Failure Analysis And Stress Corrosion Study Of Austenitic TP304 Stainless Steel Heat Exchanger Tube

In this paper,the influence factors and cracking mechanism of the austenitic TP304stainless steel tubes which are used in the auxiliary equipment of the thermal power plant-----high pressure heater.Analyzed the corrosion,then take out the measures to prevent the stress corrosion cracking of the austenitic stainless steel heat exchange tubes.The research results have great significance for ensuring the stable and safe operation of high pressure heater,prolonging the service life of the equipment and controlling the operation of the equipment.The heat exchanger tubes used for high pressure heaters in a foreign thermal power plant supplied by our factory are all austenitic TP304 stainless steel.After running for several months in the power plant,some tubes are cracked longitudinally and circumferential,which seriously affects the operation efficiency of the whole power plant.In this paper,the reasons for the crack formation and its properties are studied through the experiment,analysis and testing of the theory and practice.It is concluded that the crack is caused by the stress corrosion cracking.According to this conclusion,the factory puts forward corresponding countermeasures for protection and improvement,so as to ensure the normal operation of the equipment.The production of stress corrosion cracking requires the simultaneous existence of 3factors,namely,specific materials,tensile stress and corrosive medium.The anodic dissolving type crack is the main factor in the stress corrosion crack of austenitic stainless steel in the pH value more than 7,and the main factor is the cathode hydrogen embrittlement cracking in the acid solution with the pH value less than 7.According to the analysis that the main reason for the cracking of the heat exchange tube is that there is chlorine ion in the medium,the residual stress is high,and the 18-8 type austenitic stainless steel tube,which does not contain the stabilizing elements such as Ti,Nb and so on.The crack of tube is concentrated in the welding area of tube and tube sheet,which belongs to anodic dissolution type stress corrosion cracking caused by Cl~-.Therefore,our factory can reduce the residual stress level by requiring suppliers to improve the manufacturing process of heat exchanger tubes.Solution annealed heat treatment is sufficient to prevent carbide precipitation and avoid corrosion tendency of austenitic stainless steel.In addition,the Cl~-content in the operating medium should be strictly controlled during the operation of the equipment so that the stress corrosion cracking of the austenitic stainless steel heat transfer tube should be prevented.