Modeling studies of a composite tube floor in black liquor recovery boilers

Stress-strain analysis of a composite tube floor in black liquor recovery b oilers used a commercially available finite element (FE) code. The analysis examined the stress state in an SS304L/SA210 composite tube floor at the n ormal operating cycle of a boiler and the stresses that develop from temper ature excursions during operation. Measurement of residual stresses from tu be manufacturing used neutron diffraction. With the residual stresses from assembly welding computed by finite elements, the residual stress measureme nts were incorporated into the FE models developed for analysis of in-servi ce conditions. Results show high compressive stresses in the overlay materi al that exceed the yield stress at normal service conditions. They signific antly exceed the yield stress during a temperature excursion and become ten sile after returning to normal service conditions. A parametric study calcu lated stresses in the floor tubes as a function of the yield stress and the coefficient of thermal expansion of the overlay material. The analysis pro vided a generalized solution of stresses in the composite tubes for many ov erlay materials. Using these results, a recommendation for overlay material s with the most suitable mechanical properties is possible.