THE INHIBITIVE ACTION OF MAGNESIUM HYDROXIDE ON HOT ASH CORROSION OF STAINLESS STEEL IN A KEROSENE FIRED FURNACE

Abstract

The inhibitive effect of magnesium oxide on the hot ash corrosion of steel structures of power generation station was studied using a kerosene fired furnace. Three alloys were selected including [SA 178A, 209 T1, 213 T11], prepared as rectangular pieces from water wall tubes and superheater tubes of a local power station. The heating chamber of the furnace had shelves on which specimens are placed. Mg(OH)₂ was mixed with synthetic slag (67%wt  V₂O₅ and 33% wt Na₂SO₄) at molar ratios of 1:1, 1:2 and 1:3, respectively and applied on the surface of the cleaned specimens. The tests were carried out at fixed (4 h) and various time intervals (2-10 h) to study the normal oxidation at various temperatures (550-950˚C). The rate of oxidation is accelerated in the presence of vanadic slag and resulted in increased corrosion rate with increasing temperature (550-950 ^oC ). X-ray diffraction indicated the formation of NaV₃O₈, Na₂O.V₂O₄.5V₂O₅, Na₄V₂O₇, VOSO₄, Na₂SO₄ and  iron oxide  (Fe₂O₃) . The weight loss of the three alloys specimens indicated a Clear reduction in the degree of corrosion with increasing Mg(OH)₂ content. The scale changed  into a powder form which can be easily removed from the surface of the specimens. The best results were obtained with the mole ratio 3:1, which gave inhibition efficiency of 85% at 550°C. The inhibition efficiency increases with temperature decrease. With the introduction of Mg(OH)₂ with the ash magnesium vanadate Mg₃V₂O₈ was a major constituent together with some MgO.