We have a steam super heater coil installed at the outlet of an incinerator flue gas duct, to cool down the flue gas to the stack, producing 24kg/Cm2 superheated steam. Flue gas composition in Kmoles/h is as follows: O2 – 10.6 N2 – 33.8 Co – 1.1 Co2 - 20 SO2 - 2.4 H2O - 16 Flue gas temperature is 850 ºC Steam inlet temperature is 220ºC Steam outlet temperature is 370ºC Material of the 2” Super heater coil is A 335 P22 (2 %BC Cr %BD Mo) Skin temperature of the coil is 500ºC The super heater coil after 3 years run has failed due to great corrosion and also deformation As vertical coils compose the super heater, deformation is more severe at bottom mid half of the coils and the great thinning by corrosion is seen on bottom elbows. The experience of the forum on a similar case story and a help to the choice of an alternate material to the A 335 P22 (2 %BC Cr %BD Mo) in this particular application should be appreciated Thanks Luis Marques

Mr. Hendrix We verified that outside surface of bottom elbows showed a rough surface with long and smooth craters with great thinning. Exhaust flue gases which contain H20, CO2, NOx and O2 can accelerate corrosion and will require > 17% Cr and >8 Ni to reduce corrosion to acceptable levels. For that reason we intend to up grade the coil material of the super heater to a TP 321 stainless steel and we would like to know if that is the good option. Inside the coils no corrosion was found Thanks Luis Marques