Analysis of residual stress in stainless steel pipe weld subject to mechanical axial tension loading

This paper presents the characteristics of welding residual stresses in circumferentially butt-welded stainless steel pipe by utilizing three-dimensional (3-D) uncoupled thermo-mechanical finite element (FE) analysis method. Moreover, stress variations in welded joints of the pipe under superimposed mechanical axial tension loading are further investigated employing the welding residual stresses and plastic strains obtained from the thermo-mechanical FE analysis as an initial condition. Results show that spatial variations of the welding residual stresses are present along the circumference and a rapid change of the residual stresses exists at the welding start/stop position, hence 3-D FE analysis is essential to accurately simulate circumferential welding of a pipe component. When mechanical axial tension loading is applied to the circumferentially butt-welded stainless steel pipe, bending moment is generated at the welded joints caused by the circumferential shrinkage of the weld region during welding; thus affecting the axial and hoop stress evolutions in the course of the superimposed mechanical loading.     

Schweißverzug,Schweißeigenspannungen und Schalenstabilität

Weld distortion, residual stress and stability of shells. Imperfections have an influence on the stability behaviour of cylindrical shells and arise, among others, from the assembling process. This article deals with numerical analyses on the welding distortion and residual stresses in the weld of cylindrical shells with single‐pass circumferential weld and their influence on the stability behaviour under axial load. Cylinders and cylinder segments made of the steel grades S235 and S355 with plate thicknesses of 1 mm to 4 mm and radii of 200 mm to 1600 mm are considered. The developmental process of the weld distortion is explained by means of a cylinder and the qualitative process of radial deformation after welding is shown. Special features for developing residual stresses are explained. The influence of the transient welding process of single‐ply radial welds on the axial limited stress of the cylindrical shell is considered using a parameter study. Regularities for welding distortion with different cylinder slenderness ratios are determined from this parameter study.     

Microstructure and transverse shrinkage stress analysis in GTA welds of P91 steel pipe

In a steam power plant, several components such as boiler tube, condenser and steam lines are made of high creep resistant steel. The P91 steel pipes are generally used in steam power plant because of high creep strength at service temperature of approximately 600oC. In the present research work, the study about shrinkage stresses and their distribution in the four quadrants of P91 pipe weld of 11 mm thickness is reported. The conventional-V and narrow-groove welds were prepared by using the gas tungsten arc welding (GTAW) process. Welding current, arc voltage, groove design, and straining length were the main parameters that affect the transverse shrinkage stresses. In the present research work, the effect of groove design on transverse shrinkage stresses has been evaluated. It also describes the effect of the number of passes on shrinkage. It is concluded that, for a given heat input, the narrow groove pipe weld joint exhibits comparatively less transverse shrinkage stress. Scanning electron microscope (SEM) with field emission gun and optical microscope has been used to characterize the weld fusion zone and HAZs of P91 pipe weldments.

     

Effect of start/stop position distribution on residual stresses in the multi-pass welded 12Cr1MoV/P91 dissimilar pipe

Welding residual stresses between 12Cr1MoV and P91 steel pipes were analyzed by experiment and finite element method (FEM). Both measured hoop and axial stresses are in general agree with the simulation results. Meanwhile, to examine the effect of start/stop welding position on residual stresses, a simulation model whose welding passes all started at the same location during multi-pass welding was compared with a model whose start/stop positions were uniformly distributed along circumferential direction of the dissimilar pipe. The results show that higher residual stresses occurred near the superimposed start/stop position than the steady region when calculated by the model whose welding passes all started at the same location. Whereas, start/stop welding positions which are distributed uniformly along the circumferential direction of the pipe can significantly relieve this effect, correspondingly leading to a more uniform residual stress distribution around the multi-pass welded dissimilar pipe.     

水分含量对PE燃气管材焊接性能的影响研究

简要介绍了对接焊口麻点状气孔形成的原因,进行了不同牌号、不同水分含量的原料对聚乙烯燃气管材对接焊口麻点状气孔试验,研究了不同管材原料的吸水性能及水分含量对管材对接焊口质量的影响程度,从而在源头上预防聚乙烯原料引起对接焊口麻点状气孔的形成,找出了科学有效的预防焊口麻点状气孔的方法。     

Comparison the capacity of box steel columns,fabricated with groove and fillet welds

Currently, box columns are fabricated by welding plates using fillet or groove welds. According to probable seismic failure mechanism of these columns, their nonlinear behavior in terms of ductility and strength is necessary. In this research, a variety of columns with different welding patterns including groove and fillet welding with various overlap values and weld legs are numerically modeled and their nonlinear behavior is studied in finite element domain by using ABAQUS software. Suitable welding pattern is proposed by evaluation the energy absorption as well as stress distribution and concentration in box section. Results indicate that the section fabricated through groove welding has the best nonlinear performance and in the next priority, the sections with overlap size and weld leg equal to 20 and 80, or 50 and 50 percent of plate thickness, respectively, lead to suitable performance.     

组装焊缝形式对箱形截面支撑力学性能的影响研究

为考察全熔透和部分熔透两种组装焊缝形式对箱形截面钢支撑受力性能的影响,本文对中央电视台新台址建设工程中的箱形截面支撑进行了单调受压、轴向反复拉压试验;同时,采用ABAQUS有限元软件实现了对部分熔透试件未熔透处的接触模拟和滞回性能模拟。试验与有限元分析结果表明,中央电视台新台址工程中宽厚比为10的板件可采用部分熔透的组装焊缝形式。考虑板件宽厚比、偏心加载以及残余应力的参数分析结果表明,板件宽厚比小于20的轴心受压支撑以及板件宽厚比不大于10的偏心受力支撑中,箱形截面翼缘与腹板的连接可采用部分熔透的连续焊缝。     

焊接残余应力对Y型相贯节点极限承载力影响分析

采用ANSYS的热 结构间接耦合、生死单元技术模拟Y型相贯节点的焊接过程;将牛顿-拉普森法和弧长法结合,求解Y型相贯节点极限承载力,给出求解流程;分析支管外径与主管外径比、支管倾角、主管径厚比等几何参数对Y型相贯节点极限承载力的影响,将考虑和不考虑焊接残余应力的计算结果进行对比分析。研究结果表明:焊接残余应力降低了Y型相贯节点的极限承载力;支管外径与主管外径比β越大,主管的径厚比γ越小,支管倾角θ越小,则Y型相贯节点极限承载力降低越多;结构设计时,保证强度和安全的前提下选择合适的支管外径、主管壁厚和支管倾角,可减小焊接残余应力对Y型相贯节点极限承载力的影响。     

Steel Frame Welding Robot Systems and Their Application at the Construction Site

Two welding robot systems have been developed to rationalize steel–frame construction. Both systems consist essentially of two portable cartesian–coordinate welding robots mounted on a carriage together with their ancillaries. After the robots are mounted on a beam or column by an operator, they measure the groove shape of the joint seam, determine the optimal welding conditions, and carry out welding from the first to the last layer without operator intervention.
An important feature of the column–beam welding system is the curved torch, with which the robot can continuously weld the bottom flange of a beam through a scallop. Since the pantograph of the carriage can extend three floors, up to 12 joints can be welded from one carriage position.
In welding column–column joints, two robots traveling on a circumferential rail installed near the seam of a rectangular hollow section weld the joint in combination. The robots can continuously weld a seam containing corners without weld defects even in joints with a misaligned groove.
Each system has been applied to actual construction sites and has proved effective in stabilizing the quality of welds and in raising welding productivity.     

球罐球壳板组对焊缝清根坡口的磁粉检测

大型球罐压力容器的切片球壳板都采用现场焊接成整体的安装工艺。球壳板厚度通常都在30mm以上,为避免焊后根部和内外表面存在裂纹、未熔合、未焊透、夹渣等缺陷而造成质量隐患,所以在焊接过程中必须对焊缝进行多次磁粉检测,包括焊接前的球壳板坡口检测、焊接过程中焊缝的坡口清根检测、焊后热处理前的焊缝及热影响区检测和水压后的焊缝和热影响区检测。而其中清根坡口磁粉检测则尤为重要。检测结果表明,在球罐赤道带以上焊缝容易产生应力裂纹、未熔合等缺陷,而清根坡口磁粉检测可以有效检测出根部的表面开口和近表面缺陷。     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.     

Schweißen unter dynamischer Einwirkung

Welding under dynamic loads. During maintenance and repair works it is often necessary to weld a dynamically strained structure, i.e. to weld while the welding flanks are moving. No rules or standards are focussed on this problem. Therefore complex auxiliary constructions are necessary to relieve the strain of the structure, if an unloading is possible at all. Thus criteria are developed which indicate under which conditions welds with moving flanks can be produced successfully. Many experimental welding simulations are performed by means of a bi‐axial, automatic test equipment to investigate to which extent welds in motion can be made with acceptable results. In this paper the results of the static and dynamic load‐tests of welds produced under motion are presented.     

Double-angle shear connections with small hollow structural section columns

This paper describes an experimental study on double-angle shear connections when used with small-size hollow structural section columns. Twelve connection specimens were tested to confirm the practice of either fitting the connection angles to the narrow column face by shortening the outstanding legs or by employing flare bevel groove welds. Test results demonstrated that both rotational and shear resistances of the connections were satisfactory when either of the two details was used. In the meantime, the flare bevel groove welds, made by a gas metal arc welding process, were also tested for the purpose of determining their effective throat.     

管道沟槽式连接制作及安装过程中的质量控制

管道沟槽连接在机电安装工程中的应用越来越广,为保证沟槽连接管道安装的质量,本文从沟槽管件的质量、管道沟槽、管件安装及管道安装等各方面进行了分析。并总结出了在施工过程中,如何控制沟槽连接管道的安装质量。     

深埋曲线钢顶管受力特性现场监测试验研究

为了研究深埋曲线钢顶管施工过程中的力学特性,依托拱北隧道曲线顶管管幕工程,对曲线顶管管节轴向与环向应变进行了现场监测分析。实测数据结果表明,管节应变随顶进距离增大而略微增加,但基本保持在一定范围内。管节在顶进过程中应力曲线发生波动,停止顶进后逐渐趋于平稳。管节轴向应力主要受顶进力影响,而环向应力主要取决管节外侧环向荷载,曲线顶管管节弯曲内侧存在压应力集中。由于存在泊松效应,大埋深条件下管节顶部和底部轴向应力受环向变形控制。随着与机头距离增加,管节由轴向两侧受压逐渐转变为单侧受压,受压区位于管节弯曲内侧,应力集中更加显著。     

三种典型焊接结构残余应力的消除法

本文解剖了三种典型钢结构的焊接残余应力,并采用目前较为先进的方法进行了焊后处理,均达到了良好的效果。这三种结构的板厚从20～60mm,重量从8～300t,且焊缝的坡口形式均为V型。对工程实际中消除焊接残余应力、残余变形、稳定结构尺寸等具有一定的参考作用。     

X型冷弯薄壁圆钢管相贯节点有限元分析

推导了考虑焊缝尺寸情况下圆钢管X型节点环向模型的强度公式,通过有限元软件ANSYS模拟分析了相贯节点的受力情况,并对焊接过程中出现焊瘤缺陷的情况提出建议。     

The strength of inclined fillet welds

The strength of a fillet weld which is required to transmit a shearing force only and which is inclined to the line of action of the applied force is investigated theoretically. A very simple expression based on the weld geometry and the weld metal ultimate tensile strength is developed. Results previously published by the author for longitudinal and transverse fillet welds can be obtained as special cases of the general solution presented in this paper. The residual stresses that are present in welds when they are loaded in the as-welded condition are allowed for in the theory. The predictions of the theory are compared with the few experimental results that are available and are found to provide reasonable estimates of the strength of welds inclined at 30° and 60° to the line of action of the applied force.     

3D residual stress modelling of welded high strength steel plate-to-plate joints

A numerical investigation on the residual stress distributions near the weld toe of plate-to-plate Y-joints fabricated by using high strength steel (HSS) plate is carried out in this study. A full 3D sequentially coupled thermal–mechanical modelling procedure is employed for residual stress analysis for the HSS plate-to-plate joints. Two specimens respectively fabricated by welding at ambient temperature and at a preheating temperature of 100 °C are investigated. The 3D numerical models reveal that while high tensile transverse residual stress, which is perpendicular to the weld, is generated near the weld toe of the joint middle section, proper preheating could significantly reduce the magnitude of the residual stress. In addition, it is found that the welding direction between successive weld pass could also affect the maximum residual stress value near the chord weld toe.     

焊接铝合金压杆屈曲性能试验研究

铝合金焊接后除了产生残余应力外,在焊缝附近还将产生强度明显降低的热影响区。对贴角焊和剖口焊两种焊接方式的工字型铝合金中心受压杆件进行了试验研究,并将试验结果同即将颁布的国标《铝合金结构设计规范》及欧洲规范进行了比较。研究表明,通常情况下,对于贴角焊构件,规范结果和试验结果吻合较好;而对于剖口焊构件,规范结果偏保守。