Weld Failure Research Articles

Numerical study on the ratcheting performance of rail flash butt welds in heavy haul operations

The ratcheting performance of a new R400HT rail flash butt weld was numerically evaluated under a typical heavy haul in-service condition. Due to varying mechanical properties across the rail weld, the weld region was divided into 23 zones in the numerical study. A dynamic finite element simulation of wheel–rail weld rolling contact was first carried out to obtain the total vertical contact force and its variation along rolling distance. Multiple quasi-static wheel–rail weld contact simulations were then performed by applying the total vertical contact force to determine the non-Hertzian contact pressure distribution when the wheel was located at different positions across the weld in the rolling direction. Based on each normal contact pressure distribution, the Haines and Ollerton's strip theory and Carter's theory were employed to estimate the corresponding longitudinal surface tangential traction distribution. Finally, a cyclic loading simulation was conducted to evaluate the ratcheting performance of the rail weld in terms of RCF initiation life by repeatedly translating these normal contact pressure and longitudinal tangential traction distributions on the running surface. The results reveal that the subzone with the lowest hardness in the softened zone has the shortest RCF initiation life among the weld region, followed by the region around the bond line. The parent rail provides the longest RCF initiation life and therefore has the best resistance to RCF. Additionally, the existence of the softened zone can shorten the RCF initiation life of the parent rail and the bond line section, particularly the regions located adjacent to the softened zone. The possible location of RCF initiation in the softened zone of the rail head can reach deeper than those in the parent rail and the region around the bond line. The results can help us understand the failure of flash butt rail welds in heavy haul operations and the numerical method can be applied to study different rail welds and rail welds under different conditions such as in a curved track.

Cracks Forming and Propagation Mechanism for the Q345 Steel during Cooling

Cracks always occur for the Q345 steel during cooling, which usually lead to Welding failure. Through investigation of the cracks forming position and propagation path, its forming and propagation mechanism for the melted Q345 steel during cooling was studied in detail by using of SEM, EBSD and Nano Indenter equipment in this paper. SEM observation results imply that cracks mainly initiated at martensite phase region close to basal material. Moreover, it also can be observed that the cracks always propagated along the martensite lath or packets boundaries, but not the original prior austenite grain boundaries. The hardness differences between cracks adjacent positions and matrix is about 2.48 GPa, which is larger than that of melted region and matensite (0.70GPa). In addition, EBSD results show that the average prior austenite grains boundaries angles (30-50º) are always smaller than that of martensite lath and packet boundaries (>50º). Combining investigation of the cracks forming position, propagation path and microstructure misorientation, it proves that the occurrence of the cracks at junction of martensite phase region close to basal material is related with larger hardness difference or larger residual stress between martensite and ferrite, while cracks propagation path is controlled by the boundaries angles or local misorientation. The cracks incline to propagate along or deflect to large martensite lath and packets boundaries.

Oxidation damage and interfacial failure of dissimilar metal welds containing ferritic heat resistant steels

The ex-service steam tubes containing dissimilar metal weld (DMW) between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102 and austenitic stainless steel TP347H were obtained from coal-fired thermal power plants in China, and their microstructures at the nickel-based weld metal (WM)/ferritic steel interfaces and oxidation characteristics were investigated. After operating for 15,000 h at steam temperature of 541 °C and steam pressure of 17.5 MPa, a G102/TP347H DMW failed along the WM/G102 steel interface, which was a dangerous premature failure mode without obvious plastic deformation. This interfacial failure was attributed to the interaction between oxidation and cracking along the interface, where fracture appeared to be related with the strain concentration at the interface. Oxide notch along the WM/G102 steel interface was the precursor of premature interfacial failure of DMW involving G102. For the DMW involving high Cr ferritic steel T91, ferritic steel side could form a Cr-rich passive film during service and thus would not be further oxidized after operating for 67,000 h at steam temperature of 541 °C and steam pressure of 3.5 MPa. It was concluded that oxidation played a more important role in failure of these DMWs, and retarding the development of oxidation and avoiding the interfacial oxide notch would dramatically improve the service performance of steam tubes containing DMWs.

Experimental and Numerical Research on the Laser Impact Welding of Ti/SS

The welding of Ti/SS metal foil was realized by laser impact welding. The interface morphology and mechanical properties of welding specimens were studied by systematic experiments, and the experimental phenomena were revealed by smoothed particle hydrodynamics numerical simulation. Results indicated that the plastic deformation of the composite plate and the springback of the welding spot center were small under low laser pulse energy and enlarged under high laser pulse energy. Impinging jet, interface wave, and interface cracking were found at the micro-interface of the welding specimens. Increasing the laser pulse energy resulted in the transition of the interface waveform from straight to microwave and finally to wave primarily because of the change in interfacial impact pressure and effective plastic strain. Energy dispersive spectroscopy analysis showed that the trace element diffused at the welding interface, and no intermetallic compounds were formed. SPH simulation revealed that the thickness of the high-temperature layer was related to the thickness of the diffusion layer. As the distance between the test point and welding interface increased, the hardness decreased. The maximum tensile force of the welding specimens increased with laser pulse energy. The failure mode of the interface was welding spot edge fracture failure.

Mechanical properties and fracture behaviors in remote laser spot welding of quenching and partitioning 980 steel

Quenching and partitioning (Q&P) steel is one of most critical third generation steels in the automotive industry, which provides excellent mechanical properties and have a huge potential to significantly reduce vehicle weight and improve fuel efficiency. One of the bottlenecks for their applications in the automotive industry is the poor weldability. In this paper, a newly-developed remote laser spot welding (R-LSW) process was used to weld Q&P steel with laser beam moving along a spiral path. The welds with full penetration were obtained with laser power ranged between 2400 W and 3600 W, the weld morphology and mechanical properties of the joints were consistent, except for a little drop in case of 3600 W with the crater size of 0.65 mm. Under the shear tensile force, all the welds failed in partial thickness-partial pullout (PT-PP) mode, which was attributed to the formation of a large weld diameter. The weld failure process can be divided into four stages: (I) crack initiation; (II) crack propagation along the thickness and circumference of the joint; (III) crack propagation along the circumference of the joint; and (IV) instantaneous fracture. Furthermore, it was found that the coarse grain heat affected zone (CG-HAZ) has a lowest fraction of high-angle grain boundaries (HAGBs), resulting in the crack propagated along the CG-HAZ during stage II. During crack propagation, the fracture took place as a ductile fracture, but the instantaneous fracture occurred in quasi-cleavage characteristic.

Improvement of weld heat affected zone (HAZ) using Taguchi method

Heat Affected Zone (HAZ) is the area on a weldment mostly affected by the intensity of the applied heat without melting. This area mostly deteriorates faster due to microstructural changes that occur due to the intensity of the applied heat during welding operations. Weld structural failures can be catastrophic and unpredictable at times. When there is no loss of human life involved, damages as a result of weld failure usually takes more time and cost more to repair/replace. For these reasons, a weld with good quality integrity cannot be over-emphasized. The larger the HAZ, the wider the area with microstructural alteration, the lesser the quality integrity of the weldment. In this study, extensive research was conducted to reduce weld HAZ using the Taguchi method. This method makes use of signal to noise ratio of responses to achieve optimality. From applying this model, it was observed that the best input parameters, that improved the weld quality was achieved. These input parameters were current of 120A, voltage of 10V and gas flow rate of 144L/min. From the analysis of variance (ANOVA), it was found that current contributed about 9.58% to the weld quality, which was the most influential process parameters. The confirmation test done, shows that the weldment produced by using the optimum process parameters had an improvement of 1.37db and 0.88mm reduction in HAZ, over the weldment made by existing parameters.

Non-contact in-process ultrasonic screening of thin fusion welded joints

Joining of metal structures, or welding, plays a critical role in our modern world, where safety critical welds of thin sheet metals are used in pipework, nuclear cannisters and aircraft ducting among others. A potential failure in such welds could prove to be catastrophic, hence the need for thorough inspection and testing. With the ever-increasing automation of welding operations, manually deployed Non-destructive Evaluation (NDE) has become a major bottleneck in the supply chain. This paper introduces for the first time, non-contact gas-coupled ultrasonic sensors deployed in-process during weld deposition, for screening of weld penetration directly at the point of manufacture. 3 mm thick mild steel plates were butt-welded together using Gas Tungsten Arc Welding (GTAW) while non-contact air-coupled ultrasonic transducers, generating surface guided Lamb waves, performed inspection screening of the weld seam. Optimised Signal-to-Noise Ratio (SNR) was achieved through a customised acoustic matching layer, low-noise amplifiers and real-time signal processing. By performing multiple trials at varying levels of welding input power (0.59 kJ/mm to 1.03 kJ/mm), it was demonstrated that the amplitude of the through transmission A0 Lamb wave is correlated to the Weld Penetration Depth (WPD) and can be used for on-line weld quality screening. Advantages of the outlined method include higher production rates, reduced levels of scrap and higher production quality in regards to thin metal sheet welded components.

Experimental study on corrosion resistance of coiled tubing welds in high temperature and pressure environment.

Coiled tubing (CT) has been widely used for oil and gas exploitation, however corrosion of CT under high pressure and high temperature (HPHT) environment was often reported, also corrosion induced failures of CT welds were often observed to occur during service. Corrosion related behaviors of CT welds are not clear. Therefore, a study of the corrosion resistance of CT welds under HPHT environment is carried out. In order to efficiently evaluate the corrosion resistance of welds, some test samples were obtained by linear cutting out of a CT110 in service on the site. The water samples from gas field were used as the test reagent to simulate the actual corrosive medium. Based on the results of weight loss test under HPHT corrosive environment and tensile test under room conditions, the corrosion sensitivities of the welding seam and base material under various temperatures and partial pressures of CO2 as well as the mechanical properties of the corroded CT were compared and evaluated quantitatively, the corrosion morphologies and material products of the test samples were analyzed by scanning electron microscope (SEM). The test results showed that the corrosion rates of the welding seam in a HPHT caldron were 1.7, 2.0 and 1.2 times of the base metal’s when the total pressure is 4MPa, and the temperature is 30°C, 60°C and 90°C, respectively. The corrosion rates of the welding seam is 2.0, 2.1 and 2.0 times of the base metal’s when the partial pressure of CO2 is 0.1MPa, 0.2MPa and 0.3MPa, respectively. The yield strength of the weld seam after corrosion test was found to be reduced by 4.8% (the yield strength of the base metal was reduced by 4.0%) and its tensile strength was reduced by 8.2% (the base metal was reduced by 7.1%). This indicates that CT weld seam is more susceptible to corrosion than CT base material under service condition.

Failure Prediction and Classification in Natural Gas Pipe-Lines Using Artificial Intelligence

Gas pipelines are often subjected to various kinds of damages such as corrosion, welding failure, and excavation damages, due to harsh environmental conditions. The failure in gas pipelines may lead to catastrophic damages e.g. human life loss, economic loss, etc. Predicting pipeline health is of critical importance to avoid these damages. In this study, 875 incidents are extracted from US DOT PHMSA from 2002 to 2020. For each of the incident, different parameters such as Age, NPS, Wall Thickness, Material, Operating Pressure, Location, and Area is analyzed. Two supervised learning techniques Artificial Neural Networks and Support Vector Machine are used to predict and classify different natural gas pipeline failures i.e. Corrosion, Pipeline Material, or Weld Failure and Excavation Damage by using actual pipeline incident data. One-Way ANOVA F-test is used to select the important features of the input dataset. The supervised models (Backpropagation Neural Network and SVM) are trained and tested on the input data. The performance of the models is assessed based on accurate predictions made by the trained models on the testing dataset.

Effect of pre-weld tempers on mechanical and microstructural behavior of dissimilar friction stir welds of AA2014 and AA7075

In this work, friction stir welding of AA2014 and AA7075 has beenperformed indifferent combinationsof T6 and O temperto study the influence of base metal temper on microstructure, mechanical properties, and fracture behavior of developed welds. Four dissimilar welded joints have been developed using optimum process parameters:AA2014-T6 with AA7075-T6, AA2014-O with AA7075-T6, AA2014-T6 with AA7075-O, and AA2014-O with AA7075-O. The stir zonemicrostructurehas been dominated by the base metal placed on the advancing side and hasequiaxed grains without constituent particles. Weld joints' strengthhas beeneither nearly equal or higher than that of low strength base metal,whereas the weld failure has takenplace from the base metal region when at least one base metal was in O temper and from Stir Zone (SZ) when base metal was in T6 temper.

How to prevent damages of transporting pipeline girth welds?

Girth welds of hydro-carbon transporting pipelines play important role of the life and the lifetime, during both the construction and the operation. In consideration of the huge number of girth welds, the highlighted attention to those is worthy and necessary. The aims of the article are twofold: on the one hand, collecting the influencing factors on the failures of girth welds; on the other hand, answering the question assumed in the title of the article: how to prevent damages of transporting pipeline girth welds? The answers build upon the demonstrated influencing factors, using examples, and systematically respond to those.

A study on HAZ behaviour in 800 MPa cold rolled and hot rolled steel weld

Abstract In the automotive sector, the demand for advanced high strength steels (AHSS) is increasing day by day. Based on the application, cold rolled and hot rolled steels are used for various components in a vehicle body. Typically, cold-rolled grades with dual-phase, DP780 steel is used in the form of welded blanks. Hot rolled grades with Ti-Nb microalloy content, like HS800 steel are used in as long members. Welding is an important step to be considered in the design of materials for mass production as required in the automobile sector. In this investigation, Pulsed Gas Metal Arc Welding (P-GMAW) is carried out on both steels with a solid filler wire of strength 800 MPa. Static tensile tests indicated that failure in both steels welds occurred in the heat-affected zone region. The crack initiation and propagation behaviour were compared in both steels. In DP780 steels, the presence of the acicular ferrite and acicular martensite resisted the crack initiation and propagation in the weld region whereas, the chaotic nature of the acicular ferrite in HS800 steel. Microstructural studies revealed that the reason for heat affected zone (HAZ) failure in HS800 steel is due to the presence of hard TiN particles with a size of more than 1 μm which causes decohesion in the matrix. In DP780 steel failure is due to the presence of tempered martensite in the subcritical heat affected zone (SCHAZ). This study divulges the influence of filler wire chemistry, dilution, and welding parameters on cold rolled and hot rolled AHSS steels used in the automotive industry.

Dissimilar Metal Welds used in AUSC Power Plant, Fabrication and Structural Integrity Issues

ABSTRACTIn the current era, the Advanced Ultra Super-Critical (AUSC) plants have been used to substantially increased efficiency with environmental protection. AUSC components boiler header, re-heater and super-heater tube etc. are fabricated by using advanced materials to join by the welding process. Any failure of the power plant can lead to grave consequences, not only of substantial financial losses but additionally immensely treasured and irreparable human life loss. In this review, the dissimilar metal welds (DMWs) have many issues such as metallurgical issue, cracking, carbon migration, welding electrode selection, creep properties, suitable welding process and structure integrity issues which enhanced the failure of weldments. The results of our review showed that DMWs of AUSC power plant are joined by activated flux Tungsten Inert Gas (A-TIG) and Pulse A-TIG process to increase the productivity and cut the significant fraction of cost. However, A-TIG process with Post Weld Heat Treatment (PWHT) improved the mechanical properties and high-temperature creep resistance properties of DMWs. This state of the art is encouraged the researchers about the enormous future scope.

Prediction and Selection of the Best Process Parameters to Improve Toughness of Mild Steel Welded Joints

Poor combination of input process parameters has resulted in an innumerable amount of weld failure due to its negative influence on the microstructural and mechanical properties of the welded joints. To improve the welded joint, it is imperative that the material toughness be optimized. The aim of this study is to predict and enhance the toughness of mild steel welded joint using Response Surface Methodology (RSM). 10 mm mild steel plate was cut into 200 piece coupons measuring 27.5 × 10 × 10 mm for the experiment, after welding of the piece, 100 specimens of 55 × 10 × 10 mm were produced and the experiment was performed 20 times. Charpy impact tester was employed to measure the degree of toughness of the material, and results were analyzed using RSM. The results produced an optimum impact test of 275.514 joules at a desirability value of 95.6%. This optimum impact test was achieved through the use of current of 120.00 amp, voltage of 20.00 volt and gas flow rate of 12.00 L/min. The weld current was found to have a greater influence on the impact strength of the weldment as compared to voltage and gas flow rate at a moderate level.

A wavelet analysis-based matching pursuit algorithm for an accurate ultrasonic TOFD measurement

The time-of-flight diffraction (TOFD) technique is used as an important non-destructive testing method in weld integrity evaluation and failure analysis. However, an accurate measurement of the time-of-flight (TOF) has proven to be difficult due to the low time resolution of the measured signal. Conventional deconvolution techniques have been used to improve the time resolution of the signal but are not effective for ultrasonic TOFD signals because the frequency contents of the signals are non-static in space-frequency distribution. To overcome this problem, a method is proposed in this paper that estimates the TOF in two steps. In the first step, the measured signal is decomposed into a series of narrowband signals using a wavelet transform and an atom dictionary is adaptively established according to the characteristics of a selected narrowband signal. In the second step, matching pursuit (MP) is used to derive a sparse representation of the selected narrowband signal. A steel specimen with artificial defects is prepared, experiments are carried out and the results confirm the efficacy of the proposed algorithm.

Research Status and Prospect of Laser Impact Welding

The demands for the connection between thin dissimilar and similar materials in the fields of microelectronics and medical devices has promoted the development of laser impact welding. It is a new solid-state metallurgical bonding technology developed in recent years. This paper reviews the research progress of the laser impact welding in many aspects, including welding principle, welding process, weld interface microstructure and performance. The theoretical welding principle is the atomic force between materials. However, the metallurgical combination of two materials in the solid state by atomic force but almost no diffusion has not been confirmed by microstructure observation. The main theories used to explain the wave formation in impact welding were compared to conclude that caved mechanism and the Helmholz instability mechanism were accepted by researchers. The rebound of the flyer is still a critical problem for its application. With proper control of the welding parameters, the weld failure occurs on the base materials, indicating that the weld strength is higher than that of the base materials. Laser impact welding has been successfully applied in joining many dissimilar materials. There are issues still remained unresolved, such as surface damage of the flyer. The problems faced by laser impact welding were summaried, and its future applications were proposed. This review will provide a reference for the studies in laser impact welding, aiming process optimization and industrial application.

Structural Analysis and Fatigue Test of Helium Inlet for EAST PF Coil

The operating temperature of the EAST PF coils is 4.5 K which are cooled by supercritical helium through a helium inlet located at the jacket. The leakage was occurred in one PF helium inlet after the steady operation of EAST for 12 years. The finite element model of PF helium inlet is established and the structural analysis is performed. The static assessment shows that thermal load and G11 enforced displacement are the main causes of weld failure. PFhelium inlet is only subjected to the cyclic electromagnetic force under normal circumstances, which is designed to withstand 2e5 cycles at 4.5K. The FEM results show that the helium inlet on PF coil can bear the electromagnetic force during the service life. The fatigue test was performed on a full-size sample with a double strain range of at 4.5 K, and the fatigue specimen was fractured at 24570 cycles at the clamp welding region. The lifetime of the helium inlet can withstand more than 2e5 cycles, which is met the test required cycles. Therefore, the good structural performance of the PF helium inlet which can meet the EAST design requirements, and it can be fabricated for prototype coil applications.

Effect of Double Pulse Resistance Spot Welding Process on 15B22 Hot Stamped Boron Steel

Double pulse resistance spot welding process by applying a second step welding current is a new pathway to alter the mechanical properties for advanced high strength steels. Herein, the resistance spot welding (RSW) of hot stamped boron steel 15B22 by one-step and two-step welding with different welding currents is investigated. The results of the tensile–shear test, size of the weld nugget, hardness distribution, microstructure, and failure mode of different welding parameters are analyzed. The weldment of the two-step RSW with a higher heat input exhibits a lower tensile–shear load and lower fracture energy when the size of the weld nugget is large. The microstructural study reveals the appearance of a partially melted zone and sub-critical heat affected zone in the weldment where the fracture readily occurred. Thus, the two-step RSW process weakens the strength of the sample, which is attributed to the partial softening in the weldment due to the higher heat input.

Microstructure Characteristics and Its Effect on the Fracture in the Triple Junction Region of Friction Stir Welded Mg Alloys Subjected to Tension.

Because of the tensile strength decreasing of the friction stir welded wrought magnesium (Mg) alloy compared to the base material, the reasons for the failure of weld has been focused on. After the fracture in transverse tension, the crack went through the welded joint from the center of the weld to the transition zone between the thermal-mechanical affected zone and weld zone. In the present study, the microstructure characteristics and its effect on the facture in the triple junction region is investigated. Based on the metallography and the electron back-scattered diffraction (EBSD) technology, it was observed that a twin band extended from the triple junction region to the middle of weld. The profuse twinning in the twin band was considered to play an important role on the crack propagation from the stir zone edge to the crown zone.

Failure analysis of a reheater tube dissimilar metal weld failure in a 500 MW power plant

Dissimilar metal welding (DMW) finds extensive use in final sections of reheater tubing where the expected temperatures reach the maximum. Dissimilar weld failures are reported to occur at the weld interface, the heat affected zone and in the base metal depending on the operating parameters and stress level experienced during service. This paper presents a failure investigation of a reheater tube dissimilar weld failure, where the observed crack path cannot be described by any previously reported literature. The investigation leads to find the combination of i) tube restraint ii) shallow weld angle and iii) overheating conditions to be the root cause of failure. Recommendations are made based on the observations to prevent recurrence of reheater tube dissimilar weld failure.