalWaterOxygen(atmospheric corrosion)Acid(chemical corrosion)High temperatureCorrosionTriangleElectrolyteMetalOxidize
4 Example of Atmospheric Corrosion Corrosion on wing of Navy aircraftF/A-18C HornetContrast. What exactly is shown in the pictures? Too wordy.
5 Example of Stress Corrosion Aloha Flight 243 (28 APR 1988) Stress Corrosion Crackingtensile stress and corrosive environmentscracks are initiated at corrosion areastensile stresses propagate the crackcorrosion further deteriorate crack
7 FORMS OF CORROSION • Stress corrosion • Galvanic • Waterline corrosion work togetherat crack tips.• GalvanicDissimilar metals arephysically joined. Themore anodic onecorrodes. Zn & Mgvery anodic.• Waterline corrosionMaximum amount of corrosion takes place beneath the surface of the water meniscus• PittingDownward propagationof small pits & holes.9
8 GALVANIC SERIES • Ranks the reactivity of metals/alloys in seawater PlatinumGoldGraphiteTitaniumSilver316 Stainless SteelNickel (passive)CopperNickel (active)TinLeadIron/SteelAluminum AlloysCadmiumZincMagnesium8
9 Factors influencing corrosion Nature of metalPurity of metalTemperatureHumidity of airPresence of impurities in airInfluence of pH
11 Applications of Cathodic Protection Galvanized SteelZinc coatingSacrificial AnodesShip HullsSubs (free flooding areas)Los Angeles Class SubArleigh-Burke Destroyer
12 GalvanizingGalvanizing is the process of coating iron or steel sheets with a thin coat of zinc to prevent them from rusting.It is most widely used for protection of iron from atmospheric corrosion in the form of roofing sheets , wires , pipe , nail , bolts , screw , bucket etc,
13 Tinning Tinning is coating tin over the iron or steel articles. It possesses considerable resistance against atmospheric corrosion.Moreover because of non-toxic nature of tin , tinning is widely used for coating steel , copper and brass sheets , used for manufacturing containers for storing foodstuffs , ghee , oil etc.Tinned-copper sheets are employed for making cooking utensils and refrigeration equipment.