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The cruciform welded joint is a weak position of filter press to cause fatigue failure under cyclic conditions. In this study, cavitation jet peening (CJP) treatment is proposed to improve the fatigue life of SAF2205 cruciform welded joints. The effects of different CJP treatment positions on the residual stress, microstructure, and microhardness were studied. The results show that different CJP treatment positions have different on residual stresses and fatigue life. The order of the residual stress in fracture position from large to small is the fully treated specimen, untreated specimen, one‐sided treated specimen, and diagonal treated specimen, which is exactly opposite to the order of fatigue life from large to small. After the diagonal CJP treatment, the fatigue life is increased by up to 242.19%, and the residual stress at the weld toe is reduced by more than 80%. A strengthening layer with thicknesses of about 400 μm is formed. [ABSTRACT FROM AUTHOR]

Various types of solid-state phase transformation (SSPT) occur during the SA508 steel welding process, especially for multi-pass welding. The multiple thermal cycles lead to a more complex microstructure distribution and significantly influence the residual stress distribution. Therefore, to better control the microstructure and residual stress, it is necessary to optimize the process parameters which are closely related to the welding thermal cycles. This study established a thermo-mechanical-metallurgical multi-field coupling model and then validated it using X-ray and neutron diffraction residual stress measurement tests. Furthermore, the influence of welding heat input and preheating temperature on the formation of phase constituents and the ultimate residual stress field were analyzed in detail, concomitantly with a comprehensive discussion on their underlying mechanisms. The results showed that the increase of heat input expanded the domain occupied by the bainite phase, accompanied by the increase of compressive stress region. Moreover, the rise of preheating temperature promoted the bainite phase transformation, thus decreasing the longitudinal compressive stress and the stress gradient. The variation induced by welding parameters was closely related to the welding cooling rates. To obtain a full bainite and low residual stress condition of welded joint, it becomes imperative to exercise control over cooling rates, maintaining them at approximately 1.0 °C/s. • Increase of heat input expands the area of bainite phase and compressive stress. • Increasing preheating temperature magnifies transverse tensile stress. • As Cooling rate increases, bainite content decreases and martensite content increases. • To get welded joints free of martensite, the cooling rate should be below 1 °C/s. [ABSTRACT FROM AUTHOR]

The measurement of welding residual stress (WRS) is necessary to formulate the stress control strategies, in order to ensure the reliability of engineering structures during their service life. The instrumented indentation technique can detect surface residual stress nondestructively with an acceptable accuracy, making it a desirable option for in-situ applications. However, it is difficult to meet the requirement for stress-free samples, particularly in the case of welded joints with non-uniform mechanical properties. In this work, the impact of stress-free indentation curves on determining WRS is furtherly studied based on the previously proposed indentation energy difference method. The WRS in a mismatched welded plate is measured using single reference method and distributed reference method, respectively. The study suggests that using the single reference method can lead to significant errors in determining the sign and magnitude of WRS in the weld zone. A prediction model combining the continuous spherical indentation (CSI) method and Back Propagation (BP) neural network is proposed to obtain the stress-free indentation curves of local positions nondestructively. And the CSI-BP method is verified through reverse finite element analysis and experiments. • The WRS were measured by indentation energy difference method. • A continuous spherical indentation -BP neural network prediction model was established to estimate the stress-free indentation curves for unknown materials. • A single reference method and two distributed reference methods were compared in the WRS measurement. [ABSTRACT FROM AUTHOR]

Abstract This paper studied the distribution of weld residual stress in a spiral welded pipeline by finite element method (FEM) and experimental measurements, and the effect of helix angle on residual stress has also been investigated. Both the FEM and experiment results show that the residual stresses in HAZ are larger than those in weld. The error between FEM and experiment results is within 14%, proving that our FEM is correct. There is a peak-shape stress distribution through the weld thickness and the residual stresses in the inner surface are larger than those in the outer surface. Different helix angle has a different equivalent weld length along the hoop and axial directions, which generates different hoop and axial plastic strains, leading to different hoop and axial residual stresses. As the increase of the helix angle, both the radial and hoop residual stresses decrease, while the axial residual stresses increase. As the helix angle increases from 20° to 50°, the hoop stresses in HAZ decrease by 65%, while the axial stresses increase by 120%. The residual stresses are influenced by the pipe dimension (pipe diameter, thickness, weld profile), welding technology (heat input, welding speed) and material grade. When the helix angle is between 40° and 45°, both the hoop and axial residual stresses are reduced to the minimum. The most suitable helix angle is suggested to design around 40°–45°. Graphical abstract Image 1 Highlights • Effect of helix angle on residual stress for oil pipelines is investigated. • HAZ is a weakest zone for X70 steel spiral pipes. • The residual stresses are easily influenced by the pipe dimension and welding technology. • The most suitable helix angle is suggested to design around 40°–45°. [ABSTRACT FROM AUTHOR]

This paper investigated the fatigue life of a dissimilar welded joint between SAF2205 duplex stainless steel and 304 austenite stainless steel. A nonlinear fatigue damage model based on continuum damage mechanics (CDM) is used to estimate the fatigue life, and the effect of the residual stress is studied. The results show that large residual stresses were generated in the dissimilar welded joint and agree well with the indentation measurement results. The fatigue test specimens were cut from the welded sample, and the residual stress relaxed significantly after longitudinal cutting, especially for longitudinal residual stress. Considering the transverse residual stress, the estimated fatigue life is more consistent with the experiment. The residual stress mainly affects the mean stress, rather than the stress amplitude. As the longitudinal residual stress relaxed significantly after cutting, the effect of welding residual stress on fatigue life can be seriously overestimated. The width of fatigue test specimen should be at least 30% of the as-weld sample for fatigue design in consideration of the residual stress relaxation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Residual stress reduction in penetration weld nozzle by overlay welding was studied. [•] The overlay weld can decrease the residual stress in the weld root. [•] Long overlay welding is proposed in the actual welding. [•] Overlay weld to decrease residual stress is more suitable for thin nozzle. [ABSTRACT FROM AUTHOR]

In this study, a wavelength-dependent neutron diffraction method used to measure the residual stress in thick duplex stainless steel (DSS) welded plate was proposed, which was validated by contour method. By choosing appropriate wavelength, the penetration capability of neutron was improved. The neutron with appropriate wavelengths was then applied to investigate the through-thickness volume fraction, macroscopic and phase-specific residual stress in a 55 mm thick DSS welded plate. The results showed that a wavelength at 2.395 Å had more superiorities than the conventionally-used wavelength at 1.593 Å in the measurement of longitudinal and transverse stresses of a thick DSS plate. In general, high tensile stresses were generated in austenite while high compressive stresses were found in ferrite. For elastic mismatch residual stresses, their maximum values in austenite and minimum values in ferrite were located near the mid-thickness region. Reasons for the formation and characteristics of the phase-specific stresses were also discussed. Besides, large tensile macroscopic stresses were found near the surface whilst significant compressive stresses were found to generate in the mid-thickness of weld metal. • A wavelength-dependent neutron diffraction method for measuring stress is developed. • Altering wavelength enhances the penetrability of neutron in duplex stainless steel. • Macroscopic, phase-specific residual stresses and volume fraction are obtained. • High tensile stress is found in austenite while compressive one is found in ferrite. [ABSTRACT FROM AUTHOR]

Abstract: Bonded compliant seal is a new sealing design for planar solid oxide fuel cell. During brazing, large residual stresses are generated which have a great effect on failure of the brazing connection. Therefore, how to decrease the residual stresses is a critical issue for structure integrity. This paper presents a study on decreasing residual stresses by using short-time creep relaxation effect. A sequential-coupled calculation model is developed based on finite element method. The brazing temperature field is firstly obtained by simulating the convection and radiation heating, and then the residual stress is calculated by a thermal-elasto-plastic-creep model. The calculated results are verified by neutron diffraction measurements. During cooling, a short holding time at 600 °C is designed to relax the residual stress by creep effect. The results show that this effect has a remarkable impact on decreasing the residual stress. The stresses in cell, Ag–CuO and foil have been reduced by about 26.9%, 13.6% and 22.1%, respectively, as the holding time increases up to 40 h. When the holding time exceeds 40 h, the residual stresses remain almost unchanged. It is thus suggested that the holding time should be reasonably determined to allow sufficient stress relaxation. [Copyright &y& Elsevier]

Highlights: [•] Effect of multiple repairs on residual stress, microstructure and hardness for a clad plate has been studied. [•] A diffusion layer with martensite is generated around weld-base metal interface. [•] Along the weld–clad metal interface, short ferrite is generated in the fusion zone. [•] As the repair times increase, the content of short ferrite is increased. [•] It is proposed that the stainless steel clad plate cannot be repaired more than 2 times. [ABSTRACT FROM AUTHOR]

Abstract: 316L type stainless steel is widely used in chemical industries due to its excellent resistance to corrosion. But the welding residual stresses have a great effect on stress corrosion cracking. This paper used finite element method to study the effect of heat sink on residual stress. The effects of contact length and the average heat transfer coefficient on residual stress have been investigated. It is found that the heat sink technology can decrease the residual stress greatly. Compared to the model without heat sink, 20% of the peak longitudinal stress has been reduced. The heat sink decreases the dwell time during cooling from 850 °C to 400 °C, which is helpful to decrease the risk of sensitization of 316L stainless steel. With the contact length increase, the transverse stress is decreased. Further increase of the contact length has no positive effect on reducing the longitudinal stress. With the average heat transfer coefficient increase, the transverse stress is decreased greatly while the longitudinal stress decreases slightly, and some tensile residual stresses have been changed to compressive in some zone. [Copyright &y& Elsevier]

Abstract: The lattice truss sandwich structures are considered as the most promising advanced lightweight materials used in modern industries and aircrafts. Most sandwich panel structures are fractured at brazed joints named node failure during static and dynamic testing, which is mainly influenced by brazing residual stresses. Finite element method (FEM) was used to study the brazing residual stresses in a stainless steel X-type lattice truss sandwich structure. And the nanoindentation experiment is used to verify the validity of FEM. The effects of braze processing parameters including applied load, face sheet thickness, truss thickness and truss length on residual stresses have been investigated. It is shown than the residual stresses are concentrated on the brazed joint, which has a significant effect on node failure. As the applied load increases, the residual stresses decrease first and then remain unchanged, and the optimal applied load is around 1MPa. As the face sheet thickness increasing, the residual stresses are increased. Too thin face sheet can cause large residual stresses on the top surface of face sheet. With truss thickness and truss length increase, the residual stresses are decreased first and then increased. The optimized face sheet, truss thickness and truss length are found to be 2mm, 1mm and 26mm. [Copyright &y& Elsevier]

Abstract: Clad plates are widely used in the construction of corrosion resistant equipment. During the repair of clad plates, residual stresses are generated and influence the structure integrity. This paper uses the finite element method (FEM) to predict the residual stresses in a repair weld of a stainless steel clad plate. The effect of repair width on residual stresses has also been investigated by numerical simulation. Due to the material mismatching between clad metal and base metal, a discontinuous stress distribution has been generated across the interface between clad and base metals. The peak residual stress occurs in the heat affected zone (HAZ) of the base metal, because the yield strength of the base metal is larger than that of the clad metal. With an increase in repair width, the residual stresses are decreased. When the repair width is increased to 24 mm, the residual stresses in the weld have been decreased greatly and the peak residual stresses have been reduced to less than the yield strength. Therefore, the recommended repair width should not be less than 24 mm, which provides a reference for optimizing repair welding technology for this stainless steel clad pate. [ABSTRACT FROM AUTHOR]

Abstract: This paper uses finite element method (FEM) to predict the residual stress and plastic strain in the brazed joint of sealing foil-to-window frame in bonded compliant seal (BCS) design in a planar solid oxide fuel cell (PSOFC). The effects of window frame material type, sealing foil thickness, filler metal thickness and window frame thickness on residual stress and plastic strain are discussed. Large residual stress is generated in the joint, and the stress and strain are concentrated around the fillet. It is proved that the BCS design can mitigate and trap some residual stress by plastic deformation within the sealing foil. The residual stress and the ability of trapping stress of sealing foil are affected by window frame material and structure thickness. Based on the comprehensive considerations of the impact of residual stress and plastic strain, Alloy 625 as a window frame material is found to be better than Haynes 214, Hastelloy X and SUS 316L. The optimum thickness of sealing foil and filler metal BNi2 are found to be 150μm and 75μm, respectively. The residual stress and plastic strain are increased with the increase of window frame thickness. [Copyright &y& Elsevier]

Abstract: This paper presented a finite element (FE) modeling of the temperature field and residual stress of the vacuum brazing for a counterflow stainless steel plate-fin structure. A sequential coupling calculation procedure was developed by using commercial program ABAQUS. The brazing temperature field and brazed residual stress distribution regularities have been successfully achieved. The results show that the brazed joint suffers high tensile residual stress and the fillets become the weakest zone. In the plate, the longitudinal stress is large and would have to play the main role on strength while the transverse and shear stress are very small. The residual stresses in fin are complex and their distribution in the parallel fin is much different from that of vertical fin. These results provide the theoretical knowledge for the optimization of process and the control of brazed residual stresses for stainless steel plate-fin structure. [Copyright &y& Elsevier]

Abstract: In this study, design optimization of brazed residual stress in stainless steel plate–fin structure was investigated theoretically. A sequentially coupling finite element analysis (FEA) program was developed to simulate the brazed residual stress distribution, with an emphasis on the material selection for plate–fin metal and filler metal. The properties of three different stainless steel for plate–fin and three different materials for filler metal were incorporated into nine different FEA models. The results show that large residual stresses are generated in brazed joint due to the yield strength mismatching between base metal and filler metal. It is found that the best models are 304 or 347 stainless steel for base metal and BNi4 for filler metal. The residual stresses in the brazed joint are mainly affected by yield strength mismatching. But the yield strength mismatching has little effect on the residual stresses for the base metal. [Copyright &y& Elsevier]

Abstract: Stainless-steel plate–fin heat exchanger (PFHE) has been used as a high-temperature recuperator in microturbine for its excellent qualities in compact structure, high-temperature and pressure resistance. Plate–fin structure, as the core of PFHE, is fabricated by vacuum brazing. The main component fins and the parting sheets are joined by fusion of a brazing alloy cladded to the surface of parting sheets. Owing to the material mismatching between the filler metal and the base metal, residual stresses can arise and decrease the structure strength greatly. The recuperator serves at high temperature and the creep would happen. The thickness of the filler metal plays an important role in the joint strength. Hence this paper presented a finite element (FE) analysis of the brazed residual stresses and creep for a counterflow stainless-steel plate–fin structure. The effect of the filler metal thickness on residual stress and creep was investigated, which provides a reference for strength design. [Copyright &y& Elsevier]

The welding residual stresses (WRS) in a cracked head-cylinder joint of a large rectifying tower were studied by finite element method (FEM) and experimental study. The effects of welding layer sequence, cover welding direction and weld reinforcement have been fully studied. The results showed that the stress concentration and plastic strain accumulation caused by unreasonable welding process and structural discontinuity are the main reasons of cracking. Furthermore, the order of welding layers has a significant influence on the distribution of axial stress: the inside and outside alternating welding process is superior to non-alternating welding process. The direction of cover welding markedly influences the hoop stress: the location of maximum stress is related to the welding start-end position. Besides, the removal of weld reinforcement after welding helps to release sub-surface tensile stress and solve the stress concentration problem. • Recommendations regarding welding procedure in large pressure vessels were proposed by FEM and experiment study. • High tensile WRS and large PEEQ at the weld toe directly contributed to the cracking. • The axial stresses can be effectively reduced by alternating welding. • The position of peak stress is related to the cover welding direction. • Removing the weld reinforcement helps to further control WRS. [ABSTRACT FROM AUTHOR]

Strip clad welding is a key manufacturing process of large pressure vessel and repair welding was usually used to repair the defects of strip welded structure, which generates very complex residual stresses and have a great effect on structure integrity. Therefore, in this paper, the residual stress distributions and their evolutions during strip clad welding, post-welding heat treatment (PWHT) and repair welding of a large pressure vessel were investigated. A new strip cladding heat source model considering the magnetic pinch effect was proposed. The predicted welding pool size by the proposed heat source model has a good agreement with the experiment results. And the predicted residual stresses in every stage agree very well with those by indention measurement method. The residual stresses after strip clad welding along the through-thickness direction present tension-compression-tension distribution. The PWHT has little eliminating effect on tensile residual stress on cladding layer, and even worsens the discontinuity stress distributions across the interfaces between the clad metal and base metal. After repair welding, local detrimental tensile residual stresses were generated in the repaired zone. A new heat treatment method based on distinct temperature regulation is proposed, which has a good ability to eliminate the tensile stress of the cladding layer to compressive stress and has a good application in engineering. Image 1 • An improved moving heat source model for strip cladding was proposed. • The simulated temperature and stress field and agree with the experiment very well. • PWHT cannot completely eliminate the cladding residual stress. • The residual stress on bottom surface was affected by the initial stress model. • A new PWHT method based on distinct temperature regulation was proposed. [ABSTRACT FROM AUTHOR]

• The effect of cold bending on the properties of 316L stainless steel welded joint was studied. • As the bending angle increases, tensile transverse stress on outer surface increases. • Microstructure has not been changed significantly after cold bending. • The hardness value increases as the bending angle increases. The cold bending process is often applied to the welded structures during manufacturing, but how it influences the properties of the welded joint is still poorly understood. Therefore, in this paper, four samples were cut from the as-welded plate and bent to 0° (i.e. without bending), 30°, 60° and 90° to study the effects of cold bending on welding residual stress, microstructure and mechanical properties of Type 316L stainless steel welded joint. The results showed that large tensile transverse residual stresses were generated at about 25 mm from the welding centreline (WCL) on the outer surface. When the welded joint was bent to 90°, no shear bands or deformation induced α' martensite was formed due to the high stability of the austenitic phase, indicating that the microstructure has not been changed significantly. Although the hardness values in the welded joint were all increased with the increasing bending angle, the hardness variation around the mid-thickness was not as significant as the other regions. [ABSTRACT FROM AUTHOR]

• The overload effect on fatigue crack of 2205 duplex stainless steel is researched. • The residual stress by overload is researched by neutron diffraction and FEM. • The fracture is analyzed by the scanning electron microscope. • The prolonged fatigue life is related with the overload ratio, position and load ratio. • The retardation region is related with the overload ratio, position and load ratio. The effect of tensile overload on fatigue crack behaviors of 2205 duplex stainless steel has been studied by experimental and finite element methods (FEM). The residual stresses were measured by neutron diffraction technique and simulated by FEM. The results show that the fatigue crack propagation is obviously delayed due to larger residual plastic strain caused by overload. Both the magnitude and region of compressive residual stress increase correspondingly. The retardation region caused by overload is well characterized by the peak position difference of residual stress. The retardation region is closely related with the overload ratio, overload position and load ratio. [ABSTRACT FROM AUTHOR]

Shot peening is one of the most famous mechanical surface treatments to improve fatigue performance of metallic components, which is attributed to high amplitude compressive residual stresses. A numerical approach is developed to analyze the residual stresses in 301LN metastable austenitic stainless steel by shot peening. The material behavior is described by a proposed constitutive model in which strain-induced martensitic transformation, isotropic hardening and kinematic hardening effects are taken into account properly. Both single shot and random multiple shots peening were simulated and analyzed. A numerical method is presented with the Python programming language to make the multiple shots follow a random probability distribution. Results demonstrate that the simulated equivalent plastic strains and martensitic volume fractions agree well with the experimental ones, which verify the validity of the constitutive model. Besides, the numerical method is effective at achieving a realistic surface coverage. The maximum compressive residual stress by the Johnson–Cook model is 12% higher than that of the proposed model. Additionally, each hardening effect has an effect on the simulated residual stress. The developed numerical approach can provide a feasible simulation of the shot-peening process and makes an accurate prediction of the residual stress field in 301LN steel. [ABSTRACT FROM AUTHOR]

The support platform is an essential component of a hydrogenation reactor, providing stable support for internal components and ensuring efficient reactions. However, the manufacturing method of overlay welding and complex structure of support platform unavoidably generates welding residual stresses (WRS) and stress concentration, posing a threat to operational reliability. In this paper, the WRS distribution and cracking causes of the support platform of hydrogenation reactor was studied by the finite element method (FEM) combined with experimental research. Four manufacturing processes for the support platform were compared in terms of their residual stresses, and the influence of welding heat input and fillet size on the WRS was discussed. The results indicate that the abrupt increase in residual stresses at the fillet region following the machining of the base layer has enhanced the likelihood of crack occurrence. The cumulative effect of stress concentration resulting from improper welding processes and structural discontinuities, along with the tensile stress during normal operating conditions, renders the surface layers susceptible to cracking during service. The manufacturing process significantly influences the distribution of residual stresses. To obtain a reliable and crack-resistant large-sized hydrogenation reactor support platform, a welding procedure with a certain machining allowance at the support platform location prior to overlay welding should be adopted. The fillet size has a notable effect on the residual stresses at the fillet region of transition layer. Recommended fillet sizes are 15 mm radius for the base layer, 11 mm radius for the transition layer, and 8 mm radius for the surface layer. Additionally, the heat input greatly affects the hoop stresses in the transition layer, in order to avoid the occurrence of cracks, a recommended heat input of approximately 20 kJ/cm is suggested. • Residual stress distribution and crack causes of the support platform were analyzed. • Surface layer fillet is more prone to cracking. • Manufacturing with a machining allowance as the root has optimal stress distribution. • Increasing fillet size significantly reduces residual stress of transition layer. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) is the main failure mode of tube-to-tubesheet welded joints in a heat exchanger, and weld residual stress can play an important role in the development of these cracks. Local post welding heat treatment (PWHT) is a feasible method to reduce weld residual stress for tube-to-tubesheet welded joints. In this paper, the residual stress evolution and relaxation mechanisms during local PWHT were discussed in depth. The effects of PWHT temperature and hold time on residual stress were clarified. A compressive stress manufacturing method based on local PWHT was proposed. The results show that the stress concentration at the root of tube-to-tubesheet welded joints is the main reason for the SCC of heat exchangers. The residual stresses in the weld and heated affected zone (HAZ) are significantly reduced during local PWHT. The residual stress relaxation of tube-to-tubesheet welded joints can be attributed to the creep strain development and deformation during local PWHT. The extrusion of the tube and tubesheet at cooling stage results in the generation of compressive stress at the root of tube-to-tubesheet welded joints. PWHT temperature has significant effect on the residual stress in the weld and HAZ in comparison with PWHT hold time. The application of the proposed compressive stress manufacturing method realizes the fabrication of compressive stress at the root of tube-to-tubesheet welded joints, and improves the economic benefit by reducing PWHT hold time. This work will provide a good guidance to reduce the SCC risk of heat exchangers. • The stress concentration at the root of tube-to-tubesheet welded joints was found to be the main reason for SCC. • The residual stress relaxation mechanisms of tube-to-tubesheet welded joints during local PWHT were clarified. • PWHT temperature had significant effect on the residual stress in the weld and HAZ in comparison with PWHT hold time. • The proposed local PWHT method realized the fabrication of compressive stress at the root of tube-to-tubesheet welded joints. [ABSTRACT FROM AUTHOR]

Stainless steel bipolar plates are regarded as a good substitute for traditional graphite bipolar plates in proton exchange membrane fuel cells. Stamping is a first selection for the manufacture of stainless steel bipolar plates. In addition to paying more attention to the stamping channel shape, a good prediction, and an efficient evaluation of the formed residual stress and thinning of bipolar plates are necessary. In this paper, the formed stress and deformation of SS304 stainless steel BPP with a thickness of 0.1 mm was investigated by a 2D plane strain FE model. Numerical results showed that formed BPP has a large residual stress, especially in the bending zone. Residual stresses distribution along the inner surface, outer surface, and direction of thickness was non-uniform. Geometrical dimensions have a great effect on residual stress and formed thickness. With an increase of the upper die width and die depth, the peak residual stress increased, and the formed thickness became less uniform. With an increase of the curve radius, the residual stress decreased, and the formed thickness became more uniform. [ABSTRACT FROM AUTHOR]

Bipolar plates are regarded as the core of the proton exchange membrane fuel cell. In order to obtain a connected stainless steel bipolar plate with low residual stress and small deformation, the brazing process is commonly used for bipolar plate connection. In this study, a numerical model was developed to calculate the residual stress in a brazed joint. Clamp pressure, brazing gap, and solder type were investigated. The results showed that clamping pressure had little influence on residual stress and the residual stress decreased with an increase in the brazing gap, which provided a reference for controlling brazed residual stresses for stainless steel bipolar plates. [ABSTRACT FROM AUTHOR]