Alloy degradation in a co-firing biomass CFB vortex finder application at 880 °C.

Graphical abstract Highlights • For alloys 310S and 800H/HT; N penetrated the surface scales and formed internal Cr nitrides. • For alloys 310S and 800H/HT; the nitride formation lowered the Cr activity and inhibited the internal Cr permeation. • For alloys 310S and 800H/HT; Na 2 SO 4 and NaCl reacted with Cr 2 O 3 to form chromate and elemental S and Cl. • For alloys 310S and 800H/HT; Cl attacked the alloy interiors in a developed stage of corrosion. • For alloy 600; no internal nitrides or major sodium chromate formation were found. Abstract Mechanisms of alloy degradation in a fireside N-S-O-C-H-Cl-Na-K atmosphere at 880 °C were elucidated using SEM-EDS, chemical equilibrium calculations, and XRD. Alloys 310S, 800H/HT, and 600 were studied after 0, 8000, and 16,000 h exposure in a boiler co-firing biomass waste. For 310S and 800H/HT it was shown that nitrogen formed internal Cr nitrides lowering the Cr activity and inhibiting internal alloy Cr permeation, and that NaCl and Na 2 SO 4 reacted with Cr oxide to form chromate and to accelerate the S and the Cl pickup. Alloy 600 showed no nitride or major chromate formation. [ABSTRACT FROM AUTHOR]