corrosion nivi

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HAND MADE IS DIFFER FROM INDUSTRY

CORROSIONFACTORS INFLUENCING THE RATE OF CORROSION

CORROSION Corrosion is the deterioration of materials by chemical interaction with their environment.

Recipe for corrosion

1 Active metal 2 Water

3 Oxygen (atmospheric corrosion)

4 Acid (chemical corrosion)

5 Salt

6 High temperature

Corrosion TriangleElectrolyteMetal

Oxidize

EFFECTS OF CORROSIONCOLLAPSE OF SHIPS

SHUT DOWN OF FACTORIES

LOSS OF EFFECIENCY

REDUCED VALUES OF GOOD

5 LOST OF SUR FACE PROPERTIESREDUCED STRENGTH

7 ESCAPE OF FLUIDS

5

TYPES OF CORROSION 1 CREVICE CORROSION

PITTING CORROSION

GALVONIC CORROSION

1 Required ConditionsTwo dissimilar metals in contactOxygen dissolved in water

2 Both Cu and Zn are oxidized in the presence of oxygen in water.

3 The electric potential of copper is 1.90 and for zinc is 1.65.

4 Electrons flow from least potential to higher potential.

Copper does not corrode and zinc corrodes at an accelerated pace.

CORROSION PROTECTION

Preventing the Corrosion of Iron (cathodic protection/sacrificial anode

COATINGS

Impressed Current Cathodic ProtectionPower Supply

Shipboard Power

Controller

Shipboard Power

InsulationPt AnodeReference ElectrodePaintLayerHull

e-e-

CORROSION RATE LOSS OF MATERIAL PER UNIT TIME IS CALLED CORROSION RATE.

mdd = weight loss in mg surface area in dm2 immersion period

INFLUENCING THE RATE OF CORROSION NATURE OF METALS RELATIVE AREAS: WHEN THE AREA OF CATHODE IS LARGER AND THE AREA OF ANODE IS SMALLER OVER VOLTAGE: CORROSION RATE IS INVERSELY PROPORTIONAL TO THE OVER VOLTAGE OF A METAL IN THE CORROSIVE ENVIRONMENT CR= 1 OVER VOLTAGE

NATURE OF METALPOSITION IN EMF SERIES: CORROSION DEPENDS ON THE POSITION OF THE MATEL IN THE EMF SERIES.HYDROGEN IN EMF SERIES GETS GREATER CORRODING NATURE VIGOROUSLY.PURITY OF METAL: THE METAL SHOULD BE PURE IN STATE . IMPURITIES PRESENT IN THE METAL ENCOURAGE GALVANIC CORROSION .

NATURE OF THE SURFACE FILM THE NATURE OF THE FILM FORMED ON THE METAL SURFACE WHICH CAN BE DECIDED BY PILLING - BEDWORTH RULE. 1 ALKALI AND ALKALINE EARTH METALS SUCH AS Mg,CA etc..FORM OXIDE ,WHOSE VOLUME IS LESS THAN THE VOLUME OF THE METAL 2 HEAVY METALS LIKE Al , Cr ,etc. FORM OXIDE ,WHOSE VOLUME IS GREATER THAN THAT OF THE MATEL

NATURE OF THE CORROSION PRODUCT IF THE CORROSION PRODUCT IS SOLUBLE IN THE CORRODING MEDIUM ,THE CORROSION RATE WILL BE FASTER . SIMILARLY ,IF THE CORROSION PRODUCT IS VOLATILE , THE CORROSION RATE WILL BE INCREASE.

NATURE OF THE ENVIRONMENTa) TEMPERATURE : AS TEMPERATURE INCREASES,RATE OF CORROSION INCREASES

b) HUMIDITY: AS IN THE ENVIRONMENT INCREASES CORROSION RATE INCREASES CORROSION INCREASES

NATURE OF THE ENVIRONMENTc) PRESENCE OF CORROSIVE GASES: THE ACIDIC GASES LIKE , (CO)2,(SO)2,H2S AND FUMES OF HCL,H2SO4,etc..PRODUCE ELECTROLYTES ,WHICH ARE ACIDIC .SO THE ELECTROCHEMICAL CORROSION INCREASES .

d)EFFECT OF PHFormation of hydrogen at lower pH means that depolarization with oxygen and hydrogen evolution are both playing a role.

POURBAIX DIAGRAM1 EXPLAINS THE CONDITIONS WHICH A METAL UNDERGOES CORROSION2 IT IS THE EXAMPLE OF IRON SYSTEM3 IN Eg : a) INCREASING THE ELECTODE POTENTIAL b)DECREASING ELECTRODE POTENTIAL c)INCREASING PH VALUE4 DEPENDING ON EXPERIMENTAL CONDITIONS ,IRON,WILL BE PASSIVE OR UNDER GO CORROSION

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