EFFECT OF OXIDATION AND HOT CORROSION ON ELECTROCHEMICAL BEHAVIOUR OF BOILER STEELS

Abstract

The resistance to electrochemical corrosion was studied on the T-22 boiler grade steel samples subjected to high temperature oxidation in air and molten salt (Na2SO4 +25% NaCl) It under cyclic heating condition for 50 cylces, each cycle consisting of Ihr. heating and 20 minutes cooling. Oxidation kinetics was established by thermo gravimetric methods by measuring the weight el1anges at the end of each cycle. The oxidised samples with scaled surface were investigated for eleetroehemical corrosion using potentiodynamic and static immersion test methods. X-Ray analysis, Scanning Electron Microscopy (SEM), EDAX and AFM were used as characterisation tools. The steel suffered oxidation attack (hot corrosion) in the presence of molten salt which resulted in intense spalling of the scale In addition to this, the substrate was found to he depleted in chromium. It is also found that neither the air oxidised scale nor the salt coated scale were 4 protective against the elcctrocheinieal attack in the long run.