600MW超临界锅炉汽水分离器内压应力有限元分析

采用有限元方法对600 MW超临界锅炉汽水分离器进行应力计算,得出了汽水分离器进口连接管区域内压引起的机械应力分布规律和应力集中状况.计算结果表明,该区域存在着明显的应力集中现象,最大应力出现在筒体内壁靠近连接管椭圆孔长轴处,应力集中系数为3.48,筒体外壁同样存在应力集中,但应力水平比内壁低.汽水分离器各连接管的应力分布规律基本相同.将6根连接管与1根连接管时筒体的应力分布进行了比较,结果表明,接管数目的增加使汽水分离器应力集中更加明显.     

超临界锅炉寿命损耗在线监测系统研究

采用三维有限元计算对超临界锅炉厚壁部件在内压作用下的应力场进行了分析，并计算出了汽水分离器应力集中系数；采用GB／T9222—88之附录D为汽水分离器寿命损耗在线监测计算标准。对过热器和再热器出口集箱采用ASME-47为在线监测计算标准。开发了适用于超临界锅炉厚壁承压部件寿命在线监测系统。该系统利用计算机、DAS／DCS和MODBUS通讯协议对超临界锅 炉壁承压部件寿命进行管理，并提供开放数据接口。     

超临界锅炉启动分离器疲劳寿命分析

通过创建启动分离器的三维实体模型,运用有限元方法模拟超临界直流锅炉的启动分离器在机组冷态启动过程中的温度分布和峰值应力,分析了启动分离器冷态启动中的寿命损耗。结果表明:启动分离器启动过程中,温度最高的区域出现在汽水引入管与启动分离器内部相接处,启动分离器内、外壁温差会大于汽水引入管的内、外壁温差;最大峰值应力出现在汽水引入管和分离器筒体切向出口部位;疲劳应力损坏发生在应力集中部位,其修正后的应力幅对应的循环次数为12 700次,远大于锅炉寿命期内的冷态启动次数,可以确保锅炉安全启动和运行。     

1000MW锅炉汽水分离器的瞬态应力有限元分析

选取1 000MW锅炉汽水分离器为研究对象,根据机组运行曲线确定边界条件,建立其三维有限元模型。计算了冷态启动工况下的瞬态热应力、机械应力和总应力,讨论了热应力、机械应力和总应力的分布规律,分析了影响应力的各种因素,找出了汽水分离器最大应力点位置及随时间的变化规律。     

基于Elman神经网络的超超临界机组汽水分离器应力在线软测量模型

根据超超临界锅炉汽水分离器的结构特点建立了三维有限元模型,以某1000MW机组为例模拟了其启动过程的总应力场．将有限元法和神经网络法相结合,以有限元计算结果作为训练样本,以介质压力和筒体壁温序列为辅助变量,建立了基于Elman神经网络的分离器应力动态软测量模型,通过模型的训练,确定了准确的应力预测模型结构．应用电厂实际运行监测数据对所建立的Elman网络软测量模型进行验证,结果表明：模型计算结果可很好地逼近有限元结果,预测精度高,实时性好,可为锅炉寿命的在线监测提供数据支持．     

600MW超临界压力锅炉汽水分离器在启动过程中介质对内壁放热系数及筒壁温度场的研究

本文闸述了600MW超临界压力锅炉汽水分离器模型,在锅炉实际启动参数下介质对内壁放热系数的模拟试验研究。试验参数 P为3～11MPa,质量流量G为0.2～0.35kg/s,干度x为0.2～0.8。由导热反问题方法,获得了动态过程中介质对分离器模型内壁的放热系数计算公式。并实际计算了锅炉在冷态启动过程中汽水分离器壁温分布,为进一步进行汽水分离器热应力计算和优化启动过程提供了比苏尔寿公司更可靠、精确的依据。     

超临界直流锅炉蓄热的分析与计算

根据水和水蒸气的热力性质,将超临界直流锅炉蒸发受热面分为过冷水段、过渡段和过热段,通过机理分析和模型简化,采用集总参数法建立蒸发受热面、分离器和过热器的模型,利用锅炉结构设计数据计算不同负荷下锅炉的蓄热系数,并对某1 000MW超临界机组锅炉进行实例计算.结果表明:当锅炉在亚临界状态下运行时,随着压力的变化,水冷壁内工质蓄热的变化量大于超临界状态下的变化量;金属的蓄热远大于工质的蓄热,过热器的蓄热占整个锅炉蓄热的70%左右;超临界锅炉的蓄能系数随着压力的升高而减小.     

灵活性运行的锅炉联箱应力分析及寿命计算

以某灵活性运行的超临界锅炉末级过热器出口汇集联箱为研究对象,结合锅炉负荷从200 MW到600 MW再到180 MW变化时的实时运行数据,采用Ansys有限元软件进行热应力、机械应力以及两者共同作用的总应力分析,讨论了各种应力在联箱中的分布情况。根据疲劳-蠕变交互作用下的累积损伤计算方法对联箱在灵活调峰运行时的疲劳和蠕变寿命损耗进行了评估。结果表明:灵活性运行时由于交变产生的热应力对联箱疲劳寿命影响较小,蠕变是影响其寿命损耗的主要因素。     

国产600 MW超临界机组直流锅炉启动系统

上海锅炉厂有限公司首次引进美国ALSTDM公司技术生产600MW超临界直流锅炉,超临界锅炉与亚临界锅炉在启动过程中有很大区剐,超临界锅炉在国内的现有运行机组中为数不多,且大多数采用的是外置式汽水分离器。本文通过对该直流锅炉启动系统的结构特点的简要介绍,阐述了600MW锅炉启动系统的工作过程,分析了锅炉启动系统中工况疏水的调整原则,对同类型机组在调试和运行方面将有一定的借鉴作用。     

超临界直流锅炉实际蓄热系数计算分析

为获得直流锅炉实际蓄热系数,分析锅炉在亚临界或超临界状态下的不同运行特性,根据工质相变对水冷壁进行汽水分段,针对锅炉的各汽水流程部件计算汽水蓄热系数和金属蓄热系数,结合汽轮机调门开度及热耗率变化影响,提出了实际蓄热系数计算方法。以某660 MW超临界机组为例进行计算,结果表明:金属蓄热系数大于汽水蓄热系数,随着负荷升高,汽水蓄热系数变化不大,金属蓄热系数减小;考虑到汽轮机热耗率变化的影响,不同负荷下实际蓄热系数之间偏差有所缩小。     

旋转机械蠕变引起的转子渐进式弯曲研究

针对某大型汽轮发电机组高中压转子上发生的启停机振动差异现象,从大外力作用下蠕变变形的角度进行分析,建立转子蠕变弯曲计算模型,分析外力与作用时间等因素对蠕变弯曲的影响。结果表明:大不平衡力作用下转子会发生因蠕变引起的弯曲变形,变形量随时间延长逐渐增大并最终趋于稳定;蠕变对振动的影响主要表现在临界转速区域,因启停机过程变形量差异而导致振动有较大差异。     

砂岩蠕变力学特性及流变模型研究

水利枢纽工程中库岸高边坡流变现象显著,是工程长期稳定性的潜在隐患。以某大型水利枢纽工程近坝库岸高边坡石英砂岩为例,采用RLW-2000岩石三轴流变试验系统进行不同应力状态下的蠕变力学试验。结果表明,岩石瞬时应变、蠕应变随围压的增加而逐渐增大,初始、稳态和极限加速蠕变速率随围压的提升而递增;围压促进砂岩蠕变变形发展,高围压下的初始蠕变速率可能大于低围压下的极限加速蠕变速率;砂岩在围压5、10、15MPa下的长期强度分别为24.8、32.3、39.7MPa,长期强度随围压的增强而逐渐增大。结合试验成果,分析砂岩的流变性态为粘性-粘弹性-粘塑性,基于统一流变力学模型理论,确定H-H|N-N-N|S模型结构。由于传统元件模型难以辨识不同加速蠕变阶段曲线形态,引入SN和SP非线性元件改进传统模型,得到一个新的非线性蠕变力学模型,并将其拓展到三维情形。辨识蠕变试验数据,对比预测曲线和试验数据,证明了所建模型的可行性和合理性。研究成果可为水利枢纽工程的长期稳定性分析提供参考。     

启动分离器大管接头设计及制造中的问题与措施探讨

600 MW超临界锅炉部组件--启动分离器的设计过程中,分离器大管接头的设计与制造是关键之一.对以前超临界项目启动分离器的设计与制造中所遇到问题的分析与解决,更加说明分离器大管接头设计对车间制造、工地现场安装及锅炉运行的影响.在超临界锅炉启动分离器的设计中吸取前面的经验与教训,在设计方面已形成比较系统、精确的计算方法,而且在车间的制造中难度也能有所降低.     

金沙江向家坝水电站坝基砂岩蠕变特性研究

选取了金沙江向家坝水电站坝基的典型砂岩试样,采用三轴压缩试验对砂岩蠕变特性进行研究,分析了流变失稳破坏时的特征及砂岩的轴向、侧向和体积应变的全过程蠕变曲线异同点,对砂岩的长期强度进行预测分析。试验结果表明,砂岩存在一个起始蠕变应力阈值,每级荷载下的蠕变曲线之前都存在一个瞬时应变且随着围压的增大和偏应力的增大幅度越来越小,轴向瞬时应变与偏应力具有很好的线性关系;侧向和体积变形则存在明显的蠕变三阶段,加速阶段要比轴向快且两者的蠕变曲线形状相似,在同一围压和同一级偏应力下侧向蠕变量比轴向及体积的大,其蠕变发展最快;砂岩的长期强度可用等时偏应力应变曲线簇来进行确定,采用体积偏应力应变曲线簇更适宜,在已有的流变模型中伯格斯模型能较好的反映砂岩蠕变特性。     

Creep behaviour of Waspaloy under non-constant stress and temperature

Abstract

Current creep models are derived using data from constant stress (or load) creep tests and are capable of accurately predicting creep behaviour when applied conditions are constant or near constant. However, analyses of creep curve shapes for the nickel based superalloy Waspaloy, when applied stress and/or temperature vary greatly during testing, have shown that predictive methods based purely on strain, time or life fraction are insufficient and cannot predict the observed creep rates. This is important when considering stress concentration features where stress relaxation due to creep can significantly alter the distribution of stress and thus affect fatigue life. When both stress and temperature are changed during a creep test, dislocation movement must proceed through a dislocation network formed under different conditions, resulting in greater than expected creep rates. It is proposed that this is due to a reduction in effective internal stress due to changes in dislocation structure.     

A CDM-based study of fatigue–creep interaction behavior

Under stress control mode, the damage evolution during fatigue, creep and their interaction behavior actually is a ductility exhaustion process in response to cyclic and static creep. Based on the ductility dissipation theory and effective stress concept of continuum damage mechanism (CDM), a new fatigue–creep interaction damage model has been developed in this paper, where the change of the inelastic strain energy density is used to define the damage variable. To assess this damage model, high temperature fatigue–creep interaction experiments have been carried out for 1.25Cr0.5Mo steel under stress control mode employing a trapezium waveform. The damage evolution laws of 1.25Cr0.5Mo steel under various combinatorial conditions with different maximum stresses and stress amplitudes are derived. Results indicate that the damage parameter and damage model presented in this paper are applicable to describe the damage evolution for fatigue–creep interaction.     

Creep deformation characterization of heat resistant steel by stress change test

To evaluate the creep deformation mechanism of heat resistant steel, stress change tests were conducted during creep tests for Modified 9Cr–1Mo Steel and 2.25Cr–1Mo Steel. In this study it was confirmed that the dislocation behavior during the creep tests was in viscous manner because of no instantaneous plastic strain observed at stress increments. Transient backward creep behavior was observed after stress reduction for these steels in this work. Mobilities of dislocation were evaluated by observed backward creep behavior after stress reductions. Internal stresses were evaluated by the changes of creep rate in stress increments. And mobile dislocation densities were evaluated with the estimated mobilities of dislocation and the changes of creep rate in stress increments. It was found that the variation of evaluated mobile dislocation densities during creep deformation showed the same tendency as the variation of creep rate. Therefore mobile dislocation density is the dominant factor that influences the creep rate variation in creep deformation of these steels in this work. The mobilities of dislocation showed a good correlation with 1/T and related with solute amount of Mo that is a solution hardening element.     

Creep strain growth behaviour of Hastelloy X above 800°C under thermal-stress cyclings

Actual structural components at high temperature are usually not only subjected to steady mechanical and cyclic loads but also accompanied by temperature variation. Creep ratcheting due to cyclic thermal stress is one of the typical examples. The creep strain growth behaviours of Hastelloy X above 800°C under thermal stress cyclings have been discussed. (1) Cycle dependent creep ratchet strain growth can be estimated to be ΔT, where is the thermal expansion coefficient and ΔT is temperature difference across a body. (2) Time dependent strain growth with temperature variation can be derived by time fraction, virtual activation energy and creep strain of the base temperature. (3) Decreasing creep rate will appear in the neighbourhood of 15–20% of rupture time and increasing creep rate will occur after this, which is almost linear on a logarithmic time scale and Hastelloy X shows softening behaviour on creep after exposure at the higher temperature.     

不同加卸载条件下孟底沟水电站花岗岩蠕变特性研究

针对孟底沟水电站坝区花岗岩开展了不同加卸载应力条件下的三轴蠕变试验,系统分析了不同加卸载过程中坝区花岗岩的变形特征、蠕变速率和破坏强度的变化规律,揭示了蠕变破坏模式。结果表明,孟底沟花岗岩存在蠕变应力门槛值,蠕变后期存在完整的减速、等速和加速蠕变阶段,岩石产生大量塑性变形,体积由压缩转为扩容;轴压恒定相比偏应力恒定卸围压蠕变更具时效特征,卸围压条件下出现劈裂和剪切共存的破坏模式;岩石破坏强度低于常规峰值强度,卸围压相比加轴压方式岩石强度下降幅度更大,粘聚力的降低是造成强度折减的主要因素。