Performance of composite tube cladding materials in kraft recovery boiler floor environments

Composite tubes with an external cladding of 304L stainless steel on a carbon steel tube were introduced in black liquor recovery boilers to prevent excessive corrosion of carbon steel tubes caused by hot reducing and sulfidizing gases. Although composite tubes performed well in reducing the rate of corrosion in the lower furnace of the boilers, cracks in 304L layer were found in some of these composite tubes. Previous studies to investigate the cause of these cracks points to the mechanism of stress corrosion cracking (SCC) in shutdown or boiler startup environments. In the present study, a number of cladding materials were tested to rank their relative corrosion and SCC performances in simulated boiler shut-down environments.