Dynamic studies on the inhibitive action of magnesium stearate on hot corrosion in a kerosene fired Furnace

The inhibitive effect of magnesium stearate (MS) on the hot corrosion of steel structures of power generation station was studied using a kerosene fired furnace. Three steel alloys were selected including [SA 178A, 209 T1, 213 T11, ASME Code], prepared as rectangular pieces (10 x 20 x 5 mm) from water wall tubes and superheater tubes of a local power station. The specimens were mechanically polished with emery paper (100, 320, 600 and 1000) under running tap water and rinsed with distilled water and benzene. The heating chamber of the furnace had shelves on which specimens are placed. The vanadic slag (synthetic ash) chosen was an intimate mixture of 67%wt (V2O5) and 33% wt (Na2SO4). Mixtures of magnesium stearate, MS: synthetic ash of 1:1, 1:2 and 1:3 molar ratios of were applied onto the surface of the specimens. The heating program was carried out at various time intervals (2-10 h) to study the normal oxidation at different temperature (550-950°C). Constant time heating programs involved heating at the specified temperatures for 4 h. The rate of oxidation is accelerated in the presence of vanadic slag (mixture of Na2SO4 with various Na-V-O bronzes and resulted in increased corrosion rate with increasing temperature (550-950° C). X-ray diffraction analysis indicated the presence of iron oxide (Fe2O3) with the vanadic slag materials. The weight loss of the three alloys specimens indicated a Clear reduction in the degree of corrosion with increasing MS content. The scale changed into a powder form that can be easily removed from the surface of the specimens. The best ratio from MS: Ash is 3:1, which gave inhibition efficiency of 85% at 550°C. The inhibition efficiency increases with temperature decrease. With the introduction of MS with the ash magnesium vanadate Mg3V2O8 was a major constituent together with some MgO resulting from the thermal decomposition of MS.