Failure Analysis On Duplex Stainless Phosgene Reactor And Study On Corrosion Properity

Multiple cracks were founded in phosgene reactor manufactured by SAF2205 duplex stainless steel. The nature and formation mechanism of the cracks in the weld metal and heat affected zone of this reactor are researched in this paper. Based on this, the effect of high temperature aging and stress on the metallograph and corrosion property is studied. The results are shown in the following.Firstly, failure analysis is carried out on the cracks of reactors. Most cracks present transgranular propogation by replication metalloraphy, Some of the cracks are formed by connecting pitting corrosion and the fracture morphology presents typical of the river pattern with corrosion products containing chloride ions. Some secondary austenite with Widmanstatten structure and some small strip s phase precipitates were found on the weld. Above all indicate that this failure of phosgene reactor is mainly due to pitting and stress corrosion cracking.Secondly, SAF2205 and SAF2507 duplex stainless steel are selected to be applied 200MPa stress and no stress respectively aging for different time in the 600℃heat treatment to simulate weld thermal cycle. High temperature aging and stress relative to SAF2205 and SAF2507 duplex stainless steel anti-corrosion sensitivity are explored preliminary through the electrochemical methods. The sample after heat treatment reduce its corrosion resistance severely due to the reduction of ferrite content and the formation of precipitated phase. However, the passivition current density is reduced in 200MPa stress compared with no stress condition.