The third stage superheater(using TP347H steel) of a biomass fired boiler suffered serious surface corrosion after being in service for 4 000 hours.Microstructure analysis

energy spectrum analysis and X-Ray diffraction analysis were conducted on the corroded tubes.The results showed that

uniform corrosion and grain boundary attack both occurred.In corrosion layer there were mainly chlorine and potassium compounds while the chromium content was low.The grain boundary corrosion products mainly consisted of Cr and Fe oxides

among which the Cr content was higher.The chlorine in biomass was considered as the major factor that causing the rapid corrosion on tube surface

and the eutectic with low melting point formed by alkali metal and Fe and other elements enhanced the corrosion.Thus

some measures like cofiring the biomass with coals were proposed to reduce the corrosion rate of tubes in biomass boiler.