THE EFFECT OF NI ON THE SECONDARY CORROSION PROTECTION OF FE BASED MODEL ALLOYS AT 600 °C

Abstract

The formation of secondary protective oxides has been investigated for three different alloys with different wt% nickel. The presence of alkali salts causing severe corrosion of stainless steel in biomass- and waste- fired boilers. All the alloys showed a breakdown of the primary protective oxide scale after exposure to K2CO3 and KCl for 24 hours at 600°C. The samples were sprayed with 1 mg/cm2 of saturated alkali salts before being placed in the furnace. An increased amount of nickel resulted in an increased formation of nickel oxide (NiO) and a decreased formation of iron oxide (Fe2O3). The increase in formation of nickel oxide showed a connection to lower mass gain for all the samples exposed to alkali salts. The nickel oxide was shown to grow slower than the iron oxide and had better protective properties. The alloy containing 34 wt% nickel was specifically targeted by water containing environment.