Current understanding of cracking of recovery boiler primary air port composite tubes

Co-extruded 304L stainless steel/SA210 carbon steel tubes have been widely used in the floors and lower walls of black liquor recovery boilers in order to provide needed corrosion resistance. However, cracking has been found in the stainless steel layer of both floor and wall tubes, and the cracks in the tubes that form primary air port openings have, in some cases, advanced into the carbon steel portion of the tubes. A few tube failures have …