Corrosion behavior of various steels in black liquor recovery boiler environment

It is important to examine characteristics of ash in order to understand th e high temperature corrosion behavior of steels in the black liquor recover y boiler (BLRB) environment. The ash collected from the corroded superheate r tubes was mainly composed of alkali-sulfates, alkali-chlorides and all;al i-carbonates. The mole ratio of Na/K in the ash from BLRB ranged from 3 to 17. The concentration of sulfates varied over a range from 50 to 90 wt%, an d chlorides from 0.1 to 10 wt%. On the base of these results, the corrosion behavior of various steels and the effect of alloying elements on the corr osion behavior of stainless steels in the BLRB environment were studied. From the results, Cr, Mn and Mo were significantly beneficial elements. N a nd Ni were also beneficial above 600 degrees C while C was an extremely har mful element. Subsequently, a new corrosion resistant stainless steel was s elected as the material for the superheater in the BLRB.