Fillet Welds Research Articles

A Study on the Application of Laser Cleaning on the Weld of the Gas Fuel Supply Pipe for DF Engine

While producing gas fuel supply pipes for duel fuel (DF) engines, a welding process is essential. Accordingly, specimen management before and after welding is crucial to obtain highly reliable weldments. In this study, we developed an environmentally friendly laser cleaning technology to address a toxic work environment and environmental pollution problems caused by chemical cleaning technology utilized in post-welding treatment of gas fuel supply for DF engines. An experiment was conducted by implementing surface laser cleaning of the butt and fillet weldment specimens according to process parameters. Conditions of process parameters were identified for facilitating laser cleaning and used in prototype production. The prototypes were processed through laser and chemical cleaning, and the quality of the end products was compared. The results indicated that the proposed method satisfactorily cleans the prototype surface without generating a toxic work environment and environmental pollution problems. Moreover, the roughness of approximately 5 μm was achieved on the laser cleaned surface. This is considered to be able to increase the adhesion of the paint compared to the smooth chemical cleaned surface during the painting for anticorrosion of the product.

Effects of Fillet Weld Size and Sleeve Material Strength on the Residual Stress Distribution and Structural Safety While Implementing the New Sleeve Repair Process.

The process optimization and structural safety improvement of the in-service repair welding of the X80 pipeline are very important. In this paper, the temperature, microstructure, and stress distribution were analyzed using the combination of TMM (thermal-metallurgical-mechanical) simulations and the corresponding verification experiments. The effects of the sleeve material strength and the fillet weld size were discussed. The results showed that the fillet weld zone was mainly composed of ferrite and bainite when the material of the sleeve pipe was Q345B. Furthermore, the sleeve pipe’s HAZ (heat affected zone) was dominated by lath martensite, lath bainite, and granular bainite. Moreover, granular bainite and a small amount of ferrite were found in the HAZ of the X80 pipe. It was found that, as the fillet weld size increased, the welding residual stress distribution became more uniform. The hoop stress at weld toe reduced from ~860 MPa of case A to ~680 MPa of case E, and the axial stress at weld toe reduced from ~440 MPa of case A to ~380 MPa of case E. From the viewpoint of welding residual stress, fillet weld size was suggested to be larger than 1.4T. The stress concentration and the stress distribution showed a correlation with the cracking behavior. Weld re-solidification ripples on the weld surface and weld ripples between welding passes or near the weld toe could cause stress concentration and the corresponding crack initiation. Furthermore, when the material of the sleeve pipe changed from Q345B to X80, the high-level tensile stress zone was found to be enlarged. The hoop stress at weld toe increased from ~750 to ~800 MPa, and the axial stress at weld toe increased from ~500 to ~600 MPa. After implementing the new sleeve repair welding process where X80 replaces the material of sleeve pipe, the cracking risk in sleeve pipe will improve. From the perspective of the welding residual stress, it was concluded that the fillet weld size reduction and the sleeve material strength improvement are harmful to in-service welded structures’ safety and integrity.

Optimized design of fillet welds in RHS joints for EN 1993‐1‐8

Optimized design of fillet welds in RHS joints for EN 1993‐1‐8

Multiaxial Fatigue Assessment of Typical Fillet Welded Details: Nominal Stress Approach-based Simplified Formulae

Multiaxial Fatigue Assessment of Typical Fillet Welded Details: Nominal Stress Approach-based Simplified Formulae

Residual shearing strength of fillet weld connections after exposure to elevated temperature

Experimental and analytical studies are carried out to investigate the residual shearing strength of fillet welded connections after exposure to elevated temperatures. Transverse fillet welds and longitudinal fillet welds were designed in the test, and four weld leg heights were considered. Fourteen specimens were manufactured for each weld leg height, including seven heating temperatures and two cooling methods, obtaining a total of 112 specimens, along with 8 unheated specimens for comparison. The load-displacement curves and stress-load ratio curves were obtained to evaluate the shearing strength, residual deformation, stress development, stiffness and ductility of the fillet welds. Test results exhibit the transverse fillet welds are mainly integral fracture, while longitudinal fillet welds occur obvious local and global cracks. The weld leg height has the greatest influence on the shearing resistance of fillet welds, followed by the elevated temperature and cooling method. When the heating temperature is between 400 °C-600 °C, an increasement in residual shearing strength can be noticed. Meanwhile, the residual deformation is positively correlated with the weld leg height. Additionally, water-cooling fillet welds are superior to room-temperature-cooled fillet welds in terms of stiffness and ductility. Moreover, the formulae for predicting the residual shearing strength of the fillet welds after exposure to elevated temperatures are proposed.

Metallurgical Failure Investigation of Fractured Dog Bone Seal Retainer Ring Fillet Welds in the Turbine Exhaust Casing of a Heavy-duty Gas Turbine Engine

Abstract Short fillet welds used to fasten a large retainer ring to so-called dog bone seals failed in the turbine exhaust casing of a non-OEM heavy-duty gas turbine engine used for power generation. The subject fillet welds fractured due to high cycle fatigue loading. Neither weld imperfections nor any other material defects were found that could have contributed to the failure. It was concluded that an unfavorable design, specifying very short fillet welds for fastening the dog bone seal segments to the retainer ring, was the root cause of failure. In a purely static loading situation, this design would probably not have failed. However, in a dynamic loading scenario as is the case in any gas turbine engine exhaust, such a design is simply not sturdy enough.

Reliability assessment of connections with slip-critical bolts and fillet welds in combination

This paper quantifies the reliability level of connections combining slip-critical bolts and longitudinal fillet welds using a probabilistic approach that integrates finite element (FE) modeling, meta-modeling, and Monte Carlo simulation. The proposed approach relies on experimental results to calibrate a FE model and quantify the uncertainties associated with various input parameters. The calibrated FE model is next integrated into a low-rank tensor approximation process to provide the variance-based sensitivity measures associated with the considered random variables. The influential variables, along with the calibrated FE model, are then used to evaluate the reliability by means of accelerated Kriging Monte Carlo simulation (AK-MCS). Finally, the proposed approach is applied to combination bolted-welded connections under direct tension to evaluate their reliability considering different faying surface conditions. The results of the conducted sensitivity analysis indicate that variability in weld geometry, bolt pretensioning forces, and friction coefficient of steel surface would significantly contribute to the variability of the load-carrying capacity of the investigated connections. In addition, the reliability of the combination connections with Class A and B faying surfaces is evaluated based on code provisions.

Online programming system for robotic fillet welding in Industry 4.0

PurposeFillet welding is one of the most widespread types of welding in the industry, which is still carried out manually or automated by contact. This paper aims to describe an online programming system for noncontact fillet welding robots with “U”- and “L”-shaped structures, which responds to the needs of the Fourth Industrial Revolution.Design/methodology/approachIn this paper, the authors propose an online robot programming methodology that eliminates unnecessary steps traditionally performed in robotic welding, so that the operator only performs three steps to complete the welding task. First, choose the piece to weld. Then, enter the welding parameters. Finally, it sends the automatically generated program to the robot.FindingsThe system finally managed to perform the fillet welding task with the proposed method in a more efficient preparation time than the compared methods. For this, a reduced number of components was used compared to other systems: a structured light 3 D camera, two computers and a concentrator, in addition to the six-axis industrial robotic arm. The operating complexity of the system has been reduced as much as possible.Practical implicationsTo the best of the authors’ knowledge, there is no scientific or commercial evidence of an online robot programming system capable of performing a fillet welding process, simplifying the process so that it is completely transparent for the operator and framed in the Industry 4.0 paradigm. Its commercial potential lies mainly in its simple and low-cost implementation in a flexible system capable of adapting to any industrial fillet welding job and to any support that can accommodate it.Originality/valueIn this study, a robotic robust system is achieved, aligned to Industry 4.0, with a friendly, intuitive and simple interface for an operator who does not need to have knowledge of industrial robotics, allowing him to perform a fillet welding saving time and increasing productivity.

Mitigation of welding induced buckling with transient thermal tension and its application for accurate fabrication of offshore cabin structure

Offshore cabin structure is usually fabricated by welding with 6–8 mm steel plates as lightweight application, and welding distortion is inevitable generated to influence its dimensional accuracy. In particular, welding induced buckling will occur under conventional welding procedure due to the geometric feature of cabin structure. Typical fillet welded joints in considered cabin structure were numerically examined beforehand, while thermal and mechanical behaviors were represented with non-linear thermal elastic plastic FE computation. Then, welding inherent deformation was proposed as driving force for welding distortion prediction, which can be evaluated by integration of residual plastic strain for each typical welded joint. Since transient thermal tension is applied during fillet welding with numerical investigation, self-constraint supported by base materials on welding line will become weak. Thus, less plastic strain is generated during welding process, and magnitude of welding inherent deformation will be significantly reduced. Elastic FE computation with welding inherent deformation as mechanical load was carried out to predict out-of-plane welding distortion of considered cabin structure, while cases of conventional welding and welding with transient thermal tension were examined. Better fabrication accuracy can be obtained with application of transient thermal tension due to less welding inherent deformation.

On the weld root fatigue strength and improvement techniques for non-load-carrying transverse attachment joints with single-sided fillet welds and made of mild and ultra-high-strength steels

The present study experimentally and numerically investigates the fatigue strength of non-load-carrying transverse attachment joints prepared with single-sided fillet weld. Constant amplitude fatigue tests are carried out on specimens made of S355 and S1100 steel grades to obtain the fatigue strength of these joints. In addition, the study evaluates fatigue life improvement technique for these joints comprising the use of a curved plate edge shape in the attachment, which results in varying weld penetration and weaved weld root shape. Numerical analyses are carried out to determine the applicability of the effective notch stress concept in assessing the fatigue strength of the studied joints. The experimental results show that the weld root to the base plate is the critical fatigue failure mechanism, and characteristic design fatigue strengths of FAT97.7% = 109 MPa and FAT97.7% = 97 MPa (with a slope parameter of m = 3) in the nominal stress system for the S355 and S1100 grades with a straight root geometry are obtained, respectively. Using a curved plate edge shape and varying weld penetration, the fatigue strength could be improved by up to 25% for the S1100 grade. The numerical analyses reveal that the effective notch stress modeling technique of the fictitious notch radius significantly affects the stress concentration factors, while the fillet-type modeling technique at the weld root showed more accurate results than the keyhole shape.

A comparison of stress analysis and limit analysis approaches for single and multiple nozzle combinations in cylindrical pressure vessels

The finite element method is the most commonly used approach when solving complex practical cylinder-cylinder junctions in pressure vessels. This is used when the geometrical arrangement is out with the permitted scope of the design-by-rule approaches or when detailed stress information is required as in a fatigue assessment. High-stress concentrations occur on the crotch corner for cylinder-cylinder joints, and it is possible to reach solutions for this problem by using both theoretical and numerical solutions. However, those approaches do not fully overlap nor have the same underlying assumptions. As such, an innovative high-fidelity finite element model has been developed to provide a holistic unified approach which can tackle a wide range of problems. In this study, various detailed nozzle design challenges were investigated including single and multiple nozzle combinations, nozzle-cylinder systems with different size ratios, fillet weld applications, limit loads and external loading cases were analyzed. The results obtained are compared with well-respected calculation methods such as WRC537, and a new approach is presented for the analysis of cylinder-cylinder combinations.

A Method of Feature Extraction of Position Detection and Weld Gap for GMAW Seam Tracking System of Fillet Weld With Variable Gaps

Seam-tracking technology based on vision sensing is the key technology to realize robot intelligent welding. Because of changes in the weld gap, the diversity of workpiece material and surface conditions, and the interference of welding noises, it is extremely difficult for the robot to realize real-time seam-tracking in gas metal arc welding (GMAW) of large structures. So, a method of position detection and weld gap feature extraction is proposed for GMAW seam-tracking system of fillet weld with variable gap. This method established a highly robust weld feature extraction model based on a low-cost structured-light vision sensor. In this model, using the reflection characteristic of the stripes on fillet weld, a feature extraction method for variable gap weld based on column gray difference operator was proposed. To overcome the interference of welding noises, this model adopted the AND logic operation method between adjacent sampled images. To overcome the interference of uneven and strong reflection conditions, an optimized random sampling consistency (RANSAC) algorithm was proposed and used for weld feature extraction. The optimized RANSAC algorithm used the linear slope of the stripes to optimize the random sampling process of the algorithm. The experimental results showed that the average detection errors of the proposed method in the Y-axis and Z-axis directions are 0.19 mm and 0.23 mm, respectively, at a welding speed of 1000 mm/min. The proposed method could realize seam tracking of the variable gap fillet weld and still had good robustness under the uneven and strong reflection of the workpiece surfaces.

Optimized design of fillet welds in RHS joints for EN 1993‐1‐8

AbstractISO 14346 permits fillet welds in rectangular hollow section (RHS) joints to be designed either (i) to develop the capacity of the connected brace or (ii) to resist the actual load(s) in the brace (i.e. as “fit‐for‐purpose”). However, no methods for design according to approach (ii) are given in the ISO or any European standard. In this paper, data from 41 weld‐critical tests on RHS gapped K, T, Y and X joints under brace axial load(s) are analysed to determine a reliable method for the design of fillet welds as “fit‐for‐purpose”. “Weld effective length” formulae are evaluated in conjunction with EN 1993‐1‐8 (directional and simplified methods) according to the standard procedure of EN 1990. A reliable method, based on ISO 14346, is proposed for calculating the design resistance of all‐around fillet welds in RHS gapped K, T, Y and X joints. Updates to the minimum fillet weld throat thicknesses required to develop the capacity of a connected RHS brace are also discussed.

Liquid Metal-Assisted Cracking During Hot-Dip Galvanizing of Complex Structures: A Case Study

A pipe rack assembly uses hot-dip galvanized trusses joined together by screw connections. The welded trusses were manufactured with ASTM A572 gr.50 W steel profiles. Two of them fractured during the galvanizing bath. The fractures presented typical characteristics of the LMAC — liquid metal-assisted cracking mechanism. In both cases, the fracture was located in the structural element base metal and followed the fillet weld to the neighboring elements at a distance beyond the heat-affected zone. The trusses height was greater than the depth of the molten zinc vat, and double immersion is required for complete galvanization. The failed trusses had a particular geometry, distinct from the others. The design of the trusses was verified taking into account the thermal stresses generated by the partial immersion in the zinc bath. Among all, only the two broken trusses were exposed to stresses of thermal origin substantially higher than the material yield strength. Metallographic analysis revealed secondary intergranular cracks near the fracture surface. The crack roots contained zinc. In addition, the secondary cracks had a large opening in relation to the depth, which indicates material plasticization in the root region.

A new design model for welded joints

AbstractIn the AiF‐FOSTA research project P1020 [1], a new design model for welded joints was developed. In this context, a small scale test on flat tensile specimens was designed, with the help of which various influences on the strength and ductility of the welds were investigated. Furthermore, extensive tests were carried out on overlap joints, cruciform joints with double fillet welds as well as partially and fully penetrated butt joints. This was done to calibrate the weld construction factor αw, which takes into account the influence of the type of joint on the load‐bearing capacity. In the following article, after a short summary of the current state of research, the design model, and the results from the parameter studies on flat tensile tests are described in more detail in [2–4]. Subsequently, the test program on welded joints and the calibration of the weld construction factor αw are presented. Finally, the results of the design model and the tests carried out are compared with test results from other research projects and the design model of prEN 1993‐1‐8 [5].

REINFORCING I-BEAMS WITH WEB OPENINGS USING FILLET-WELDED PERFORATED PLATE

In beam-to-column connections in steel structures, it is crucial for stresses to be transmitted from the beam to column smoothly. However, openings of I-section steel beam web are often made at the end of the beam when piping facilities pass through the beam. Openings at the end of the I-section steel beam reduce its flexural strength, shear strength, and deformation capacity of the steel beam ends. If the openings are made at the end of a beam, the beam should somehow be reinforced to achieve acceptable stress transmission performance and good deformation capacity. There are several existing ways of reinforcing openings at the end of a beam in Japan; however, simpler and more economical reinforcing methods are desired. In this paper, a new reinforcing method of openings at the beam ends is proposed. The proposed reinforcement is a perforated steel plate connected to the beam web using fillet welding. The proposed method is simple, easier to produce, and easier to construct compared to conventional methods. An experiment was conducted to verify the performance of the proposed reinforcing method. The results of the experiments showed that the proposed reinforcing method can be designed conservatively using Kato’s formula.

Feasibility of slotted end connections improved with thicker sections in tension: Experimental and numerical investigation

Gusset plate slotted end connections are effective and convenient techniques for connecting tubular members in building structures. A net section crack is the dominant failure mode found in conventional slotted end connections unless strengthening measures are adopted. The improved connection involves a thick-walled circular hollow section (CHS) set at both ends of the member to increase the area of the net section. A series of laboratory tests and associated numerical models were conducted to investigate the mechanical performance of the improved slotted end connection under axial tensile loading. The load-displacement relationship, stress distribution characteristics, and typical failure modes are all incorporated and discussed. Different from tear-out failure or net section crack failure in a conventional connection, the improved connection shows gross section cracks after experiencing extensive gross section yielding. The improved connection enables the length of the fillet weld (LW) to be greatly reduced without causing a reduction in the load-bearing capacity. With the gradual increase in the length of the fillet weld (LW = 60, 90, and 120 mm), the axial load-bearing capacity of the improved connection is approximately 34.6%, 15.8%, and 4.9% higher than that of the conventional connection, respectively. From the validated FE analysis, the local stress concentration near the slot end can be reduced by approximately 50%, and the shear lag has little effect on the strength of the net section. The load-bearing capacity, ductility, and failure modes of the improved connection show better performance than those of the conventional connection.

Isogeometric Analysis and Bayesian Optimization on Efficient Weld Geometry Design for Remarkable Stress Concentration Reduction

Shape optimization combined with Isogeometric Analysis will be an efficient design method since exact Computer Aided Design geometries can be used for numerical analysis thanks to the same basis functions. In this study, authors developed an in-house research software JWRIAN-IGA and applied it to optimize the weld geometries of two models, namely a T-joint fillet weld and an elongated boxing fillet weld to reduce stress concentration. A gradient-free stochastic global optimization algorithm, Bayesian Optimization was used to sought optimal geometry parameters. It was shown that the optimized geometry was efficiently designed and the stress concentration in the welds for both cases was greatly reduced.

Influence of welding processes and weld configurationon fatigue failure of natural gas branch pipe

Fatigue test was executed to evaluate the fatigue performance on the fillet and butt weld joint of the natural gas branch pipe. Diameter of the branch pipe, throat thickness, geometrical shape of the fillet weld and welding processes were adopted to assess the fatigue strength of the branch pipe. SMAW and GTAW process were used to compare the welding process and the mechanical performance of the fillet weld joint. API 5 L Gr. B pipe and fitting of ASTM A105 were used for the fillet weld joint. There was no difference in tensile strength with variation of the welding process of the fillet weld joint. All tensile specimens were failed at the base metal of the pipes not weld joint. Fatigue life of the fillet weld joints was improved with larger pipe diameter, the leg length of the branch pipe direction, throat thickness and area of the weld metal. Failure of the fatigue specimens were occurred at the toe or root of the fillet weld joint.

An experimental study on the seismic behavior and replaceability of the replaceable steel shear links

The reinforced concrete columns and steel beams (RCS) composite frames have received popularity in low to moderate seismic regions due to advantages of the system. However, the poor repairable capacity and deteriorating pinched hysteretic behaviour of the traditional RCS framed structure limit the application in practice under earthquakes. This study presents a modified RCS framed structure with replaceable members aiming to enhance the energy dissipation and resilience capability. The structural configuration character and the general predetermined levels of lateral response of the proposed RCS framed structure with replaceable members is first introduced. Seven quasi-static loading tests were subsequently conducted to evaluate the seismic behavior and replaceability of the replaceable shear links. Parameters including the link length ratio, stiffener configuration and link-to-column connection were examined. The test results depicted that the specimens exhibited the shear dominated behavior. The major failure features of the shear links included web-to-stiffener weld tear, web buckling and web fracture. All tested specimen showed a stable bearing strength, large inelastic rotation capacity and excellent energy dissipation behavior. The same link length ratio of the specimens with different specialized connections presented the similar behavior. Noted that end plate and web stiffeners connection can alleviate the stress concentration on the fillet weld of the flange-to-end plate weld and optimize the performance of the shear link. The average overstrength factor and inelastic rotation capacity of the test specimens were 1.9 and 0.087 rad significantly exceeding 1.5 and 0.08 rad provided by the AISC 341-16 provisions for the EBF links, respectively. In addition, the replaceability of the specimens was evaluated underwent the entire loading process. Compared with the T-shaped and Π-shaped plate connections, replacement of the shear link with the end plate demanded the least effort and time.