Material and coating selection
Carbon steel with lining, 316L, duplex, solid alloy: what each one is actually good for on FGD duty.
There is no single correct material for FGD ductwork. There is a correct material for each position, and the three positions differ enough that one specification cannot cover them all.
Carbon steel with epoxy or glass-flake lining
The cheapest option and the right one for large flat surfaces above the dew point. Glass-flake epoxy handles chlorides better than a plain epoxy and is the usual choice for absorber walls and large duct panels. It fails at edges and at fixings, so the specification has to say how cut edges are sealed and which washers are used.
316L
The default for wetted surfaces on the clean gas side. Adequate up to roughly 20,000 mg/l chloride at 50 °C. Above that, or where the temperature drifts and condensation becomes intermittent, pitting starts in the heat-affected zone of welds. Specify solution annealing on welds, not just post-weld cleanup.
Duplex 2205
The step up when chlorides are high or the duty is variable. Higher strength means a thinner blade, which reduces actuator torque, and the chloride resistance is materially better than 316L. It costs more per kilogram and less per year on the right duty.
Solid alloy edges
The blade edge sees the highest velocity and the most condensate. A solid 904L or alloy 20 strip on a 316L blade is often the most cost-effective combination: the expensive material is used only where it is needed, and the edge can be replaced when it wears.
What to send us
Gas analysis including chloride and SO₃, operating and design temperature at each position, whether the plant runs wet or dry during standby, and the water chemistry if washing is used. Those four items decide the material and they cost nothing to provide.
Talk to us about this duty
Send the duct section, design temperature, pressure difference and the duty point. We reply with the gate type, the material selection, the drive and a general arrangement drawing for approval.