Influence Of Warm Bending On Load-Bearing Performance Of 2.25Cr-1Mo-0.25V Plate-Welded Ring Shell

2.25Cr-1Mo-0.25 V steel has been widely used to manufacture hydro-processing equipment operating under harsh environments for its good mechanical properties.The long-term service in high-temperature,high-pressure,and hydrogen-facing environments would deteriorate the mechanical properties of 2.25Cr-1Mo-0.25 V steel.Warm bending,a common fabricating process of 2.25Cr-1Mo-0.25 V steel ring shells,inevitably changes the mechanical properties of 2.25Cr-1Mo-0.25 V steel,but its detailed effect remains obscure.This restricts the development of structural integrity evaluation for in-service hydrogenation reactors.In this work,we investigated the effect of warm bending on the microstructure and mechanical behavior of 2.25Cr-1Mo-0.25 V steel by experiments and simulations.The main research work and conclusions are summarized as follows:(1)The effect of warm bending and 705℃×8h tempering on the high temperature strength of 2.25Cr-1Mo-0.25 V steel was studied by experiments.First,a series of hightemperature tensile tests were carried out,in which test materials were extracted from a actually fabricated ring shell and its raw plate.Thereafter,the microstructures of test materials were qualitatively / semi-quantitatively analyzed by various characterization techniques,such as scanning electron microscope(SEM),electron backscatter diffraction(EBSD)and three-dimensional high-resolution X-ray computed tomography(3D μ-XCT).Finally,warm bending induced microstructural degradation as well as their implication for high temperature strength was discussed in detail.Tensile test results showed that warm bending leads to a significant decrease in material strength at the surface region of virgin plate but a slight decline at the central region of virgin plate.An inhomogeneous material strength distribution was thereby revealed along the thickness direction of the ring shell,which could not be completely eliminated by subsequent tempering at 705°C for 8 hours.Moreover,microstructural observations demonstrated that warm forming leads to multiple microstructural deterioration,including carbide coarsening,ferrite matrix softening,void defect increasing,etc.Their combined action could explain the inhomogeneous material strength distribution in hydrogenation reactor shells.(2)The effect of warm bending and 705℃×8h tempering on the creep rupture life of 2.25Cr-1Mo-0.25 V steel was studied by experiments.First,a series of creep rupture tests were carried out at 482°C and 350 MPa,in which test materials were extracted from an actually fabricated ring shell and its raw plate.Thereafter,the microstructures of test materials were qualitatively / semi-quantitatively analyzed by various characterization techniques,such as transmission electron microscope(TEM),EBSD and 3D μ-XCT.Finally,warm forming induced microstructural degradation as well as their implication for creep rupture life was discussed in detail.Creep rupture test results showed that warm bending leads to a significant decrease in creep lifetime at the surface region of virgin plate but a slight decline at the central region of virgin plate.An inhomogeneous creep perfermance distribution was thereby revealed along the thickness direction of the ring shell,which could not be completely eliminated by subsequent tempering at 705°C for 8 hours.Moreover,microstructural observations demonstrated that warm deformation leads to multiple microstructural deterioration,including carbide coarsening,ferrite matrix softening,void defect increasing,etc.Their combined action appears to accelerate the creep fracture of 2.25Cr-1Mo-0.25 V steel.(3)The creep rupture life prediction model was established for warm formed2.25Cr-1Mo-0.25 V steel.First,we collected creep data of 0.5Cr-0.5Mo,1Cr-0.5Mo,1Cr-1Mo-0.25 V,2.25Cr-1.6W,2.25Cr-1Mo,5Cr-0.5Mo and 2.25Cr-1Mo-0.25 V steel.Thereafter,a multi-fidelity neural network(MFNN)was constructed based on this dataset,where a modified θ parameter method was also embedded.Finally,to take the effect of plastic deformance into consideration,a series of creep rupture tests were performed on 650°C pre-strained 2.25Cr-1Mo-0.25 V steel.And a transfer learning(TL)neural network was constructed to modify the output of MFNN based on the experimental results.Results showed,MFNN + TL could be utilized to predict the482°C 350 MPa creep rupture life of 650°C pre-strained 2.25Cr-1Mo-0.25 V steel.(4)The prediction method was presented to predict the influence of warm forming and creep on the load-bearing property of 2.25Cr-1Mo-0.25 V steel ring shell.First,high-temperature tensile tests were performed on pre-strained and pre-creeped materials,and a shallow neural network(SNN)was constructed based on the experimental results.Then,a finite element model(FEM)for warm bending of 2.25Cr-1Mo-0.25 V steel is established,which could quantity the equivalent plastic strain distribution of as-formed ring shell.Subsequently,the combining of MFNN,TL,SNN and FEM could predict the material strength distribution of in-service hydrogenation reactor ring shell.And,using shakedown analysis,the bearing capacity of 2.25Cr-1Mo-0.25 V steel ring shell with different sizes was calculated.Finally,the influence of warm bending on the long-term service safety and integrity assessment of hydrogenation reactor was discussed in details.