Stresses In Welded Joints Research Articles

Strength analysis of welded joints in support structures of heavy machinery subjected to changeable loading conditions

The durability of bearing units of large machines depends mainly on the condition of their welded joints. With this in mind, we developed numerical models of the analyzed bearing units, for which we performed FEM simulations of the stresses in welded joints in several basic load cases. In each of the respective variants the technical condition of the bearing nodes was different and it corresponded to the severity of the degradation processes. Different positions of the superstructure in relation to the undercarriage were also taken into account. The simulations used the hot-spot method dedicated to FEM analyses of complex welded structures. We discovered that the loads have a significant influence on the values and distribution of von Mises principal stresses and their axial components. Based on the carried out analyses, we identified the most unfavorable load cases that generate the highest stresses in the welded joints of the assessed nodes. We also demonstrated that the applied method effectively assesses the stresses of welded joints subjected to variable working loads.

Nondestructive evaluation of residual stresses in welded joints on the base of a combination of ultrasonic testing and speckle-interferometry

Nondestructive evaluation of residual stresses in welded joints on the base of a combination of ultrasonic testing and speckle-interferometry

Thermo-Mechanical Study of TIG Welding of Ti-6Al-4V for Residual Stresses Considering Solid State Phase Transformation

To overcome the detrimental effect of residual stress in welded joints, which affects the overall performance of the welded structure, this paper studies the magnitude and distribution of residual stress after welding and local post-weld heat treatment (PWHT). The coupled thermo-metallurgical-mechanical model for welding 6 mm thick Ti-6Al-4V (TC4) titanium alloy plates was established, the evolution of the SSPT and its effect on the residual stress were quantitatively analyzed, and a parametric analysis of local PWHT was performed. The results demonstrated that there was good agreement between the numerical results and the experimental data. Due to the cooling rate reaching 327 °C/s, the volume fraction of α、 in the fusion zone (FZ) reached 0.218 after welding and decreased by 90.83% after PWHT when the heating temperature was 700 °C. The peak value of the longitudinal residual stress can reach 686.4 MPa after welding with SSPT, which was 11.38% lower than that without SSPT, and it decreased by 65.6% after PWHT when the heating temperature was 900 °C. The research results demonstrate that SSPT has a significant effect on residual stress, and PWHT can obviously reduce the residual stress, which provides a certain reference for welding TC4 titanium alloy plates.

NUMERICAL ANALYSIS OF STRESS AND STRAIN STATE IN MEMBRANE WALLS WELD JOINTS PERFORMED BY SUBMERGED ARC WELDING

The article presents investigation on stress and strain state in weld joints of boiler membrane wall by performing numerical analysis (finite element method). The main purpose was to create 3D model which will correspond to real membrane wall geometry under consideration, which will allow to perform strength simulation of numerical models considering variable parameters depending on the temperature. The model was fragment of boiler membrane wall made of X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar welded with submerged arc method. The research included the assumption of boundary conditions such as temperature cycles, welding method, type of mounting and base materials or heat treatment cycle. Three simulations have been performed depended on base material and temperature cycle adopted. As a result of the simulations, the distribution of temperature, displacement and stress in analyzed cases were obtained. The numerical simulation in dissimilar welded joints X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar heat treated afterwards, showed that the differences in linear expansion coefficients favour the development of cracks in the welds caused by increased level of stress. In parallel materials used for boiler membrane walls are the reason for difficulties in determine the proper technology of welding, preheating temperature and post-weld heat treatment parameters. Simulations indicated that the state of stress in weld joint is dependent on type of parameters adopted, and in closest scenario to real conditions, simulation showed that post-weld heat treatment had no positive effect on the stress state caused by discrepancy in linear expansion coefficients of both base materials.

Mitigation of Porosity and Residual Stress on Carbody Aluminum Alloy Vibration Welding: A Systematic Literature Review

Fatigue resistance is influenced by porosity and residual stress in welded joints. Fatigue failure in some means of transportation is caused by the inability to withstand the load received from the car body and passengers while operating. This study uses a systematic literature review (SLR) method to identify the effect of vibration welding on porosity and residual stress. Vibration can reduce the empty cavity (porosity) and increase the density of the weld. The ultrasonic vibration spot resistance (UVSR) method with 20 kHz on AA6082 is able to reduce residual stress up to 53% and is effective for homogenization of concentrated residual stress up to 57%.

Study on Susceptibility and Mechanism of Reheat Cracking in Welded Joint of Type 347 Austenitic Stainless Steel

The reheat cracking susceptibility of welded joints has been evaluated by 900°C high-temperature constant load test and 750°C–900°C high-temperature slow strain rate tensile (SSRT) test on welded joints of TP347 steel, and the influencing factors and mechanism of reheat cracking in welded joints have been further investigated by microcosmic characterization techniques of SEM and EDS, etc. The result shows the critical fracture stress of TP347 steel welded joints at 900°C is 24 MPa, which is much lower than 80% of the high-temperature yield strength of base material, indicating that the reheat crack of the welded joint is highly sensitive at this temperature; the average reduction of area (RoA) of welded joints obtained by 750°C–900°C SSRT test at each temperature is below 20%, which means all welded joints have a reheat cracking susceptibility in this temperature range, and the reheat cracking susceptibility increases with the rising of temperature. Based on study and analysis using microcosmic methods of optical microscope, scanning electron microscope, and energy spectrum analysis, it is found that welded joints of TP347 steel have a high reheat cracking susceptibility because the high temperature accelerates the diffusion of Cr, Nb, and impurity elements to the grain boundary, and a large quantity of carbides and low-melting-point eutectics are collected and precipitated at the grain boundary to reduce the plasticity of the grain boundary. Since there is a high welding residual stress in welded joints, cavities are formed under the action of the stress at a high temperature, and the merging of cavities causes the formation of cracks which extend along the grain boundary.

Numerical investigation of residual stresses in welded joints of cylindrical shell

Welded cylinder structures such as pressure vessels and pipes for transportation have been applied in power stations, aerospace, and shipping industries. The study of weld-induced residual stress is vital in predicting the life of welded cylinder vessels. Depending upon the required diameter and length, they are welded by either circumferential welding or longitudinal welding. In the present work, a sequentially coupled thermal, structural analysis is carried out on circumferential and longitudinal butt weld joints of AH-36 cylinder components. The thermal field distribution and subsequent residual stresses during Gas Tungsten Arc Welding (GTAW) are studied. The moving heat source considered for analysis is based upon Goldak’s double ellipsoidal model. The weld-induced axial and hoop stresses are evaluated on both the outer and inner surfaces of the cylinder. The results for circumferential and longitudinal butt weld joints are compared. The magnitude of peak hoop and axial stresses in longitudinal butt weld joints are 45% and 95% higher than in circumferential butt weld joints. The developed analysis model, used to evaluate the thermal histories and residual stresses, is validated with experimental measurements.

Determining Residual Stresses in Weld Joints of DN 850 Pipes by Spot Drilling Combined with Electronic Speckle Pattern Interferometry

Residual welding stresses affect significantly the strength, durability, and performance of structures. Therefore, there is an urgent need for developing and implementing techniques and equipment that allow reliably estimating stresses in experiments. This paper considers some aspects of the joint implementation of electronic speckle pattern interferometry and the spot drilling technique to determine these characteristics under the field conditions. The results of determining the distribution of residual stresses in the weld joint areas of DN 850 pipes are given for various welding modes. The study results are of independent significance and herewith, demonstrate the efficiency of the equipment developed to solve similar problems.

Failure analysis of cracking in S30408 weld joint between cylinder and flange of pure steam sterilization pot

The sterilization pot is widely used in the production and processing of food. The cracking failure of S30408 cylinder-flange weld joint of sterilization pot was analyzed by through the analysis of the composition, macroscopic fracture morphology, metallographic morphology, residual stress, microhardness and finite element modelling. The reasons for cracking and corresponding preventive methods were put forward. The cracking in inner surface of flange is induced by the stress corrosion cracking and accelerated by fatigue. The corrosion resistance deterioration of materials and the existence of dissolved oxygen and chloride ions are the main reasons to induce cracking. The cyclic tensile stress in weld joint accelerated crack propagation in inner surface. In order to avoid crack of sterilization pot, the reduction method on welding residual stresses should be performed and the contents of chloride ion and dissolved oxygen in the medium should be strictly monitored.

ОСОБЕННОСТИ РЕМОНТА СВАРНЫХ КОНСТРУКЦИЙ БОЛЬШИХ ТОЛЩИН ИЗ ТИТАНОВОГО СПЛАВА ВТ6ч.

The technology of electron-beam welding (EBW) of structures of large thickness made of titanium alloy Ti–6Al–4V has been developed. A complex of metallographic studies of welded samples has been carried out. Tests to determine the mechanical characteristics of repair welded joints, that these joints made by EBW are equal in strength to the base material. The analysis of the level of residual stresses in various parts of the welded joint after repeated repair passes has been carried out. It was found that the subsequent vacuum annealing reduces the level of residual stresses in welded joints to 50 %. The analysis of the elemental composition showed that the elemental composition of the samples from the center of the weld to the base metal practically does not change for welding with the number of repeated passes up to 3.

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.

Структурно-фазовое состояние и остаточные напряжения в сварном соединении сплава ВТ20, полученном электронно-лучевой сваркой

Структурно-фазовое состояние и остаточные напряжения в сварном соединении сплава ВТ20, полученном электронно-лучевой сваркой

Recommendations for the measurement of residual stresses in welded joints by means of X-ray diffraction\u2014results of the WG6-RR test

Residual stresses in welded joints are often of extended interest in order to evaluate unexpected failures or distortions. Since the possibilities to calculate residual stresses in welds are still strongly limited, the measurement techniques are still of great importance. Several measurement techniques with particular possibilities and limitations are available today where especially the different diffraction methods are used mostly. The material, weld type, and the size of the components are important for the quality of the results obtained with different methods as well as the environment where the measurements have to be carried out. The paper shall give an overview of the results of a round robin test on the application of XRD on butt welded joints which has been carried out in cooperation of different experienced laboratories. The results show the high reliability of XRD measurements in welds, if the measurements are performed under well-defined boundary conditions. The experiences can be used as a recommendation about useful measurement conditions the expectable quality of the results.

Residual stress estimation in defect assessment procedures at weld toe and away locations on girth welds: Review of key parameters

The distribution of residual stresses in welded joints plays an important role within the fracture evaluation guidelines recommended in structural integrity assessment codes such as BS7910, API 579 RP-1/ASME FFS-1 and R6. The residual stress profile recommendations in these standards are based on extensive experimental results and finite element modelling (FEM) based parametric residual stress evaluations at the weld centerline and weld toe positions. The upper bound residual stresses’ profiles based on these recommendations vary significantly from one type of welding process to another for a given weld configuration with identical welding conditions. These fitness-for-service codes (FFS) depict great variability in estimating residual stress profiles during defect assessment, as BS 7910 & R6 recommends a constant profile at a distance away from welds and API 579 provides a single curve for all locations in the axial direction. Thus, conservatism is widely associated with these recommended profiles in fracture potential evaluation and assessments, leading to suboptimal recommendations. In this manuscript, a detailed review is undertaken of residual stress estimation in various FFS codes, showing vast variability among them for locations away from the weld toe on girth welds. Key distinct parameter characteristics, pipe radius to thickness ratio and heat input are detailed and found to have a significant effect on residual stress profiles in structural integrity assessment, using a stress decomposition technique. These recommendations establish an overall analysis of the interrelationship between key parameters, considering a generalized broad range of applications. A framework is proposed, based on the current review, for conducting detailed investigation by employing thermomechanical numerical modelling, coupled with measurement results (nondestructive and semi-destructive) from an experimental study, as input to machine-learning algorithms for application guidance to engineers.

Experiments and Numerical Simulations of the Annealing Temperature Influence on the Residual Stresses Level in S700MC Steel Welded Elements.

The article presents the results of research on the influence of temperature and time changes of the annealing process on the values and distribution of stresses in the simulated heat-affected zone of S700MC steel welded joints. For this purpose, tests were carried out on a thermal cycle simulator, as well as heating the prepared samples in accordance with the recorded welding thermal cycles, and then annealing at temperatures from 200 to 550 °C. The stresses values in the tested samples before and after the annealing process were measured by using X-ray diffraction (XRD). The performed tests were verified with the results of numerical analyses using the finite element method (FEM) performed in the VisualWeld (SYSWELD) environment as, on the one hand, the verification of the obtained results, and, on the other hand, the source of data for the development of a methodology for conducting analyses of heat treatment processes of S700MC steel welded structures. Also presented are three examples of numerical analyses for Gas Metal Arc (GMAW), laser and hybrid welding and then the annealing process of the obtained joints at selected temperatures. The main purpose of the work was to broaden the knowledge on the influence of annealing parameters on the values and distribution of stresses in welded joints, but also to signal the possibility of using modern software in engineering practice.

Contributions Regarding the Use of Mechanical Vibrations in Order to Improve the Properties of Steels and Welded Joints Used in Metal Constructions

The paper presents aspects regarding the influence of vibrations on the mechanical properties of welded joints, made with basic materials of Spanish and Romanian origin. In this research is presented the practical way to make the necessary assemblies for the proposed tests. The tests show that vibrations have a significant contribution to the quality of welded joints. This is explained by the appearance of several crystallization centres which makes the structure finer. By using vibrations, the atoms are rearranged in the structure, ensuring a proper de-tensioning. The stresses induced in welded metals are significantly reduced by the use of vibration during welding process. The addition materials have a significant contribution to the emergence of stresses in welded joints as well. These stresses can contribute to the appearance of microstructural constituents with significant hardness. The welding equipment and technologies used also have a significant contribution to the emergence of the remaining stresses. For example, the submerged arc welding technology (SAF) can introduce very high internal stresses. By using vibrations during the welding process, it is achieved a fine structure and a significant reduction of remaining stresses in the welded joints.

Calculation of pipeline pressure testing for the reduction of residual stress in tee joints

Oil and gas pipeline accidents most frequently occur in output places and weld joints. Increased stress in weld joints can be explained by the presence of stress concentrators and residual welding stresses. Pipeline pressure testing can reduce the value of residual welding stresses. The article considers the method of calculating coefficients of stress concentration depending on the construction, geometrical dimensions and the type of tee welding joints. The authors calculated and proved that reinforcing tee joints by means of a coupling ring increases the number of welding joints and coefficient of stress concentration. The study theoretically proves the possibility of reducing residual stresses in tee joints choosing the right mode of pipeline pressure testing and defines the limits of changes in pipeline pressure testing which ensure plastic deformation of metal in welding joints alongside the elastic deformation of the main material of the tee joint.

Ensuring industrial safety of pipelines with developed hard sections

Oil refining and petrochemicals have a wide demand for pipelines from heat resistant chromium steels. One of the main reasons for frequent failures of more stressed joints may be the presence of wide solid and brittle layers having significant areas in metal volume with maximum clusters of imperfections of metal structure and creating excessive concentration of additional residual deformations and stresses in welded joints, which are most saturated with defects inherent in welded joints. Presence of such extended sections leads to reduction of process strength of welded joints, increases tendency to formation of cold cracks and sharply limits time of laying of thick-walled welded joints of pipelines before subsequent high-temperature thermal treatment. The work carried out studies on welding pipe blanks in order to compare different methods of 5CroMo16 steel treatment during welding and determine the most efficient mode. Regularities of stressed state of different-module structural elements with wide solid layers are established.

Fatigue life prediction of welded joints from nominal system to fracture mechanics

This paper presents methods for determining the fatigue life of welded joints with particular emphasis on typical joints. Possible methods for computational determination of the stresses in welded joints are shown, starting with those based on nominal stresses according to different proposals, through structural stresses, including the ‘hot spot’ type, to the most complicated linear fracture mechanics. With this background, the recommendations of the International Institute of Welding (IIW) for determining the fatigue life of welded steel joints of flat components under uniaxial tensile–compression conditions are presented. The paper focuses on the problem of determining and evaluating the fatigue life of selected types of welded joints in accordance with the guidelines of the IIW and the safety analysis of welded structures. The study shows the extent to which the simplest method based on the amplitude of nominal stress can be used for calculating fatigue life based on two selected types of joints with different asymmetry coefficients, R = −1 and 0, and joints without geometrical notch. The analysis was based on steel welded joints of four different materials. The results show that the FAT characteristics are always good except for the FAT 90 category, where, for a lower fatigue life, we approach a dangerous fatigue life estimation. For K-type cruciform joints, the FAT model can be used for all the stress ratios. In other cases, such compliance cannot be accepted. For the category FAT 90 X-type butt joints, a new category FAT '134 and a new slope, m = 5, are proposed. For type X butt joints without notch, the slope m = 12 and a new category FAT' 525 are proposed.

Finite-element inverse analysis of residual stress for laser welding based on a contour method

The thermal effect of laser welding degrades the local material properties, and this inevitably leads to thermal deformation and thermal residual stress in welded joints. In this study, the residual stress distribution of laser-welded Al–Li alloy parts was measured by a combination of the contour method and finite-element simulation. First, the contour deformation of the cutting surfaces of welded parts resulting from the release of residual stress was measured by a coordinator. Then, the reverse contour deformation was applied to the finite-element model as the displacement boundary condition to invert the full-field residual stress of the cutting surface. Furthermore, a thermal/structural sequential coupling analysis method was used to establish a complete three-dimensional finite-element model of a laser-welded plate and calculate the residual stress field, taking the actual weld morphology as the characteristic parameter of the heat source, using the improved conical heat source model of laser welding. The result is consistent with the results of the contour method.