Brittle fractures of the drums of high-pressure boilers: Main causes and methods for preventing them

Factors causing damage to the metal of the drums of high-pressure boilers, as well as the known cases of drum failures, are analyzed. The totality of factors determining the operational reliability of drums is systematized. The process-related mechanism governing the destruction of the drums at the Kurgan cogeneration station and TETs-3 Yaroslavl cogeneration station, and the general factors caused these drums to fail are identified. Recommendations for reducing the risk of drum failures are formulated.     

Studying the metal of steam boiler drums made of grade 16GNM steel after its long-term operation

Results from a study of the structure and properties of the metal of drums made of Grade 16GNM steel that have been in operation for a long period of time are presented. A change in the strength characteristics and fracture ductility of metal with respect to its initial properties indicated in its certification data is analyzed. It is shown that changes in the strength properties of the metal of drums do not demonstrate any stable trends with an increase in the time of its operation.     

基于振动法的磁记忆检测系统研究与设计

提出基于振动法的金属磁记忆信号检测方法。设计相应的金属磁记忆检测系统,包括带有磁场屏蔽外壳的传感器探头结构、磁记忆信号预处理模块和正交矢量锁相放大模块,并基于 STM32F107VCT6芯片设计下位机模块。利用研制的系统对经过加工的标准试件进行检测,通过测量法向磁场梯度的方法可以检测出试件应力集中区域,验证法向磁场梯度和应力集中系数的关系。     

50MW汽轮机断裂叶片及断口的磁记忆研究

从断裂叶片及断口应力分布研究及评估的角度,在对事故叶片进行动、静应力分析基础上,进行了现场50MW汽轮机断裂叶片及断口应力分布的磁记忆检测,研究了断裂叶片及断口应力分布的磁记忆信号特点。结果表明,叶片型线部分出气侧较进气侧磁感应强度过零点信号多,形状复杂;叶根部分断口上出气侧裂纹起始区磁感应强度变化幅度很大,而中间过渡区幅值变化最小,进气侧瞬断区的幅值变化最大且具有过零点的特征。这些磁记忆数值记录了叶片断裂过程的应力变化和分布,磁记忆检测结果与盲孔法应力分布检测结果有较好的一致性。     

Experience in Reconstructing the PT-60-90 Turbine by Reconditioning Heat Treatment of the High-Pressure Cylinder Shell

Experience in reconstructing the PT-60-90 turbine at Salavatskaya CHPP upon the operation for more than 350000 h is described. In the course of reconstruction, the life of the turbine was restored, its economic efficiency was increased, process extraction of 1.27–1.57 MPa was changed to uncontrolled extraction, and additional extraction of 3.43 MPa was arranged. The high-pressure cylinder (HPC) shell was restored by reconditioning heat treatment (RHT), and the rotor was replaced by a new modernized one. To select the optimal conditions of the reconditioning heat treatment of the HPC shell (of the PT-60-90 turbine) manufactured from 20CrMoPL grade steel, the results of previously conducted tests of the shell metal of the same grade were integrated. The heat treatment was carried out on modernized furnace equipment using means of and methods for controlling the temperature and heating and cooling rates. Detailed nondestructive inspection of the upper and lower HPC halves was performed. The locations, distribution, sizes, and types of the defects were identified. The detected defects and austenitic build-ups were removed, welded with pearlite electrodes, examined, and subjected to heat treatment (tempering). The actual heat treatment conditions were analyzed and, based on the obtained data on the mechanical properties of the metal, the tempering temperature and time were specified. Complete investigation of the metal of both HPC halves was conducted prior to the reconditioning heat treatment. The reliability of the metal of the cylinder shell after RHT was evaluated by the mechanical properties, such as tensile strength, critical ductile-to-brittle transition temperature (crack resistance), and stress-rupture strength. It was established that, after RHT, the characteristics of the metal, such as yield strength, ultimate strength, elongation per unit length, contraction ratio, hardness, and impact toughness, significantly improved and, on the whole, the quality of the metal met the requirements of the normative documentation for newly manufactured castings. The heat resistance of the metal of the cylinder shell after RHT also increased, which can ensure the operation of the HPC shell for more than 200 000 h provided that the recommendations for regular inspections of its condition are followed.     

磁旋转编码器多极磁鼓的研制

通过分析磁编码器的原理和结构，采用粘结磁体做磁编码２器多极磁鼓记录介质材料，运用一体成型工艺，研制出了多种型号的磁鼓，并经鼓进行了充磁和气隙磁性能分析。     

圆孔缺陷直径与应力集中对金属磁记忆信号的影响

制备了含有圆孔缺陷的试样,通过磁学分析和磁记忆检测,研究了圆孔缺陷直径和应力集中对磁记忆检测结果的影响。结果表明,磁场强度梯度平均值K_(ave)和最大值K_(max)、磁场强度梯度曲线围成的面积S(K)、金属极限状态系数m_(max)随着圆孔缺陷直径的增大而增大;缺陷位置因磁导率变化而引起磁记忆信号变化;缺陷位置磁场强度梯度曲线相邻两个峰值的间距W_(P-P)随着圆孔缺陷直径的增加而增大。同一缺陷的磁场强度最大值H_(max)、磁场强度曲线围成的面积S(H)随着外加载荷的增加逐渐增大。     

基于金属磁记忆技术的车桥桥壳损伤检测

为探索金属磁记忆现象的物理本质,深入研究车桥桥壳损伤的磁记忆无损检测方法,首先对标准试件进行测试,然后对某系列新桥壳进行疲劳试验,得出桥壳危险区域不同位置、不同加载次数下磁记忆信号法向分量及其梯度值K的变化,并用X射线检测残余应力与磁记忆检测结果进行对比;再以疲劳试验为基础,针对退役驱动桥壳进行变形量测定及对其危险区域进行磁记忆检测,确定桥壳变形量与磁记忆信号间的关系。研究表明:施加载荷前桥壳表面的初始磁状态不同,施加载荷后磁记忆信号呈现规律性的变化;随着循环次数的增加,梯度K值峰值增大;利用磁记忆检测与X射线复合检测的方法能较好的判断出构件缺陷;桥壳的变形量和磁记忆信号梯度K值以及加载的循环次数之间有良好的对应关系,可以为驱动桥壳再制造检测提供依据。     

An Approach to Assessment of the Lifetime Characteristics of Steels under Creep Conditions Using Fracture Mechanics Criteria

The current status of activities associated with the assessment of conditions and prospects for prolonging the service life of equipment operating for a long time at thermal power stations (TPS) is described. The history of the creation and development of an industry system for diagnosing and prolonging the lifetime of heat-generating and mechanical equipment is briefly outlined. The core of the system was the results of investigations into long-term strength and creep of heat-resistant steels, and a regulatory base governing effective application of the system was formed and continuously improved within the system framework. It is noted that more and more extensive investigations resulted in the attempts to extend the criterial strength base using the cracking resistance criteria, including local creep fracture criteria. The advantages and disadvantages of the most-used local control method, i.e., the replica method, are analyzed. It is proposed to use the fracture mechanics criteria and, in particular, the threshold stress intensity factor (SIF) below which creep cracking does not occur in analyzing the process of steel creep fracture. It is demonstrated that the threshold SIF for a specific material depends functionally not only on the temperature but also on the loading time. Considering this fact, it is proposed to account for the accumulation of local (at the crack tip) and total damageability of the metal in the concept of threshold SIF. A similar approach can also be used for describing the subcritical crack growth. Therefore, it is proposed to construct crack growth diagrams using isochronous curves for the specified test times. It is demonstrated that dimensions of allowable flaws that do not lead to crack propagation can be predicted for given operating conditions. The cases were analyzed that occurred while obtaining results of examination of a structural member operating under creep conditions for prediction of the size of allowable (nonpropagating) crack-like flaws. This analysis has revealed that the application of the threshold SIF criterion and isochronous creep crack growth rate diagrams can be useful for setting forth the substantiated frequency of examinations for high-temperature equipment and establishing the time by which the equipment service life can be prolonged.     

磁记忆诊断技术中应力集中水平定量评估方法

讨论了采用金属磁记忆法检测设备结果的处理步骤,提出了在应力集中区按漏磁场梯度确定金属极限状态的方法。     

基于Ba铁氧体的磁编码器多极磁鼓制备与性能

以Ba铁氧体磁粉为原料制作了直径为40 mm的磁编码器磁鼓,通过扫描电镜观察了磁鼓磁层的显微结构,并进行了磁鼓的磁滞回线和磁极数量的写入和读出测试,对磁鼓空间磁场的分布和影响磁鼓磁极的因素进行了初步分析。发现磁鼓在写入256对磁极信号时,信号输出波形规整,信噪比良好,而且相比于Co-γ-Fe2O3磁鼓具有更高的抗干扰能力。如果能够更好地提高磁层致密度以及适当减小磁层厚度,Ba铁氧体磁粉是一种制做磁编码器多极磁鼓的有效材料。     

Application experience of grade 10Kh9MFB chromium steel for steam shutoff and control valve bodies

In 2014–2015, the engineers of JSC “NPO “TsNIITMash”, in cooperation with JSC “Energomash (Chekhov)—ChZEM”, developed a technology for manufacturing D _u = 250 mm valve bodies from 10Kh9MFB chromium steel by electroslag melting (ESM) and produced their pilot copies within the frame of import substitution program. This article provides results of research into determining the design values of metal characteristics, including short-term mechanical properties at working temperatures and impact and long-term strength. The test specimens have been sampled from the following four zones: bottom, central, branch-pipe, and head. Tensile short-term rupture testing has been performed at temperatures of 350, 450, 500, 550, 600, and 650°С. Testing for long-term strength has been carried out at temperatures of 550, 575, 600, and 625°С and stresses of 156.8, 137.2, 117.6, and 98 MPa. To estimate brittle fracture resistance, impact-strength tests have been run at temperatures of–20 and–10°С; 20 and 50°С. The specimens have been sampled from the middle of the blank section. All short-term mechanical properties and impact strength are in agreement with the requirements imposed on the metal of hot-deformed steam piping made of 10Kh9MFB steel as per TU (Technical Conditions) 14-3R-55-2001. The absence of microliquation of alloying elements and the high homogeneity of chemical composition (as demonstrated with nine specimens) have also been experimentally confirmed. Metallographic analysis has shown that the structure of the tested metal is that of tempered martensite with local areas of tempered bainite. Overall, the microscopic structure of metal is practically the same in all the studied zones. Service-life calculation of pilot valve bodies has proved conformity with the safety-margin regulations. Such properties of electroslag melting blank as long-term strength and allowable stress correspond to the level of deformed metal and to regulations.     

The possibilities of fracture mechanics as applied to problems of strength, service life, and substantiation of safe operation of heat-generating and mechanical equipment

The fundamentals of fracture mechanics are briefly outlined, and its possibilities as a tool for estimating the longevity and bearing capacity of equipment components the metal of which contains cracklike flaws are pointed out. Experimentally obtained kinetic crack resistance diagrams lying at the heart of methods for determining the survivability of structures are given for some steels. Practical application of the methods of fracture mechanics is demonstrated on a particular example of substantiating temporary operability of a boiler drum having cracklike flaws near the holes for water downtake pipes.     

金属检测法在火电厂检修中的应用

为防止压力容器及承压管道因材料性能不足而给火电厂的安全运行带来隐患,介绍了常用的裂纹无损探伤检测方法、现场金相检测法、壁厚检测法、硬度检测法等金属检测方法;对磁粉检测法、渗透检测法、超声检测法、X射线检测法的原理、适用范围、使用步骤进行了详述;以某П型锅炉机组的中修为例,阐述了各种检测方法的选取和检测点的选择,展示了部分检测照片,并对裂纹检测结果给出了处理意见和方法,以更好地服务于机组的安全运行。     

基于主动磁检测技术的车辆检测新方法

为了给智能交通管理系统提供交通信息,提出了一种车辆检测的新方法.主动磁检测器包括一个发射线圈和一个接收线圈,发射线圈持续地辐射交流磁场,当车辆从检测器上方通过时,车辆的金属外壳中就会产生涡电流,从而产生涡流二次场,那么接收线圈周围的磁场就会发生改变.通过测量接收线圈周围的磁场是否改变来达到检测车辆的目的.检测概率为96...     

长杆吹灰器套管断裂原因分析

针对某发电公司发生的吹灰管套管断裂事故,对断口焊接区域和附近母材进行化学成分检验、金相检验、小负荷硬度检验、常温力学性能检验和现场分析,认为该吹灰器套管断裂是在特定结构及运行条件共同作用下所导致的疲劳断裂,并提出了有针对性的建议。     

金属磁记忆检测中应力集中区信号的识别

金属磁记忆技术可以快速检测出铁磁构件的应力集中区,对其故障进行早期诊断。磁记忆信号非常微弱,容易受到外来噪声和干扰影响,使得难以准确确定应力集中区。针对含有噪声非平稳性的漏磁信号,在原有信号特征量梯度的基础上,给出了新的时域空间梯度和峰-峰值组合特征量,以及能量峰值处理方法,有效消除了随机噪声对磁记忆信号的影响,提高了应力集中区的识别率;从磁记忆信号的奇异性检测角度出发,通过多尺度小波系数的平方相关一致性来确定真正的应力集中区;实验验证了所提方法的有效性。     

P91主蒸汽管道焊缝断裂韧度与其它力学性能的关系

文中对P91钢两类焊缝的拉伸、冲击、硬度，特别是断裂韧性进行了试验研究。结果表明：强度、硬度高，冲击韧性低的R焊缝具有低的断裂韧度，强度、硬度低，冲击韧性高的D焊缝具有高的断裂韧度；R焊缝的低韧性主要与其晶粒粗大、网状晶界及焊接过程中焊接线能量和电流偏大有关，而D焊缝的低强度与高的断裂韧度则与焊后二次回火时温度过高有关。对于R焊缝，用厚度12mm的三点弯曲(SEB)试样测得的条件Kic(kq)与厚度25mm的紧凑拉伸(CT)试样测得的有效Kic基本一致。     

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up–cooling down, opening–closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 10³ cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.     

锅筒筒体和圆筒型集箱体弯曲应力的计算机校核

本文介绍了按照GB9222－88的规定，利用计算机在Win95－Win98环境下对锅筒筒体和圆筒形集箱筒体的弯曲应力进行核核的方法。