Weld Reinforcement Research Articles

Failure analysis on tube weldment cracking of a high-temperature carbon black air preheater

In this study, the failure analysis on weldment joining the medium-to-high temperature steel tube (the jointed materials are S30815 and HK40Nb, respectively) sections of a high-temperature carbon black air preheater was conducted. The root cause of the cracking is identified as metal dusting appearing in the high-temperature carbon black flue gas environment, as indicated by the result of the macroscopic analysis, the chemical composition analysis, the metallographic examination, and the corrosion product analysis. As revealed by the result, the metal was directly exposed to the flue gas due to the damage of the surface protective film (i.e., Cr2O3) of the stainless-steel tube weldment. The result suggested that elemental sulfur within the flue gas and overheating in the operation destroyed the oxide film. Under the effect of the high carbon activity in the flue gas, carbon atoms were driven to attack metals. The accumulated carbon particles arising from weld reinforcement promoted the failure of the weldment. To prevent metal dusting, it is recommended to increase the amount of water vapor in the flue gas for the reduction of the carbon activity, choose high-temperature resistant materials for the prevention of direct contact between the flue gas and the material, and improve the welding quality to prevent the flue gas from being disturbed.

A Study on Fatigue Crack Reinforcement of Bridge Deck and U-Rib Weld after Considering Residual Stress

In order to study the fatigue performance of the initial crack between the CFRP reinforced deck and the U-rib weld after considering the residual stress, the welding residual stress of the deck and the U-rib weld was analyzed by the welding subprogram of ABAQUS, and then the segment model of the deck and the U-rib of the steel bridge deck was established by using the interaction technology of FRANC 3D-ABAQUS, and the stress intensity factor of the crack between the deck and the U-rib weld under the vehicle-only, vehicle-residual stress combined loads, and CFRP-strengthened combined loads were analyzed. The growth analysis of cracks before and after reinforcement was carried out. The results show that the amplitude of the stress intensity factor of the crack tip is less than the threshold when only the vehicle is applied, and the crack will not spread. After considering the residual stress, the maximum KI value of the crack at the welding toe is increased by 6.9 times compared with the maximum value of the vehicle only, and the maximum KI value at the welding root is increased by 10.7 times; the reinforcement method of CFRP pasted on the lower surface has a reinforcement effect on the fatigue crack at the welding toe, but the fatigue crack at the welding root has no reinforcement effect; the reinforcement effect of the welded toe crack increases with the increase of the number of CFRP layers, length, and width. When the weld toe crack after reinforcement extends to half the thickness of the deck, the number of car-residual stress combined load cycles increases by 43% compared to when it is not reinforced.

X-ray tomography of failure behaviors of arc welded AA2219 joints under tensile and cyclic loading

As one of the main structural materials widely used for the new generation of launch vehicles, the tensile properties and microstructural characterization of tungsten inert gas (TIG) welded 2219 aluminium alloy has been studied extensively. However, there are significant differences between fatigue fracture and tensile fracture modes. In this paper, the tensile and fatigue damage behaviors of arc-welded AA2219 joints were investigated in depth. Combined with the microstructure observation and fracture analysis done by using X-ray computed tomography, the main factors that affect the fatigue damage behavior are discussed. The results show that there are a large number of porosity defects in the weld zone, showing an aggregation distribution at the weld toe and weld pool line. The fine-grain zone around the fusion line is the softening zone of the welded joint. For tensile conditions, the cracks were initiated at the softening zone and extended along the fusion line to the final fracture. Under fatigue loading conditions, the weld reinforcement leads to the stress concentration at the weld toe, and at the same time, a lot of pore defects at the weld toe, which causes crack initiation at the pores in the weld toe. Due to the small plastic zone at the fatigue crack tip, the crack propagates almost perpendicular to the loading direction in the heat-affected zone, driven by a mode I crack. A large number of gas pores in the weld zone have no substantial effect on fatigue crack propagation.

In-situ electrochemical testing and fluid dynamics simulation of pipeline defects under flow accelerated corrosion

The pipeline defects of flow accelerated corrosion (FAC) on the corrosion behaviors and localized corrosion mechanisms on different locations of the depressions and the welded joint with weld reinforcements were investigated using wire beam electrode (WBE) techniques and fluid dynamics simulations. The results revealed that the swirling vortex inside the depression and the local jet impact by the fluid separation in the weld reinforcement can accelerate the localized corrosion. Also, the depressed upper and trailing edge regions and the weld toes on both sides of the weld reinforcement experience considerable pressure fluctuations, enhancing interfacial mass transfer processes and inducing cavitation for severe localized corrosion failure. Furthermore, the galvanic corrosion strength factor (g) indicated an enhanced susceptibility of localized corrosion in depression and welded joints with weld reinforcement.

Investigation on corrosion tendency behaviour of TA2 titanium alloy welded joints under flow scouring conditions using the array electrode method

PurposeThe corrosion behaviour of titanium alloy surface when fluid with different flow rates flows through welded joints with different residual heights was explored.Design/methodology/approachThe experiment uses a combination of array electrodes and simulation.FindingsIt is found that when the weld reinforcement exists, the corrosion tendency of both ends of the weld metal is greater than that of other parts of the welded joint due to the influence of high turbulence kinetic energy and shear stress. The presence of weld reinforcement heights makes the fluid behind it fluctuate greatly. The passivation films of both the base metal (BM) at the rear and the heat-affected zone (HAZ) are more prone to corrosion than those of the front BM and HAZ, and the passivation film is rougher.Originality/valueThe combination of test and simulation was used to explore the influence of electrochemical and hydrodynamic factors on the corrosion behaviour of titanium alloy-welded joints when welding residual height existed.

Inspection for non-planar shaped welded joints of pipes using FMC ultrasonic technique

In applying ultrasonic testing (UT) to pipes with welded joints, one of the challenges is about the access limitation of UT probes caused by non-planar weld reinforcement profiles. One way to avoid this problem is to remove weld reinforcement for ensuring the contactability of a probe on welded parts. However, the removing process for flatten weld reinforcement needs extra day per joint and might damage pipes surface. To overcome this issue, we have been developing a proprietary UT method that enables inspection of non-planar welded joints using the Full Matrix Capture (FMC) and the Total Focusing Method (TFM). A specially designed wedge is used between a probe and a welded part in order to extract the weld surface shape from the recorded data. In the TFM, multilayer propagation paths are analyzed with considering refractions at interfaces between the layer and the weld surface. The analysis is based on the Fermat's principle of least time, whereas this is generally known to be a time-consuming process. With the aim of performing real-time scanning in inspection to pipes on weld reinforcement, the shape of the wedge is optimized for welded joints to reduce the calculation time of the multilayer analysis. In this presentation, we will report the developed FMC/TFM technique and, furthermore, the validation results using pipe specimens with weld reinforcement.

Lateral behaviour of steel plate shear wall with cold-formed steel strips reinforcing door opening

Holes in the walls of buildings are occasionally necessary to fulfil buildings’ functional requirements. When a steel plate shear wall (SPSW) is used as the primary lateral force-resistant structural member in a building, the effect of such openings on the mechanical properties of the SPSW is non-negligible. In this study, reinforcement of SPSWs with door openings using prefabricated cold-formed steel (CFS) strips is proposed. The proposed method can improve the mechanical properties of SPSWs with openings without inducing the residual deformation and stress caused by the typical welding reinforcement method. Cyclic loading tests were conducted to analyse the lateral resistance of two perforated SPSW structures reinforced using the proposed method: one SPSW with a door opening in the centre, and another with the door opening positioned at its edge. The test results showed that the openings reduced the lateral stiffness and strength of the structures. Specifically, a 30.84% decline in ultimate strength was observed for specimens with central door opening, while a 32.78% reduction was noted for specimens with edge door opening. Finite element models were derived and evaluated based on these results, and an SPSW with openings reinforced by CFS strips was modelled as equivalent to an SPSW without openings for analysis. The proposed simplified analysis model realises the weakening effect observed in a perforated SPSW by reducing the thickness of the equivalent unperforated SPSW. Finally, the equivalent analysis model (EAM) proposed herein was compared with experimental results, with the errors in yield strength and ultimate strength both within 5%. The results demonstrating that the proposed EAM is accurate and reasonable.

CFD-DPM modelling of solid particle erosion on weld reinforcement height in liquid-solid high shear flows

Liquid-solid two-phase flow erosion can lead to great economic losses and safety concerns in the oil & gas storage and transportation industry. The solid particle erosion on weld reinforcement height (WRH) in liquid-solid high shear flows were systematically investigated by coupling the computational fluid dynamics (CFD) and the discrete phase model (DPM) method. The effects of liquid velocity, WRH height, particle flow rate, and particle size on the particle erosion in the WRH region were analyzed. Increasing erosion rate was observed with increasing liquid velocity. The erosion rate first increased and then decreased with increasing WRH height. The increasing erosion rate was observed with both increasing particle flow rates and particle sizes. The existence of defects on the WRH surface significantly increased the maximum erosion rates. This work can provide scientific guidelines for the corrosion protection and safe operation of long-distance oil & gas pipelines.

Fracture mechanism of aluminum/steel laser-arc welded-brazed joints during quasi-static tensile and dynamic fatigue tests

The primary focus of this study was the fracture mechanism of aluminum/steel laser-arc welded-brazed joints under quasi-static tensile and dynamic fatigue conditions. Digital image correlation (DIC) was applied to record the tensile and fatigue fracture process, while finite element method (FEM) was employed to analyze stress distributions during fatigue tests. The tensile results indicated that the weld reinforcement changed the strain evolution and significantly improved mechanical properties of aluminum/steel joints. During fatigue tests, the weld reinforcement enhanced fatigue properties and changed the joint geometry of aluminum/steel joints, leading to the emergence of distinct failure behaviors. At larger stress loads, the maximum cyclic stress on the interface surpassed the interfacial bonding strength, which resulted in a gradual shift of strain concentration from the weld toe to the interface. At smaller stress loads, the interfacial region exhibited tremendous crack resistance, and strain gradually accumulated in the weld toe, which led to fatigue damage. Interestingly, the strain in the interfacial region became more significant during the fatigue process after removing the weld reinforcement. Overall, this study shed light on the fracture mechanism of aluminum/steel joints under different loading conditions. Knowledge of this mechanism is essential for developing reliable aluminum/steel structures.

Theoretical and experimental analysis of the correlation between magnetic memory signals and cumulative ductile damage of butt weld under low cycle fatigue

Welded structures experiencing superimposed cyclic loads with large plastic strain during a strong earthquake can easily lead to ductile or fatigue fracture. A newly developed self-magnetic flux leakage (SMFL) nondestructive detection technology named metal magnetic memory (MMM) is a valid approach to monitoring the development of fatigue damage in ferromagnetic materials. To investigate the correlation between MMM signals and cumulative ductile damage for butt weld under low cycle fatigue (LCF), combining strain-based Jiles-Atherton hysteresis model, magnetic charge model, and cumulative damage mechanics model, the theoretical relations between normal component HSF(z) of MMM signals and cumulative ductile damage D for single V groove butt weld were established in this paper. Relevant monotonic tensile tests and strain-controlled LCF tests were conducted, and the HSF(z) signals on the surface of welding specimens under different cyclic loads were measured. Comparing with experimental results verified the feasibility and accuracy of the theoretical relations. The results indicated that the peak-valley gradient Kp-v on the HSF(z) signals curve was decreased monotonously as the cumulative ductile damage D increased and the rate of decrease also diminished gradually. A possible exponential descending tendency of Kp-v with increasing D was demonstrated. Besides, the influences of weld width and weld reinforcement on the correlation between Kp-v and D were discussed theoretically in detail. This research provided a potential possibility for the assessment of the cumulative ductile damage at the welding joints under LCF based on MMM technology.

Impact of Electrode Rotation on Aluminum GMAW Bead Shape

Aluminum gas metal arc welding (GMAW) uses inert shielding gas to minimize weld pool oxidation and reduce susceptibility to porosity and incomplete fusion defects. For aluminum shipbuilding, naval welding requirements highly recommend the use of helium-argon mixtures or pure helium shielding gas to provide a broader heat field and better weld toe fusion. Pure argon shielding gas can be used but has been susceptible to incomplete fusion and porosity defects, where argon’s lower thermal conductivity promotes a narrower arc heat field and shallow weld fusion depth. Using helium is a concern because it is a finite resource that costs approximately five times more than argon. The rotating electrode pulsed GMAW process was investigated to improve argon shielding fusion characteristics and reduce helium usage. Argon-shielded bead-on-plate tests were used to evaluate the relationship between ER5183 electrode rotation parameters and arc power on constant deposit area bead shape. These tests were compared to stringer beads (no oscillation) that were made with argon, helium, and helium-argon shielding gases. Electrode rotation improved underbead fusion depth width and toe fusion. With preferred rotation parameters, the bead width and incomplete fusion at weld toes were equivalent to helium-based welds. For weld reinforcement, electrode rotation promoted a nonsymmetric profile with deposit bias on the bead side, where rotation direction was aligned with travel direction. The bead-side deposit bias is an advantage based on preliminary horizontal V-groove welding procedures using ceramic backing. Electrode rotation can offset the effects of gravity, promoting a smoother bead and fusion profile.

Automatic Aluminum Alloy Surface Grinding Trajectory Planning of Industrial Robot Based on Weld Seam Recognition and Positioning

In this paper, we propose a novel method for planning grinding trajectories on curved surfaces to improve the grinding efficiency of large aluminum alloy surfaces with welds and defect areas. Our method consists of three parts. Firstly, we introduce a deficiency positioning method based on a two-dimensional image and three-dimensional point cloud, which enables us to accurately and quickly locate the three-dimensional defective areas. Secondly, we propose a 2D weld positioning method based on the defect area and obtain the spatial position of the 3D weld by combining the relationship between 2D and 3D images. Additionally, we propose an orthogonal projection method from the point cloud to the aluminum alloy surface to calculate the weld reinforcement. Thirdly, we present a space spiral grinding trajectory planning method for complex curved surfaces based on the characteristics of the weld reinforcement, spatial position, and spatial position information of the defect area. This method shortens the grinding time of the defect area and improves efficiency. Simulation and experimental results show that our grinding trajectory planning method is more efficient than other grinding methods in removing defects from the surface of aluminum alloys. Moreover, the defect area after grinding is smoother than before.

Characterization of galvanized steel-low alloy steel arc stud welded joint

This paper investigates the possibility of successfully welding a Low Alloy Steel (LAS) stud to Galvanized Steel (GS) plate.Arc Stud Welding (ASW) was performed on joining LAS studs to GS plates. Welding parameters were selected based on weld trails. The first tests of the welded joints were based on visual inspection for welding defects such as lack of fusion and undercut welding defects. The good quality should be free of these defects and have full weld reinforcement. Other weld qualifications included torque strength test, microhardness test, and microstructure examination.The LAS studs have been successfully welded to a galvanized steel plate using the arc stud welding process. Higher welding current with adjusted welding time (800 A, 0.3 s) gave full weld reinforcement, the best joint appearance, and strength. Martensite phase was detected in the weld area and heat affected zone (HAZ), affecting the joint mechanical properties. Hardness property varied across the welded joint, and maximum hardness was recorded at the HAZ at the stud side. Hardness increased with the increasing welding current. At 800 A, welding current hardness was 10% higher than at 400 and 600 A. Torque strength was affected by weld reinforcement, and 800 A gave the best weld reinforcement that produced the highest torque strength.The main research limitation is the difficulty of welding LAS studs and GS plates. In conventional welding methods, such as gas metal arc welding, it is hard to get full weld penetration due to the geometry restrictions of the joint, which results in partial weld penetration between the studs and the plates. Furthermore, the issue of zinc evaporation during welding can be reduced by the advantage of the very high welding speed (in milliseconds) of ASW that overcomes the problem of continuous welding that usually results in the formation of harmful porosities and poor weldability.In this research, galvanized steel plates were successfully welded to LAS studs using the ASW process. The welding parameters for this dissimilar welding joint were carefully selected. Microstructure changing due to the welding process was investigated. The joint mechanical properties were evaluated.

On the Fatigue Strength of Welded High-Strength Steel Joints in the As-Welded, Post-Weld-Treated and Repaired Conditions in a Typical Ship Structural Detail

Weld quality and life extension methods of welded details in ship structures made of high-strength and ultra-high-strength steels are of high importance to overcome the issues related to the fatigue characteristics of welded high-strength steels. The current work experimentally and numerically investigated the fatigue strength of a longitudinal stiffener detail, typically present in the bulkhead connections of ship hull. Two high-strength steel grades, namely EQ47TM and EQ70QT steels, were studied in welded plate connections using gas metal arc welding with rutile-cored wires. Fatigue tests were carried out on both small-scale specimens under axial and large-scale beam specimens under four-point bending loading. In addition to the joints tested in the as-welded condition, the high-frequency mechanical impact (HFMI) treatment was considered as a post-weld treatment technique in the fatigue test series. Furthermore, the large-scale beam specimens were pre-fatigued until substantial fatigue cracks were observed, after which they were re-tested after weld repairing and post-weld treatments to investigate the potential to rehabilitate fatigue-cracked ship details. The joints in the as-welded condition were performed in accordance with the current design recommendations. Due to the severe transition from the base material to the weld reinforcement in the joints welded with the rutile-cored wire, a successful HFMI treatment required geometrical modification of weld toe using a rotary burr to avoid any detrimental sub-cracks at the HFMI-treated region. Alternatively, the use of solid filler wires could potentially overcome these issues related to the welding quality. Repaired and post-weld-treated welds performed well in the re-tests, and the fatigue strength was almost twice higher than that of tests in the as-welded condition.

Detection of reinforcement of multi-bead and multi-layer weld in additive manufacturing based on on-line visual information of weld pool

In the multi-bead and multi-layer arc additive manufacturing process, the information of cladding reinforcement reflects the welding quality to a certain extent, so it is of great significance to monitor the reinforcement of cladding layers in real time. In this paper, a point cloud density search method is used to segment the point cloud of a single weld bead in the multi bead weld seam, and then the reinforcement of each cladding bead of multi-bead and multi-layer weld is extracted separately when the bottom plate is deformed due to high temperature, and a residual-based prediction model is constructed for quantitative forecasting of the transient reinforcement before solidification of block cladding layer in real time. The following work is completed to prove the accuracy and effectiveness of the proposed model, two different strategies are used to predict the reinforcement of multi-bead and multi-layer welds. Through the experiment, we can see the mean forecast error of the reinforcement of multi-bead and multi-layer welds is less than 0.3 mm, while the time for the model to dealing with the molten pool image is 18 ms, and the optimal strategy can make the average error better than 0.15 mm, which proves that the model constructed in this paper has great generalization performance and realizes the real-time and high-precision prediction of cladding reinforcement in the case of small deformation. The study of this paper supplies a necessary basis for the online monitoring and control of morphological defects in the process of weld processing.

Analysis of residual stresses in electron beam welding with filler wire of Ti62A alloy

Residual stress significantly affects the performance of the welded joints and the tensile residual stress easily leads to the joint fracture and failure. A three dimensional nonlinear transient thermo-mechanically coupled finite element model of Ti62A alloy electron beam welding (EBW) with filler wire was established. The influence of the welding parameters, such as welding power, groove angles and number of welding layers on the temperature and residual stress evolutions was predicted and verified against existing literature data. The calculated results indicate that the high tensile stress of heat affected zone is very likely to induce the failure of the welded joints. When the welding power is 2600 W, the longitudinal residual stress along the welding direction is more symmetrical on both sides, and the force and deformation of the weldment will be more uniform. As the groove angle decreases, the transverse residual compressive stress on the joint surface becomes larger, which results in the low risk for cracking tendency of the joint. Increasing the number of welding layers reduces the weld reinforcement and the residual stress. In addition, the decline magnitude of residual stress decreases with the increase in the number of welding layers. Both the smaller groove angle and the multi-layer welding can effectively reduce the residual stress of weldments and improve the joint performance. The findings of this study will provide a good theoretical basis for optimizing welding process.

Effect of Local Fluid Disturbance Induced by Weld Reinforcement Height on the Corrosion of a Low Alloy Steel Weld

Weld corrosion exists widely in the petrochemical industry and attracts great attention. Most research proves that weld corrosion originates from the material factors introduced during the welding process. However, it is noted that local fluid turbulence due to the weld reinforcement height (WRH) plays an important role in the non-uniform corrosion of welds in flowing media. Accordingly, the individual effect of the local flow on the weld corrosion of low alloy steel was analyzed by experiments and simulation in this study. Electrochemical measurements and morphology observation were conducted, combined with flow field analyses. The results showed that local fluid turbulence due to WRH affected the non-uniform corrosion of low alloy steel welds. The upstream surface and the backflow surface had the highest and lowest corrosion rates, respectively. Interestingly, the high flow velocity surface region did not have a high-corrosion rate. This is due to the combined effects of mass transfer, charge transfer, and wall shear stress. The pitting corrosion was also discussed in view of the aspects above.

Study on MIG-TIG hybrid brazing of galvanised thin sheet

To increase productivity when joining galvanised sheet metal, metal inert gas (MIG) and tungsten inert gas (TIG) arc brazing are combined in a hybrid process. This coupling of two arc processes increases brazing speed and reduces weld reinforcement and the tendency to spatter. Because the arcs are 6 mm apart, they influence each other. Therefore, the blowing action is a major challenge in hybrid arc brazing. A current modulation and the optimal relative position of the arcs to each other are compulsory conditions. Selected brazing parameters are tested in order to verify the hybrid arc brazing. Overlap joints are brazed on galvanised sheets. The mechanical-technological properties of the brazed joints are determined. It has been shown that hybrid brazing can achieve significantly higher brazing speed with the same or better brazing quality compared to standard arc brazing. For the realisation of the hybrid arc brazing process, software-controlled welding machines are used, which will replace conventional power sources in the future.

Relieving Residual Stress of 316L Stainless Steel by Acoustic/Thermal Composite Treatment

The influence of temperature, vibration time, amplitude, and other factors on the residual stress release effect was studied using the method of low-temperature heating and high-frequency ultrasonic vibration, and excellent control parameters were obtained. In addition, the influence of cutting weld reinforcement on the residual stress release was also studied. The results demonstrate that the highest relative residual stress release rate was 280.29%, the average release was over 150 MPa, and the efficiency was higher than that of the general stress release methods. After cutting the reinforcement, only a small part of residual stress was released, influencing the overall residual stress distribution relatively little. The experimental material was a butt-welded 316L stainless steel plate μ-X360s diffractometer, and this was used for measuring the residual stress.

Effect of in-situ transverse magnetic field on the fluid flow, microstructure evolution and corrosion resistance of GMAW 316L stainless steel

In order to modify heat and mass transfer, alter crystal orientation and suppress elemental segregation of the molten pool by electromagnetic stirring effect, a new in-situ transverse magnetic field generated by clamp-type electromagnet integrated with a 6-axis robot was firstly applied to real-time control the arc characteristic and fluid flow when welding 316L stainless steel by GMAW-CMT. As the magnetic field intensity at the end point of the wire increases from 0 mT to 14.6 mT and then 20.7 mT, the 316L welding bead morphology becomes flatter, and their cross sections clearly exhibit a lower welding reinforcement, a wider welding width and a smaller welding penetration. Microstructure observations show that the application of in-situ transverse magnetic field in GMAW-CMT process can contribute to the lower inner porosity, the smaller stress concentration, the more dispersed austenite grain orientation and the elimination of residual skeletal ferrite distributed in the austenite matrix. CPP and EIS tests indicate that 14.6 mT molten pool exhibits the highest pitting corrosion resistance and the most compact passive film, which is related with the finer cellular γ grain with dispersed orientation and less Cr-Mo atomic segregation on the boundary. The deflection of arc column and the fragmentation of dendritic tips induced by the Lorentz force under the appropriate transverse magnetic field are verified, which provides great potential for optimizing weldment performance.