Fouling and corrosion of bed nozzles in a bubbling fluidized-bed power boiler

An inspection of the floor in a bubbling fluidized-bed power boiler during a planned shutdown revealed significant corrosion of the type 310H stainless steel (UNS S31009) bed nozzles. One severely corroded bed nozzle was removed, along with samples of the deposit encasing the surface of the bed nozzle, for a subsequent failure analysis. The deposit covering the external (fireside) surface of the bed nozzle was almost entirely sodium and potassium chlorides, which covered a thick layer of corrosion product on the bed nozzle surface. The corrosion product was predominantly oxides of chromium, nickel, and iron. Chlorides were also found interspersed through the layer of corrosion product. It is concluded that the fireside corrosion was predominantly caused by chlorine-containing compounds (active oxidation). Overheating induced by the fouling, particularly within the air holes, is believed to be a major factor influencing corrosion.