锅炉集箱管座坡口结构分析

本文对上海锅炉厂集箱管座坡口的形式与美国ABB-CE公司的集箱管座坡口形式进行了比较、分析,对ABB-CE公司的集箱管座坡口利用位移分析的方法进行了研究和探索,并结合具体实例作了计算,期望能对目前工程师们常用的J型坡口标准作一些有实用价值的解释。     

1000t/h锅炉末级再热器出口集箱管座角焊缝产生裂纹的原因与措施

末级再热器出口集箱管座发生裂纹,是长期困扰燃煤电厂的重大设备隐患。通过分析末级再热器出口集箱管座上部角焊缝热影响区产生裂纹的原因及焊接装配形式的分析,认为不合理的焊接接头型式、较大的拘束应力和长期高温运行后导致金属热强性降低,是集箱管座产生裂纹的主要原因。为此,按照DL/T869—2012标准要求,将承插式焊接接头改为全焊透焊接接头,用加强型管座提高焊接接头强度,控制焊接工艺参数等措施,提高了焊接接头的强度和高温力学性能,消除了超标焊接隐患。12号锅炉从2011年12月大修后运行至今,末级再热器出口集箱焊口经过多次磁粉探伤,均未发现裂纹等超标缺陷,证实了改进集箱管座焊接接头型式是正确的。     

12Cr1MoV钢焊接接头蠕变、蠕变～疲劳交互作用裂纹开裂和扩展特性研究

结合火力发电设备大型锅炉集箱管座焊接接头破裂情况,本文重点研究了12Cr1 Mov钢母材、手工焊的焊缝、热影响区的蠕变、蠕变～疲劳交互作用下裂纹开裂和扩展特性,同时也测定了母材、焊缝和热影响区的蠕变断裂韧性值,用来评定焊接接头抗蠕变脆性特性的好坏.另外还研究了回火温度对12Cr 1 MoV钢母材,焊缝和热影响区裂纹开裂和扩展及蠕变断裂韧性影响,从改善焊接接头抗裂纹开裂和扩展能力新观点出发,来确定焊后最佳热处理。     

锅炉集箱管座内孔脉冲钨极氩弧焊封底

本文提出的锅炉集箱管座内孔脉冲钨极氩弧焊封底,可以获得“全焊透”的管座角焊缝,能在根本上避免泄漏事故,提高角焊缝的承压强度,也是解决管座角焊缝内外全自动焊的基础。这一工艺方法的采用,具有很大的技术经济意义,以年产150万千瓦电站锅炉的工厂计算,仅在大幅度降低返修和免除泵水所带来的收益即可达数十万元。至于为电厂提高运行可靠性,减少事故停炉带来的利益更以千万元计。所介绍的焊机机头和电气控制线路,能达到集箱管座角焊缝焊接的程序控制要求。本文讨论了脉冲氩弧焊焊接规范主要参数的选择,引用了等值电流的概念。收弧裂缝是一种较为独特的热裂缝,近似于弧坑裂缝而又不同于通常阐述的弧坑裂缝。收弧裂缝主要发生在脉冲氩弧焊双面成形焊缝的背面,且正对主脉冲所形成的弧坑。提出了解决收弧裂缝的主要工艺措施是选用一种脉冲衰减的焊接规范。本文还列举了集箱管座内孔脉冲氩弧封底焊在电站锅炉生产中的应用实例。     

超临界机组低温再热器出口集箱12Cr1MoVG管座角焊缝裂纹原因分析

神华国能宁夏煤电有限公司1号机组低温再热器出口集箱管座角焊缝多次出现开裂问题,通过金相组织分析、电镜扫描、化学成分分析以及硬度试验,表明管座角焊缝产生裂纹的原因与材质及硬度无关;进一步进行小试样再热裂纹试验。结果表明:管接头在其工作温度区间具有较大的再热裂纹敏感性,而连接管在此温度的再热裂纹敏感性较低,即部分集箱管接头的再热裂纹敏感温度处于其工作温度区间,因此在热应力等因素的综合作用下产生了开裂。     

600MW机组超临界“W”火焰锅炉水冷壁联箱管座角焊缝裂纹分析与对策

对国产600MW机组超临界"W"火焰锅炉水冷壁上联箱管座产生大量裂纹的原因进行了综合分析,并利用ANSYS应力软件对该联箱管座进行了胀差应力模拟计算。分析和计算结果表明,管屏管间壁温偏差大、设计不合理,在管座角焊缝出现大的交变胀差应力是产生裂纹的根本原因。在此基础上,提出了通过割除管间鳍片增加管座光管长度,改变联箱炉顶密封结构的方案,使问题得到成功解决。     

T91与12Cr1MoVG异种钢焊接接头的硬度分析

采用自动钨极氩弧焊对12Cr1MoVG与T91异种钢进行焊接,研究在不同工艺实验条件下对异种钢焊接接头硬度的影响。研究结果表明,在不同工艺实验条件下,异种钢的焊接接头焊缝形貌基本一致,焊缝呈现倒梯形上下2层结构。经历热处理后的异种钢焊缝中心的硬度HV约为250,而未经历热处理的异种钢焊缝中心的硬度HV约为300,最高HV达到390,且异种钢焊接接头硬度靠近T91一侧硬度呈现突变上升。     

超高压锅炉异种钢管焊接工艺制订原则

阐述了奥氏体不锈钢与低合金钢异种接头的焊接性和焊接工艺性，分析了异种钢焊缝焊接工艺制定的原则，认为选用镍基材料作为焊接材料并采用适当的工艺措施可保证焊缝质量及延长异种钢接头的寿命。     

基于超声相控阵技术的集箱管座角焊缝缺陷检测方法

超声相控阵技术是一种先进的超声检测技术,它具备常规无损检测技术(如常规超声、射线)所不具备的优势,越来越被人们所认可。简要介绍了超声相控阵技术的基本原理,同时基于超声相控阵的原理对集箱管座角焊缝缺陷检测的可行性进行分析并通过试验加以论证。总结了集箱小径管座角焊缝相控阵检测的特点。     

异种钢环缝自动TIG焊接工艺研究

低合金钢（铁素体钢）与镍基合金（不锈钢）锻件之间的异种钢对接焊缝越来越多的应用于换热设备的设计和制造过程中.自动TIG窄间隙焊接工艺已经成为异种钢对接焊缝的主要工艺方法.研究自动TIG焊接工艺,对焊接材料的选择、母材性能参数及焊接工艺等进行了介绍,通过焊接评定试验对焊接工艺进行试验论证和总结,并成功应用于换热设备异种钢环缝的焊接.     

The behavior of welded joint in steel pipe members under monotonic and cyclic loading

Most steel pipe members are joined by welding. The residual stress and weld metal in a welded joint have the influence on the behavior of steel pipes. Therefore, to accurately predict the behavior of steel pipes with a welded joint, the influence of welding residual stress and weld metal on the behavior of steel pipe must be investigated.In this paper, the residual stress of steel pipes with a welded joint was investigated by using a three-dimensional non-steady heat conduction analysis and a three-dimensional thermal elastic–plastic analysis. Based on the results of monotonic and cyclic loading tests, a hysteresis model for weld metal was formulated. The hysteresis model was proposed by the authors and applied to a three-dimensional finite elements analysis. To investigate the influence of a welded joint in steel pipes under monotonic and cyclic loading, three-dimensional finite elements analysis considering the proposed model and residual stress was carried out. The influence of a welded joint on the behavior of steel pipe members was investigated by comparing the analytical result both steel pipe with a welded joint and that without a welded joint.     

汽轮机焊接转子接头残余应力研究二:带有弹性槽的30Cr2Ni4MoV模拟件热处理前后残余应力变化

在测试25Cr2Ni2MoV钢核电转子模拟件外圆、内圆、剖面处热处理前后的残余应力分布的基础上,进一步研究了弹性槽对根部打底焊缝处残余应力的影响,测量了盖面焊缝下方4～5层焊道处残余应力的分布。结果表明,弹性槽对缓解根部应力有显著作用,盖面焊缝下方4～5层焊道处存在超过屈服极限的纵向拉应力;热处理后,残余应力大大降低,且保持较好的应力状态。相关测量工作肯定了实际生产工艺对控制残余应力的有效性。     

新疆克拉玛依市供水系统工程高压岔管群体型结构整体受力计算三维有限元优化分析

针对克拉玛依市中心城区供水系统工程的高压力水头、庞大且复杂的供水管线系统及超越规范的结构形式等诸多设计难点,通过建立贴边岔管群的整体受力模型进行三维有限元分析,找出岔管群中最薄弱钢岔管,使其应力满足要求,再逐级量化每个岔口应力,获得了岔管群中每个钢岔管在运行期时所处应力状态。结果表明,通过21组方案优化#1～#5钢岔管群结构尺寸,用最少的方案确定出每个钢岔管的最优体型;#5钢岔管群中的③支管处的补强板为最不利点;由于钢岔管补强板焊缝处属于变截面段,管壁刚度差异明显,导致补强板外边缘焊缝处的局部拉应力过大,需严格把关焊缝质量关键,尽量避免产生这类局部拉应力过大现象。     

Temperature distribution and residual stresses due to multipass welding in type 304 stainless steel and low carbon steel weld pads

Welding is a reliable and efficient metal-joining process widely used in industry. Due to the intense concentration of heat in the heat source of welding, the regions near the weld line undergo severe thermal cycles, thereby generating inhomogeneous plastic deformation and residual stresses in the weldment. Plates of different thickness are used in industry and these plates are normally joined by multipass welding. In a multipass welding operation, the residual stress pattern developed in the material changes with each weld pass. In the present experimental work, thermal cycles and transverse residual stresses due to each pass of welding have been measured in the weld pads of AISI type 304 stainless steel and low carbon steel with 6, 8 and 12 mm thickness. X-ray diffraction method was used for residual stress measurements. The welding process used was the Manual Metal Arc Welding (MMAW) process. In this paper, the peak temperatures attained at different points during deposition of weld beads in stainless steel and low carbon steel weld pads are compared. The residual stress patterns developed, the change in the peak tensile stress with the deposition of weld beads, and the relation between the peak temperatures and the residual stresses in the weld pads are discussed.     

Measurement and prediction of residual stress in a bead-on-plate weld benchmark specimen

This paper presents measurements and predictions of the residual stresses generated by laying a single weld bead on a flat, austenitic stainless steel plate. The residual stress field that is created is strongly three-dimensional and is considered representative of that found in a repair weld. Through-thickness measurements are made using the deep hole drilling technique, and near-surface measurements are made using incremental centre hole drilling. Measurements are compared to predictions at the same locations made using finite element analysis incorporating an advanced, non-linear kinematic hardening model. The work was conducted as part of an European round robin exercise, coordinated as part of the NeT network. Overall, there was broad agreement between measurements and predictions, but there were notable differences.     

The NeT bead-on-plate benchmark for weld residual stress simulation

Fracture mechanics based structural integrity assessments of pressure vessels and piping are widely used to support the economic and safe management of operating engineering plant. Assessments of defects at weldments can be highly sensitive to the through-thickness distribution of residual stress assumed in the fracture calculations. Increasingly, finite element modelling approaches are applied to predict residual stress in engineering structures arising from the welding process. However, such methods are complex and require analysts to make many assumptions and approximations. Guidelines covering the calculation of residual stresses in weldments are being prepared for inclusion in the R6 defect assessment procedure and will be accompanied by a series of validation benchmarks. The benchmarks will allow analysts to evaluate and improve the accuracy of weld modelling approaches and assess their suitability for use in fracture assessments. The first part of this paper presents an austenitic stainless steel bead-on-plate weldment validation benchmark based on the extensive round robin measurements performed by members of the European NeT project. The benchmark defines thermal and residual stress performance targets against which a weld simulation approach can be evaluated. Guidance is also provided on how to validate predicted residual stress profiles for use in a high integrity fracture assessment. The second part of this paper provides a commentary on how the weld simulation accuracy and performance targets have been established.     

Monticello recirculation piping replacement problems, contingencies, and evolving work scope

This paper describes the many significant items that were added to the initial workscope during the detailed preparation and actual replacement of the Monticello reactor recirculation piping. These included chemical decontamination, weld stress improvement, manifold reconfiguration, electro-polishing, extra machining and welding of nozzles, piping scope additions and the replacement of jet pump nozzles. Lessons are drawn for future replacement work.     

Evaluation of residual stresses in dissimilar weld joints

Dissimilar metal joints between pipes of ferritic and austenitic steels are widely used in steam generators of power plants. Failure analysis carried out on a dissimilar weld joint and a literature survey have shown that a significant number of failures have occurred in the heat affected zone (HAZ) region on the ferritic steel side of such dissimilar weld joints. Residual stresses present in the weld joint are one of the main factors, which cause failures in dissimilar weld joints. A typical dissimilar pipe weld joint, representing a joint used in an Indian Fast Breeder Test Reactor (FBTR) was fabricated between 2.25Cr–1Mo ferritic steel and AISI type 316 stainless steel with and without Inconel-82 buttering on the ferritic steel side. Residual stress profiles across these weld joints were determined using the X-ray diffraction (XRD) technique. This study indicated that the Inconel-82 buttering layer employed in the dissimilar weld joint is useful in reducing the residual stresses in the HAZ of the ferritic steel and thus the buttering will be beneficial to avoid/minimize residual stress related failures of dissimilar weld joints.     

NET TG1: Residual stress assessment by neutron diffraction and finite element modeling on a single bead weld on a steel plate

In the context of the efforts of Task Group 1 (TG1) of the European Network on Neutron Techniques Standardization for Structural Integrity (NET), the Joint Research Centre (JRC) participated in the experimental round robin campaign for residual stress analysis on a single weld bead on a steel plate. In parallel, the University of Patras (UP), in collaboration with the JRC, contributed to the corresponding numerical analysis round robin exercise.Neutron diffraction measurements were performed on a specimen, designated as A12, using the residual stress diffractometer at beam tube HB5 at the High Flux Reactor (HFR) in Petten, The Netherlands. Several line scans of strains and stresses were performed in accordance with an experimental protocol devised for this exercise and their results are presented in this paper. Two scans were made along the weld longitudinal direction beneath the upper surface of the plate, three were made in the weld transverse direction, and three through the thickness of the plate. The measured residual stresses are presented in detail. The measurements confirm that the stress distribution around this single weld bead on a plate is intrinsically 3-dimensional.The procedure followed by UP in the numerical assessment of the problem is presented in detail. The numerical results are presented in direct comparison to the JRC measurement data.     

Fatigue behaviour of oblique nozzles on cylindrical shells submitted to internal pressure and axial forces

In detailed analytical checks against fatigue failure, the local notch stress approach can be considered as one of the most advanced methods for predicting the fatigue behaviour of a mechanical structure. However, it is based on a detailed strength analysis, including macroscopic notch effects, of the real structure, e.g., at weld seams. In this paper, the fatigue behaviour of oblique nozzles on cylindrical shells submitted to internal pressure, axial force and combined loading is analysed according to these principles. Detailed three-dimensional, parametric, finite element models based on brick elements are applied to describe the mechanical behaviour of the structure for a wide range of relevant geometrical parameters. The results of the serial finite element analyses are approximated analytically and thus can be offered to potential users to determine the stresses at arbitrary points of the nozzle-to-vessel junction and to predict the most probable location of fatigue failure.