600 MW超临界锅炉高温过热器T23和T91金属氧化膜热应力分析

以某600 MW超临界锅炉高温过热器为研究对象,分析了氧化膜厚度、生长温度和热膨胀系数等参数对金属管内蒸汽侧氧化膜热应力的影响.基于有限元方法建立了圆管数值计算模型,计算得到不同厚度和不同生长温度下T23和T91金属蒸汽侧氧化膜从生长温度冷却至常温时的热应力变化,并依据热应力的变化特征确定了这2种金属管材蒸汽侧氧化膜易发生脱落的温度范围.结合锅炉出口蒸汽温度与高温过热器指定位置处氧化膜温度的关系,提出用出口蒸汽温度判别氧化膜是否处于易发生脱落的温度范围的方法,给出了该锅炉停炉时的出口蒸汽温度值.结果表明：2种金属管材在冷却过程中低于一定温度时,其氧化膜的应力达到或接近最大应力值,可以依此判断氧化膜是否处于易发生脱落的危险区域.     

600MW超临界锅炉高温过热器T23和T91金属氧化膜热应力分析

以某600MW超临界锅炉高温过热器为研究对象,分析了氧化膜厚度、生长温度和热膨胀系数等参数对金属管内蒸汽侧氧化膜热应力的影响.基于有限元方法建立了圆管数值计算模型,计算得到不同厚度和不同生长温度下T23和T91金属蒸汽侧氧化膜从生长温度冷却至常温时的热应力变化,并依据热应力的变化特征确定了这2种金属管材蒸汽侧氧化膜易发生脱落的温度范围.结合锅炉出口蒸汽温度与高温过热器指定位置处氧化膜温度的关系,提出用出口蒸汽温度判别氧化膜是否处于易发生脱落的温度范围的方法,给出了该锅炉停炉时的出口蒸汽温度值.结果表明:2种金属管材在冷却过程中低于一定温度时,其氧化膜的应力达到或接近最大应力值,可以依此判断氧化膜是否处于易发生脱落的危险区域.     

锅炉高温受热面蒸汽侧氧化膜在线监测技术研究

建立了高温受热面炉内壁温在线监测模型、氧化膜生长模型、氧化膜应力在线监测计算模型和氧化膜脱落评估模型等.在此基础上,开发了锅炉高温受热面蒸汽侧氧化膜管理系统,并利用该系统对某600MW超临界锅炉高温受热面炉内管壁温度和蒸汽侧氧化膜厚度及应力状态进行实时计算与分析.结果表明:利用该系统可以减小沿烟道宽度方向的热偏差,有效降低偏差屏的炉内温度,减缓管内氧化膜生成速率;通过对温度变化速率、氧化膜应力状态的实时监测,可以积极预防氧化膜的脱落和堆积.     

蒸汽侧氧化膜对锅炉T91钢管蠕变断裂寿命的影响

建立了电站锅炉T91钢管蠕变断裂寿命计算模型,定量分析了蒸汽侧管壁温度和等效应力对T91受热管蠕变断裂寿命的影响,并对不同热负荷、不同尺寸受热管的计算结果进行了比较.结果表明:蒸汽侧氧化膜导致管壁温度升高是缩短部件蠕变断裂寿命的主要原因,等效应力增大是次要原因;受热管的蠕变断裂寿命随蒸汽侧氧化膜厚度的增加呈抛物线缩短;随管子热负荷的增加,蒸汽侧氧化膜对受热管蠕变断裂寿命的影响程度加剧;蒸汽侧氧化膜对外径较小的厚壁管子蠕变断裂寿命的影响较大.     

10CrMo910钢管蒸汽侧氧化膜的形态特征

对某电厂锅炉过热器和再热器受热面10CrMo910钢管蒸汽侧氧化膜进行了金相、扫描电镜、能谱和X衍射等试验分析,研究了蒸汽侧氧化膜的形态特征及其形成规律.结果表明:蒸汽侧10CrMo910钢管氧化膜分为内、外2层,内层为富含孔洞的富Cr层的非均质氧化膜,外层为疏松而细小的Fe3O4和Fe2O3;金属基体与内层氧化膜的界面处存在内氧化,使界面结合紧密;内层与外层氧化层界面不明显,离解后的氧化物颗粒较少,界面黏附强度较高,且内、外层氧化膜均由纳米和微米级颗粒组成,由于热膨胀系数不同导致应力大部分由氧化颗粒间空隙吸收;10CrMo910钢管蒸汽侧氧化膜难以剥落,且增厚的氧化膜容易导致受热面钢管长期处于过热状态.     

蒸汽侧氧化膜对超临界机组T92钢管壁温的影响

通过建立T92钢受热管及其蒸汽侧氧化膜的数值分析模型,定量分析了不同厚度氧化膜对T92钢受热管壁温的影响,并在此基础上得出了不同受热条件下导致T92钢管超温运行的氧化膜的临界厚度值.结果表明:随着氧化膜厚度的增加,管壁平均温度和平均温度升高幅度均呈近似线性增加;且管内壁温度越高、管外热流密度越大,氧化膜的临界厚度值越小.因此,当T92钢应用于高温受热面时,需综合考虑壁面热负荷和管内壁温度对氧化膜临界厚度的影响.     

超临界机组的合金管蒸汽侧氧化膜生长与剥落研究进展

超临界机组高温合金管氧化膜剥落问题是困扰机组安全与经济运行的难题,严重制约了机组蒸汽参数和效率的提高。特别是,在超临界机组采用给水加氧处理方式(OT)后,奥氏体不锈钢管内壁氧化膜大面积剥落事故屡见不鲜,尤以TP347H合金管为甚。本文总结了近年来国内外针对超临界机组合金管氧化膜研究的进展及相关成果,首先介绍了超临界蒸汽环境中合金管氧化机理和原子迁移机制,综述了铁素体和奥氏体合金表面氧化膜的形貌特征,分析了蒸汽溶氧对氧化膜生长速率、形貌和缺陷的影响。氧化膜完整性是决定合金抗腐蚀性能的重要因素,但在机组运行过程中氧化膜应力破坏了氧化膜完整性。进一步总结了国内外氧化膜应力和剥落研究的数值分析及实验研究情况,为我国超临界机组氧化膜剥落故障诊断研究提供参考。     

过热器和再热器氧化皮开裂与剥落的预测与控制

建立了应用于过热器和再热器的铁素体钢和奥氏体不锈钢管蒸汽侧氧化皮发生开裂和剥落时的临界应变随氧化皮厚度变化的模型,根据临界温度降幅与临界应变的关系,得到临界温度降幅与氧化皮厚度的关系.铁素体和奥氏体不锈钢管的氧化皮发生开裂和剥落时的临界应变均随氧化皮厚度增大而减小.公开发表的氧化皮厚度及其应力与所建立模型的临界值相吻合...     

锅炉高温受热面蒸汽侧氧化皮的形成及剥落机理研究进展

综合分析了各种类型的锅炉耐热钢管蒸汽侧氧化皮的微观形貌、氧化皮的层结构和成分组成。锅炉耐热钢蒸汽侧所生成的氧化皮有双层和3层结构,双层和3层结构的氧化皮的剥落位置发生在不同的亚层。对锅炉管内壁氧化皮剥落部位进行氧化皮生长的跟踪研究,可以得到氧化皮进一步生长的规律。氧化皮各层氧化物与基体金属间由于线性热膨胀系数差异所产生的热应力是导致氧化皮产生开裂和剥落的最根本原因,防治氧化皮大面积剥落的措施主要是抑制氧化皮生长速率和减少热应力的大幅度变化。由于实验室的试验条件难以模拟实际锅炉的蒸汽参数和应力变化,开发实验条件接近实际锅炉的蒸汽氧化试验是研究新型耐热钢内壁氧化皮生长及剥落机理的发展方向。     

燃气轮机排气温度对联合循环热经济性的影响

针对燃气轮机排气温度对整体机组变工况运行的重要性,以某三压再热余热锅炉型燃气-蒸汽联合循环机组为研究对象,将余热锅炉侧换热器分为单相换热器和蒸发换热器两类,并采用"效能-单元数"法编写换热模块,分析了燃气轮机排气温度对蒸汽系统热力参数的影响,结合"热经济分析"法探讨燃气轮机、余热锅炉及汽轮机效率的变化,进而得出机组效率和标准煤耗量随燃气轮机排气温度的变化.结果表明:模型在燃气轮机排气温度小扰动工况下有效可行,对进一步分析燃气扰动工况和机组优化运行有一定的实际参考价值.     

Online determination of transient thermal stresses in critical steam turbine components using a two-step algorithm

The article presents a novel algorithm for robust calculation of thermal stresses in steam turbine components during transient operating conditions. Stress calculations are performed in 2 steps: in the first step an unsteady radial temperature distribution in the component model is computed, and based on this thermal stresses at critical locations are determined in the second step. The radial temperature distribution is obtained by solving the Fourier-Kirchhoff equation for a cylinder or sphere by means of a finite difference method. The thermal stresses are computed using the Duhamel integral and Green functions evaluated with a constant heat transfer coe?cient and used with an equivalent steam temperature obtained from the surface heat flux.     

Mathematical modelling of the transient response of pipeline

Steam pipelines applied in power units operate at high pressures and temperatures. In addition, to stress from the pipeline pressure also arise high thermal stresses in transient states such as start-up, shutdown or a load change of the power unit. Time-varying stresses are often the cause of the occurrence of fatigue cracks since the plastic deformations appear at the stress concentration regions. To determine the transient temperature of the steam along the steam flow path and axisymmetric temperature distribution in the pipeline wall, a numerical model of pipeline heating was proposed. To determine the transient temperature of the steam and pipeline wall the finite volume method (FVM) was used Writing the energy conservation equations for control areas around all the nodes gives a system of ordinary differential equations with respect to time. The system of ordinary differential equations of the first order was solved by the Runge-Kutta method of the fourth order to give the time-temperature changes at the nodes lying in the area of the wall and steam. The steam pressure distribution along pipeline was determined from the solution of the momentum conservation equation. Based on the calculated temperature distribution, thermal stresses were determined. The friction factor was calculated using the correlations of Churchill and Haaland, which were proposed for pipes with a rough inner surface. To assess the accuracy of the proposed model, numerical calculations were also performed for the thin-walled pipe, and the results were compared to the exact analytical solution. Comparison of the results shows that the accuracy of the proposed model of pipeline heating is very satisfactory. The paper presents examples of the determination of the transient temperature of the steam and the wall.     

Thermo-mechanical simulation for nozzle header of once-through steam generator by experiment and finite element method

The thermo-mechanical behaviour of the nozzle header of a steam generator developed for an integral reactor was investigated using experimental and finite element methods. The nozzle feedwater header suffers from severe thermal transient loadings during the operation of the nuclear reactor. The nozzle header is exposed to the low temperature inlet feedwater and the high temperature outlet superheated steam and the other side of the nozzle header contacts with the high temperature primary coolant. The temperature gradients result in high thermal stresses in the nozzle header. The thermal transient loading has been simulated in a test loop. The input and thermo-hydraulic parameters of the primary and the secondary system were. Strain gauges and thermocouples attached to the highly stressed region monitored the thermo-mechanical behaviour of the nozzle header. In parallel with the experimental study, the transient behaviour of the nozzle header was simulated by utilizing a commercial finite element code. The fluid temperature and pressure obtained from the test loop were used as inputs to the finite element analysis. As a result of this investigation, the thermo-mechanical load carrying capacity of the developed steam generator nozzle header was proved numerically and experimentally.     

Thermoelasticity problem for a multilayer coating/half-space assembly with undercoat crack subjected to convective thermal loading

The transient thermal stress crack problem for a half-space with a multilayer coating under thermal surface loading containing an undercoat crack, perpendicular to the interface, is considered. The problem is solved using the principle of superposition and uncoupled quasi-static thermoelasticity. Transient temperature distribution and corresponding thermal stresses for the uncracked multilayer assembly are obtained in a closed analytical form using the model with generalized thermal boundary conditions of heat exchange of a half-space with ambient media via the coating. The crack problem is formulated as a perturbation mixed boundary value problem, in which the crack surface loading should be equal and opposite to the thermal stresses obtained for the uncracked medium, and is reduced to a singular integral equation and solved numerically. Numerical computations are performed for the analysis of influence of the coating upon thermal stresses and thermal stress intensity factor.     

Thermal analysis of cooled supercritical steam turbine components

This paper describes thermal analysis methodology results for the supercritical steam turbines. The analysis presented here concerns the external cooling of the turbine components. Due to the supercritical parameters of the live steam, the inlet areas of the high and intermediate pressure parts are exposed to the steam at high temperature level. The design solutions applied to the turbines so far aim to protect the inlet areas. Basic solution incorporate protective screens, which are made of a material more resistant to the high temperature than the rest of the components. Additional protection is provided by the external cooling. The applications of both methods described above allow to increase the live steam temperature. The conducted analysis determined the temperature field in the steam, which cools the rotor, as well as the distribution of the temperature and stresses in the rotor. The obtained results were then applied to the investigations concerning the durability of the rotor.     

基于“环境破坏说”的氧化皮剥落理论

在“环境破坏说”的基础上阐释了锅炉高温受热面氧化皮剥落的理论．双层氧化皮内、外层界面存在的空穴是氧化皮剥落的内因,氧化皮承受的应力是氧化皮剥落的外因．氧化皮空穴的成因又可分为内因和外因,内因主要是金属含铬量,外因主要包括蒸汽参数和蒸汽含氧量等．主蒸汽含氧量与铬酸根含量之间具有显著的正相关性,而主蒸汽氢电导率是反映氧化皮铬蒸发的特征指标．外层氧化皮剥落以后,内层氧化皮会继续增厚,但难以剥落．对于已经发生了氧化皮大面积剥落的超（超）临界锅炉,如果检查确认高温受热面氧化皮剥落比较完全,剥落之氧化皮清理比较彻底,则在相当长时期内氧化皮剥落问题都将不再是运行忧患．     

冷启动工况下汽轮机转子的疲劳损伤

在对600MW汽轮机高压转子冷启动工况下的温度场、热应力进行了瞬态有限元分析的基础上给出了热应力随启动温升率的变化关系,进而采用转子材料的低周疲劳曲线计算出不同启动温升率下转子的低周疲劳损伤。为现场运行制定安全、经济的启动过程提供了一定的理论依据。     

Transient Thermo-Mechanical Analysis of Functionally Graded Hollow Circular Cylinders

Thermo-mechanical analysis of functionally graded hollow circular cylinders subjected to axisymmetric mechanical and transient thermal loads is carried out in this study. Thermo-mechanical properties of functionally graded materials (FGM) are assumed to be temperature independent and vary continuously in the radial direction of the cylinder. Employing the Laplace transform, the Galerkin method and series method for ordinary differential equations, solutions for the time-dependent temperature and transient thermo-mechanical stresses are obtained. As an example, a molybdenum/mullite FGM with material properties obeying the exponential law is considered. Effects of heat transfer coefficients and gradient parameters of FGM on the time-dependent temperature and transient thermal stresses are discussed in detail.     

DQM-Based Thermal Stresses Analysis of a Functionally Graded Cylindrical Shell Under Thermal Shock

The transient thermal stresses of a functionally graded (FG) cylindrical shell subjected to a thermal shock are investigated. The dynamic temperature fields of FG shells are obtained by using the Laplace transform and power series method. The differential quadrature method is developed to obtain the transient thermal stresses by solving dynamic governing equations in terms of displacements. The effects of the material constitutions on the transient temperature and the thermal stresses are analyzed in the cases of obverse thermal shock and reverse thermal shock. It turns out that the thermal stresses could be alleviated by means of changing the volume fractions of the constituents.