This paper addresses experience with inspection, repair, and prevention of cracking at primary air port openings in a black liquor recovery boiler originally built using type 304L stainless steel-clad composite tubes for the lower waterwalls. The extent of cracking found during every 6-month interval inspection increased over a 3-year period and then decreased over a subsequent 3-year period as the cracking was removed, weld repairs were performed, some of the openings were replaced using alternative metallurgies, and efforts were made to minimize temperature fluctuations at the primary air port openings. Weld repairs made using ERNiCrMo-3 filler metal did not re-crack. Different-design openings using type 304L stainless steel composite tubes did not show any improvement in resistance to cracking. Openings replaced using Alloy 625 spiral weld overlaid tubes experienced both cracking and corrosion. Openings replaced using composite tubes with Alloy 825 cladding resisted both cracking and corrosion.
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