Papers by Keyword: Welding

Abstract: Fatigue life prediction of a welded structure is a complex phenomenon due to the nature of fatigue and the welding process. Additionally, Finite Element Method (FEM) results are extremely sensitive to the size of elements. Therefore, it is difficult to adopt a method to estimate the fatigue life, especially for welded structures. Besides, mesh size independence is a critical issue to perform fatigue life prediction methods that eliminates the need for excessive element numbers in the mesh. This paper investigates the Master S-N Curve Approach (MCA) using the output parameters of the mesh insensitive Structural Stress Method (SSM). MCA based on SSM employs structural stresses recovered from nodal forces and nodal moments. To recover these inputs, FEM model should be established properly. Thus, boundary conditions and applied loads were prepared for the model according to the BS EN 13749:2021. The submodeling technique in ANSYS software was used to analyze the bogie structure. To justify the mesh independence for the model, different mesh sizes were tested. In a specific range for shell bodies, SSM was shown to provide sufficient mesh independence feature. Furthermore, MCA was compared with Hot Spot Stress Method and Nominal Stress Method based on their fatigue life estimations.

Abstract: The main objective of this work is to optimize welding parameters of AISI 430 FSS welds, focused to minimization of ferrite grains size using Taguchi’s design. Two input parameters of speed and welding current; were chosen to select the minimum grain size and to ascertain their effects on ferrite grain size. ANOVA method was used to evaluate the influence of varying factors on the overall quality of welds. Optimal combination of the parameters were be predicted by S/N analyses, it was accessed on employing an 80 A with 6mm/s. Experimental characterizations of optimum weld joint were performed by using tensile test assisted by image correlations, optical and electronic microscopy. As a result, welding speed had the main influence on grain size by 84.30%. Optimum welding parameter offered finest microstructure with low rate of martensite precipitates in both fusion zone and heat affected zone, and best combination of strength and ductility, it presented a homogeneous distribution of tensile stresses that caused a ductile fracture in base material. ,it is found that that optimized welding parameters permit to give greater resistance to corrosion, which exhibit a lower corrosion current, indicating that coarse ferrite grains are more susceptible to corrosion compared to fine grains.

Abstract: Gleeble 3800-thermomechanical simulator was used to simulate the heat affected zone of quenched and tempered 0.16 wt.% C steels with variation of molybdenum-and niobium contents. The purpose of the study was to evaluate the effect of alloying content on the properties of the coarse-grained zone of HAZ region (CGHAZ) and partially re-austenitised inter-critical zone (ICHAZ) with two different t_8/5 times (5 s and 15 s). Results showed that Mo and Nb decreased the amount of softening in the HAZ-region, especially with longer t_8/5 -time (15 s). 0Mo steel had mixed microstructure of bainite and martensite in the CGHAZ region with t_8/5 time of 15 s, which led to higher degree of softening compared to other steels. Shorter t_8/5 time of 5 s produced martensitic microstructure in CGHAZ region in all cases leading to higher hardness values. Impact energy values at-40 °C were at least 34 J/cm² in all cases. Highest hardness values in the ICHAZ-region were achieved in the case of 0.5Mo steel. Also, at-40 °C impact energy values of ICHAZ were at least 34 J/cm² in all cases, however Mo-free steel achieved clearly higher impact energies in ICHAZ region, which is result from softer microstructure with relatively low hardness compared to other steels. Overall, it can be concluded that longer t_8/5 time can be used, which corresponds to higher heat input in welding, if Mo and/or Nb alloying is used.

Abstract: Problems with corrosion in boilers and their parts can be solved by the application of different nickel alloys like 622, 625 or 686 by a variety of welding processes. This solution is used mostly in Waste-to-Energy plants or biomass stations burning waste wood, but it can also be found in the recovery boilers used in the paper industry. The most common material grades include low alloyed boiler steels like 16Mo3, 13CrMo4-5 and 10CrMo9-10. When there is a need to increase steam temperature and pressure more complicated alloys to become a natural choice. This paper focuses on the fabrication experience of welding of 7CrMoVTiB10-10 base tube with Inconel 625 weld overlay and presents a welding solution of matching filler metal used for root pass and S Ni 6625 filler metal for a fill-up and the cap performing a full strength weld without the need of overlay peeling and manual tie-in overlay. This method of welding saves a lot of time during execution in the workshop and on-site during installation and assures much better quality in the end. All examinations were performed to allow welding procedure qualification according to ASME and EN standards.

Abstract: Welding processes are commonly used in the industry for the manufacture of large parts or due to their complex geometry that does not allow the part to be manufactured as a whole. Nevertheless, the union can show worst mechanical properties than the rest of the piece, affecting negatively its service behavior, so it is necessary evaluate weald seam to ensure the correct process application. Electrical welding operations are commonly used due to the reduced equipment size or their possibilities application in numerous metallic materials. Notwithstanding, different variables have to be taken into account during the metal deposition, as intensity or speed deposition, among others. Weald seam geometrical evaluation is usually utilized to validate the union surface conditions. Despite this, surface irregularities caused during the process make its difficult to measure correctly with conventional equipment. However, laser profilometry is a non-contact technique that can be used to generate 3D profile of weald seam, facilitating its measurement with high accuracy. Therefore, in this work an initial analysis of the influence of material deposition speed and arc welding intensity on the weald seam geometry will be carried out using a laser profilometry equipment. In addition, to ensure a correct information acquisition, the laser profilometer requires a constant speed movement in relation with the weald seam analyzed, so new equipment has been manufactured, using additive manufacturing techniques, to support the profilometer throughout the information acquisition process.

Abstract: The process of welding is prone to many defects and these defects can cause the formation of many defective regions. It is necessary to identify the regions of defects as these may cause problems and breakages. In this work, we have proposed a method to detect and identify the defects that are commonly seen in seam welds. Manually identifying the detects is not only error prone and time consuming, most of the defects are not visible to the human eyes. In recent days, X-ray images of weld seam are used for this purpose. In this paper we have applied computer vision techniques and proposed an image processing pipeline to generate a binary segmentation of the image to identify the regions of slag and porosity defect seen in weld seams. From the experimental results on the publicly available dataset, GDX-ray images, it could be observed that, there is a significant improvement in detecting various defects with the proposed approach.

Abstract: This paper presents the development of numerical models which were used to simulate the behaviour of welded joints containing different combinations of multiple defects under tensile loads. Four representative combinations of defects were selected (including undercuts, incomplete root penetration, misalignments...), based on practical experience. In order to create accurate and functional models, this research involve a number of stages. This paper will focus on the various improvements made to the models, which started in relatively simple form. For this purpose, initial experimental and numerical analyses were carried out on specimens made of low-alloyed low-carbon steel S235, and after their accuracy was verified, the same methodology was applied to specimens made of higher quality material, steel S275. Improvements made to the models involved geometry, different combinations of boundary conditions and loads, and some were based on stress-strain states obtained by a combination of tensile testing and digital image correlation. The final result was a set of detailed numerical models which accurately simulated the behaviour of welded joints with multiple defects in them.

Abstract: Welding process is very important in numerous industries ranging from automotive and aviation to shipbuilding and pressure vessel production. Nowadays new methods to improve the productivity and quality of various welding techniques are searched. In many industrial applications even small process optimizations may lead to significant cost and energy savings and new applications. Large plate welding is particularly important in shipbuilding industry. It is common to weld multiple times to join thick plates, but this approach is not optimal from energy and time effectiveness and outcome quality is limited. Alternative is single high heat input welding, which causes various problems related to rapid local overheating and the formation of inhomogeneous post-weld microstructure. There are several heat affected zones near the weld pool, which has different properties and microstructure due to different cooling rates and heat flux orientation during solidification. Since welding is a complex multiphysical process there are various parameters such as electric current, oxygen presence, heat flow and weld pool flow which influence the quality of welding joint and efficiency of the process. In this paper we aim to experimentally and theoretically investigate how to modify heat and mass transfer in the weld pool and heat affected zone by static magnetic fields. Electromagnetic force is one of the ways how to affect the weld pool flow and to influence the heat and mass transfer from the weld pool to the base metal. Our research demonstrates that moderate DC magnetic field can cause various effects on the post-weld morphology, depending on the magnetic field direction. Analytical estimates and similarity analysis for high heat input welding on EH36 shipbuilding steel shows that electromagnetic methods, like application of DC magnetic field can be promising approach for improved welding outcome in some cases.

Abstract: Using austenitic steel in welding structures requires both destructive and non-destructive testing (NDT) to approve the use of intended welding specification, but also testing of material properties, even if they are guaranteed by manufacturer. In this particular case, X2CrNiMo17-12-2 (commercial trademark AISI 316L) is the material that has to be partly replaced by NiCr21Mo (commercial trademark Incoloy 825) in a piece of process equipment exposed to elevated temperature and highly corrosive environment. This research presents an investigation of overmatching V groove welded joint made of these two austenitic steels. Due to materials properties and specific application conditions, low heat input TIG welding was utilized. Mechanical properties of welded joint have been examined to check criteria which guarantees safe work and integrity of welded components. Chemical composition of used filler material was close to the one of NiCr21Mo alloy, providing weld overmatching, which needs to be checked as well. Mechanical testing (tensile, bending, impact, hardness), macro-and microstructure analysis provided detailed insight into welded joint characteristics and a ground for further investigation concerning heterogeneous austenitic welded joint, taking into account overmatching effect.

Abstract: Ni-based metallic amorphous alloys in ribbons shape are used in the manufacture of electrical resistances due to their high electrical resistivity, a value that does not change with temperature. The production of such resistances involves joining processes of amorphous ribbons. The amorphous alloys are difficult to weld by conventional melting processes, even in the presence of inert gas. Consequently, this paper presents the research carried out regarding the capacitor energy storage welding technique of Ni₆₃Cr₁₂Fe₄Si₈B₁₃ amorphous ribbons. The structural analysis was done by microscopy, X-ray diffraction, and differential scanning calorimetry, and the mechanical behavior was determined by nanoindentation. The joints obtained showed that the proposed welding technology is appropriate for this type of joint.