【作者】 袁军；

【导师】 徐鸿；

【作者基本信息】 华北电力大学 ， 热能工程， 2014， 博士

【摘要】 随着工业技术的发展,火电机组逐步向大容量、高参数方向发展,对锅炉受热面材料的要求更为严格。由于材质的使用不当和对受热面材料的高温失效特性的研究不足,导致高温对流受热面的爆管增多。在高温高压的环境下工作的受热面管道,除了承受复杂的多轴应力作用,同时在管道的外侧和内侧还存在磨损与氧化腐蚀的作用；因此,研究在复杂环境下高温管道的失效机理和进行管道的寿命评估,对于电站锅炉受热面的安全运行具有重要作用。在多轴应力下,对高温材料的蠕变失效机理及模型的研究还不是很充分,本文通过对铁素体钢T92进行单轴和多轴的蠕变实验,研究了在不同温度和不同多轴载荷下的材料力学行为,对材料的断口形貌和微观组织的变化进行分析,建立了多轴载荷与微观组织变化的定性关系；从断口形貌中,分析材料在长期多轴蠕变过程中,脆性与韧性之间的相互转换与多轴度的关系,从微观角度解释了T92的缺口增强现象。在模型研究方面,针对普通的蠕变模型无法描述在高温条件下,应力应变的对数关系呈现非线性的问题,提出了一种新的改进模型,并给出了模型参数的确定办法。通过有限元软件的二次开发,对改进模型进行了验证,并对T92钢的缺口增强现象进行了模拟。结果表明,文中的改进模型能够对缺口试样进行有效的蠕变寿命预测。管道内侧的氧化腐蚀是引起管道超温和爆管的重要因素之一,本文针对T24和P92钢在高温条件下的氧化皮的成型和脱落机理进行研究。分别在550℃和600℃,25MPa超临界水蒸汽中,针对无氧、100ppb、300ppb和2000ppb四种溶解氧浓度,对T24和P92钢进行了氧化实验研究。分析了蒸汽温度、金属Cr含量和溶解氧量对T24和P92钢氧化腐蚀速度的影响,并建立了对应氧化腐蚀模型。通过火电厂的实时监测系统进行数据通讯,对炉膛的进行实时的热力计算,求得实时的管道温度值；在此基础上,实现在对直管段或管道弯头的应力及蠕变变形计算,动态得到管道的蠕变寿命损耗。在化学水测量的基础上,对管道的氧化皮生长进行动态预测。结合离线监测数据,形成一整套对锅炉管道进行综合风险评估的信息管理平台,可对火电厂的锅炉受热面的检修进行合理的指导。更多还原

【Abstract】 With a development of industrial technology, thermal power units are involving gradually to the high-capacity and high-parameter direction and it is more stringent to choose materials for boiler heating surface. Improper use of material and lack of research on failure mechanism of high-temperature heating surface material results in an increase in high-temperature convection heating surface tube explosion. The heating surface working at high temperature is restrained to multi-axial stress as well as wearing on the fire-side and oxidation corrosion on the steam-side of the tube; therefore, investigation on the failure mechanism of tubes at elevated temperature in a complex environment and life assessment plays an important role to the safe operation of power plant boiler heating surface.The study on creep failure mechanism and model of high-temperature under multiaxial stress is not sufficient. In this paper, uniaxial and multiaxial creep tests of ferritic steel T92have been conducted and the mechanical behaviors of materials at different temperatures and multiaxial loads have been studied. The fracture morphology and the microstructure evolution of the material were analyzed and the qualitative relationship between multixial loads and microstructure evolution was proposed. The correlation of the transformation from brittle to ductile and multiaxis degree during the process of long time creep has been analyzed from the fracture morphology and the explanation of notched strengthening enhancement phenomenon was given from a micro perspective. In terms of the model, the present model can not describe the nonlinear problem of the creep stress-strain constitutive relation at the elevated temperatures. A modified model has been developed and the way to determine the model parameters was presented. With the help of user programmable features of finite element software, the model was validated and the notched strengthening phenomenon of T92steel was simulated. The results showed that the proposed improved model can predict the creep life of notched specimens effectively.One of the important factors leading to tube overheat and explosion is the steam-side oxidation corrosion. Study on mechanism of oxide scale forming and shedding of T24and P92steel in high temperature has been studied. For four types of dissolved oxygen concentration, namely, no oxygen,100ppb,300ppb and2000ppb, the oxidation experiments of T24and P92steel under an environment of25MPa supercritical water were conducted at550℃and600℃respectively. The effects of steam temperature, the amount of Cr and dissolved oxygen content on the corrosion rate of oxidation of T24and P92steel has been analyzed and the corresponding oxidation corrosion model has been built.Through the real-time monitoring system of thermal power plant data communications, the real-time thermal calculation on the furnace was conducted and the real-time tube temperature was obtained. On this basis, the calculation of the stress and creep deformation of straight pipe or pipe elbows could be done and the pipe creep life loss can be dynamically obtained. According to the chemical water measurements, the growth of oxide scale of pipes could be predicted dynamically. Combined with off-line monitoring data, a set of information management platform for comprehensive risk assessment of boiler tubes has been designed and it could help guide the overhaul of thermal power plant boiler heating surface reasonably.更多还原