【作者】 王凯；

【导师】 刘新宝；

【作者基本信息】 西北大学 ， 化工过程机械， 2023， 硕士

【摘要】 我国能源结构以化石能源为主,必然存在能源紧缺与碳排放问题。因而提升煤电转化效率和发展清洁煤发电技术成为重要的解决途径之一。作为清洁煤发电技术之一的超超临界技术,因其低煤耗、高效率、少污染而备受青睐。因优良的高温力学性能、抗蠕变以及优异的加工性能,P91钢被广泛应用到发电机组过热器、再热器以及蒸汽管道中。然而,这些设备长期服役于高温、高压环境下,将不可避免地发生蠕变损伤以至最终失效。为保障机组设备安全稳定运行,需对服役设备安全状态及剩余寿命进行可靠评估,以预防潜在设备失效问题。因此,本研究以P91钢为考察对象,首先研究传统双曲正弦函数(Sinh)模型中初始参数取值变化对蠕变行为的影响,构建了基于蒙特卡洛模拟方法的概率Sinh模型,并初步对P91钢长时蠕变寿命预测进行了尝试;同时,考虑到概率Sinh模型外推能力的不足,引入与Sinh模型优势互补的Wilshire模型,通过提出Sinh-Wilshire改进模型对P91钢长时蠕变寿命进行了有效预测。具体研究内容以及主要结论如下:(1)通过高温单轴拉伸试验获得P91钢在853 K、873 K以及893 K温度时的力学性能参数,包括抗拉强度(σTS)、屈服强度(σ0.2)以及延伸率(δ)。同时,以2/3 σ0.2的应力水平为参考标准,分别在上述三个温度下由低到高选取180 MPa-190 MPa-200 MPa、155 MPa-160 MPa-165 MPa-175 MPa-190 MPa 以及 135 MPa-145 MPa-155 MPa等应力条件进行了相应的高温蠕变持久试验,获得了蠕变应变曲线及蠕变应变速率曲线。(2)利用传统Sinh模型,通过对上述P91钢蠕变实验数据的拟合计算分析了模型中相关待定参数(蠕变应变曲线轨迹控制参数λ、损伤曲线控制参数φ、初始损伤ω0以及初始应变εpr)取值的分布规律。在此基础上,借助蒙特卡洛方法,通过构建概率Sinh模型系统研究了这些参数的不同取值对P91钢蠕变行为和损伤演化的具体影响,并对长时蠕变寿命进行了初步预测。结果表明,初始损伤ω0对蠕变行为的影响最为显著,而损伤曲线轨迹控制参数φ对损伤演化的影响最为显著;在本研究蠕变条件下,Sinh模型预测的蠕变曲线和实验数据间的方差与蠕变应力之间存在指数关系;对104h以上的P91钢蠕变寿命预测时,结果误差较大。(3)针对上述概率Sinh模型在外推长时P91钢蠕变寿命时存在的精度显著下降问题,通过对其进一步分析后,并与Wilshire模型耦合提出了 Sinh-Wilshire改进模型。同时,利用上述P91钢蠕变实验数据,对Sinh-Wilshire改进模型中的相关参数进行了标定。此外,利用该模型及其标定后的参数值对P91钢长时蠕变寿命进行了外推预测。结果表明,相比于传统的Larson-Miller(L-M)参数法,Sinh-Wilshire改进模型的预测值(2 × 105 h以内)与已有的NIMS、ECCC实验数据具有更高的一致性,同时远超3倍的预测比也体现了该模型优异的外推能力。更多还原

【Abstract】 Chinese energy structure is dominated by fossil energy,which resulting in energy shortage and carbon emission.Improving coal-power conversion efficiency and developing clean coal power generation technology have become one of the important solutions.As one of clean coal power generation technologies,the ultra-supercritical thermal power generation technology is favored for its low coal consumption,high efficiency,and less pollution.Thus,P91 steel is widely used in unit superheaters,reheaters,and steam pipelines due to its excellent high-temperature mechanical properties,creep resistance,and processing properties.However,this equipment will inevitably undergo creep damage and eventually failure after long-term service in high-temperature and high-pressure environments.In order to ensure the safe and stable operation of unit equipment,it is necessary to reliably evaluate the safety status and remaining life of equipment in service to prevent potential equipment failures.In this study,P91 steel was taken as the research object to study the influence of initial parameter value changes in the traditional hyperbolic sine function(Sinh)model on creep behavior.A probability Sinh model based on Monte Carlo simulation method was constructed,and a preliminary attempt is made to predict the long-term creep life of P91 steel;At the same time,considering the insufficient extrapolation ability of the probabilistic Sinh model,the Wilshire model that complements the advantages of the Sinh model is introduced and a Sinh-Wilshire modification model is constructed to predict the long-term creep life of P91 steel.The specific research content and main conclusions are as follows:(1)Mechanical property parameters of P91 steel at 853 K,873 K and 893 K were measured by high-temperature uniaxial tensile test,including tensile strength(σTS),yield strength(σ0.2)and elongation(δ).According to the stress selection criteria for creep test of 2/3 0/0.2,corresponding high-temperature creep endurance tests were conducted under stress conditions such as 180 MPa-190 MPa-200 MPa,155 MPa-160 MPa-165 MPa-175 MPa190 MPa and 135 MPa-145 MPa-155 MPa,selected from low to high at the above three temperatures,respectively.The creep strain curves and creep strain rate curves were drawn.(2)Using the traditional Sinh model,the distribution pattern of the relevant undetermined parameter(primary creep strain εpr,initial damage ω0,creep strain curve trajectory control constant λ and damage curve trajectory control constant φ)values in the model was analyzed by fitting the creep experimental data of P91 steel mentioned above.On this basis,using Monte Carlo method,the specific effects of different values of these parameters on the creep behavior and damage evolution of P91 steel were systematically studied by constructing a probability Sinh model,and preliminary predictions were made for long-term creep life.The results show that initial damage ω0 has the most significant effect on creep behavior,and damage curve trajectory control parameter φ has the most significant effect on damage evolution.Under the creep conditions of this study,there is an exponential relationship between the variance,which between the creep curve predicted by the Sinh model and the experimental data,and the creep stress.When predicting the creep life of P91 steel over 104 hours,there is a significant error in the results.(3)In response to the significant accuracy degradation problem of the probability Sinh model in extrapolating long-term creep life of P91 steel,a Sinh-Wilshire modification model was proposed after further analyzing and coupling with Wilshire model.Meanwhile,the relevant parameters in Sinh-Wilshire modification model were calibrated by using the creep experimental data of P91 steel,which mentioned above.In addition,the model and its calibrated parameter values were used to extrapolate and predict the long-term creep life of P91 steel.The results show that compared to the traditional Larson-Miller(L-M)parameter method,the predicted values(within 2 × 105 hours)of Sinh-Wilshire modification model have high consistency with existing NIMS and ECCC experimental data.The prediction ratio far exceeding three times also reflects the excellent extrapolation ability of the model.更多还原