Flow-accelerated corrosion behavior of 13Cr stainless steel in a wet gas environment containing CO_2

This work investigated the flow-accelerated corrosion （FAC） behavior of 13Cr in a wet CO2-containing environment at different flowing gas velocities mid impinging mlgles, with the natural-gas pipeline environment simulated by a self-assembled impingement jet sys- tem. Surface molphology determination, electrochemical measurements, mid hydromechaziics numerical analysis were cmlied out to study the FAC behavior. The results demonstrate that pitting corrosion was the primary mode of corrosion in 13Cr stainless steel. High-flow-rate gas destroyed the passive film mid decreased the pitting potential, resulting in more serious corrosion. The corrosion degree witk various im- pact mlgles showed the following order： 90~ 〉 60~ 〉 45~. The shear force and the electrolyte from the flowing gas were concluded to be the determinm^t factors of FAC, whereas the shear force was the main factor responsible for destroying the passive film.

Flow-Accelerated Corrosion in Pipe Wall Downstream of Orifice for Water and Air-Water Bubble Flows

An orifice is used widely as a flow meter or a contraction device in pipeline systems in hydro-power plants, thermal power plants, and chemical plants because of its simple construction, high reliability, and low cost. However, it is well known that flow-accelerated corrosion (FAC) occurs on the pipe wall downstream of the orifice. Some of the authors have examined FAC through experimental and numerical analyses and have reported that one of the major governing parameters of FAC for single-phase water flow is the pressure fluctuation p’ on the pipe wall, and also that pipe wall thinning rate TR can be estimated by p’. In addition, they have presented the effects of the ori-fice geometry on p’ or TR, and have described a method for suppressing p’ or TR. In the present study, FAC for a two-phase air-water bubble flow is examined and compared with the single-phase water flow experimentally. Further, it is shown that because p’ is also considered a governing parameter of FAC for a two-phase air-water bubble flow, TR can be estimated using p’. It is also indicated that, by using a downstream pipe with a smaller diameter than that of the upstream pipe, p’ or TR can be suppressed.

某核电厂蒸汽发生器排污净化系统泵出口管道泄漏原因

国内某机组运行15 a后,蒸汽发生器排污净化系统泵出口管道发生泄漏。采用超声波测厚、化学成分分析、金相检验、扫描电镜观察、能谱分析及流场模拟计算等方法,分析了管道泄漏的原因。结果表明:低温流动加速腐蚀(FAC)导致管壁减薄,最终导致管道泄漏,管件材质、几何形状,介质pH、温度、溶解氧含量及流速等是发生FAC的重要因素。

Analysis of Material Loss Behavior According to Long-Term Experiments on LDIE-FAC Multiple Degradation of Carbon Steel Materials

Recently, damage caused by liquid droplet impingement erosion (LDIE) in addition to flow-accelerated corrosion (FAC) has frequently occurred in the secondary side steam piping of nuclear power plants, and the damage-occurring frequency is expected to increase as their operating years’ increase. In order to scrutinize its causes, therefore, an experimental study was conducted to understand how the behavior of LDIE-FAC multiple degradation changes when the piping of nuclear power plants is operated for a long time. Experimental results show that more magnetite was formed on the surface of the carbon steel specimen than on the low-alloy steel specimen, and that the rate of magnetite formation and extinction reached equilibrium due to the complex action of liquid droplet impingement erosion and flow-accelerated corrosion after a certain period of time. Furthermore, it was confirmed at the beginning of the experiment that A106 Gr.B specimen has more mass loss than A335 P22 specimen. After a certain period of time, however, the mass loss tends to be the opposite. This is presumed to have resulted from the magnetite formed on the surface playing a role in suppressing liquid droplet impingement erosion. In addition, it was confirmed that the amount of erosion linearly increases under the conditions in which the formation and extinction of magnetite reach equilibrium.

Comparison between FAC Analysis Result Using ToSPACE &CHECWORKS Programs and Experimental Result

A number of piping components in the secondary system of nuclear power plants (NPPs) have been exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, LDIE (Liquid Droplet Impingement Erosion), and SPE (Solid Particle Erosion). Those mechanisms may lead to thinning, leaking, or the rupture of components. Due to the pipe ruptures caused by wall thinning of Surry Unit 2 in 1986 and Mihama Unit 3 in 2004, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage the wall thinning of pipes caused by FAC and erosion, KEPCO-E & C has developed ToSPACE program. It can predict both FAC & erosion phenomena, and also be utilized in the pipe wall thinning management works such as susceptibility analysis, UT (Ultrasonic Test) data evaluation as well as establishment of long-term inspection plan. Even though the ToSPACE can predict the five aging mechanisms mentioned above, only the FAC prediction result using ToSPACE was compared herein with the experimental result using FACTS (Flow Accelerated Corrosion Test System) to verify the ToSPACE’s capability. In addition, the FAC prediction result using ToSPACE was also compared with that of CHECWORKS that is widely used all over the world.

压水堆核电厂二回路管道设计应对FAC策略

介绍流动加速腐蚀(flow-accelerated corrosion,FAC)的研究结果,针对FAC发生的机理和主要影响因素,提出在压水堆核电站二回路汽水管道设计中应对FAC的策略,从设计源头减少核电厂常规岛FAC产生的影响。

Development of Safety Factors for the UT Data Analysis Method in Plant Piping

There are several thousand piping components in a nuclear power plant. These components are affected by degradation mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, and LDI (Liquid Droplet Impingement). Therefore, nuclear power plants implement inspection programs to detect and control damages caused by such mechanisms. UT (Ultrasonic Test), one of the non-destructive tests, is the most commonly used method for inspecting the integrity of piping components. According to the management plan, several hundred components, being composed of as many as 100 to 300 inspection data points, are inspected during every RFO (Re-Fueling Outage). To acquire UT data of components, a large amount of expense is incurred. It is, however, difficult to find a proper method capable of verifying the reliability of UT data prior to the wear rate evaluation. This study describes the review of UT evaluation process and the influence of UT measurement error. It is explored that SAM (Square Average Method), which was suggested as a method for reliability analysis in the previous study, is found to be suitable for the determination whether the measured thickness is acceptable or not. And, safety factors are proposed herein through the statistical analysis taking into account the components’ type.

压水堆核电厂二回路系统溶解氧含量的控制策略

采用失重法和模拟腐蚀试验研究了溶解氧含量及联氨与溶解氧含量比值对压水堆核电厂二回路系统材料流动加速腐蚀(FAC)的影响,并结合经验反馈,给出了二回路系统溶解氧含量的控制策略。结果表明:在0~30μg/kg溶解氧范围内,溶解氧含量对凝结水管道材料A515碳钢均匀腐蚀的影响不大,低压加热器至除氧器之间的管道材料P11低合金钢的FAC速率随溶解氧含量的升高而减小;由于溶解氧含量较低,联氨与溶解氧含量比值超过了8,因此联氨含量的提高对该钢腐蚀速率的影响较小;在2 mg/kg的低溶解氧条件下,690TT合金的裂纹扩展速率(CGR)较低,在饱和溶解氧条件下,690TT合金的CGR提高了1.08~3.53倍;建议采取分段控制的方式控制压水堆核电厂二回路系统的溶解氧含量,将凝结水至除氧器之间的溶解氧质量分数提高至5~30μg/kg,将除氧器至蒸汽发生器之间的溶解氧质量分数控制在5μg/kg以下,并加入联氨,使联氨与溶解氧含量比值维持在5~8以上。

核电行业中流动促进腐蚀的模型和数值模拟研究进展

对核电行业中流动促进腐蚀的现象、危害、现有模型和不同的数值模拟方法进行了介绍和评述,并指出了下一步的主要研究方向.

表面纳米化处理对Cr5Mo钢流动加速腐蚀性能的影响

采用超声喷丸(USSP)技术对Cr5Mo钢表面进行纳米化处理,研究了试验钢表面的组织及显微硬度,并对超声喷丸前后试样在含H2S流动去离子水溶液中的流动加速腐蚀性能进行了研究,并对腐蚀产物膜的微观形貌进行了观察。结果表明:经USSP处理后,试样表面形成了一定深度的纳米晶层,该晶层内的平均晶粒尺寸约为20nm;表面纳米化能够明显提高试样表层的显微硬度,并且处理时间越长,显微硬度越大,变形层厚度越大;与原始粗晶试样相比,表面纳米化试样的抗流动加速腐蚀性能增强,表面生成的腐蚀产物膜较致密;随着USSP处理时间的延长,腐蚀产物膜的致密度和完整性变差,耐蚀性能逐渐下降。

空冷凝汽器流动加速腐蚀的影响因素

测量了空冷凝汽器流用Q235钢在不同试验环境中的表面极化电阻,研究了其流动加速腐蚀(FAC)的各种影响因素,并提出了防护方案。结果表明,提高初凝水的pH,提高初凝水中溶解氧含量,降低空冷凝汽器温度等方式可以抑制空冷凝汽器的流动加速腐蚀。

流动加速腐蚀评价程序CHECWORKS及其核电厂老化管理应用

流动加速腐蚀(FAC)是核电厂二回路管线最主要的失效原因之一,严重影响核安全运行。CHECWORKS是美国电力研究院(EPRI)基于FAC经验模型设计开发的商用计算机程序,用以预测FAC速率及其相关的水化学、热工水力参数等。从发展历史、应用现状、程序特点等方面对CHECWORKS进行了综述,为该程序在我国的推广以及在核电厂老化管理中的应用起到积极作用。

超临界机组疏水系统发生流动加速腐蚀的影响因素以及预防

电厂汽水管道运行中流动加速腐蚀(FAC)现象普遍存在,危及电厂安全。随着机组参数的提高,针对超临界机组,通过模拟与现场实时数据分析得到疏水系统与给水系统一样存在较高的流动加速腐蚀现象。流体动力学、环境和材料因素是造成流动加速腐蚀的主要因素。由沧东电厂660 MW超临界机组的实时数据分析得到p H值、电导率、含氧量对其疏水系统发生流动加速腐蚀的影响关系,结合其采用的水处理方式,分析超临界机组疏水系统发生FAC的机理和原因,给出预防和抑制超临界机组疏水系统发生流动加速腐蚀的有效措施。

船体在海水中流动加速腐蚀数值分析

为了预测动态海洋环境下船体表面的腐蚀速度,同时为防腐设计提供可靠的参考,本文采用数值模拟的方法建立了流动加速腐蚀计算模型。首先对船体周围的海水流场建立了CFD模型,并进行了计算,得到了速度、压力、氧浓度分布等流场信息;然后根据这些信息建立了船体在流动海水中的FAC模型,并进行求解,得到了船体表面各点的传质系数和腐蚀速度分布。结果表明:船体后部和侧后部因为氧的浓度较大,其腐蚀速度明显比其部位大,而且随着流速的增大,腐蚀速度也变大,在没有保护涂层的情况下,最大腐蚀速度可达22 mm/a,比静态条件下大得多,因此当采用阴极保护时,应充分考虑这些部位,以便合理地布置阳极位置。

汽包锅炉给水加氧处理技术及应用条件分析

概述了锅炉给水加氧处理技术的发展过程及应用,重点介绍了给水加氧处理技术的原理及经济效益,对汽包锅炉应用给水加氧处理的条件进行了分析,并对国华定洲电厂应用该项技术的可行性进行了探讨。

三通管浓差腐蚀数值分析

为了揭示浓差腐蚀的机制,本文以三通管为研究对象,采用数值模拟技术建立了浓差腐蚀模型。利用FLUENT对管道流体进行了计算,得到了壁面离子导电层的氧浓度分布;将离子导电层提取出来,进行离散化处理,并根据氧浓度计算出表面单元的自然腐蚀电位和电流密度,再根据基尔霍夫第二定律,推导出关于表面离子导电层单元腐蚀电位的离散方程组。求解方程组,得到了单元极化后的腐蚀电位,并据此求出表面最终腐蚀电流密度分布。结果表明:不考虑浓差腐蚀时,管道壁面氧浓度高的部位,自然腐蚀电位较高、自然腐蚀电流密度较大;而氧浓度较低的部位,自然腐蚀电位较低、自然腐蚀电流较小;而当考虑浓差腐蚀时,自然腐蚀电位较高的部位将发生阴极极化,腐蚀速度有所降低;而自然腐蚀电位较低的部位将发生阳极极化,腐蚀电流有所增大,这大大地改变了腐蚀电流的最初分布,并且腐蚀电位有趋于均匀化的趋势。

某350 MW超临界机组给水铁含量超标原因分析及处理

某350 MW超临界机组自完成168 h满负荷试运一年以来,给水铁含量长期超标。通过查定和分析发现,其主要由给水处理工况控制不当、除氧器加热汽源蒸汽品质差、高压加热器疏水管道冲刷腐蚀产物、汽泵前置泵汽蚀等原因所致。经采取有效措施处理后,给水含铁质量浓度稳定在2~4μg/L,达到含铁质量浓度小于5μg/L的标准要求。

A335P11钢在流动加速腐蚀条件下的管壁减薄行为

模拟了核电厂常规岛二回路工况,研究了此工况条件下A335P11钢弯管测试段、变径测试段及三通测试段的腐蚀减薄现象。结果表明:发生流动加速腐蚀(FAC)最严重的部位是弯管内弧面、变径管的渐缩管段出口处以及三通测试段的辅出水口处。

核电站二回路汽水管道环焊缝根部流动加速腐蚀及检测

核电站二回路汽水管道环焊缝根部由流动加速腐蚀(FAC)引起的局部减薄现象应引起业界重视,如不进行有效的检测和监督,会导致高能管道泄漏或破裂,分析了相关经验反馈、焊缝根部流动加速腐蚀机理和主要影响因素。结合腐蚀敏感环焊缝结构、材质等特点,探讨了不同检测方法的优缺点,特别是环焊缝根部局部减薄超声衍射时差法的检测原理、试验和应用情况。结果表明,碳钢、低合金钢汽水管道环焊缝FAC发生的部位显著地受到焊缝及其邻近母材铬含量差异的影响,超声衍射时差法可用于检测FAC引起的汽水管道环焊缝根部局部减薄。

基于双环电阻传感器的X65管道流动加速腐蚀监测

在内径150mm的循环管路中开展了变流速工况下流动加速腐蚀试验,通过双环电阻传感器监测了X65管道内流动加速腐蚀的规律。同时,对每个流速状态下目标管段的流场进行了计算流体动力学(CFD)分析,并使用数码相机与扫描电子显微镜对双环电阻传感器测量环即管道周向的腐蚀形貌进行了观察。结果表明:由于弯管的影响,管道的外侧腐蚀比内侧严重,CFD结果也显示管道的外侧流速与壁面剪切力比内侧大;但是流动加速腐蚀并不完全由流场分布决定,形貌结果表明锈层的积累会对X65管道的腐蚀规律产生明显影响。