Welding-induced Residual Stresses Research Articles

Identifying multiple synergistic factors on the susceptibility to stress relaxation cracking in variously heat-treated weldments

The 347H austenitic stainless steel has been widely used for pressure vessels and pipeline (PVP) applications due to its excellent creep and corrosion resistance, which fit ideally to the harsh conditions in petrochemical industries, fossil fuel or nuclear power plants, and modern energy storages. However, a failure mode has been commonly observed with cracks emerging at the heat affected zone (HAZ) of weldments during post-weld heat treatment (PWHT) or under intermediate to high temperature service conditions. This phenomenon is termed as Stress Relaxation Cracking (SRC) since the purpose of PWHT is to relieve the welding-induced residual stress fields, or as Stress Age Cracking (SAC) if failure happens during service. A leading literature explanation of this failure suggests that the residual stress relaxation and the precipitation dissolution and/or re-precipitation occur in the same temperature range, which can lead to locally high strains and thus to crack at the grain boundaries. Since in situ spatial measurements of residual stress fields, microstructural evolution, and failure processes are nearly infeasible, this work recourses to a micromechanical finite element framework that models the high temperature failure as the nucleation and growth of grain boundary cavities, whereas various parameters such as thermomechanical loading history and its evolution, the competition of grain-interior dislocation creep and grain-boundary diffusion in failure lifetime, and microstructural heterogeneities (such as the precipitate free zone near grain boundaries) can be quantitatively incorporated. It can be concluded from these microstructure-explicit simulations that an accurate knowledge of residual stress evolution and a carefully calibrated set of material constitutive parameters are the essential prerequisites for lifetime predictions. The understanding of individual governing factors also leads to a mechanistic interpretation of the observed SRC susceptibility C-curves. These results suggest that the criticality of residual stress evolution, but not the precipitation-induced local strains, be the leading factor for SRC.

Experimental and numerical investigation on residual stress and deformation of welded I-section curved steel beams

This paper presents an experimental and numerical investigation on welding-induced residual stresses and deformations of in-plane curved welded I-section steel beams. Two welded curved beams with different curvatures were investigated. After welding the curved beam, the residual deformations were measured by a 3D scanner. The residual stresses were subsequently obtained through a high-precision sectioning method. The effects of curvature on the magnitude and distributions of residual deformations and stresses at the specific sections were analysed with the test results. It was found that the residual deformation gradually increased from the weld region to both ends of the flange plate, and the torsion in the web plate became severe with a decrease in curvature of the curved beam. Moreover, the welding process of the curved beam was simulated using the finite element (FE) method. The developed FE model was validated against the test results, and thereafter, parametric analyses were conducted to assess the influence of welding sequence, welding speed, and curvatures of the curved beam on the welding residual stresses and deformations. The numerical results demonstrated that the residual stresses and deformations were significantly influenced by welding speeds, but the influence from curvature of the curved beam was relatively small. Finally, a reasonable welding sequence, welding speed, and curvature of the curved beams were recommended.

Stress relaxation cracking susceptibility evaluation in 347H stainless steel welds

AbstractStress relaxation cracking (SRC) has been reported as a dominant failure mechanism for 347H stainless steel welds at elevated service temperatures, occurring in either the heat-affected zone (HAZ) or fusion zone (FZ). In this study, SRC susceptibility of physically simulated HAZ and cross-welded E347-347H stainless steel welds was studied using a four-step accelerated SRC test with a thermomechanical physical simulator. The stress and temperature range studied represents weld-induced residual stress at 150–600 MPa and post-weld heat treatment temperatures between 800 and 1050 °C. For all temperature conditions, the cross-welded samples failed at a lower critical stress threshold than the simulated HAZ. A finite element model of a 50.8-mm-thick single-V groove weld was used to generate the residual stress maps induced by a 40-pass welding procedure, which in combination with the experimental threshold stress map predicted potential SRC failure locations. Postmortem microstructural evaluations were performed to identify contributing characteristics to SRC. It was found that HAZ samples exhibited a combination of creep void development, secondary cracks with intergranular fracture near grain boundary carbides, and eutectic phases. FZ samples showed brittle fracture with cracks propagating along straight, non-tortuous interdendritic grain boundaries.

Distribution and Characteristics of Residual Stresses in Super Duplex Stainless Steel Pipe Weld

This paper explores the distribution and features of residual stresses formed by super duplex stainless steel pipe welding. Experimental investigations, which encompass an elevated temperature tensile test and metallographic observation along with a hardness test and residual stress measurement, were first conducted to obtain the mechanical properties at high base metal temperatures and to confirm whether or not the duplex stainless steel undergoes martensitic phase development during the welding process. Finally, experiments were performed to scrutinize the residual stress evolution through the metallurgical phase transformation in the weld region and its vicinity. A sequentially coupled 3D thermal, mechanical and metallurgical finite element (FE) model capable of incorporating the experimental consequences was established next. A 3D FE simulation of the girth welding process was conducted, and the axial and hoop residual stress profiles along the girth were evaluated. The results substantiate that martensitic phase evolution occurs in the process of cooling during the welding of super duplex stainless steel, and they also highlight the significance of taking the metallurgical phase transformation into account in the numerical reproduction of the girth welding process for the accurate expression of weld-induced residual stresses, which is especially important for precisely predicting hoop residual stresses.

Effects of pre-tension and fatigue loadings on the evolution of welding residual stresses in welded plates

Welding-induced residual stresses evolve under external loading and fatigue actions. This paper examines the effects of a variety of influencing factors on the residual stress evolution, such as the pre-tension, load ratio, variable amplitude loading, overloading, plate thickness, and crack depth, for which a comprehensive understanding is yet to be nurtured. The experimental and numerical findings demonstrate that the variable amplitude loading and overloading impose significant effects on the evolution of residual stresses during the cyclic loading test. Based on the experimental observations and numerical analysis, this paper presents four evolution forms of residual stresses and reveals their mechanical principles by the effective stress-strain curves in both the undamaged specimens and the fatigue-cracked specimens. The interaction between the positions with different incremental plastic strains changes the magnitude of residual stress and thus dominates the residual stress evolutions.

Advanced numerical simulations on S690 cold-formed square hollow sections under compression

Based on a number of numerical investigations into welding simulations, highly non-linear welding-induced residual stresses within high strength S690 welded H-sections have been evaluated successfully, and surface residual stresses along their flange / web junctions have been carefully calibrated against measured data. This modelling technique has been extended to cover residual stresses of cold-formed circular hollow sections recently, and also of cold-formed square hollow sections as described in this paper. Hence, a full presentation on the proposed approach of integrated and coordinated numerical simulations on various mechanical, heat transfer and thermomechanical, and stresses analyses on these cold-formed square hollow sections is described. Subsequent structural analyses of these models on both stocky and slender columns of these cold-formed square hollow sections are then carried out. Structural adequacy of the proposed approach is thoroughly demonstrated through a systematic calibration against various measured data – both temperatures and residual stresses of these sections induced during fabrication, and load-deformation curves of these sections under compression. It should be noted that the proposed approach provides a scientific mechanism to determine directly residual stresses due to transverse bending and longitudinal welding as initial materials imperfections in these high strength S690 cold-formed square hollow sections. With an adoption of the lowest eigenmodes of these columns as their initial geometric imperfections after adjusted with measured or design values of the member out-of-straightness, both the effects of initial materials and of initial geometric imperfections onto the structural performance of these columns are readily quantified separately.

Generation and distribution mechanism of welding-induced residual stresses

Welding-induced residual stresses (WIRS) can have influence on the performance and service life of the welded structures. The present study experimentally and numerically investigates the reason and mechanism behind the generation and distribution of WIRS concretely. The results show that the thermal shrinkage process and phase transformation process are the main sources generating welding-induced longitudinal residual stress (σLRS). Nevertheless, except for these two processes, the quenching process would be another source producing transverse residual stress (σTRS). In the current work, it is found that the maximum σLRS generally reaches the yield strength (σy) of base metal (BM) at ambient temperature (TRT) for both transforming and non-transforming materials but located at different areas. In the single-pass weldments without external restraint, σTRS profile on the top surface is usually always M-shaped for the non-transforming materials but W-shaped instead for the transforming materials. The distribution mechanism behind the M-shaped or W-shaped σTRS profile is systematically clarified here.

Influence of initial residual stresses on welding residual stresses in ultra-high strength steel S960

In general, the as-received steel components before welding have usually suffered from numerous manufacturing processes. There is no doubt that initial residual stresses (IRS) remain in the steels with different magnitudes and even signs if no any stress-relieving process is applied before welding. Nevertheless, the relationship between IRS and welding residual stresses (WRS) is still not unclear yet, especially in ultra-high strength steels (UHSS). The current work aims to elucidate the influence of IRS on WRS in ultra-high strength steel S960. The X-ray diffraction (XRD) was applied to measure both IRS and WRS here. The experimental results exhibit that IRS in the weld area are completely eliminated because of the metallurgical and mechanical melting effect, which have no influence on WRS. In the heated zone out of the weld area, initial longitudinal residual stress (σRSL) can significantly affect welding σRSLonly if it is in tension. In the cold area, WRS are the combination of IRS and welding-induced residual stresses (WIRS). Furthermore, IRS play the dominant role here in general. No matter how much and what sign IRS are in the cold area, IRS here almost have no impact on WRS in the weld area.

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

Residual stress prediction of arc welded austenitic pipes with artificial neural network ensemble using experimental data

The prediction of weld-induced residual stress assists the structural integrity assessment of welded structures. In this study, residual stress measurements of girth welded austenitic stainless-steel pipes were used to develop two Artificial Neural Network (ANN) ensemble models to predict through-thickness residual stress profiles in Weld Centre Line (WCL). One model was developed for axial and the other for hoop residual stress prediction. The inputs of the models were the pipe radius to thickness ratio, the thickness, the heat input (weld arc electrical energy per unit run length [kJ/mm]) and the normalised through-thickness position. The hyperparameters were tuned, and the models were trained with various initial weight vectors, creating an ensemble of ANNs. The models’ performance was assessed by a test set and by sensitivity studies which revealed the models’ output trends.

Numerical Simulation of the Welding Process during the Main Circulation Pump Impeller Repair

Paper presents a numerical simulation of the main circulation pump impeller damaged parts repair/replacement welding process, for the prediction of welding-induced residual stresses. 3D numerical model creation of the impeller flange and central hub welded joints. Thermal and stress-strain analysis of assessed parts using the finite element method. Calculation of equivalent residual stresses in the area of examined welded joints. Applicability of results in further impeller integrity analyzes. The results confirmed the suitability of the chosen welding procedure and technology.

Evaluation of welding-induced residual stress and distortion in A-TIG welding of duplex stainless steel

Applying non-uniform heat in welding causes residual stress and distortion, which affects the life of components. In the present study, the residual stress and distortion of Duplex 2205 stainless steel in A-TIG welding were investigated numerically and experimentally. The optimal welding parameters for highest penetration depth in welded samples were obtained experimentally. Uncoupled thermal-mechanical analysis using ABAQUS 2017 software has been done. Goldak's parameters were measured by empirical tests. The results include simulation diagrams of four samples consisting of the optimal sample without flux powder and three samples with the highest penetration depth. The simulation results show that the sample without flux has a higher maximum temperature and lower welding-induced distortions. The efficiency used in this research changes using and not using powder; it is concluded that, in similar conditions in A-TIG welding, fewer values of parameters are needed to achieve the appropriate result comparing conventional TIG. The efficiency of workpieces with flux should be considered about 20% lower to have similar results to the conventional TIG. The numerical modeling results showed a good agreement with experimental data both for temperature distribution and welding-induced residual stress and distortion. The distortion in the pieces with conventional TIG welding has increased to 11% at the farthest point from the welding line. The error obtained from comparing the results in residual stress is between 12 and 34%.

Modeling of welding residual stress in a dissimilar metal butt-welded joint between P92 ferritic steel and SUS304 austenitic stainless steel

In this study, a butt-welded joint between P92 ferritic steel and SUS304 austenitic stainless steel was fabricated with a nickel-based filler material. Based on Sysweld software, three-dimensional thermal-metallurgical-mechanical coupled finite element analyses were performed to investigate the hardness and welding residual stress in the welded joint. In the material behavior model, various factors influencing the formation and distribution of hardness and welding residual stress were carefully considered, including the austenitic transformation, martensitic transformation, and the tempering of martensite in P92 steel; the isotropic strain hardening, annealing effect, and melting effect of all materials; and the differential thermal expansion between dissimilar metals. The neutron diffraction method and hole-drilling strain gauge method were applied to measure the profiles of residual stress of the welded joint, respectively. Hardness mapping was performed on a weld cross-section specimen. The predicted results of welding residual stress and hardness are in good agreement with the measurements, respectively. The peak residual stresses in longitudinal and transverse directions are above 600 MPa in P92 steel. There are high tensile residual stress and significant cold work near the weld root in SUS304 stainless steel. The solid-state phase transformation induces compressive longitudinal residual stress in the heat-affected zone, high tensile transverse residual stress near the weld toe in P92 steel, and a significant stress gradient. The tempering effect can reduce the hardness and tensile residual stress in the heat-affected zone of P92 steel. The formation mechanism of welding-induced residual stress was illustrated based on the Satoh test. The effects of peak temperature, internal restraint, and differential thermal expansion are found to be decisive for the formation of residual stress. Large tensile residual stress can be generated with internal restraints, which promote the stress increase and lead to material yielding. A restraint factor was proposed for the quantitative assessment of stress evolution.

Evaluation of strain based ECA method in DNVGL-RP-F108

Pipelines may be subject to strain-controlled external loads exceeding yield strength of materials due to many causes, e.g., soil settlements and ground movement. There are several strain based fracture mechanics assessment methods to determine the maximum tolerable defect sizes in girth welds in pipelines. One of these methods is the DNVGL-RP-F108 procedure which was developed from a joint industry project for assessing reeled pipes and has been used for both offshore and on-shore pipelines. However, as with other methods, it requires the weld strength either even- or over-matching the parent steel which may be difficult to achieve for high strength steels. There are also uncertainties about the adequacy of the DNVGL-RP-F108 guidance addressing the effects of internal pressure and welding-induced residual stresses. In this study, the maximum tolerable defect sizes in the girth welds of an X70 spiral welded pipeline were determined using the DNVGL-RP-F108 approach. The effects of several variables on the assessment results, including weld strength mismatch, stress-strain curve magnitude, internal pressure level, fracture toughness, residual stresses and misalignment, were also investigated. A comprehensive finite element analyses were performed to verify the crack driving force determined by the DNVGL-RP-F108 approach. It was found that the DNVGL-RP-F108 approach can be conservatively applied to girth welds with a weld strength under-match by 5% in all cases, and even by 10% for most cases, for the conditions investigated. It was also revealed that use of this guidance could be unduly conservative for strength over-matching welds.

Residual stresses study in butt welded joint of Inconel 617 alloy and effect of post weld heat treatment on residual stresses

Distribution of weld-induced residual stress plays a significant effect on the service life of a welded component. The accumulation of high residual stress accelerates the crack propagation even if the crack is of microscopic level, reducing the service life of the welded component. Prior understanding of residual stress distribution can aid in the design of a component with an adequate factor of safety and reduce the probability of failure. In the present study, two separate circumferential butt welded pipes were fabricated using Alloy 617 and then subjected to post weld heat treatment) at 720°C and 980°C. The deep hole drilling method was used to measure the distribution of residual stress. The fabrication of the welded joint was done using the hot-wire TIG welding process. High welding speeds are possible with hot-wire tungsten inert gas (TIG) welding because it uses less heat than conventional TIG welding. Using hot-wire TIG welding, the welded joint's mechanical properties, such as hardness, are improved in addition to its metallurgical properties. The computational approach is provided to analyze temperature and residual stress fields in multi-pass TIG welds with different passes. Based on ABAQUS FEA software, a coupled thermomechanical computational approach was developed to analyze the residual stress distribution on the welded joint. A 3D finite element model for Alloy 617 tube was created to estimate the welding stress field in two separate multi-pass welded joints. Mixed hardening model (kinematic and isotropic) was used during the numerical analysis. The effectiveness of the computational approach was verified with experimental measurements. The magnitude of hoop and axial residual stresses were observed to be maximum at a depth of 6 mm from the upper surface. The stress gradient in the welded zone and heat-affected zone is dramatically reduced by 70–80% of the as-welded condition during the post weld heat treatment at 980°C.

Austenitizing Temperature Effects on the Martensitic Transformation and its Influence on Simulated Welding Residual Stresses in a Microalloyed-Steel

This study focused on the effects of different peak (austenitizing) temperatures (Tp) over the martensite start temperature (Ms) and its influence on the final residual stresses after welding simulation. For this purpose, the expansion coefficients obtained through physical (dilatometric) simulations of a high-strength low-alloy steel were considered for three peak temperatures: 1300 °C, 1150 °C, and 920 °C and a cooling rate of 25 °C/s. Aiming at clarifying the physical phenomenon behind GTAW welding, one carried out nonlinear transient thermomechanical finite-element (FE) analyses to reconstitute the welding process and simulate the subsequent formation of residual stresses in the HAZ. Once the heat source simulation was calibrated, four material models were created, one for each Tp, and a fourth model considering a constant expansion coefficient, without considering the martensite transformation for comparison. A Three-bar model was evaluated to isolate the effects of Tp (Ms) in the residual stresses. A composite plate model was also considered, in which the sheet HAZ was subdivided according to the reached peak temperature, and the respective material models were applied. The results show the importance of martensite transformation on the welding-induced residual stress and a clear trend of decreasing tensions with lowering the Tp, especially over HAZ.

Combining welding-induced residual stress with thermal and mechanical stress in continuous welded rail

Continuously welded rail (CWR) with flash-butt welded joints has become standard practice for railway construction around the world. The welding process during rail installation or repair forms a residual stress field in the weldment altering locally the distribution and amplitude of the total stress that develops when the rail is in service. This paper presents a computer simulation approach to study the combined residual, thermal, and mechanical stress caused by the fastener system that develops in rail during the in-track welding and installation. The proposed approach simulates within a Finite Element Analysis framework the rail welding and installation sequence using detailed thermal and mechanical models of the weldment formation, and in-track installation. The model is validated with experimental measurements reported in the literature. It is implemented in a study that demonstrates the combined effects of such stresses with stress that develops in the rail during a daily solar-induced thermal cycle. A non-trivial stress gradient is observed where the mean tensile stress in the weldment is elevated relative to the rail at large. The higher mean stress warrants further investigations in view of fatigue performance under wheel loading. The proposed computer simulation approach is a tool that will enable future investigations focusing on more detailed examinations of weldment behavior, particularly concerning fatigue failures and track configurations, as well as in optimizing welding parameters to control the development of residual stresses.

Influence of welding method on residual stress and metallography of a mild steel welded butt-joint plate

During welding process and cooling process after welding, residual stress will be generated and the microstructure of the weld joint will be changed inevitably, which will be harmful for mechanical performance of welded structures. Hence, it is necessary to study welding-induced residual stress and metallic phase transformation, so as to provide guidance for optimization of welding process. In this paper, three butt-joint plates were fabricated by using different welding methods including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). Secondly, welding residual stress was measured through blind-hole method. Thirdly, the microstructure of the welded joint was analyzed. Fourthly, thermal elastic-plastic finite element method (FEM) was used to numerically simulate the welding process. Finally, heat cycling curves of typical gauged points were extracted, the mechanism of how welding induces residual stress and phase transformation was analyzed from the perspective of cooling rate. Experimental and numerical results show that compared with longitudinal stress, the influence of welding method on transverse stress is more significant. When SMAW is used for welding process, the distribution of transverse residual stress is more uniform than that using GMAW and SAW. Under the three welding methods, the welded joints show similar metallographic compositions. However, the content and distribution of different metallographic compositions are quite different.

Buckling resistance of steel circular tubes strengthened by welding cover plates

Welding under service load generates welding-induced residual stresses and deflection, affecting the stability of compression members strengthened by welding cover plates notably. Hence, the associated stability check is more complicated than that of their unstrengthened counterparts. This paper is aimed to propose a stability design method for such strengthened circular tubular members. A model for the welding-induced residual stress is proposed, and its influence on member stability is evaluated through parametric FE analysis. Results show that, for hot-rolled circular tubes, the column curve used for buckling resistance calculation is reduced from column curve “a” prior to strengthening to column curves “b” and “c” after strengthening, depending on the thickness of strengthening plates. Formulas to predict the welding-induced deflection and equivalent residual imperfection are proposed and validated, and the influence of the equivalent residual imperfection on member stability is evaluated through parametric FE analysis to derive the resistance reduction factor, which is also related to normalised slenderness ratio. Having determined the column curve and resistance reduction factor, a stability design method for strengthened circular tubular members is proposed, which is demonstrated to be more accurate than that codified in Chinese code GB 51367. In addition, the service load-generated stress limit for safe and effective strengthening is put forward.

Solid phase transformation effects on stress and strain in the thick plate EH40 welded butt joint

To accurately predict welding-induced residual stress and strain of high strength steel thick plate EH40 butt joint in single-pass full penetration laser welding, a complete solid phase transformation model according to the actual weld microstructure was proposed through material constitutive development. At the same time, the Case 1 considering the traditional thermo-elastoplastic were used as comparative study. The simulation calculation results and experimental results of each phase content were compared and verified. The stress and strain distribution of welded joints and the evolution mechanism of nodes in three zone including fusion zone, heat-affected zone and base metal were deeply studied and compared. The results indicated that the solid phase transformation had an obvious effect on the peak and distribution of longitudinal, transverse, normal and equivalent residual stress, as well as the stress gradient at the junction of heat-affected zone and BM. It increased the peak value of longitudinal residual compressive stress from –103 MPa to –768 MPa, with an increase of 645.6%. The stress gradient at the junction of heat-affected zone and base metal was up to 1299 MPa. The state distribution of longitudinal and transverse stress in the weld and its vicinity were completely opposite to the Case 1. The peak value of transverse plastic compressive strain increased from –0.059 to –0.111, with an increase of 88.1%. The fusion zone and heat-affected zone of the plastic strain in welded joints were more easily observed. It was found that martensitic transformation was the main reason for the obvious difference of stress and strain distribution and the evolution mechanism of stress and strain in the later stage of cooling stage.