Sanicro 67/4L7 - a New Composite Tube for Recovery Boilers, 2012 TAPPI PEERS Conference

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Since the early 1970’s, recovery boilers around the world have been designed with composite tubes in the most corrosive lower-part of the furnace. The current demand for higher efficiency and safety in today’s state-of-the-art recovery boilers has increased the requirements on the materials used. It is mainly in the most vulnerable positions that more corrosion resistance material is required i.e. floors, airports and smelt spouts. The tubes in these positions are more extensively subject to thermal shocks and corrosive environments and higher demand is put on corrosion and cracking resistance. Sanicro 67/4L7 is a newly developed composite tube consisting of an outer high alloyed component of UNS N06690 (Alloy 690) and an inner medium-carbon steel of SA-210 A1. Laboratory testing in simulated lower furnace environments have verified that the new composite tube has superior corrosion resistance in comparison with other candidates, both in regard to general corrosion and stress-corrosion cracking. Welding trials also show good weldability of composite tube UNS N06690/SA210 A1.