三维管接头焊后局部热处理加热宽度准则

提出了直接定量评定管接头焊后局部热处理应力释放效果的方法。构造了三维管接头焊接应力和局部热处理温度场,采用粘弹塑性有限元方法对管接头焊后不同局部热处理条件不应力分布特征进行了研究,对单道焊情况,不同焊接规范下的焊接应力分布具有相似性,焊接顺序对应力峰值位置的影响较小。对管接头热点处焊接应力在不同局部热处理条件下释放程度做了分析,在局部热处理加热宽度足够大情况下残余应力明显下降,周向和轴向应力分量与加热宽度的关系不同,周向和轴向应力的最优加热宽度分别为3.46√-Rr的4.8√-Rt。通过对局部热处理主要工艺参数的计算,推荐了正交管接头局热处理加热宽度准则。     

局部焊后热处理加热宽度的直接评定方法

局部焊后热处理通常用改善焊接接头的性能和消除焊接残余应力。影响局部焊后热处理的因素很我,其中加热宽度是最重要的一个控制参数。然后对于加热宽度的确定,各国标准规定就很不一致。本语文采用粘弹塑性有限元分析,提出一个基于残余应力消除效果的局部焊后热处理的直接评定方法。该方法可清楚地显示整个热处理过程的应力变化并可找到临界的加热宽度。对存在原始焊接残余应力随加热宽度的增加而降低,当加热宽度达到一定值,残余     

BT20钛合金电子束热处理残余应力计算

利用三维有限元分析软件，模拟了BT20钛合金薄板焊态和焊后电子束局部热处理的实际焊接温度场以及残余应力的分布。结合数值计算，讨论了不同的热处理方式以及热处理工艺参数对焊接接头残余应力分布的影响。结果表明，在钛合金薄板焊缝的背面进行电子束局部热处理，可以显著降低焊缝中心处的残余拉应力。数值计算结果还表明，在其它工艺参数相同的情况下，随着局部热处理加热宽度和加热时间的增加，焊缝及近缝区的纵向残余应力随之降低，同时产生残余应力的范围也随之增大。     

局部加热法影响转轮焊接残余应力的试验分析

针对焊缝成形的特点,提出了改善叶片焊接残余应力分布状态的局部加热法,并在利用平板试验得到局部加热合理位置的基础上,利用局部加热法对某水电站转轮的焊接残余应力场进行了调控.结果表明,对于500 mm×500 mm×16 mm的平板,局部加热法降低残余应力效果最好的位置是在距加热区域边缘约60 mm处;局部加热法可以使叶片的危险区域产生残余压应力;从降低叶片出水边附近焊接残余应力的效果来看,热处理后进行局部加热的效果要优于热处理前进行的局部加热.     

加热面积对球罐局部热处理应力消除效果的影响

针对球罐局部热处理缺少标准支持问题,采用数值模拟方法分析了加热面积大小对焊接残余应力清除效果的影响.结果表明,局部加热过程本身引起的热应力是影响局部热处理效果的控制因素;工程中经常采用的局部热处理工艺,由于加热面积太小,不会取得理想的应力消除效果;增加加热面积可有效提高残余应力消除率,采用足够大的加热面积可达到整体热处理的效果.但局部热处理加热面积的选择会受到球罐体积和壁厚的显著影响,对于相同的残余应力消除率期望值,较大的体积和壁厚均需要采用较大的加热面积.     

残余应力释放工艺对T形接头焊接残余应力及疲劳寿命的影响

为探究过载处理与热处理工艺对T形接头焊接残余应力释放及其作用下疲劳寿命的影响，对T形接头焊接过程进行有限元模拟，揭示了焊接残余应力分布特征及其对焊后疲劳寿命的影响规律，分析了过载处理与热处理对焊接残余应力释放效果及疲劳耐久性的影响，进一步探究了保温时间与热处理温度对T形接头焊接残余应力影响。结果表明：采用过载处理与热处理方法，T形接头焊接残余应力分别降低了63.8%与61.0%,其疲劳寿命分别延长了1倍与5倍；焊接残余应力的释放主要发生于热处理开始阶段，保温阶段残余应力的释放较小，冷却阶段残余应力有略微反向增大。为利于释放焊接残余应力，建议在冷却阶段严格控制构件均匀降温；焊接残余应力随热处理温度提高而减小，且保温时间对焊接残余应力影响不太明显。     

局部加热冷却法对水轮机转轮焊接残余应力场的影响

针对焊缝成形的特点,提出了改善叶片焊接残余应力分布状态的局部加热冷却法,并利用数值模拟技术研究了局部加热冷却法对转轮残余应力场的影响,得到了叶片危险区域的残余应力在局部加热过程中的变化情况以及转轮局部加热的优化方案.结果表明,采用局部加热冷却的方法可以有效地减小叶片危险区域的残余拉应力峰值.残余应力的降低效果与加热时间、加热温度以及加热面积成正比,并且焊接残余应力随加热距离的增加呈先降低后增大的趋势.     

钛合金电子束焊接和局部热处理后残余应力分布特征

采用小孔法测定了14.5mm厚TC4钛合金平板电子束焊接,研究了电子束焊接和局部热处理集成加工工艺下残余应力的分布,分析了局部热处理对焊接接头残余应力分布特征的影响.结果表明,在实验条件下电子束局部热处理后纵向残余拉应力的分布区间由焊接状态下焊缝中心线两侧距焊缝中心线5mm的区域减小到2mm的区域,纵向残余拉应力峰值同焊接状态相比降低了76%,横向残余压应力峰值降低了65%.电子束局部热处理未扫描的母材区域,残余应力数值同焊接状态相比几乎没有变化.     

局部热处理改善TC21钛合金板电子束焊接残余应力研究

针对TC21钛合金电子束焊接接头残余应力过大问题,通过局部热处理工艺来改善其分布,分别采用X射线检测法和小孔法两种方法对电子束局部热处理后焊接残余应力的分布进行了测试研究。试验结果表明:两种测试方法测试结果趋势相同。焊后焊缝区残余应力较大,横向残余拉应力最高达到736 MPa,纵向残余压应力最高达到-468MPa,而经电子束局部热处理后,焊缝区横向及纵向残余应力峰值同焊接态相比都降低了70%~75%,而母材区域由于焊接态时残余应力较小,经过局部热处理扫描和未经过局部热处理扫描的区域残余应力几乎没有变化。     

主副加热分布式热源局部热处理方法

局部热处理是保证承压设备全寿命周期安全性的重要手段.文中以某二甲苯塔分段筒节为研究对象,提出了一种主副加热分布式热源局部热处理方法,在传统单加热基础上,距离焊缝一定位置施加副加热区,主加热用于改善焊缝微观组织、消除部分残余应力,副加热在焊缝产生反变形,抵消主加热产生的“收腰变形”,消除焊缝内表面残余应力.采用试验、数值模拟和理论分析,建立了主副加热局部热处理有限元模型,研究了副加热带温度、宽度、主副加热间距对应力消除效果的影响规律.结果表明,采用传统单加热热处理方法,降温阶段,焊缝受到拘束作用在内表面产生新的二次应力.主副加热分布式热源局部热处理利用副加热区的反变形,可以在焊缝内表面产生压应力.主副加热带宽度、间距和副加热温度是应力消除效果的关键因素,提出了主副加热局部热处理工程设计方法,为重大承压设备局部热处理提供依据.     

NUMERICAL SIMULATION OF MECHANICAL BEHAVIOR DURING LOCAL POSTWELD HEAT TREATMENT

1.IntroductionStresscorrosioncrackingduetothecombinedeffectsofserViceenvirollrnentandlOcalizedweld-indllcedstresshajsbeenrecognizedasaseriousProblemintheweldingindustryforanumberofyearsLI].InordertoimprovetheductilityofweldssusceptibletocrackingandrelievetheresidualstressesthelOcalpostweld11eattreatmentisusuallyperformedwhenitisunpracticaltoheattreatthewholevesselinafurnace.TwoprimarybenefitsofPWHTarethetemperingandtherel~tionofresidualstresses.Benefits,suchasimprovedductilityltoughnessand…     

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.     

Effects of a double sided heating method and its controlling parameters: Development of a residual stress control method for butt-welded pipe joints (1st Report)

Abstract

This paper describes a new stress improvement method to reduce tensile residual stress on the inner and outer surfaces near butt-welded pipe joints. Its procedure is as follows. An annular region on both sides of the weld line is heated from the outside at the same time to generate a temperature differential between the weld line and region being heated. The region being heated and the welded joint are not actively cooled after completion of heating. That is to say, the proposed method involves the whole circumference on both sides of the weld line simply being left to cool after heating and includes no water cooling or movement of heating position as required by the low-temperature stress relaxation method. A tensile strain is generated on the inner surface near the welded joint to produce plastic deformation by tensile stress when the annular region is heated. The tensile stress after cooling is reduced by this plastic deformation. The two sided heating method can therefore be expected to exert a satisfactory and stable residual stress control effect.

The authors show the mechanism and effect of the proposed method by an FEM analysis. The effects of the controlling parameters of the method – such as e.g. the heating width, heating position, and heating conditions (intensity and time) – on the residual stress are studied. The proposed method is applied in practice to 4BSch40 (OD = 114.3 mm, t = 6.0 mm), 4BSch160 (OD = 114.3 mm, t = 13.5 mm), and 20B (OD = 508.0 mm, t = 8.0 mm) stainless steel pipe welded joints, and the changes in the residual stress are measured. The measured welding residual stress on the inner surface near the GTA (TIG) welded joints is more than + 200 MPa. The residual stress on the inner surface near the welded joints decreases, changing to compression in all joints after treatment by this method.     

一种消除小直径管道焊接应力技术的数值分析

小直径管道的应力腐蚀问题一直是工程界较难解决的问题，作者针对这一难题，提出了一种新型的消除应力方法——温差形变处理技术。利用MSC．Marc大型通用非线性有限元分析软件，对小直径管道环缝焊接接头的原始残余应力及温差形变法消除残余应力进行了有限元模拟，得到了一系列关于加热位置、加热宽度和加热持续时间的数据和规律。结果表明，采用温差形变处理技术，在内外表面的焊缝处都可以得到零值左右的残余应力，从而为进一步的试验分析工作和工程应用奠定了基础。     

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.     

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.     

核电SA508-3钢大型筒体环焊残余应力分析

为了准确地预测核电SA508-3钢的大型筒体环焊温度和残余应力变化规律,基于ANSYS有限元软件,引入子结构法优化焊接模拟过程,并比较模拟结果与试验数据.结果表明,文中采用的计算方法成功地模拟了更加接近真实的筒体环焊过程,且模拟结果与实测值基本吻合;焊缝上所有节点的热循环曲线相似,热影响区的模拟宽度为4 mm左右;筒体外表面焊缝中心线上任意节点的残余应力大小相近,仅在靠近筒体外表面焊缝中心线附近存在一定的轴向压应力,其它区域大部分为拉应力,环向保持较高的拉应力;筒体焊后产生内凹残余变形;结果可为分析大型筒体环焊残余应力提供参考数据.