Subir Paul* and Sulagna Sarkar* Pages 80 - 88 ( 9 )
Metallic structures in the oil and gas production site are severely degraded due to sweet and sour corrosion, and due to the presence of CO2 and H2S in fluid environments. The corrosion behavior of 304 austenitic stainless is investigated with the variation concentration of CO2 or H2S and CO2 + H2S to understand the effect of each singly and in combined form. Potentiodynamic polarization studies show that a small amount of CO2 helps in forming a calcareous deposit of protective layer on passive film of 304 steel, while an increase in CO2 concentration breaks the layer, giving rise to sweet corrosion. The presence of S2- damages the passive and protective layer of the steel and increases concentration, also increases the degradation rate. Electrochemical impedance studies reflect, lower polarization resistance and impedance at higher concentration of CO2 or H2S, the fact supports polarization outcome. Corrosion products of sweet and sour corrosion are identified by XRD which reveals different types of Iron carbides and iron sulphides corresponding to sweet and sour corrosion respectively. Image analysis under SEM shows the presence of uniform to localized corrosion and the presence of sulfide cracking in sour corrosion and general corrosion with protective carbide layer in sweet corrosion.
Sweet corrosion, sour corrosion, polarization, Impedance, XRD, SEMIntroduction.
Dept of Metallurgical and Material Engineering, Jadavpur University, Kolkata, Dept of Metallurgical and Material Engineering, Jadavpur University, Kolkata