Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants

The residual stress evolution in a safe-end/nozzle dissimilar metal welded joint of CAP1400 nuclear power plants was investigated in the manufacturing process by finite element simulation. A finite element model, including cladding, buttering, post-weld heat treatment (PWHT) and dissimilar metal multi-pass welding, is developed based on SYSWELD software to investigate the evolution of residual stress in the aforementioned manufacturing process. The results reveal a large tensile axial residual stress, which exists at the weld zone on the inner surface, leads to a high sensitivity to stress corrosion cracking (SCC). PWHT process before dissimilar metal multi-pass welding process has a great influence on the magnitude and distribution of final axial residual stress. The risk of SCC on the inner surface of the pipe will increase if PWHT process is not taken into account. Therefore, such crucial thermal manufacturing process such as cladding, buttering and post-weld heat treatment, besides the multi-pass welding process, should be considered in the numerical model in order to accurately predict the distribution and the magnitude of the residual stress.     

Microstructure,hardness and residual stress distribution in maraging steel gas tungsten arc weldments

Abstract

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr K_α radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld.     

Modifying residual stress levels in rail flash-butt welds using localised rapid post-weld heat treatment and accelerated cooling

Abstract

Flash-butt welding is used in the manufacture of continuously-welded rails. Finished welds typically exhibit high tensile residual stresses in the rail web and at the upper surface of the rail foot, which may increase the risk of fatigue failure in service. An understanding of the influence of the welding process, including post-weld cooling, on the residual stress distribution is necessary to improve the performance of flash-butt welds by post-weld heat treatment (PWHT), since incorrect treatment may have adverse effects on both residual stress and weld material characteristics. A finite element model has been developed to simulate post-weld cooling in flash-butt welded AS60 kg m^–1 rail. Computed thermal histories for normal (air) cooling, rapid PWHT, and accelerated cooling (water spray) were used as inputs to calculate sequentially coupled stress–time histories, including phase transformations. In addition, the localised influence of the initiation time for rapid PWHT, after final upset, on the reduction of tensile residual stresses was investigated. Heating the rail foot immediately after final upset reduced tensile residual stresses in the web region of the weld. Preliminary numerical predictions showed that water quenching the entire weld region too soon after the austenite–pearlite transformation is completed can induce further tensile residual stresses without affecting the microstructure. The results of the numerical analysis can be used to modify the flash-butt welding procedure to lower residual stress levels, and hence improve weld performance.     

焊后热处理对输送H_2S介质压力管道维修焊接接头组织性能的影响

采用手工钨极氩弧焊(TIG焊)打底,焊条电弧焊(SMAW)填充、盖面的焊接工艺对输送H_2S介质压力管道(20钢)进行维修焊接,并对其焊接接头进行720～750℃下保温1h的焊后热处理.对热处理前、后焊接接头组织和性能进行分析研究,结果表明:720～750℃×1h热处理使焊缝区与热影响区成针状分布的魏氏组织铁索体晶粒得到细化,并使其呈退化形态;焊缝区、热影响区与母材的显微硬度整体呈下降趋势;焊接接头抗拉强度大幅度提高,断裂均处在远离焊缝的母材上.焊后热处理有效地降低了焊接接头的残余应力,改变了残余应力的分布特征,使其分布趋于"均匀",拉应力大幅度降低.     

Internal residual stress measurement on inertia friction welding of nickel-based superalloy

The internal residual stress in the narrow inertia friction welding (IFW) welds of FGH96 nickel-based superalloy was measured with the contour method (CM). The as-welded internal hoop and axial residual stresses were obtained after two cuts and the detailed steps of the CM measurement were described. In addition, the hole-drilling method was used to obtain the surface stress. Furthermore, the internal hoop residual stress of a FGH96 superalloy IFW specimen after post-weld heat treatment (PWHT) was also measured with the CM after a single cut. The measured results show that the peak hoop residual stress is not symmetrical about the weld centreline. Axial residual stress on the outer surface at the weld centreline is compressive stress, while tensile stress appears on the inner surface, and it varies linearly along the thickness. The peak values of hoop tensile and compressive stresses decrease dramatically after PWHT.     

Investigations into the tendency to stress corrosion of joints welded in austenitic and duplex steels

Austenitic stainless steel is welded as a cladding on the inner surface of a reactor pressure vessel (RPV) made of low alloy steel. In order to assess the structural integrity of the RPV precisely, the residual stress distribution caused by weld-overlay cladding and post-weld heat treatment (PWHT) is evaluated. Since the cladding layer is very thin compared to the vessel wall, it is necessary to evaluate the residual stress distribution around the weld fusion line, which can be very steep. In this study, cladded specimens were fabricated using different welding methods. Residual stress measurements using both sectioning and deep hole drilling (DHD) methods were then performed to evaluate the residual stress distributions through the weld fusion line. Three-dimensional thermal-elastic-plastic-creep analyses based on the finite element method were also conducted to evaluate the residual stress caused by weld-overlay cladding and PWHT. It was shown that analytical results provided reasonable agreements on weld residual stress with experimental results. It was also clarified that the main cause of residual stress due to welding and PWHT was the difference of thermal expansion between weld and base metals.     

Cr-Mo钢管子局部焊后热处理加热宽度准则的确定

采用粘弹塑性有限元方法从应力释放角度讨论了Cr-Mo钢局部热处理下各种优化加热条件.研究表明,局部热处理过程产生的瞬态和残余应力受蠕变性能和温度关系弹性模量等因素的影响.当加热宽度足够大时,局部热处理后的应力与炉中热处理的应力接近.通过与现有标准的比较,从应力释放角度位于焊缝中心5√Rt的加热宽度较为合理.提出了考虑焊接冷却过程Cr-Mo低温膨胀现象的相变模型.给出了焊接残余应力与局部焊后热处理应力的试验结果与模拟结果的对比.     

双相不锈钢管道全位置焊接残余应力三维有限元数值模拟

以热弹塑理论为基础，利用ANSYS非线性分析有限元程序，对双相不锈钢管道接头环焊缝残余应力进行三维数值模拟。建立了管道全位置焊接瞬态温度场和应力场三维移动热源模型，获得了环焊缝焊接接头轴向和环向残余应力的分布规律：在管道接头内表面的焊缝及近缝区的轴向和环向残余应力均为拉应力，随着离开焊缝距离的增加，由拉应力逐渐过渡为压应力。在管道接头外表面焊缝中心处的轴向残余应力为压应力，而环向残余应力为拉应力。从环向位置上的应力变化规律可以看出正半周和负半周的应力分布具有明显的对称性。研究结果为优化生产工艺，控制残余应力提供了理论依据。     

数值计算模拟工艺参数对管道环焊缝残余应力的影响

以热——弹塑性理论为基础,建立了厚壁管环焊缝残余应力的二维轴对称有限元模型,利用ANSYS有限元程序分析了三种焊接工艺参数对管道环焊缝残余应力的影响,计算中考虑了材料热物理性能参数和力学性能参数的温度相关性.结果表明,管道内表面焊缝和近缝区的轴向和环向残余应力均为拉应力,而管道外表面焊缝和近缝区的轴向残余应力和环向残余应力均为压应力;接头内表面应力水平高于外表面;残余应力的最大值均位于距管道外表面一定距离处,其数值接近于材料的屈服应力;随着焊接热输入的增加,残余应力峰值变化不大,塑性变形区宽度增加.     

铍环激光束钎焊过程的数值模拟

采用MARC软件对铍环激光束钎焊过程的温度场和应力场进行有限元分析，温度场分析得到与铍环实际激光束钎焊基本一致的焊缝形状，应力场分析表明，焊接后轴向应力和环向应力在焊缝中心的钎料上为压应力，在铍玻外表面热影响区的内表面均为拉应力，径向应力为压应力，焊接残余应力主要分布在离焊缝2mm的范围内，焊接后铍环内外表面发生径向收缩，将有限元分析得以的铍坏外形面的轴向残余应力结果与实测结果进行了比较，二者所反映的应力变化趋势基本一致。     

X80管线钢环焊缝接头残余应力的数值模拟

利用SYSWELD有限元分析软件,以热弹塑性理论为基础,采用双椭球焊接热源模型,对X80管线钢环焊缝接头的焊接温度场和应力场进行了模拟仿真.得到了焊接残余应力的分布规律,即焊缝及近缝区的残余应力值较大,远离焊缝中心残余应力值逐渐减小;由于表面和心部散热条件不同,造成了管道表面和心部的残余应力方向上的差异或数值大小的不同.研究了焊接工艺参数对残余应力的影响规律.结果表明,随着热输入的增大和预热温度的提高残余应力值逐渐降低;为了减小焊接残余应力,应尽量采用较大热输入和较高预热温度进行焊接.     

Welding of ASTM A106 Gr. B steel pipes for high-temperature service – part 1 – residual stress analysis

Welding is the principal process of manufacture used in the fitting and repair of tube sections. However, there is a lack of information about the alterations mechanically/metallurgically caused by the welding heat cycle, especially about the behaviour of the residual stresses. The objective of the first part of this work was to evaluate the welding residual stress in small diameter pipes used in oil refineries. Two-inch diameter pipes were welded using the manual GTAW process. AWS ER 70 S3 filler rods with diameters of 2.5 and 3.25 mm were employed. An electronic power supply was used, together with data acquisition systems to control the welding parameters. Stress measurements were carried out with an X-ray mini diffractometer. The axial residual stress profiles determined in the outer surface of the pipes were formed by compressive stresses in the weld region (the fusion zone and heat affected zone) and for tension stresses in the areas more distant from the weld bead. The evidence suggested that on the inner surface of the pipes, the stress profile is the opposite from that observed for the outer surface, with tension stress in the welding zone and compressive stress in the region further from the weld bead.     

Finite Element Analysis of High Temperature Piping Creep for Considering the Effect of Inner Pressure and Welding Residual Stress

利用大型有限元分析软件Abaqus的多次顺次耦合功能,先对P91钢高温主蒸汽管道焊接接头焊态和焊后热处理状态进行残余应力分析, 然后采用Norton蠕变本构关系,根据P91耐热钢在625℃下焊缝、热影响区和母材的不同蠕变参数,对内压以及内压与热处理后残余应力共同作用下的接头蠕变进行有限元分析,分别得到了焊接残余应力和焊后热处理残余应力的分布规律,同时预测了在高温环境下服役105h后蠕变应变分布. 结果表明,由于高温管道的壁厚以及约束等影响, 焊后产生了较大的焊接残余应力,通过焊后热处理可以有效地降低焊接残余应力.但由于热处理残余应力的存在, 仍对高温管道焊接接头的蠕变有较大影响,并且在焊缝与热影响区的交界处存在着较大的蠕变应变.     

Effect of low transformation temperature weld filler metal on welding residual stress

Abstract

The effect of weld filler metal austenite to acicular ferrite transformation temperature on the residual stresses that arise during the gas metal arc welding of a low carbon steel has been examined using a finite element model. It was found that the stress levels in the weld can be tailored by the appropriate selection of the filler metal and compressive, near zero or tensile residual stresses produced. Reasonable agreement was obtained between the model and the stresses measured using neutron diffraction both in welds using conventional and low transformation temperature filler metal.     

Residual welding stresses in laser beam and tungsten inert gas weldments of titanium alloy

Abstract

The residual welding stresses in laser beam (LB) and tungsten inert gas (TIG) weldments of a titanium alloy in thin plate form were investigated experimentally in the present work. A hole drilling technique was used to measure the residual stresses in the weldments. The effects of the welding method and post-weld heat treatment (PWHT) on the residual stresses were analysed. The results show that (i) the residual stress distribution in the LB welded joints is similar to that obtained for traditional fusion welding processes, although the distribution zone is much narrower in LB welding, (ii) the residual stress in the heat affected zone for LB welding is about 100 MPa lower than that for TIG welding, and (iii) PWHT in vacuum greatly relieves the welding residual stress.     

Recent developments in repair welding technologies in Japan

Abstract

Developments in some difficult repair welding technologies in Japan during the past decade are reviewed. The topics covered include the repair welding of bridges in service, the temper bead method which makes it possible to omit post-weld heat treatment (PWHT) of repaired pressure vessels, the seal welding of a reactor vessel in which stress corrosion cracks were detected, low heat input repair welding of neutron irradiated stainless steel and nickel based alloys, the prevention of solidification cracking in repair welding of aged heat resistant cast steels, the development of welding materials for the mending of single crystal nickel based superalloy turbine blades, underwater repair welding of nuclear reactors, the reduction of residual stresses in repair welding, and an ultrasonic testing method for nickel based weld metals. The local PWHT of creep resistant ferritic steel tubes is also reviewed.     

铝合金薄板焊接应力三维有限元模拟

采用热弹塑性有限元方法,对铝合金薄板脉冲TIG焊接接头的焊接应力进行了三维数值模拟,考虑材料性能随温度的变化,对焊接残余应力进行测量.结果表明,铝合金薄板中的焊接应力产生、发展很快,加热结束后不久应力便趋于稳定.热源前缘和两侧区域存在数值很高的纵向和横向动态压应力,焊缝中心的纵向残余拉应力低于母材的屈服强度,距焊缝中心10 mm处的最大纵向残余拉应力达到母材的屈服强度,并且拉应力区较宽,远离焊缝区域的纵向残余压应力数值较大,因此铝合金薄板焊接结构易发生动态和焊后失稳,横截面上纵向残余应力的数值模拟结果与实测结果基本一致.     

Influences of post-weld heat treatment on fatigue crack growth behaviour of strength mismatched HSLA steel welds

Abstract

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) compared with the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the influences of post-weld heat treatment (PWHT) on fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. The Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single 'V' butt joints. Centre Cracked Tension (CCT) specimens have been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R = 0). From this investigation, it has been found that the fatigue performance of over matched joints is superior compared to under matched and equal matched joints. Moreover, PWHT reduced the magnitude of the tensile residual stress field in the weld region and subsequently enhanced the fatigue performance of the joints irrespective of weld metal strength mismatch.     

Effects of post-weld heat treatments on the residual stress and mechanical properties of electron beam welded sae 4130 steel plates

The distribution of the residual stresses of electron beam welded SAE 4130 and the effect of stress relief after various post- weld heat treatments (PWHT) were measured using X- ray diffraction. The mechanical properties and microstructure were also examined. Experimental results show that the tensile residual stress increased with the heat input of the electron beam. Most of the residual stresses were relieved by the PWHT at 530 °C for 2 h followed by furnace cooling to 50 °C. The strength of the welds decreased slightly, and the elongation of the welds increased after PWHT.     

焊缝屈服强度对SM490A钢焊接残余应力预测精度的影响

基于有限元分析软件MSC. Marc,开发了用于模拟焊接温度场、焊接应力场和应变场的热-弹-塑性有限元计算方法. 以低合金高强度钢SM490A为研究对象,采用移动热源和实测得到的YGT50焊缝与母材高温热物理性能和力学性能数据,数值模拟了SM490A钢单道堆焊接头的焊接残余应力. 并重点讨论了高组配接头焊缝的屈服强度对焊接残余应力的峰值和分布的影响. 结果表明,对于高组配接头,当把焊缝和母材不加区分(等强匹配),两者都采用母材的屈服强度来计算焊接残余应力时,得到的焊缝处纵向残余应力明显低于实测值;当分别采用焊缝和母材的屈服强度来计算焊接残余应力时,得到的焊缝处纵向残余应力与试验值非常接近.