Zerstörungsfreie Prüfung von Tiefspaltschweißnähten mittels Durchstrahlung und Ultraschall

Non destructive testing of Narrow-Gap welded joints using radiographic and ultrasonic methods . The intensified demand for economical sources of electrical energy has led to nuclear power plants with increasingly larger pressure vessels, particularly for BWR and PWR installations. The wall thicknesses of these vessels now exceeds 200 mm. The fabrication of these heavy structural components to close construction tolerances has required the development of economic welding processes, which in general are fully mechanised. One such process which has been successfully applied to the joining of heavy sections is Narrow-Gap welding. Investigations on Narrow-Gap welded joints using conventional nondestructive testing methods, such as radiographic and ultrasonic methods, have revealed that weld defects in these weld seams can be readily determined since for this process, the possible zones of weld failures are clearly defined over a very small region. The assessment of the test results according to accepted standards for pressure vessel construction has revealed, that providing the welding conditions are carefully controlled, acceptable weld quality is ensured.     

Residual stress reduction in the penetration nozzle weld joint by overlay welding

Stress corrosion cracking (SCC) in the penetration nozzle weld joint endangers the structural reliability of pressure vessels in nuclear and chemical industries. How to decrease the residual stress is very critical to ensure the structure integrity. In this paper, a new method, which uses overlay welding on the inner surface of nozzle, is proposed to decrease the residual stresses in the penetration joint. Finite element simulation is used to study the change of weld residual stresses before and after overlay welding. It reveals that this method can mainly decrease the residual stress in the weld root. Before overlay welding, large tensile residual stresses are generated in the weld root. After overlay weld, the tensile hoop stress in weld root has been decreased about 45%, and the radial stress has been decreased to compressive stress, which is helpful to decrease the susceptibility to SCC. With the increase of overlay welding length, the residual stress in weld root has been greatly decreased, and thus the long overlay welding is proposed in the actual welding. It also finds that this method is more suitable for thin nozzle rather than thick nozzle.     

基于BP神经网络薄板P-PAW搭接的间隙自适应工艺参数优化

对大型LNG燃料薄膜舱中1.2 mm厚SUS304L不锈钢板薄板的搭接焊,存在的搭接间隙会带来焊缝成形不良等严重影响船舱安全性的问题。本文通过激光传感器检测搭接间隙变化,设计了不同的峰值电流和焊接速度在不同间隙下的工艺实验,研究了间隙对焊缝成形质量的影响机制;基于BP神经网络建立不同间隙下的脉冲等离子弧焊(P-PAW)的工艺参数和间隙及焊缝成形尺寸之间的拓扑关系模型,通过工艺实验获取模型的训练样本,实现了基于BP神经网络的间隙自适应工艺参数优化系统。结果表明,该系统实现了不同搭接间隙下进行实时工艺参数优化的功能,并对搭接间隙在0～0.6 mm变化时所带来的空洞等缺陷起到了有效的抑制作用,实现了良好的焊接成形一致性控制,提高了在LNG薄膜舱中不锈钢板焊接的自适应能力。     

Hybrid fiber laser – Arc welding of thick section high strength low alloy steel

Hybrid laser – metal active gas (MAG) arc welding is an emerging joining technology that is very promising for shipbuilding applications. This technique combines the synergistic qualities of the laser and MAG arc welding techniques, which permits a high energy density process with fit-up gap tolerance. As the heat input of hybrid laser – arc welding (HLAW) is greater than in laser welding, but much smaller than in MAG arc welding, a relatively narrow weld and restricted heat affected zone (HAZ) is obtained, which can minimize the residual stress and distortion. Furthermore, adding MAG arc can increase the penetration depth for a given laser power, which can translate to faster welding speeds or fewer number of passes necessary for one-sided welding of thick plates. In this work, a new hybrid fiber laser – arc welding system was successfully applied to fully penetrate 9.3 mm thick butt joints using a single-pass process through optimization of the groove shape, size and processing parameters.     

Effects of microstructure and residual stress on fatigue crack growth of stainless steel narrow gap welds

The effects of weld microstructure and residual stress distribution on the fatigue crack growth rate of stainless steel narrow gap welds were investigated. Stainless steel pipes were joined by the automated narrow gap welding process typical to nuclear piping systems. The weld fusion zone showed cellular–dendritic structures with ferrite islands in an austenitic matrix. Residual stress analysis showed large tensile stress in the inner-weld region and compressive stress in the middle of the weld. Tensile properties and the fatigue crack growth rate were measured along and across the weld thickness direction. Tensile tests showed higher strength in the weld fusion zone and the heat affected zone compared to the base metal. Within the weld fusion zone, strength was greater in the inner weld than outer weld region. Fatigue crack growth rates were several times greater in the inner weld than the outer weld region. The spatial variation of the mechanical properties is discussed in view of weld microstructure, especially dendrite orientation, and in view of the residual stress variation within the weld fusion zone. It is thought that the higher crack growth rate in the inner-weld region could be related to the large tensile residual stress despite the tortuous fatigue crack growth path.     

Control of submerged arc weld penetration by radiographic means

The application of real-time radiography for in-process weld quality evaluation is discussed. The advantages of this technique are on-line testing of weld penetration and the possibility of using this information for welding current control. The experimental system developed includes the arc welding unit, the welding manipulator, the real-time X-ray machine and the videorecording and computerized image processing units. In this system welding current can be remotely controlled during weld observation. The experimental results are demonstrated for the submerged arc welding process. In this process the welding pool is covered by a thick layer of welding flux and is therefore optically invisible. By using computer data on the grey levels of the weld images and their histogram distributions, the three-dimensional shape of the submerged arc pool can be recognized, image-digitized and analysed in real time at the rate of 30 frames per second. The depth of the welding pool which characterizes the weld penetration is a very important characteristic of the weld quality. This characteristic can be measured in real time and used for weld tracking and welding current control.     

Study of Hollow Cathode Arc Welding Technology for Ti Alloys

In this paper, technology margin experiment of hollow cathode fusion arc welding (FAW) and penetrating arc welding (PAW) is presented in detail. The advantages of PAW. compared with FAW, are better weld formation, narrower welds, as well as a larger welding technology margin. Technological experiment and hydraulic test for the Ti alloy pressure vessels with PAW are described. Also, the weld formation control on Ti alloys is preliminarily analyzed. Finally, conclusions are addressed.     

Microstructure characteristics of thick aluminum alloy plate joints welded by fiber laser

It's difficult to weld high strength thick plate since the groove is huge when using traditional arc welding, and the weld tends to be softened and large deformation could occur after multi-layer welding. All of these can affect the industrial application of high strength thick plate wielding. In this case, developing advanced welding technology and welding material is necessary to optimize the microstructure and performance of the welds. Fiber laser has many advantages such as good monochrome and high quality laser beam. In order to decrease the heat damage to the base metal from the welding heat source, low heat input is employed for welding thick plate. Fiber laser is applied in the welding of 20 mm thick Al–Zn–Mg–Cu alloy with super narrow gap filler wire. The microstructure comparison of Al–Mg–Mn alloy and Al–Mg–Mn–Zr–Er alloy welded joints reveals that a huge amount of fine equiaxed grains is formed in the weld zone of Zr and Er micro-alloying Al–Mg–Mn alloy welding wire and a great number of precipitation strengthening phases are precipitated in the weld zone after the heat treatment of welded joints in the entirety.     

窄间隙P-GMAW多信息融合侧壁熔合状态识别研究

窄间隙焊缝坡口间距小且焊道较深,摆动中心与焊缝中心偏差较大时,坡口两侧侧壁受热不良,易发生未熔合缺陷。为了及时了解窄间隙侧壁熔合情况,掌握侧壁内部焊接质量,本文提出了一种基于BP神经网络和D-S证据理论的多信息融合方法,预测侧壁熔合状态。对窄间隙焊接未熔合缺陷产生机制进行了分析,研究发现焊接电弧信号和熔池变化与侧壁成形质量存在密切关系,为此进行了一系列偏差实验,建立了电弧电信号和电弧熔池图像信号的实时采集系统,采用批量特征提取算法,提取了与侧壁熔合状态密切关联的峰值电流、峰值电压、电弧弧长、熔池长宽比、熔池面积和熔池周长等特征参量。采用BP算法训练神经网络,在此基础上通过D-S证据理论进行决策级融合。实验结果表明,该模型识别率可达96.667%,避免了神经网络识别时的误诊,获得了比单一传感信息更好的预测结果,提高了熔合状态识别的准确度和可靠度。     

Joining of blanks by cold pressure welding: Incremental rolling and strategies for surface activation and heat treatment

The cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld‐ability is presented. The application of innovative strategies based on electrochemical methods for an optimized conditioning of metal surfaces is investigated. The results account for a noticeable increase in the weld strength of steel‐aluminum joints after a surface activation consisting of either an electrochemical roughening or electrodeposition of a bifunctional organosilane thin film. In addition to the surface activation process regimes for the pre‐ and post‐welding heat treatment is investigated. Both weld strength and weld ability are improved due to heat treatments of steel sheets with various coatings and uncoated aluminium. The cold pressure welding is hereby done by incremental rolling, a new design process that allows for the manufacture of linear and curved joints between sheet metal blanks.     

Vision-based weld seam tracking in gas metal arc welding

A low-cost visual sensing system is developed to realize weld seam tracking in gas metal arc welding (GMAW). The system consists of a commercial CCD camera, narrow-band composite filter lens, an image capturing card, an industrial computer, a welding control unit, a GMAW power source, and a worktable. Images of root gap and its vicinity are captured in the GMAW welding process by the system. The captured images are processed by an algorithm on the basis of the analysis of gray characteristics of the root gap to get the offsetting information between torch and root gap centerline. The offsetting information is then used to realize weld seam tracking in the GMAW process. Welding seam tracking experiment is conducted by a simple proportional (P) controller. The results show that tracking error is basically less than ± 0.5 mm.     

Study of Weld Integrity and Nugget Development in Seam-Welded Cold-Rolled High-Strength Steels

Production processes like continuous annealing and continuous galvanizing/galvannealing rely on welding of two strips across their width, for continuous operation. The operational stability of these lines depends highly on the consistency of the welding process. Any failure of weld joint during processing is detrimental to production as the recovery times are very high (~1–3 days). Two instances of similar weld failures having identical chemical composition and dimensions of the strips were investigated to identify the root cause and establish adequate countermeasures. A systematic approach to evaluate weld performance using metallographic examination was carried out. The examinations revealed that poor nugget formation was the root cause of failure. The nugget formation, its orientation and size were also evaluated after carrying out a series of trials with different welding process parameters, and an optimum condition was arrived at. In summary, the weld failure occurred due to insufficient and unbalanced nugget formation which could be rectified by modifying the welding parameters such as current, pressure and speed.     

可调压力激光焊接工艺地面模拟装置的研制

目的 针对普通激光焊接实验装置无法用于非常压极端环境下激光焊接工艺的难点,研发设计一种可用于模拟环境压力变化的激光焊接地面模拟装置,使得在地面上模拟深海高压环境激光焊接和太空负压环境激光空间制造过程成为可能。方法 针对非常压极端环境下激光焊接实验成本高以及危险性大等问题,并综合考虑高压力、低真空,以及水下高盐度、低温度和微生物等环境特点,对模拟装置的压力调节集成系统、激光入射孔以及可移动运动平台3个主要方面进行设计。自主设计研发一套具备从负压到高压压力范围可调的激光焊接地面模拟装置,并对模拟装置进行实验和性能验证。结果 研制装置压力测试的结果表明,该装置能够开展5.2 Pa(真空环境)至13.13 MPa(深海环境)压力范围条件下的激光焊接实验,为深海高压激光焊接过程以及空间负压激光制造过程提供实验基础。基于该模拟装置进行了不同压力环境下的激光焊接实验,结果表明,大气环境中随着压力的增大,焊缝熔深逐渐增大,而熔宽呈减小趋势;水下环境中随着焊接速度的增大,焊缝熔深和熔宽均逐渐减小。结论 实验结果与现有研究结果相近,可调压力激光焊接地面模拟装置的可行性和有效性得到了验证。该装置能够为未来深海高压和外太空负压激光焊接实验进一步研究提供设备支撑,具有良好的应用前景。     

Experimental investigation of local tensile and fracture resistance behaviour of dissimilar metal weld joint: SA508 Gr.3 Cl.1 and SA312 Type 304LN

The aim of the paper is to evaluate the local tensile and fracture toughness properties of the dissimilar metal weld joints between SA508Gr.3 Cl.1 and SA312 Type 304LN pipe. Weld joints have been prepared by manual gas tungsten arc welding (GTAW) process with conventional V‐groove and automatic hot wire gas tungsten arc welding with narrow gap using different filler wires/electrode such as Inconel 82/Inconel 182 and ER309L/ER308L. The tensile and fracture toughness test specimens have been machined from different regions of dissimilar metal weld such as heat affected zones, fusion lines, buttering layer, weld metal and both base metals. Tensile and fracture toughness tests have been carried out as per the ASTM standard E8 and E1820 respectively. Tensile and fracture toughness results of all the regions of dissimilar metal weld joints have been discussed in this paper. Metallurgical and fracture surface examinations have also been reported to substantiate the tensile and fracture toughness results. Need for the local properties for integrity assessment of the dissimilar metal weld joints has also been brought out.     

Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

基于P-GMAW摆动电弧传感的窄间隙坡口宽度自适应焊接

针对窄间隙自动化焊接过程中,组对误差、焊接热变形等因素导致的坡口宽度不一致问题,本文提出采用电弧传感方式对坡口宽度进行检测,并根据检测结果调节工艺参数,保证焊接质量的方法。通过研究坡口宽度偏差的提取算法,分析窄坡口条件下脉冲熔化极焊接的峰值电流、基值电流和平均电流信号的传感特征,提出以脉冲周期内的电流均值作为特征信号,利用侧壁平均法进行偏差提取的传感方式;确定了坡口宽度变化时,焊枪摆幅、焊接速度的调控方法,实现了适应坡口宽度变化的自动化焊接。窄间隙焊接试验表明,上述方法能够有效识别坡口宽度变化,及时对摆幅、焊速进行调整,可在坡口宽度变化时,保证侧壁熔合质量和焊层厚度均匀。研究结果对单道多层窄间隙焊接实现焊接自动化,保证焊接质量具有一定的参考价值。     

The application of shoulderless conical tools in friction stir welding: An experimental and theoretical study

A friction stir welding (FSW) tool geometry, consisting of a shoulderless conical probe, is investigated for application to closed contour welding, variable thickness welding, and open-loop control welding. By use of a tapered retraction procedure and a ramped rotational velocity, a conical tool may facilitate material disengagement with minimal surface defects in applications which do not permit weld termination defects (e.g. pipes, pressure vessels, fuselages, nosecones). In addition, because the vertical position of the tool relative to the material surface is less critical with a conical tool than with other tool designs, it can be used in a open-loop fashion (i.e. without process force feedback control) and on materials whose thicknesses are highly variable. The use of a conical probe without a shoulder is not documented in the literature and it is the aim of this work to establish the conditions for mechanically sound welds. Effective tool geometries and process variables are found via experimental analysis. Thermal, tensile, macrosection, and process force data are presented along with a computational fluid dynamics (CFD) process model. It is concluded that this type of tooling is capable of producing acceptable welds when applied to butted aluminum plates and that similar methods would likely be effective in the applications described previously.     

焊接参数对中频逆变铜管焊接质量的影响

根据压缩机的使用要求,铜管焊缝应具有较强的密封性、焊接强度和良好的物理性能。本文针对壳体与铜管中频逆变焊工艺,通过调整焊接压力、焊接时间和焊接电流3个主要参数的对比试验,确定合理的焊接参数。试验结果对实际控制铜管焊接质量具有一定的指导意义。     

Comparative study on CO2 laser overlap welding and resistance spot welding for galvanized steel

The CO₂ laser overlap welding and the resistance spot welding are respectively investigated on DC56D galvanized steel used for auto body. The characteristics of the two types of welding methods are systematically analyzed in terms of the weld molding, tensile-shear performance, microstructure, hardness, and corrosion resistance of welding joint. The results show that, the fusion widths of the upper and lower surface are almost the same for the resistance welding joint, and the weld nugget is surrounded by the heat-affected zone. While the laser welding joint belongs to deep penetration welding, the weld fusion width presents wide at the top and narrow at the bottom, and the heat-affected zone is situated on both sides of the weld pool. Compared with resistance spot welding joint, laser welding joints have much more ultrafine microstructures, much smaller heat-affected zones, as well as greater resistance to deformation and corrosion. In addition, the tensile-shear performance of laser weld joints is superior to that of resistance welding joints under certain conditions.     

590 MPa级高强钢双面双弧立焊焊缝组织性能

为研究590 MPa级高强钢双面双弧工艺得到的焊接接头组织与性能的关系,采用钨极氩弧焊(TIG)与熔化极气体保护焊(MAG)方法获得成型良好的焊接接头,经过拉伸、冲击、弯曲试验及光学显微镜、扫描电镜、EBSD分析,对590 MPa级高强钢双面双弧立焊打底焊与盖面焊焊接接头的组织及性能进行了研究.结果表明:打底焊缝组织主要为贝氏体,盖面焊缝组织以贝氏体与针状铁素体为主;打底焊缝经历过一次热循环后组织得到一定程度的细化;打底焊缝硬度值与盖面焊缝相近,盖面焊缝热影响区最高硬度值高于打底焊缝热影响区最高硬度;2 mm坡口间隙性能较5 mm坡口间隙有较大提高,2 mm坡口间隙断口以韧窝断裂为主,5 mm坡口间隙断口以解理断裂为主.