Cracking of pin-studded carbon steel waterwall recovery boiler tubes

A tube leak occurred in the lower furnace of a rebuilt recovery boiler (750°F/625 psig) operated by a pulp and paper mill on the Canadian west coast. The leak occurred at the primary air port level at the base of a pin stud on a waterwall tube located immediately adjacent to a primary air port opening. Mill personnel were interested in obtaining a better understanding of the reason why the failure occurred, and of the most appropriate action to prevent the failure from reoccurring. Correspondingly, a collaborative project involving the authoring organizations was initiated. The primary objectives were to: (i) conduct a failure analysis to determine the likely cracking mechanism, and (ii) analyze fireside tube temperature data collected from surface-mounted thermocouples to determine the possible role of boiler operation. This report documents the major findings of this effort.