Jianming Gong

Finite Element Analysis of the Effect of Brazed Residual Stress on Creep for Stainless Steel Plate-Fin Structure

This paper presented a finite element analysis of the effect of brazed residual stress on creep for stainless steel plate-fin structure using finite element code ABAQUS. The as-brazed residual stress distribution generated during the brazing process was obtained. Two cases, which are denoted Cases I and 2, were analyzed and compared to discuss the effect of as-brazed residual stress on creep. Case 1 was to carry out creep analysis just at the internal operating pressure. Case 2 was to perform the creep analysis considering the internal operating pressure in conjunction with as-brazed residual stress. The results show that due to the mechanical property mismatch between filler metal and base metal, large residual stress is generated in the brazed joint, which has a great influence on creep for stainless steel plate-fin structure. The creep strain and stress distribution of the overall plate-fin structure is obtained. The position that is most likely to fail is the fillet for the plate-fin structure at high temperature. Especially in the fillet interface, the creep strain and stress distribution are discontinuous and uncoordinated, which have great effect on creep failure.

Numerical Analysis of Thermal Deformation and Residual Stress for the Brazed Plate-Fin Structure

Compared to traditional shell-and-tube exchangers with the same material, compact plate-fin heat exchangers (PFHE) made of brazed stainless steel have superior heat transfer capability, less volume, lighter weight and low cost. Therefore it has been widely used in many industries, such as air separation, petrochemical, aerospace, energy etc. and PFHE has been the typical candidate to realize the miniaturization of heat exchanging equipments, which are the enabling technology for the miniaturization of chemical and thermal systems. It is negligible that residual stresses and thermal distortion under the effect of thermal cycle, self-constraint and clamping pressure load during brazing for the brazed plate-fin structure that has the millimeter-level function cell. This paper presents a thermo-mechanical finite element analysis for determining the deformation and residual stress of multi-layers stainless steel AISI 304 plate-fin structure, which are counter-flow and brazed with amorphous nickel-base filler metal BNi-2, based on the actual brazing process. The feature of deformation and residual stresses distribution are reported and the effect of 3 factors including the number of layers, brazing temperature, clamping pressure loads on the residual stresses and the distortion are investigated respectively.Copyright

3-D Finite Element Analysis of the Effect of Welding Residual Stress on Hydrogen Diffusion in Hydrogen Contained Environment

The hydrogen distribution of 16MnR steel weldment in hydrogen contained environment was calculated using the finite element method (FEM). The effect of welding residual stress on hydrogen diffusion has been discussed using a 3-D sequential coupling finite element analysis procedure complied by Abaqus code. The hydrogen diffusion coefficient in weld metal, the heat affected zone (HAZ), and the base metal of the 16MnR steel weldment were measured using the electrochemical permeation technique. The hydrogen diffusion without the effect of stress was also calculated and compared. Owing to the existence of welding residual stress, the hydrogen concentration was obviously increased and the hydrogen would diffuse and accumulate in the higher stress region.

Microstructures and high-temperature mechanical properties in 9Cr–0.5Mo–1.8W–VNb steel after aging at 650°C

A series of experiments, including post-aged tensile tests, charpy impact tests, Vickers hardness test, scanning electron microscopy (SEM) examinations and transmission electron microscopy (TEM) observations, were carried out to investigate the microstructure evolution and high-temperature mechanical properties of P92 steel. Experimental results show that martensitic lath structure gradually recovers during long-term aging; meanwhile, the content and size of spheroidal M23C6 together with Laves phase distributed mainly along prior austenite grain boundaries and subgrain boundaries increase with extending the aging time, but MX in grain interior seems to be stable. The strength parameters (σys and σult), the ductile parameters (δ and Φf) and high-temperature impact absorbed energy all show an initially slight increase followed by a decrease with the increase of the aging time up to 500 h. After aging for 2000 h at 650°C, this degradation behaviour becomes stable, although the Vickers hardness is not strongly affected by the aging time. Based on the microstructural observations and high-temperature mechanical properties, the strengthening mechanism of P92 steel was discussed.

Prediction of Residual Stress Distributions in Welded Sections of P92 Pipes with Small Diameter and Thick Wall based on 3D Finite Element Simulation

Abstract This study used ABAQUS finite element (FE) software to investigate the residual stress distributions of P92 welded pipes in both the as-weld and post weld heat treated (PWHT) condition. Sequential coupling quasi-static thermo-mechanical in conjunction with moving double ellipsoidal heat source and an element add/remove technique to simulate deposition of new weld material, are combined in the 3D FE analysis. To validate the simulation results, the residual stresses in axial direction at the surface of pipe were measured by X-ray diffraction technique and compared with the results of FE analysis. Detailed characteristic distributions of the residual stresses are discussed. Results show that the FE model can predict the residual stress distributions satisfactorily. Highest residual stresses on the outer surface are found in the last weld bead to be deposited. And the highest tensile residual stress for the full welded section take place in heat affected zone (HAZ) near the middle thickness. Larger residual sstress can be found around the welding start point along the pipe circumference. Comparison of heat treated specimen and untreated specimen illustrates that PWHT has a strong effect on the residual stress field.

Carburisation layer evolution of Fe–Cr–Ni alloy in furnace after long term service: experimental study and numerical prediction

Abstract Owing to high temperature comprehensive properties, Fe–Cr–Ni alloys are designed to operate in corrosive gaseous environments of ethylene pyrolysis furnace. However, most premature failed tubes were caused by carburisation. In the present study, based on the Fick’s second law and equilibrium constant method, study on the carburised layer evolution of HP40Nb and KHR45A alloys by pack carburising experimental investigation and numerical simulation by MATLAB software were carried out. The results show that the experimental and simulated data agree with each other acceptably. The carburising layer rate of KHR45A alloy is much smaller than that of HP40Nb alloy due to higher contents of Cr and Ni element in the former. With increasing operating temperature ranging from 1000 to 1100°C, the maximum service lives of the two alloys sharply decrease.

Thermal–mechanical fatigue behaviour of P92 T-piece and Y-piece pipe

This paper presents a study on thermal–mechanical fatigue (TMF) behavior of P92 T-piece and Y-piece pipe at the most critical working fluctuations. Pressure and temperature in isothermal, in-phase (IP) and out-of-phase (OP) loading conditions were taken into account. Cyclic plasticity model considering the effect of temperature was used, in which both kinematic hardening variable and isotropic hardening variable are included. All the parameters used in the simulation were obtained from low cycle fatigue (LCF) tests at different temperatures. These parameters have been validated through the comparison of experimental data with the simulated data. Then, finite-element models (FEM) of P92 T-piece and Y-piece pipe were developed to investigate the location of the most critical region at typical thermal-mechanical loading. Simulated results reveal that the most dangerous position occurs at the region where the inner surface of horizontal pipe and branch pipe crossed for both T-piece and Y-piece pipe which is irrelevant to the types of loading. IP loading is the most serious working condition for both T-piece and Y-piece pipe. Comparing with T-piece pipe, Y-piece pipe at IP loading is the most dangerous condition.

Failure Analysis for the Welded Elbow at the Bottom of the Rectifying Tower in the Alcohol Evaporation System

Cracking was found on the welded elbow at the bottom of rectifying tower in an alcohol evaporation system. In order to determine the cause of failure, a detailed analysis was conducted. The analysis included macroscopic observation for the failed tube and optical microscopy for the morphology of cracks. The characterization of fracture was analyzed by scanning electron microscopy, and the components subjected to the cracks were analyzed using energy-dispersive x-ray spectroscopy. Results revealed that the welded elbow had suffered damage from external chloride stress corrosion cracking (ECSCC). The environmental factor responsible for ECSCC is the chloride present in the dampish insulation. The stress factor is the result of the welding residual stress induced in the material which was used to fabricate the elbow.

Damage analysis and life prediction of a main steam pipeline at elevated temperature based on creep damage mechanics

Main steam pipelines are important components of power plants and chemical plants, which operated at elevated temperature and high pressure for the long term. Creep is a potential mechanism of failure of these pipelines. In this paper, the modified Karchanov-Rabotnov creep damage constitutive equation has been incorporated into finite element program ABAQUS through its user subroutine to predict the creep damage and service life of a serviced steam pipeline made of 10CrMo910 heat resistance steel. Creep tests and short-term tensile tests at serviced temperature of 540°C were carried out to get the material constants in creep damage constitutive equation, which are necessary in the mentioned creep damage and life prediction. Based on these, the analysis on stress and damage of a main steam pipeline serviced for 150,000 hrs was carried out. Stress and damage distribution and maximum damage location of the pipeline were obtained. The damage distribution and maximum damage location of the pipelines were obtained. Furthermore, the local creep damage analysis of a T-type joint serviced for 150,000 hrs was also carried out because T-type joint used in the main steam pipeline is one of weakness in the piping system. According to the results obtained above, the life evaluation of the pipeline and the T-type joint were performed.

Study of Parameter Effects on Residual Stresses and Thermal Deformation of Brazed Plate-Fin Structure Using Finite Element Method

The brazed plate-fin structure is the key component of a compact plate-fin heat exchanger. The residual stresses and thermal deformation induced by vacuum brazing may bring negative effects on the quality and the life of the plate-fin structure. Thus, it is important to optimize the brazing parameters in order to minimize such effects. This paper presents a three-dimensional finite element analysis for determining the residual stresses and thermal deformation of a three layered stainless steel plate-fin structure fabricated by nickel-based brazing. The features of residual stresses and thermal deformation distribution are discussed. The effects of three major brazing parameters including brazing temperature, clamping pressure load, and filler metal on the residual stresses and thermal deformation are investigated, respectively.