Study Of Failure Analysis And Corrosion Behavior Of F-32 Reactor By Liquid Phase Method

Core equipment F-32 reactor of a fluorine chemical enterprise frequently fails prematurely in service.The latest failure took place for about servicing for 10 months,its form was perforation leakage.The design life of this reactor is 8 years,in order to find out the cause of premature failure and find the corresponding measures to solve or alleviate the corrosion problem,systematic failure analysis was conducted by OES?SEM?EDS and XRD aiming to perforation position,which including analysis of material composition,microstructure and surface corrosion products and so on.During the inspections,it was found that apart from failure of perforation,the welds in liquid phase of this reactor were also seriously corroded,especially the circumferential weld was thinning seriously,therefore there was a great potential safety hazard.For this reason,the corrosion reason of liquid phase welds was analyzed,meanwhile in order to find a way to slow down the corrosion rate of welds,the influences of welding process and post-weld heat treatment on corrosion behavior of materials were studied comprehensively.Through physical and chemical examination analysis of perforation position,it was found that the existence of a large number of complex sulfur inclusions in the substrate of reactor was the fundamental cause of material perforation.The nonmetallic inclusions were easy to induce pitting and eventually led to material perforation under the action of corrosive medium.Therefore,we should pay special attention to the generation and introduction of inclusions in the process of plate production and weld processing.Welding is the processing method that must be applied to the reactor,and welding inevitably brings about the change of microstructure,therefore there is an inevitable result that the deterioration of weld corrosion.The corrosion analysis of weld in liquid phase showed that the circumferential weld and longitudinal weld were also seriously corroded,the reason was that the formation of corrosion battery formed by different phases and the generation of poor-corrosion-resistance phase in microstructures;In addition,the corrosion situation of circumferential weld was more serious than longitudinal weld,which was due to the existence of more fine acicular ferrite in the former microstructure.Through the study of different welding processes and post-weld heat treatment processes,it was found that under the original stress relieving annealing process,the smaller heat input submerged arc welding had the best corrosion resistance as a whole;with the increase of welding heat input,the overall corrosion resistance of submerged arc welding had decreased;the overall corrosion resistance of manual arc welding was relatively the worst.In addition,for the manual arc welding,the 620? stress relieving annealing was most favorable for its corrosion resistance.Finally,the use of smaller heat input submerged arc welding replace manual arc welding for alleviating the corrosion problem can be considered.