目的 蒸汽发生器传热管是压水堆（PWR）核电站一、二回路的热交换枢纽,其材料耐腐蚀性能影响着压水堆核电站的使用寿命,鉴于此,研究了690-NiCr涂层管在正常工况和非正常工况下的耐腐蚀性能,揭示了温度和pH对690-NiCr涂层管氧化膜形成过程的影响。方法 采用水循环系统的高压釜设备模拟压水堆（PWR）真实工况,利用大气等离子喷涂（Air Plasma Spraying,APS）技术制备Ni-Cr涂层,设计了二回路水环境（285 ℃）、偏离工况水环境（320 ℃）、次临界水环境（360 ℃）以及不同pH值（pH=7.0、pH=9.8、pH=10.6）实验方案;通过SEM、EDS和XRD分析了氧化膜形貌及成分、元素含量和腐蚀机理。结果 在二回路水环境下,涂层管在三种pH水环境下的表面氧化物形状相似,表面覆盖颗粒状氧化物并伴随针状氧化物;在320 ℃偏离工况水环境下,涂层管在三种pH下均形成了形状不规则的颗粒状外层氧化膜和致密的内层氧化膜,外层氧化膜富含Cr,Ni次之,内层氧化膜则相反;在次临界水环境下,涂层管所形成的内外层氧化膜成分差别较小,均富含Cr、Ni元素,不同的是,pH=10.6时的氧含量较低。结论 涂层管在二回路水环境中形成了三层氧化膜,外层氧化膜主要为Cr(OH)3、Ni(OH)2和NiO;中间层氧化膜主要由单质Ni、少量NiO和Fe的氧化物构成;内层氧化膜由Cr2O3构成;随着温度的上升,涂层管表面氧化膜厚度增加,外层氧化物颗粒长大,内层氧化膜遭到破坏,保护性变差,基体的腐蚀速率增加。
Abstract
The steam generator heat transfer tube is the heat exchange hub of the primary and secondary loops of the pressurized water reactor (PWR) nuclear power plant. The corrosion resistance of its material affects the service life of the PWR nuclear power plant. In view of this, the work aims to study the corrosion resistance of 690-NiCr coated tube under normal and abnormal conditions, and reveal the effect of temperature and pH on the formation process of oxide film of 690-NiCr coated tube. Ni-Cr coating was prepared by air plasma spraying (APS) technology, and the real working condition of pressurized water reactor (PWR) was simulated by autoclave equipment of water circulation system. The experimental schemes of secondary loop water environment (285 ℃), 320 ℃ deviation from working condition water environment, subcritical water environment (360 ℃) and different pH values (pH=7, pH=9.8, pH=10.6) were designed. The morphology, composition, element content and corrosion mechanism of the oxide film were analyzed by SEM, EDS and XRD.
In the secondary loop water environment, the surface oxide shapes of the coated tubes in three pH water environments were similar, and the surface was covered with granular oxides accompanied by needle-like oxides. In the water environment of 320 °C deviating from the working condition, the coated tubes formed irregular granular outer oxide film and dense inner oxide film under three pH conditions. The outer oxide film was rich in Cr, followed by Ni, and the inner oxide film was the opposite. In the subcritical water environment, the composition of the oxide film formed in the inner and outer layers of the coated tube was less different, and both were rich in Cr and Ni elements. The difference was that the oxygen content was lower when pH was 10.6. The coating tube had three layers of oxide film in the secondary water environment, and the outer oxide film was mainly composed of Cr(OH)3, Ni(OH)2 and NiO. The intermediate layer oxide film was mainly composed of Ni, a small amount of NiO and Fe oxides. The inner oxide film was composed of Cr2O3. As the temperature increased, the oxide film on the surface of the coated tube thickened, the outer oxide particles coarsened, and the Ni and Fe ions incorporated into the inner oxide layer reduced the density of the Cr2O3 film. As a result, the inner oxide layer was damaged and became less protective, leading to an accelerated corrosion rate of the substrate. The surface of the Inconel 690-NiCr coated tube was irregular and uneven, making it difficult to calculate the exact surface area. Therefore, the corrosion rate was evaluated per unit height. As shown in the corrosion tests under different water environments, the samples generally exhibited initial weight loss, primarily due to the detachment of loosely bonded flaky coating materials after immersion for about 100 h. With prolonged immersion, the rates of oxide formation and dissolution gradually approached equilibrium. In pure water (pH=7.0), the corrosion mass change reversed after 300 h, whereas at pH=9.8, the reversal occurred after 600 h and at pH=10.6, weight loss proceeded at a relatively constant rate. After 1 000 h in all environments, the samples showed net weight gain, indicating the formation of a more compact and adherent oxide film. This dense oxide layer inhibited further dissolution while promoting continued deposition of oxides and hydroxides on the coating surface.
关键词
蒸汽发生器 /
690-NiCr涂层管 /
高温苛性溶液 /
氧化膜成分 /
腐蚀机理
Key words
steam generator /
Inconel690-NiCr coated tube /
high temperature caustic solution /
oxide film composition /
corrosion mechanism
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基金
中国博士后基金面上项目（2024M750723）
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