Gap Welding Research Articles

Effect of Groove Designs on Residual Stress and Transverse Shrinkage in GMAW and PGMAW of A333 Seamless Steel Pipes

The effectiveness of weld joints primarily depends on the fusion of base metal, minimum heat-affected zone (HAZ) and lesser residual stresses. The severity of thermomechanical effects e.g. weld shrinkages and residual stresses is significantly minimized by narrow gap welding technique over the traditional welding. This work describes the welding of A333 Grade 3 steel pipes by the application of GMAW and PGMAW techniques. The analysis is made to capture the effects of groove designs on residual stress and transverse shrinkage. The process parameters used for the analysis are voltage, current and welding speed. In this work, narrow groove design using PGMAW process is capable of reducing the number of passes and area of weld deposit by 35–40% by volume. In PGMAW, decrement in residual stresses is observed with a narrow groove compared to conventional V groove technique. The results are validated by metallurgical and mechanical investigation of welded joints. This work will help other researchers to understand the effect of narrow gap welding using an optimum number of passes for thick pipes.

Modeling for Tracking Micro Gap Weld Based on Magneto-Optical Sensing and Kalman Filtering

Seam detecting and micro weld tracking are difficult in the laser welding process. In this paper, a micro gap weld with a width of not more than 0.05 mm is detected and identified by magneto-optical (MO) imaging technology. The MO imaging law of the micro gap weld under direct-current (DC) magnetic field excitation is studied, and the relationship between the gray-scale characteristics of the weld's MO image and the leakage magnetic field strength is analyzed based on the MO effect law. A finite element (FE) model of the micro gap weld is set up, and the leakage magnetic field distributions of different lift-off heights and different excitation voltages are analyzed, which is helpful in improving the detection accuracy of the center position of the micro gap weld. A MO imaging inspection system for micro gap weld excited by a DC magnetic field is established. According to the finite element simulation results and the MO imaging experiments, the optimal excitation voltage of the MO imaging device is 15 V, and the optimal lift-off height is 1.0 mm. To reduce the influence of noise coupled with the laser welding process, the measurement precision of the micro gap weld center was improved by the Kalman filtering (KF) method. The experimental results at different welding speeds indicated that MO imaging can be used for high-precision micro gap weld center identification under optimal detection parameters.

Residual stresses in narrow-groove girth welds and applications for fitness-for-service assessment

Narrow gap welds have been increasingly used in pressure vessels and pipe components due to their unique advantages. A recent comprehensive investigation into residual stress distributions in narrow gap is presented in this paper, covering component wall thickness from 1” (25.4 mm) to 10” (254 mm), component radius to wall thickness ratio from 2 to 100, and linear welding heat input from low (300 J/mm) to high (18,000 J/mm). By means of a residual stress decomposition technique, two key parameters that govern through-thickness residual stress distributions in terms of their membrane and bending content have been identified. One is component radius to wall thickness ratio (r/t) and the other is a characteristic heat input density (Qˆ) having a unit of J/mm3. With these two parameters, a unified functional form for representing through-thickness residual stress profile in narrow gap welds is proposed for supporting defect assessment. Its adequacy for estimating residual stress distribution trends is further confirmed by comparing with thermomechanical finite element residual stress analyses for a number of selected narrow gap weld cases.

A novel approach to regulate energy allocation and melt flow in narrow gap laser welding with electromagnetic assisted wire wobbling

Abstract A novel, new approach of electromagnetic assisted wire wobbling to regulate energy allocation, melt flow and metallurgical structure is introduced in laser narrow gap welding of 316 L stainless steel. The formation of melt pool, weld surface morphologies and microstructure features in conventional laser welding, laser wobble welding and electromagnetic assisted wire wobble welding were compared. The results reveal that the forced convection generated by electromagnetic swing wire could broaden the melt pool size and compulsively push high-temperature weld metal towards groove sidewall. The wetting of liquid weld metal on groove sidewall was improved and concave weld morphology was obtained, thereby avoiding incomplete fusion of sidewall and favoring the filling of next weld bead. The temperature and element distribution in weld zone would be more uniform by the periodically and drastically forced convection, which helped to inhibit the growth of columnar crystals and promote the uniform distribution of elements. The average microhardness value in weld zone was uniform with the using of electromagnetic swing wire. Moreover, mechanisms of enhanced sidewall wetting and grain refinement were discussed in electromagnetic assisted wire wobble laser welding.

Study of the Features of Obtaining Bimetallic Pipes and Rods by Explosion Welding with Subsequent Hot Deformation

In this paper, we study the features of obtaining bimetallic pipes and rods using explosion welding and subsequent hot deformation. Explosion welding allowed obtaining continuous cylindrical two-layer billets with a combination of steel 20 + 08Cr18Ni10Ti layers with almost 100% adhesion of the layers, without surface defects, and with a specified residual deformation in diameter. We determined that replacing the atmosphere with helium in the welding gap does not reduce or eliminate microdefects in the joint. Subsequent hot plastic deformation did not affect the ratio of the component layer thicknesses. A combined technology for the production of bimetallic pipes and rods with a combination of steel 20 + 08Cr18Ni10Ti layers, which allows obtaining pipes and rods with a corrosion-resistant coating and sizes that are included in the range of pipes used in the energy industry, was developed and tested.

Influence of rotation frequency and rotation diameter on mechanical properties and microstructure of weld metal produced by MCAW-RE

The MCAW process with rotating electrode (MCAW-RE) is a variation of the conventional gas metal arc welding process, which a metal-cored wire is submitted to a rotational movement along a pre-established diameter. This process enhances narrow gap welding, since the rotational motion of the electrode allows the electric arc to reach peripheral regions of the groove, preventing lack of fusion on the sidewall. As a result, reduced costs and superior productivity compared with the conventional GMAW process are obtained. The limited literature about this process is focused on the operational characteristics, and works studying the mechanical properties are not available. Thus, this work evaluates the mechanical and microstructural properties of weld metals obtained by the MCAW-RE process in order to allow a decision about its technical feasibility to replace the GMAW process in industry. Initially, beads on plate weld tests were performed with varying rotation frequency and rotation diameter, in order to determine the parameters to be used in welded joints. High-strength steel weld metals were obtained by welding performed in steel plates with dimensions of 500 × 300 × 10 mm. Mechanical tests and metallographic examination were carried out in samples removed transversally to the weld bead. The results showed that the impact toughness of the weld metals can achieve the requirements for several industrial applications. The results showed that the GMAW process with rotating electrode-cored wire has a high potential for replacement of the GMAW in industrial applications.

In situ tensile of ultra-narrow gap laser welded joint of bainitic steel

ABSTRACT Ultra-narrow gap laser welding (ultra-NGLW) is an advanced welding technology for thick bainite steel with a welding gap of only 4 mm. We studied the failure mechanism of the tensile fracture of ultra-NGLW joints of bainitic steel via in situ tensile tests. The tests show that cracks for all micro-zone specimens propagated along the tensile direction at 42°∼45°. Further analysis of the crack tips by Electron Back Scatter Diffraction showed main cracks along directions with high Schmid Factors (SF >0.44), and micro-cracks were found on the grain boundaries of (111) and (101) grains. It was revealed that the wire-filling zone and heat-affected zone were mainly intergranular expansion, whereas in the no filling zone, the crack propagation was transgranular.

Modeling of weld formation in variable groove narrow gap welding by rotating GMAW

Abstract As an effective welding method, rotating arc narrow gap MAG welding must ensure sidewall penetration, which is hard to realize when the groove is irregular in practical production. Therefore, it is significant to construct a weld form modeling for control weld penetration under the variable groove conditions. At first, the welding experiment system and the sensor system were set up. Arc sensing and visual sensing were applied to monitor the welding process, and effective algorithms were developed to extract the weld groove features. Three typical groove forms were considered and sufficient experiments were carried out to obtain enough experimental data. Furthermore, support vector machine is used to model the process. Welding current and the shortest distance between the arc center and the groove sidewall were used to predict the sidewall penetration. The verification results show that the model is effective under the condition that the height change of the groove is not more than 2 mm, the width change is not more than 2 mm, or the inclination angle of the bottom of the groove is not more than 10 degrees. The establishment of this model is very helpful to further control the formation of narrow gap welding.

Welding Deformation of Unequal Thickness Tailor Welded Blanks under Multiple Factors

With the popularity of lightweight requirements, the application of tailor welded blanks with unequal thickness is increasing gradually. The welding deformation of tailor welded blanks with unequal thickness inclined weld is affected by the external constraints and the internal structural parameters of the plates. In this paper, the effect of the external constraints and the internal structural parameters on the multi-layer and multi-pass welding deformation of unequal thickness inclined weld was investigated. The deformation distribution law of butt welding of unequal thickness inclined weld was obtained combined with simulation and experiment results. The results showed that the spring constraint method was similar to the actual welding condition, meanwhile, the control effect of spring constraint on the welding deformation was better. The welding gap had the greatest influence on the welding deformation, followed by the angle of inclined weld, thickness of thick plate and thickness of thin plate. When the thickness difference between two plates was kept at 50%, the control effect of welding deformation was the best.

Numerical analysis of arc physical properties in narrow gap TIG welding

The arc physical properties of the plate-butt welding and narrow gap welding were simulated. The narrow gap groove affects the arc properties, and the narrow gap welding arc has its special properties. The shielding gas flows along the longitudinal direction in the narrow gap groove, and the arc temperature field constricts transversely but expands longitudinally. The high-temperature region expands and the welding heat efficiency increases. The current density is larger for narrow gap welding, which induces the larger Lorentz force to accelerate the plasma flow. The axial and radial plasma flow velocities are both larger for narrow gap welding, which leads to the larger arc pressure and shear stress. The results have good agreements with the experiments results.

Research on vehicle weld clearance detection algorithm based on image processing

The realisation of weld clearance detection algorithm is the key to vehicle weld detection based on image processing. In this paper, the weld detection area of the acquired image is set on the high resolution CCD image of vehicle weld gap, and then the weld line is detected by combining Hough transform and least squares method. Owing to abnormalities such as broken lines, overlapping lines, and slopes in the detected straight lines, all the checked straight lines are first optimised to extract valid weld straight lines. Finally, the distance of the weld gap is calculated using a formula. The method can be used to measure the weld gap of vehicles quickly and accurately.

Numerical Simulation of Constricted Sheet Tungsten Electrode Arc Characteristic with Insulating Solid Wall in Ultra Narrow Gap Welding Process

Numerical Simulation of Constricted Sheet Tungsten Electrode Arc Characteristic with Insulating Solid Wall in Ultra Narrow Gap Welding Process

New Welding Joint Geometries Manufactured by Powder Bed Fusion from 316L

Abstract In metal additive manufacturing, an increasing demand for large size parts occurs. However, because of the economics of size, the manufacturing costs for parts do not increase linearly with their volumes. It is often economically unreasonable to directly produce large size components. Instead of directly building parts, technologies like hybrid building are used. To avoid extensive clamping devices for welding, additive manufacturing can be used to design new gap geometries. With these new geometries, the positions of the parts can be defined and the deformations that are due to thermal influences by the welding process can be reduced. Nevertheless, the powder bed fusion process leads to a different microstructure that needs to be taken into account for the welding process. The new microstructure leads to an extensive shrinkage during welding that exceeds the shrinkage of conventionally produced parts. To avoid the shrinkage, the weld gap design not only has to fulfill the requirements of conventional welding but it also needs to avoid the shrinkage of the parts. The resulting shrinkage of the parts is, in one way, a disadvantage, but it can also be used as an advantage for subsequent laser welding processes. If additively manufactured parts should be laser welded to get a smooth weld surface, normally post-processing must be performed to fulfill the necessary gap distance. This can be avoided by combining different welding processes. If the backside of a part is first welded by conventional welding, the resulting shrinkage will close the gap on the structured surface. If laser welding is then applied to a structured surface, it is nearly impossible to see the weld. This article will present new designs for welding joints and show how the different welding behavior can be used to improve the additively manufactured parts for hybrid welding processes.

Narrow gap welding of low alloy and austenitic stainless steels using different Inconel alloys: comparison of microstructure and properties

In the present investigation, SA508 low alloy steel and 304LN austenitic stainless steel were joined by hot wire narrow gap gas tungsten arc welding. Inconel 82 and 52 were used as filler alloys. Evaluation of microstructure, micro-hardness, and tensile strength through in situ test in scanning electron microscope were attempted for the welded assemblies. Low alloy steel consisted of a heat affected zone adjacent to interface. A thin layer of martensite and Type-I boundary were revealed near the fusion boundary between low alloy steel and weld metal. Micro-hardness distribution showed a peak near the fusion boundary between low alloy steel and filler alloy owing to the presence of lath martensite, Type-I boundary, and complex alloy carbides. The micro-hardness was further dropped within the filler alloy. During the in situ tensile test, deformation was confined within the filler alloy, as it was the weakest link across the fusion boundary. It was revealed that the joint produced with Inconel 82 filler alloy has a better mechanical strength than the assembly fabricated with Inconel 52 filler alloy. Inferior quality of the latter was attributed to the relatively coarser grain structure and the presence of larger alloy carbides within filler alloy when compared with the former. Improved strength of the weld with Inconel 82 filler alloy was further endorsed by the lower slip distance for dislocation movement and higher strain hardening rate in comparison to the weld fabricated with Inconel 52 filler alloy.

Research on TIG welding gap corrosion resistance of X52/825 metallurgical clad pipein H2S/CO2 environment

Purpose Bimetallic composite pipe consists of a corrosion resistance alloy (CRA) layer for corrosion resistance and carbon steel for mechanical properties, which shows a promising prospect of gathering pipeline with its effective-cost and reliable corrosion resistance. However, the corrosion resistance of composite pipe is determined by the quality of its welding gap. This paper aims to investigate the TIG welding gap corrosion resistance of X52/825 metallurgical clad pipe in H2S/CO2 environment. Design/methodology/approach Corrosion tests of X52/825 welding gap were performed in a stimulated gas field solution containing both 1 MPa CO2 and 1.5 MPa H2S at 70°C for 720 h in a self-designed high temperature and high pressure autoclave. The anti-stress corrosion cracking (SCC) performance of X52/825 clad pipe ring root welding gap was investigated in both NACE A solution and the stimulant gas field solution by four point bending testing and constant load test. Then the experiments were rerun in XX high sour gas well. In addition, the alloy diffusion and microstructure characteristics of TIG welding gap were analyzed through scanning electron microscopy and energy dispersive X-ray spectroscopy technologies. Findings The results reveal that the root welding gap is almost not corroded in the stimulant gas field solution, and no micro-cracks were observed by electron microscope. Anti-SCC test results show the root welding gap does not break, indicating a good resistance to environmental-cracking in H2S/CO2 environment. The transition layer can be obviously observed in the root welding zone, and the alloy content of transition layer is diluted. However, the transition layer does not penetrate into the inner of CRA layer, which illustrates its good anti-corrosion performance. Therefore, TIG welding technology can be well used in the welding process of composite pipe. Originality/value This paper may provide theoretical reference for manufacturing and application of clad pipe.

Application of Optical Measurement Technology in Welding Simulation of Box Complex Structure

To verify the correctness of the sample quality and the finite element model, optical measurement technology is applied in this study. Unable to consider the quality of tack welding during the established modeling, a three-dimensional scanner is used to detect box complex structures after welding. The finite element model of box structure is established for the study of welding deformation of box structure with short, multi space and multi staggered distributed weld seam. The accuracy of the model is verified by global detection of the structural parts. The results show that the deformation trend warps at the boundary of the left and right plate and concaves in the center of the plate. The maximum deformation of the vertical plate center is 1.714mm. The bottom pad produces the extruding tendency, and the deformation near two sides of the plate is about 0.51mm, which is greater than that of 0.34mm away from the two sides of the plate. The deformation is not consistent in the front and back sides of the Z plate. The maximum error of the sample parts takes place in the front Z shape plate with an error of - 0.03mm~0.12mm. There is a certain size difference under the influence of the welding gap, but it still meets the requirements of the engineering application to eliminate the influence of the welding quality on the deformation measurement. By comparing the results of the simulation and the global measurement of the structural parts, the difference between the vibration seat and the front Z plate has a large difference that is 0.12mm∼0.24mm, and the deviation satisfies the requirements of the engineering application, and it can effectively guide the production.

Correlation between the Weld Residual Stresses and its Tensile and Impact Strength

In this study, the tensile strength, impact strength, and the hardness of the weld are determined. A criterion is proposed for describing the effect of residual stress on the weld mechanical properties. Dimensionless parameters such as Rya (the average of residual stress over the material yield strength), Rym (the maximum residual stress over the material yield strength), Ru2 (the difference in the residual stress over the material ultimate strength), and Ru3 (the difference ratio between the maximum and minimum of three-dimensional residual stresses over the material ultimate strength) are presented to describe the influence of residual stresses on the actual mechanical behavior of the welded pipe. Maximum Rya criterion and lowest strength are obtained at the weld gap center on the external surface of the pipe. The sharp decline in Ru2 criteria is consistent with the severe reduction in impact strength perpendicular to the weld gap.

Narrow gap applications of swing TIG-MIG hybrid weldings

To solve the lack of sidewalls penetration in gas metal arc welding (GMAW), a swing TIG-MIG hybrid welding method was proposed and applied in the narrow gap welding. The arc shapes and voltage changes in MIG, TIG-MIG hybrid welding and swing TIG-MIG hybrid welding were compared. The result reveals that the swing TIG-MIG hybrid welding can be used in narrow gap welding to attain good sidewall penetration. The assisted TIG arc can widen the MIG weld width and obtain good sidewall penetration, and stabilize the MIG welding voltage thereby improving welding quality. The melted welding wire in the MIG welding molten pool will spread to the TIG welding molten pool, which makes the weld width increased and the welding spread improved.

Research on the seam tracking of narrow gap P-GMAW based on arc sound sensing

Arc sensor is important in the automation of narrow gap welding process because only the arc signal can reflect the position of the arc in the groove in real time, as well as the heat input to the side wall. Except the current and voltage of the arc, the deviation state of the welding arc can be identified by experienced welders by the associated arc sound, therefore, the arc sound signal presents a potential welding seam tracking signal. In this study, arc sounds were acquired and processed to examine the correlation with weld deviation during narrow gap pulsed gas metal arc welding (P-GMAW). The influences of groove sidewall on the arc sound signal and the sensitive of arc sound features to welding torch deviation were studied, and the short-time energy was determined as the best parameter to reflect the arc deviation in the narrow gap grooves. Furthermore, a system was established for seam tracking using the arc sound short-time energy and the results show that the arc sound can be used as the control signal to realize seam tracking to a certain degree of precision, thus, providing a new control signal for narrow gap P-GMAW welding seam tracking based on multi-information fusion.

Stainless Steel Welding and Development Trend of Welding Technology

In this paper, the research and application status of brazing technology, pulsed arc welding technology and resurfacing welding technology in stainless steel materials are introduced. The effects of temperature, weld gap and brazing material on brazing are analyzed. The influence of pulse arc welding parameters on welding performance is analyzed; the influence of surfacing alloy on surfacing welding was analyzed; the development prospect of welding technology was analyzed.