Mechanism investigation of welding induced buckling using inherent deformation method

Due to the increasing use of thin plates in lightweight welded structure, welding induced buckling may occur in such thin plate welded structure. In this study, welding induced buckling of thin plate welded structure is investigated using the eigenvalue analysis and elastic Finite Element (FE) analysis based on inherent deformation theory, and the mechanism of welding induced buckling is clarified.Bead-on-plate welding is first examined. Measured out-of-plane welding distortion indicates that saddle type buckling is produced after cooling. Eigenvalue analysis shows the computed lowest buckling mode is the saddle type and the corresponding critical force is less than the applied tendon force evaluated by Thermal–Elastic–Plastic (TEP) Finite Element (FE) analysis beforehand. Using elastic Finite Element (FE) analysis in which all components of inherent deformation are used and also considering initial deflection, out-of-plane welding distortion is predicted with high accuracy compared with measurement. It is also concluded that tendon force (longitudinal inherent shrinkage) is the dominant reason of buckling and it determines the buckling mode, and initial deflection and inherent bending are considered to be disturbances which trigger buckling.Later, a thin plate stiffened welded structure with fillet welded joints is examined. Although welding did not induce buckling of plate fields in bending modes in the considered thin plate stiffened welded structure, the whole stiffened welded structure buckles in a twisting mode, while plate panels remain unbuckled. Eigenvalue analysis gives the twisting buckling mode as the lowest buckling mode. However, in stiffened welded structures, not only tendon force (longitudinal inherent shrinkage) but also transverse inherent shrinkage is responsible for buckling. The good agreement between computed and measured out-of-plane welding distortion shows that the elastic Finite Element (FE) analysis using inherent deformation theory is an advantage of the computational approach to predict welding distortion in large-scale and complex welded structure with enough computational accuracy.     

醋酸装置安装工程中锆管焊接工艺及应用研究

介绍了锆材Zr702焊接工艺评定试验及其在50万t/a醋酸装置安装工程中的应用,提出了焊接控制要点。工程实践表明,该工艺方案可行。     

Special features of welding highly stressed titanium alloy structures

Investigations were carried out into the quality of welded joints in submerged-arc welding and also the problems of consumption of electrode material at higher currents. Methods for improving the quality of permanent joints when using tungsten electrodes are outlined.     

Improving the Interfacial Microstructure Evolution of Ti/Stainless Steel GTA Welding Joint by Employing Cu Filler Metal

In the present work, Cu alloys as filler metals were applied to improve interfacial microstructural evolution during the process of gas tungsten arc (GTA) welding of TA15 titanium alloy with 18-8 stainless steel (SS). Results indicated that the interfacial brittle microstructure evolution of Ti/SS GTA welding joint was improved by adopting Cu alloy as the filler metal. Microstructure in the reaction zone (RZ) is composed of massive precipitations including brittle phosphide (Ti₃P), Ti₂Cu₃ and Ti(Cu, Fe) intermetallic compounds (IMCs), while the fusion zone (FZ) near SS is mainly composed of Cu-rich clumps and α-Fe+(Fe, Cr)₃P skeleton eutectic microstructure. Ti₂Cu₃ precipitations provided substrate for the heterogeneous nucleation of Ti₃P whose regular tetragonal and irregular morphologies are attributed to the proposed two kinds of forming mechanism. During the reaction of P with Ti₂Cu₃, the dropping of residual Ti₂Cu₃ contributed to the formation of macroporous in the middle of irregular Ti₃P precipitations. The dispersive distribution of massive brittle precipitations in the RZ leads to the fluctuant distribution of microhardness, which is up to about 700HV_0.5.     

Review: Low transformation temperature weld filler for tensile residual stress reduction

An attractive, alternative approach for the reduction of harmful residual stresses in weld zones is reviewed, which utilises low temperature, solid-state, displacive phase transformations in steel. The theory, latest concepts and practice for the design of such low transformation temperature (LTT) filler alloys are considered. By engineering the phase transformation temperature of the weld metal so as to take advantage of transformation expansion, the residual stress state within the weld zone can be significantly altered, most particularly where the weld thermally contracts with any movement of base parts constrained. To date, the technique has been shown to increase fatigue strength for some common weld geometries, which may enable engineering design codes to be favourably re-drafted where such LTT filler alloys are used.     

Applications of inherent strain and interface element to simulation of welding deformation in thin plate structures

Welding-induced distortion not only reduces largely manufacturing accuracy but also decreases significantly productivity due to correction works. If welding distortion can be predicted through a simple and practical method beforehand, the predictions will be helpful for taking active as well as appropriate measures to control the dimension accuracy. Based on inherent strain theory and interface element formulation, we developed a practical prediction system to compute the accumulated distortion during the welding assembly process in the current study. Using the developed prediction method, we calculated the welding distortion in a thin plate structure with considering both the shrinkage due to heat input and the gap/misalignment generated during assembly process. Meanwhile, we investigated the influences of assembly sequence and gap correction on the final distortion.     

浅谈钛材换热器的管板焊接

在氧化性、中性及含氯离子的介质中,钛的耐腐蚀性能均优于普通不锈钢和铝等。但钛材的焊接性能不好,焊接时极易产生氧化、氮化和脆化等缺陷。根据钛材的焊接特性,在焊接过程中有针对性地采取合理的保护措施,制定合适的焊接工艺,严格把好各个施工环节质量关,就能保证钛材的焊接质量。     

Physicochemical and thermo physical characterization of CaO–CaF2–SiO2 and CaO–TiO2–SiO2 based electrode coating for offshore welds

This paper investigates the physicochemical and thermo-physical properties of CaO–CaF₂–SiO₂ and CaO–TiO₂–SiO₂ based electrode coating for welding offshore structures. Twenty-one electrode coating compositions have been formulated using extreme vertices design method. The coating was crushed to powder form. The powder was characterized for weight loss, density, specific heat, enthalpy, thermal conductivity, diffusivity, and specific heat. Coating's structural analysis was done using X-Ray Diffraction and Fourier transformation. X-Ray Fluorescence, Thermogravimetric Analyzer, and Hot disc have been used to characterize the coating mixture. The regression analysis has been used to study the effect of individual constituents and their binary, tertiary interactions on the properties. The obtained output of properties has been optimized using multi-response optimization.     

Investigate the causes of cracks in welded 310 stainless steel used in the Flare tip

The present study examines the causes of the cracks in welded 310 stainless steel that has been used in the Flare tip. According to the tests, including metallographic examination, macroscopic hardness test and scanning electron microscopic analysis, the reasons for the nucleation and growth of the cracks in the weld zone have been discussed. The results show that, because of the service temperature of Flare tip between 500 and 900 °C, and hydrocarbon gases such as methane, ethane, sour gas and carbon dioxide that are the combustion products, the component surface has been oxidized and carburized. Thus, the surface carburized oxide layer and also the subsurface damage can be fertile field for the nucleation of cracks. Likewise, the presence of sigma phases, austenite dendrites and interdendritic delta ferrite can cause a drop in toughness in the weld zone and provide fields for the crack growth in the weld zone.     

The Critical Energy Release Rate of Welded Joints Between Fiber-Reinforced Thermoplastics and Metals When Thermal Residual Stress is Considered

Thermal effects on welded joints between fiber-reinforced thermoplastics (FRTPs) and metals have been investigated theoretically and experimentally. Because FRTPs use thermoplastics as the matrix resin, they have advantages over fiber-reinforced thermoset plastics (FRPs or FRSPs), including the ability to be welded. When dissimilar materials are welded together, however, thermal stress occurs due to the different thermal expansions of the materials and affects the energy release rate of the joint. Therefore, a method for evaluating the true energy release rate, including the effect of thermal stress, is necessary for strength evaluation tests. Although several theories that compensate for the thermal stress and evaluate the true energy release rate have already been proposed, they require parameters that are difficult to measure. Therefore, it is difficult to apply them in experimental investigations. In this article, a theoretical method with easily measurable parameters is proposed to calculate the energy release rate of welded double cantilever beam (DCB) joints. The effect of the thermal stress on the critical energy release rate is discussed in terms of the experimental results of a welded DCB specimen composed of a FRTP and an aluminum alloy.