Corrosion behaviour of S43035 ferritic stainless steel in hot sulphate/chloride solution
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The corrosion resistance of S43035 ferritic stainless steel at elevated temperatures of 308 K,
328 K, 348K and 378K was studied through potentiodynamic polarization test and optical
microscopy analysis in 2M H2SO4 at 0%, 1%, 3.5% and 6% NaCl. Results show that increase
in temperature and NaCl generally hinders the formation of the passive film. Changes in
corrosion rate from 308K to 378K at 0% NaCl was marginal. Metastable pitting was absent
until 378K due to increased electrolytic action of SO4
2− ions. In the presence of chlorides at
308K metastable pitting is visible delaying the formation of stable passive film. Passivation
behaviour was absent at temperatures above 308K due to polarization similar to carbon
steels and a strong decrease in hydrogen evolution over potential especially at 1% and 3.5%
NaCl. Optical images showed mild deterioration at 378K from 0% NaCl and the formation of
corrosion pits at 308K and 378K from 6% NaCl. Negative enthalpy value at 0% NaCl implies
exothermic nature of the steel corrosion reaction. Addition of chlorides changed the steel
corrosion reaction to endothermic. Increase in NaCl concentration caused a decrease in activation
energy and increase in entropy values due to decrease in passivation of the alloy and
consequently increase in corrosion rate. Statistical analysis through ANOVA at confidence
levels of 95% and 97.5% showed the strong influence of temperature variation on corrosion
rate with Fvalues
of 5.256 at 50.8% in contrast to the NaCl concentration whose value was
below the significance level.
Keywords
T Technology (General), TJ Mechanical engineering and machinery