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This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.

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]

Benefited by its high efficiency and low cost, the narrow gap welding has been widely used in thick wall pressure equipment. Considering the fact that defects in welded joints inevitable, the safety assessments for welding equipment with residual stress are crucial. However, for the thick-wall equipment using narrow-gap welding, the current safety assessment standards specifying the residual stress distribution are not detailed or missing. In this paper, the through-wall residual stress of thick wall girth welds with narrow gap welding is studied. The stress components (bending stress, membrane stress and self-equilibrating stress) at the evaluation point are obtained by stress decomposition. The effects of the heat input, the wall thickness, the radius thickness ratio and the number of welding passes on residual stress are considered, respectively. The results show that the heat input only affects the distribution of bending stress and membrane stress. The axial and hoop bending stresses decrease with the increase of the wall thickness, and the hoop membrane stress is about 0.75 times material yield strength. With the increase of radius thickness ratio, the bending stress decreases while the hoop membrane stress increases. The stress distribution is fluctuating when the number of welding layers is small, which be expressed by trigonometric function. The distribution model of welding residual stress through the wall thickness is proposed. The stress distribution obtained by the proposed prediction model is in good agreement with the finite element calculation results. • >The universal model of residual stress and stress components for girth weld with thick wall was proposed. • The stress components (bending stress, membrane stress and self-equilibrating stress) of the evaluation point are also obtained. • The effects of heat input, wall thickness, radius thickness ratio and number of welding passes on residual stress are considered, respectively. • Heat input only affect the amplitude of bending stress and hoop membrane stress. • The stress on inner surface using narrow gap welding for thick walls is compressive stress. [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]

• The corrosion on the sealing surface of the valve body was related to the galvanic corrosion in the spent acid. • Intergranular corrosion along the interface of the weld deposit for the gate and seat was derived from carbides. • The formation of carbides was induced by the C element diffusion from alloy deposits during the spray weld. The different types of corrosion behavior occurred on a 13Cr gate valve using weld deposited gate and seat after about sixteen months of service in an oilfield in China, resulting in the leakage failure. In this study, the corrosion causes were investigated through visual inspection, mechanical performance testing, scanning electron microscopy, energy dispersive spectrometer and electrochemical analysis. The results demonstrated that the corrosion on the sealing surface of the valve body was related to the galvanic corrosion between the 304 SS ring gasket and 13Cr SS ring groove, which presented a significant potential difference in the spent acid environment. In addition, due to the C element diffusion from deposits during the spray weld on the surface of the gate and seat, a large amount of Cr enrich carbides were formed at the prior austenite grain boundaries in the 13Cr SS matrix side, which further induced the intergranular corrosion and cracking along the interface in service. [ABSTRACT FROM AUTHOR]

In this study, the weld residual stresses (RS) in a 25 mm thick ferrite steel plate with newly developed low-temperature transformation (LTT) welding wire were investigated by finite element method and neutron diffraction (ND) measurement. A thermo-elastic–plastic finite element model coupled with solid-state phase transformation (SSPT) was developed to investigate the distribution and formation mechanism of RS, which has been verified by ND measurement. The results demonstrate that the developed LTT alloy can significantly reduce the RS and even generate compressive RS in the weld zone, due to the interrupted cooling shrinkage caused by the LTT. The higher inter-pass temperatures related to the microstructure evolution result in an increased region of compressive stress within the weldment. Moreover, the longitudinal RS in the weld zone gradually changes to tension as the initial temperature of martensitic transformation increases. Notably, the relaxation effect of transformation-induced plasticity on RS and its influence on model accuracy were discussed. [ABSTRACT FROM AUTHOR]

In this study, the evolution of microstructure and its correlation with hardness and pitting corrosion resistance in duplex stainless steel (DSS) welded joints were investigated. The results showed that the precipitation of chromium nitride, refined grain size and large residual deformations contributed to the increase of microhardness in the heat affected zone (HAZ) and weld metal (WM). Poor pitting corrosion resistance was found in the HAZ, especially in the high temperature heat affected zone (HT-HAZ). The chromium nitride precipitates and secondary austenite were the main pitting nucleation sites. • The evolution of microstructure in DSS welded joints was analyzed. • The microhardness and its correlation with microstructure was discussed. • The pitting corrosion resistance of different welded zones was determined. • The HT-HAZ had the worst pitting corrosion resistance. • The relationship between microstructure and pitting corrosion was unraveled. [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]

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]

Highlights: [•] Stress relaxation by cutting is studied by neutron diffraction and simulation. [•] It is correlated to the cutting length exponentially based on St. Venant’s principle. [•] The critical length to avoid relaxation is proposed as 0.3 of the initial length. [ABSTRACT FROM AUTHOR]

Abstract: This paper presented a vacuum brazing technology for 304 stainless steel plate-fin structures with BNi2 filler metal. The effect of brazing temperature on tensile strength and microstructure has been investigated. The tensile strength is increased along with the increasing of brazing temperature. The microstructure is very complex and some Boride compounds are generated in the brazed joint. Full solid solution can be generated in the middle zone of joint when the brazing temperature is increased to 1100°C. The brittle phases always exist in the fillet no matter how the brazing temperature changes, but the microstructure in fillet becomes more uniform and the tensile strength is increased with the brazing temperature increasing. In total, the brittle Boride compounds are decreased with the brazing temperature increase. Brazing with a filler metal thickness 105μm and 25min holding time, 1100°C is the best suitable brazing temperature and a tensile strength of 82.1MPa has been achieved for 304 stainless steel plate-fin structure. [Copyright &y& Elsevier]

Abstract: In this study, a geometry optimization of welding joint between tower and bottom flange in a wind turbine is performed based on residual stress considerations. A sequentially coupling finite element analysis (FEA) program is developed to simulate the welding temperature and residual stress. Using this FEA program, four FE models with different bevel are developed to calculate their residual stresses, which are compared to optimize the weld geometry. The results show that complex residual stresses are generated and concentrated in the fillet weld. Using K type bevel with internal concave fillet and outside convex fillet can obtain the minimal residual stress, which provides a reference the fabrication of wind turbines. [Copyright &y& Elsevier]

Ultra-thick duplex stainless steel welding plates are widely used in various industries. However, one of the significant concerns is the inhomogeneous microstructure and mechanical properties along the thickness, which reduces welding efficiency and degrade service performance. In this study, a 55 mm thick duplex stainless steel welding joint with an X-type weld groove was prepared to study the variation of microstructure and mechanical properties along the through-thickness direction by both the miniature tensile specimen and cross-weld tensile specimen. The correlation between the microstructure and mechanical property was also studied. The results showed that the weld metal was characterized by abundant columnar grains with decreasing austenite content from surface to mid-thickness. Besides, the total fraction of low angle grain boundaries increased more than one-fold, while the total fraction of high angle grain boundaries decreased from 48.03% to 4.52% with increasing depth to the mid-thickness. Furthermore, substantial substructured grains and recrystallized grains were dominated in the weld metal and base metal. Along the thickness direction, the mechanical strength almost decreased and the elongation of welding joint increased with the increasing distance from the surface. Microhardness had a similar trend to that of strength, which all can be attributed to the variation of austenite content and grain boundary character distribution. Along the transverse direction, weld metal had the highest strength of 597.67 MPa, followed by the heat-affected zone of 549.42 MPa and base metal of 510.20 MPa, while the trend of elongation was opposite to that of strength. The microhardness distribution was not consistent with that of strength and had a maximum at the heat-affected zone. [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]

This paper presents a study of the residual stress in the welding connection between hydrogen nozzle and spherical head in a hydrofining reactor. A sequential coupling finite element program is developed to analyze the residual stress in nozzle-to-sphere connection. The results show that large residual stresses are generated in the weld and weld/parent interface during the welding of hydrogen nozzle. Large axial stress is generated on the internal surface of hydrogen nozzle due to the angular deformation, which has a great effect on hydrogen induced cracking (HIC) and stress corrosion cracking (SCC). Based on the residual stress distribution character, a new connection structure between hydrogen nozzle and head is developed. A stressless flanging is proposed to insert into the nozzle to isolate the residual stresses, which can be useful to prevent HIC and SCC. To cover all the residual stresses effectively, the arc length of flanging should be not less than 80 mm. [ABSTRACT FROM AUTHOR]

A numerical and experimental study of welding temperature distribution and residual stresses in thick welded plates of SA738Gr.B was conducted. Within the framework of numerical investigations, the temperature field of SA738 thick plate welding was simulated and analysed by using 2-D modelling technology. The temperature field was checked by using the thermal cycle curve with the aim of increasing the computational accuracy and efficiency, and the temperature field was verified by using the thermal cycle curve and heat affected zone. The welding stress field was analysed based on the temperature field, and the indentation test method was used to verify the stress field, and the error was controlled to within 12.5%. With the help of a welding model established for SA738Gr.B thick-plate welding the sequence was simulated. Seen from welding sequence 1 to welding sequence 3, transverse stress S11 changed significantly, decreasing by 14% and 17% respectively, adjusting the welding sequence can reduce welding residual stresses. [ABSTRACT FROM AUTHOR]