Laboratory corrosion tests were conducted to clarify the effects of addition of the alloying elements
silicon and aluminum on the fireside corrosion of austenitic 20wt.% Cr -40% Ni alloy in simulated waste
to energy (WTE) plants. Test results were compared with those of Mo -added alloys obtained from the
literature. Laboratory -melted alloys of up to 2.9% Si and up to 4.2% Al were prepared and coupon
specimens of these alloys were reacted with synthetic ashes of a predominantly chloride salt mixture of
38.3wt.% Cl and of a sulfate -chloride salt mixture of 19.2% Cl –19.4% S (as SO3) in a gaseous
environment of 1500 ppm HCl -300ppm SO2 -7.5% O2 - 7.5% CO2 -20% H2O -bal.N2 (by volume) at
400-550°C for 20 h. Addition of Al to the alloys increased the corrosion resistance to chloride salt at
500°C, and to the sulfate/chloride salt mixture at 550°C, but the effect of Al on corrosion was generally
small and limited. For the chloride salt at 500°C, a drastic reduction of the corrosion weight loss was
noticed for Si -added alloys, but the beneficial effect of Si was not prominent for the sulfate/chloride salt
mixture at 500°C and 550°C. For waterwall tubes where chloride salts deposit, materials forming uniform
Al2O3 and/or SiO2 scales might be effective. On the other hand, for superheater application where
chloride/sulfate salt mixtures will deposit on tube surfaces, selecting high -Si and/or high -Al alloys may
not necessarily be an effective measure to reduce the corrosion rate of tube alloys. For these corrosion
environments, using alloys of high- Mo content such as alloy 625, in addition to good furnace design and
careful operation, is considered the right direction to combat the corrosion in actual WTE plants.