Research On The Stress Corrosion Crack Propagation Of FV520B Impeller Blade In H₂S/CO₂ Environment

FV520B steel is a kind of enterprise commonly used acid,heat-resistant stainless steel.It is improved on the basis of the traditional Cr13 martensitic stainless steel.By adding Cu,Nb,Mo and other reinforced alloy elements,its intensity,plasticity and toughness have been improved to varying degrees and improvement.FV520B steel is widely used in manufacturing the shafts,blades,rotors and other parts with high requirements,but it also is the core material to manufacture the large centrifugal compressor impeller.There is a certain corrosive media taking into account the actual service environment,it is prone to corrosion damage which will affect the use of the equipment and the service life,especially the stress corrosion cracking which is with the great risk,so it is particularly important to enhance the corrosion resistance of the steel.At present,the research on stress corrosion cracking of FV520B stainless steel is relatively few at home and abroad,and the countries and enterprises need the research data to improve and protect the equipment manufactured by this steel.In this paper,the modified wedge-shaped open loading(WOL)prefabricated crack test and the finite element simulation were used to study the stress corrosion cracking behavior of FV520B.By analyzing the influence of media environmental factors on stress corrosion cracking,simulating the crack propagation process and the distribution of internal flow field of impeller with crack defects,the comprehensive evaluation of stress corrosion cracking behavior of FV520B material was realized.Firstly,the prefabricated crack propagation process of FV520B material was simulated by commercial software Abaqus.The static crack propagation simulation shows that the maximum stress and strain are located in the vicinity of the tip of the prefabricated crack and are symmetrically distributed in the direction of the prefabricated crack.Both the Mises stress and the stress intensity factor KI increase linearly with the increase of the simulated expansion step,and the two reach the threshold of crack initiation at the 6th extension step.The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction,and the maximum Mises stress is at the crack tip,and the critical stress range of the crack propagation is 23.3?43.4 MPa.The maximum value is located in the 8th expansion step,that is,crack initiation point,followed by crack propagation,the stress-strain curve was wavy changes,until the model fracture.Secondly,simulating the actual service environment of the impeller,the stresscorrosion cracking behavior of FV520B was synthetically analyzed by WOL prefabricated crack test,SEM scanning electron microscopy and EDS energy spectrum.By micro and macro analysis of prefabricated crack specimens,it is found that there are a lot of pitting and microcracks in the vicinity of the crack tip,and there are large typical cleavage steps and cleavage planes near the edge of the crack,existing obvious river-like or fan-shaped patterns,which is consistent with the typical brittle fracture characteristics.At last,the commercial software Fluent was used to simulate the internal flow field distribution of the impeller with cracked defects in the service environment.It was found that the pressure,velocity and temperature of the fluid were increasing along the flow direction of the fluid,and the maximum value appeared in the vicinity of the impeller exit edge.The maximum pressure and velocity in the crack zone are distributed near the middle of entrance and trailing edge,the expansion of the crack is facilitated by the triple effect:the opening force perpendicular to the inlet direction ofthe crack,the corrosion extension of the crack back edge tip and the blade heat distortion.In this paper,the law of stress corrosion crack propagation is explored by the combination of fracture mechanics test and numerical simulation.It provides the basis for the design and selection of components,and the use and improvement of FV520B material is better achieved.The centrifugal compressor impeller Production,use and maintenance and so have a very important guiding significance.