Die Korrosion austenitischer Überhitzerstähle durch Alkalisulfat/Alkalichlorid-Gemische in Luft und in Verbrennungsgasen

The corrosion of austenitic superheater steels by alkali sulphate/alkali chloride mixtures in air and combustion gases In view of the fact that, in superheaters, with metal temperatures in excess of 590° C, deposits with sulphate content give rise to heavy corrosion, investigations have been carried out into the behaviour of three austenitic steels exposed to alkali sulphate/alkalie chloride mixtures at temperatures ranging from 540 to 760° C. The atmosphere above the crucibles during the tests consisted of air and a synthetic combustion gas to which SO₂ and SO₃ had been added. The tests showed that the pure sulphates are harmless, but that even a small quantity of NaCl (0.5 to 2 percent.) may result in catastrophic oxidation (at temperatures between 630 and 760° C). In the synthetic combustion. gas, potassium sulphate was found to be more corrosive that sodium sulphate. A chloride additon has no major effect except at temperatures above 630° C, presumably due to complex alkali-iron-sulphates. With all tests, corrosion was intergranular.