Cracking in water tubes in black liquor recovery boilers, especially in boiler floors and lower waterwalls, has been the source of unscheduled downtime for many years. Now, these problems may be over or at least substantially reduced as tube material specialists, Sandvik Materials Technology reveal an installation reference for stainless/carbon steel composite tubes which show no signs of cracking after eight years in service. Composite or co-extruded tubes, comprising a 304L stainless steel outer later and an SA210 Grade A1 carbon steel inner layer, have been around for over 30 years, but it was only in the early 90s that it became apparent that cracking in the 304L layer, particularly in floor tubes was a widespread problem. From over 100 installations surveyed, as many as one third of all boilers had cracking problems, some becoming evident as soon as six months after start-up.
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