Waste-to-Energy Boilers: 310S vs. Alloy 625 Cladding

 

Why 310S suffices for superheater tubes?
25% Cr content resists flue gas corrosion up to 950°C. Withstands chlorine-induced wastage at <0.5 mm/year in MSW plants. Costs $45/kg vs. alloy 625's $220/kg.

 

When alloy 625 weld overlay is justified?
For waterwall sections exposed to molten slag. Ni-Cr-Mo matrix prevents chloridation/sulfidation at 450-600°C. Reduces tube replacement frequency from 18 to 60 months.

 

Maximum ash corrosion rates?
310S: 2 mm/year in high-chlorine waste (>1.5% Cl)
Alloy 625: 0.3 mm/year under same conditions
Critical wastage occurs at metal temps >400°C with KCl deposits

 

Erosion protection techniques?
Vertical tubes: 60° spiral rifling reduces erosion 70%
Horizontal tubes: Inconel 625 shield caps on leading edges
Refractory anchoring: Alloy 601 studs withstand 1100°C

 

Failure analysis protocol?
Cross-section SEM showing chromium depletion zones
EDS mapping of Cl/S penetration at grain boundaries
Deposit analysis for Zn/Pb low-melting eutectics
Ultrasonic thickness trending every 3,000 hours