CORROSION IN OIL AND GAS INDUSTRY

CORROSION IN OIL AND GAS INDUSTRY

CORROSION- It is the deterioration of the metal layer by the reaction with the aqueous environment.

CORROSION PROCESS

Composed of three elements anode, cathode and electrolyteCorrosion takes place at anode , cathode remains unaffectedElectrolyte solution enables the transfer of electron

CORROSIVE MEDIA IN OIL AND GAS INDUSTRYCarbon dioxide H2CO3 Reaction : Fe + H2CO3 FeCO3 + H2

Hydrogen sulphide H2S Reaction : Fe + H2S + H2O FeS + 2H

These results in the corrosion (degradation of the material) which ultimately effects the mechanical properties of the material (ductility and impact strength).TYPES OF CORROSION IN OIL AND GAS INDUSTRYSweet corrosionSour corrosion Oxygen corrosionGalvanic corrosionCrevice corrosionMicrobiologically induced corrosionStress corrosion cracking

SWEET CORROSIONCarbon dioxide corrosion is its another nameBecomes active in aqueous environment (H2CO3) and increases with temperature(PH increase) TWO TYPES

PITTING CORROSION- localized corrosion , rapid penetration and removal of metal.

MESA CORROSION- localized corrosion of co2 under medium flow conditions.

SOUR CORROSIONErosion of metal surface by the attack of hydrogen sulphide.Alone it is a non corrosive, forms a weak acid with water (iron sulphide ions and hydrogen ions)FeSx ions forms scale that acts as barrier to slow corrosion at low temperature sour corrosion are uniform, pitting, and stepwise cracking H2S + Fe + H2O FeSx + 2H+ H2O Found in drilling pipies

Microbiologically induced corrosionCorrosion caused by bacterial activities, it produces CO2,H2S and organic acids that corrode the pipe by increasing the toxicity of flowing fluidBacteria's (Achromobacter, Flavobacterium and Desulfuricans ) form colonies (forming the large mass)and enhance the corrosion process under this also cause severe plugging problems.Appearance- Black slimy waste material or nodules in pipes.

GALVENIC CORROSIONCorrosion occurs when two materials are at different electrochemical potentials and are in contact with one another in electrolytic medium.Metal with most negative potential behave as anode and other cathode.It occurs in the form of intergranular corrosion bronze strainer on a aluminum hose barb.

Crevice corrosionCrevice corrosion is normally a localized corrosion taking place in narrow clearances where fluid gets stagnant in gapThis is caused by concentration differences of corodents over a metal surface. Electrochemical potential differences result in selective crevice or pitting corrosion attack.Oxygen dissolved in drilling fluid promotes crevice and pitting attack

Stress corrosion crackingSCC is the cracking induced from the combined influence of tensile stress and a corrosive medium.Corrosion is due to the corrosive environment, high PH and cracking by the stress induced due to parallel crack on the pipeline.SCC is a form of localized corrosion.

OXYGEN CORROSIONOxygen is a strong oxidant and reacts with metals very quickly.It magnifies the corrosive effect CO2 and H2S (acidic gases)The forms of corrosion associated with oxygen are mainly uniform corrosion and pitting-type corrosion.

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