Welding Stresses Research Articles

Failure analysis of an economizer tube sheet & its cover due to corrosionand imperfection

The boiler's economizer was found to be inefficient. Corrosion is suspected to be the source of the economizer's pressure reduction. The examinations included visual inspection, stereomicroscope, metallography, elemental microanalysis by EDS, and chemical composition analysis. The economizer failed due to a weld crater caused by improper welding, which induced residual welding stress. The slight sulfur content of the condensed or flue gas that causes rusting on the economizer's outer cover is not considered a severe failure issue. Material SUS304 stainless steel is the right selection for economizer materials.

Effect of residual stress in longitudinal and transverse weld on global stability of box section steel column

In order to study the influence of welding residual stress on the global stability of box section steel column, the simulation of the side effects from the welding process of Q345 box section steel column by ABAQUS thermal-structure coupling analysis was conducted. A temperature-displacement explicit analysis step was established, and the residual stress caused by the temperature difference of the welding specimen was simulated by applying the body heat flux directly to the solid element within the same thickness range of the weld seam and defining the load amplitude; The calculated welding residual stress was taken as the initial defect of the structure and the global stable bearing capacity of the box section steel column was solved by the arc length method. Considering the influence of thickness and welding residual stress on the global stability of box section steel column, the calculation results of 12 finite element models were compared. The results show that under the same body heat flux, the residual stress of steel columns with different thicknesses during welding is different, and the maximum value can reach 791MPa; Under the condition of the same residual stress, the global stability bearing capacity of the box section steel column will also change irregularity with the change of thickness, and the global stability bearing capacity can be reduced by 3.07% compared with that no residual stress.

Investigation and Prediction of the Influence of Shielding Gas Composition on Residual Stress

Residual stresses are internal stress distribution locked up within a material or weldment area. They usually exist inside the material (or weld) irrespective of external loading. These stresses are generated upon equilibrium of materials after plastic deformation caused either by applied mechanical loads, thermal loads or phase change and they play key role in the failure of these joints. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. Welding process generates residual stresses of various magnitudes, and the combination of shielding gases at various percentages might affect the amount of residual stresses in weldment. The resultant residual stress from shielding gas on welded joint is unknown and has been based on trial and error assumption. This study therefore, focused on the investigation and prediction of shielding gas mixtures to minimize residual stress formation in mild steel welded joint, employing scientific design of experiment using Box-Beckhen’s design (BBD) matrix, statistical and mathematical models to measure the residual stresses from various gas mixtures. The argon (Ar) and carbon-dioxide (CO 2 ) shielding gas variations considered for the experiment were: 100%wt. Ar and 0%wt. CO 2 ; 75%wt. Ar and 25%wt. CO 2 ; 50%wt. Ar and 50%wt. CO 2 ; 25%wt. Ar and 75%wt. CO 2 , 0%wt Ar and 100%wt. CO 2 . The weldment produced by shielding gas of 100%wt. Ar and 0%wt. Co 2 had the highest residual stress while the weldment of 50%wt. Ar and 50%wt. CO 2 , 25%wt. Ar and 75%wt. CO 2 , 0%wt. Ar and 100%wt. CO 2 produced weld with lesser residual stress values.

Analysis of crack causes and effects of the A333 low carbon pipeline steel after thermite welding

By thermite welding on steel pipelines with an anode material to protect the cathode, cathodic protection has been widely used to prevent steel base pipelines from erosion. In this paper, some cracks were found in an accidental magnetic particle examination by the workers after thermite welding on steel pipelines. Therefore, a series of characterizations were conducted on the macro/microscopic morphologies, mechanical properties of the cracked A333 low carbon pipeline steel to find out the causes and effects. The obtained results show that the coarse martensite with a certain thickness in HAZ come into being bringing about plasticity reducing, strength and hardness increasing. And large welding stress and uncoordinated deformation lead liquid copper to infiltrate into the prior austenite grain boundaries in HAZ of the pipeline causing the formation of the copper penetration cracks.

Prediction of temperature field and residual stress of oscillation laser welding of 316LN stainless steel

The finite element (FE) analysis in this study is used to predict the effect of oscillation parameters on the temperature field and residual stress and as-welded distortion of 316 LN stainless steel weld joint. The simulated results indicate the simulation temperature field is good in agreement with the geometry morphology of actual weld metal (WM), and with the increase of oscillation frequency, the simulation temperature of WM gradually decreases. However, the temperature first decreases and then increases with the increase of amplitude. The residual stress concentrates on the WM and the surrounding heat-affected zone (HAZ). With the increase of oscillation frequency and amplitude of laser beam, the compressive stress converts to tensile stress, and the residual stress and the as-welded distortion gradually present a decreasing trend. The oscillation laser welding can alleviate the stress concentration phenomenon.

Multi-Objective Optimization of MIG Welding and Preheat Parameters for 6061-T6 Al Alloy T-Joints Using Artificial Neural Networks Based on FEM

To control the welding residual stress and deformation of metal inert gas (MIG) welding, the influence of welding process parameters and preheat parameters (welding speed, heat input, preheat temperature, and preheat area) is discussed, and a prediction model is established to select the optimal combination of process parameters. Thermomechanical numerical analysis was performed to obtain the residual welding deformation and stress according to a 100 × 150 × 50 × 4 mm aluminum alloy 6061-T6 T-joint. Owing to the complexity of the welding process, an optimal Latin hypercube sampling (OLHS) method was adopted for sampling with uniformity and stratification. Analysis of variance (ANOVA) was used to find the influence degree of welding speed (7.5–9 mm/s), heat input (1500–1700 W), preheat temperature (80–125 °C), and preheat area (12–36 mm). The range of research parameters are according to the material, welding method, thickness of the welding plate, and welding procedure specification. Artificial neural network (ANN) and multi-objective particle swarm optimization (MOPSO) was combined to find the effective parameters to minimize welding deformation and stress. The results showed that preheat temperature and welding speed had the greatest effect on the minimization of welding residual deformation and stress, followed by the preheat area, respectively. The Pareto front was obtained by using the MOPSO algorithm with ε-dominance. The welding residual deformation and stress are the minimum at the same time, when the welding parameters are selected as preheating temperature 85 °C and preheating area 12 mm, welding speed is 8.8 mm/s and heat input is 1535 W, respectively. The optimization results were validated by the finite element (FE) method. The error between the FE results and the Pareto optimal compromise solutions is less than 12.5%. The optimum solutions in the Pareto front can be chosen by designers according to actual demand.

Effects of laser and GMA hybrid welding parameters on shape, residual stress and deformation of HSLA steel welds

Abstract As a high-efficiency and high-quality welding process, hybrid laser-MAG welding (HLMW) has significant potential of application in welding thick plates. In the present study, based on thermal elastic–plastic theory, a three-dimensional finite element model is developed to predict the weld shape characteristics, residual stress and distortion in HLMW for a butt joint of 12-mm-thick high strength steel plate. Metal active gas arc welding (MAG) heat input and laser energy are modeled as one double-ellipsoid body heat source and one cone body heat source with enhanced peak density along the central axis, respectively. The comparison between calculated molten pool shapes and those obtained by the experiment shows a good agreement. Then weld shape characteristic, residual stresses and distortions are calculated in four different welding process parameters. The results show that the increase of laser power and current can effectively increase the weld penetration width when the welding speed is fixed. At the top surfaces of weldment, the peak stress of high laser beam power is more significant than that of low laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone and the surrounding heat affected zone. However, at the bottom surfaces of weldment, the peak stress of low laser beam power is larger than that of high laser beam power. The peak stress of low laser beam power is much larger than that of high laser beam power. A high compressive transverse stress of low laser beam power can be found at the welding zone. The vertical deformation in low laser beam power and low arc current welding has the lowest value.

Influence of Residual Stresses on the Weld Metal Hardness of 5V Titanium Alloy

Influence of residual welding stresses on the hardness values of the weld metal is studied. The investigations were carried out on 5V titanium alloy welded joints, obtained by electron-beam welding and argon-arc welding (TIG-welding). It is shown that the nature of the residual stresses distribution depends on the parameters of welding and affects the hardness values of the weld metal. It is shown, that the difference between the hardness values of the metal after welding and the metal after partial relief of residual stresses on the investigated alloy is up to 90 MPa, which is about 3% of the weld metal hardness level.

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.

A traction force approach for fatigue assessment of complex welded structures

AbstractA new traction force approach (TFA) for weld root fatigue analysis of complex cruciform connections is introduced. The approach defines the local nominal weld stress by using a solid element model and connecting the welded parts only from the toe and root lines. This enables the peak weld forces to be distinctly defined. The TFA approach was validated with a fully connected solid element model. As a comparison, the same analyses were performed for a shell element model. The study shows that the approach that is introduced here gives a good estimate for the local weld force with a maximum error of 10% while the commonly used shell element model greatly overestimates the peak weld force, particularly for complex connections. The analysis of fatigue‐tested connections showed that by using TFA, instead of an approach based on overall nominal weld stress, the scatter range index is reduced from 3.71 to 1.98. The TFA approach is much more efficient compared to conventional approaches because of the low pre‐ and post‐processing effort.

Investigation of residual stresses in planar dissimilar magnetic pulse welds by neutron diffraction

Residual stresses are investigated for the first time in a dissimilar AA1050–DP450 steel magnetic pulse weld using neutron diffraction. Close to the joint interface, tensile residual stresses are observed in the Al sheet and compressive residual stresses are identified in the steel sheet. At the interface, longitudinal tensile stresses are dominant on the aluminum side and transverse and normal stresses show similar behavior. On the steel side, normal stresses remain small, and longitudinal and transverse residual stresses have a similar trend. It was identified that close to this tensile region in aluminum, residual stresses in steel become more compressive. These residual stress distributions essentially result from (i) the respective yield strengths of Al and steel and (ii) the high strains and high strain rates borne by both alloys due to the impact of the Al flyer sheet on the steel sheet during the process. The asymmetrical shape of the rectangular joint line entailed a lower magnitude of residual stresses along the short side of the weld.

Study of Residual Welding Stresses for Underwater Wet Welding of Low-Alloy Steel Using Magnetic Anisotropic and X-ray Diffractometry Methods

Study of Residual Welding Stresses for Underwater Wet Welding of Low-Alloy Steel Using Magnetic Anisotropic and X-ray Diffractometry Methods

Исследование остаточных сварочных напряжений при подводной мокрой сварке низколегированной стали с применением магнитоанизотропного и рентгенодифрактометрического метода

The present study possibility of assessing residual welding stresses using magnetoanisotropic and X-ray diffractometric methods. Using the method of magnetic anisotropy approve of inhomogeneity of residual stresses in specimens with surfacing made by flux-cored wire and covered electrode in air and underwater has been revealed. The use of two nondestructive testing methods made it possible to determine and compare the values of residual welding stresses.

Detection of residual stress in friction stir welding of heterogeneous aluminum/copper sheets—ultrasonic method

Detection of residual stress in friction stir welding of heterogeneous aluminum/copper sheets—ultrasonic method

A modified version of MATLAB application window for predicting the weld bead profile and stress–strain plot of AA5052 CMT weldment using ER4043

The present study deals with the extended version of our previous research work. In this article, for predicting the entire weld bead geometry and engineering stress–strain curve of the cold metal transfer (CMT) weldment, a MATLAB based application window (second version) is developed with certain modifications. In the first version, for predicting the entire weld bead geometry, apart from weld bead characteristics, x and y coordinates (24 from each) of the extracted points are considered. Finally, in the first version, 53 output values (five for weld bead characteristics and 48 for x and y coordinates) are predicted using both multiple regression analysis (MRA) and adaptive neuro fuzzy inference system (ANFIS) technique to get an idea related to the complete weld bead geometry without performing the actual welding process. The obtained weld bead shapes using both the techniques are compared with the experimentally obtained bead shapes. Based on the results obtained from the first version and the knowledge acquired from literature, the complete shape of weld bead obtained using ANFIS is in good agreement with the experimentally obtained weld bead shape. This motivated us to adopt a hybrid technique known as ANFIS (combined artificial neural network and fuzzy features) alone in this paper for predicting the weld bead shape and engineering stress–strain curve of the welded joint. In the present study, an attempt is made to evaluate the accuracy of the prediction when the number of trials is reduced to half and increasing the number of data points from the macrograph to twice. Complete weld bead geometry and the engineering stress–strain curves were predicted against the input welding parameters (welding current and welding speed), fed by the user in the MATLAB application window. Finally, the entire weld bead geometries were predicted by both the first and the second version are compared and validated with the experimentally obtained weld bead shapes. The similar procedure was followed for predicting the engineering stress–strain curve to compare with experimental outcomes.

Development of microstructure and residual stress in electron beam welds in low alloy pressure vessel steels

Reduced-pressure electron beam (EB) plate butt welds were manufactured in two low-alloy pressure-vessel steels, SA508 Gr 3 Cl 1 and SA508 Gr 2, at two thicknesses in both steels, 30 mm and 130 mm. Transient temperatures during welding were recorded using thermocouple arrays. Residual stresses in the as-welded condition and after post-weld heat treatment were measured using diverse methods: neutron diffraction and the contour method at 30 mm thickness; and deep hole drilling and the contour method at 130 mm. Incremental centre hole drilling measurements were performed at 130 mm thickness to better understand near-surface stresses. Weld and heat-affected zone microstructures and microconstituents were evaluated using a combination of hardness mapping, optical microscopy and electron microscopy. The as-welded residual stresses exhibit the characteristic M-shaped distribution for hardenable steels, reaching 500–600 MPa in tension in both steels at both thicknesses. However, the modest changes to the chemical composition and the change in plate thickness both significantly influenced microstructures, mechanical properties and residual stress distributions. These sensitivities underline the need for physically faithful models. This extensive characterisation study enables the development and validation of models that predict the development of microstructures and residual stresses in EB welds in low alloy pressure vessel steels.

Failure Analysis for Girth Weld of Gathering Pipelines

Through failure generalization, fracture feature analysis and material performance test, a comprehensively analysis was made on the fracture failure analysis for girth weld of gathering pipelines containing H2S gas. The results showed that the fracture failure might be mainly due to sulfide stress cracking in the girth weld. The crack originated from the fusion line on the inner surface of girth weld and extended along the girth weld to outside closed to bends. The sulfide stress cracking of the girth weld was caused by the intersection of multiple factors. The service condition was located in SSC 3 zone and the SSC risk of girth weld was high. The girth weld itself was not been stress-relieved, and its ability to resist SSC was poor. Due to low wall thickness, welding defects, welding stress and additional load, the actual stress of weld was higher.

Thermo-mechanical analysis of the repair welding residual stress of AISI 316L pipeline for ECA

Through-thickness residual stress distribution is a fundamental input parameter for engineering critical assessment (ECA) according to BS 7910 Annex Q. In this paper, we investigated the through-thickness residual stress distribution at a weld toe/weld centerline. Firstly, we performed a simulation of the thermo-mechanical coupled-welding residual stress with/without repair welding of a thick wall pipeline. To further investigate the effects of component radius to wall thickness ratio(r/t) and heat input on the welding stress profile, we developed a welding pass size merging strategy on a mechanical basis. At least ten weld layers were utilized in finite element analysis(FEA) to improve efficiency, without affecting the through-thickness residual stress distribution. The influence of the r/t ratio on the through-thickness residual stress distribution was determined and described as membrane stress and bending stress. Hoop and axial bending stresses at a weld toe decreased gradually with the r/t ratio increased. In contrast, the hoop membrane stress at a weld toe gradually increased with the r/t ratio increased. Moreover, a similar trend was observed at weld centerlines. Analytical equations for predicting the through-thickness residual stress were established for both original welding and in-depth repair welding processes. It was shown that the residual stress distribution after the repair welding was more efficiently improved when a smaller repair depth was selected, i.e., the improvement was adversely related to the repair depth. The residual stress for the original and the repaired welds was expressed as a logarithmic function in terms of axial bending stress, hoop bending stress, and hoop membrane stress.

Prediction and numerical simulation of residual stress in multi-pass pipe welds

AbstractA numerical simulation procedure is presented to predict residual stress states in multi-pass welds in oil transportation pipes. In this paper, a two-dimensional thermo-mechanical finite element model is used to calculate the temperature distribution, hardness, and the distribution of residual stresses during multi-pass welding of pipes of dissimilar metals and varying thicknesses. In this model, the temperature dependence of the thermal and mechanical properties of the material was considered. The present model was validated using the hardness measurement. Good agreement was found between the measurement and the numerical simulation results. The simulated result shows that the two-dimensional model can be effectively used to simulate the hardness test and predict the residual stress in the pipe weld. The simulation results and measurements suggest that the model with moving heat source can obtain a good prediction of residual welding stress. Both the two-dimensional and the three-dimensional modeling can be used to estimate the residual stresses in different weld regions and help saving time.

Assessment of Residual Stresses in a T-joint Weld by Combined Experimental/Theoretical Approach

Residual stresses are common in metal structures, essentially influencing their mechanical behaviour. We consider a combined experimental/theoretical approach to residual stresses. The theoretical basis of analysis is provided by the recently developed F0-approach, operating with explicit relation between load-free and stress-free configurations. The titanium alloy Ti-6Al-4V is modelled with the multiplicative decomposition of the deformation gradient into the elastic and the plastic parts. Isotropic hyperelastic relations between stresses and elastic strains are assumed. The weak invariance of the material model allows for incorporation of residual stresses without additional numerical costs. In order to demonstrate the new experimental/theoretical approach to residual stresses, experimentally measured stresses are extrapolated from the surface inside the welded T-joint. The robustness of the stress extrapolation procedure is confirmed on synthetic experimental data.