液化天然气（LNG）接收站气化过程中排放的海水具有低温和含余氯（NaClO）的双重特征。这类排放水既可能直接接触海水中的碳钢构件,也可能渗入附近的钢筋混凝土结构。为此,本研究选取人工海水（AS）模拟海水直接浸泡环境,选取模拟混凝土孔隙液（SCPS,pH≈10）模拟混凝土内部孔隙水环境,以系统评估余氯与温差对两种典型工况下45#钢腐蚀行为的差异化影响。同时,为反映LNG接收站排放海水的低温特征与夏季常温环境的差异,选择温度10 ℃（代表冷排水排放温度）和25 ℃（代表夏季海水常温）两个温度水平。通过电化学测试、失重法、扫描电子显微镜（SEM）、能谱分析（EDS）、X射线光电子能谱（XPS）及X射线衍射（XRD）等多种手段,系统分析了不同NaClO浓度（0、1、10、100 mg/L）与温度（10和25 ℃）条件下,45#钢在AS与SCPS中的腐蚀动力学、腐蚀形貌及产物组成。结果表明,在AS中,NaClO浓度高于10 mg/L时碳钢腐蚀显著加速。随NaClO浓度升高,碳钢表面腐蚀形态由局部腐蚀向均匀腐蚀转变。而在SCPS中,碱性环境（pH≈10）显著抑制了NaClO对碳钢的腐蚀,但高浓度NaClO仍可诱发碳钢表面更深的局部腐蚀坑。两种介质中低温（10 ℃）均能有效抑制碳钢的腐蚀速率与局部腐蚀深度。通过对实验结果的分析,进一步揭示了该环境中NaClO与温度共同作用下碳钢的腐蚀机制,为LNG接收站及其周边海洋工程中钢铁结构与钢筋混凝土结构的防腐设计与运行维护提供了一定的理论和实验依据。
Abstract
Seawater discharged during the gasification process at LNG terminals is usually characterized by low temperature and residual chlorine, mainly form of sodium hypochlorite (NaClO). This type of effluent may directly contact carbon steel components in marine environments or infiltrate adjacent reinforced concrete structures. However, the combined effect of NaClO concentration and temperature on the corrosion behavior of steel has not yet been systematically clarified. This article studies the corrosion of 45# steel under varying NaClO concentration (0, 1, 10, 100 mg/L) and temperature (10 and 25 ℃) in artificial seawater (AS) and simulated concrete pore solution (SCPS, pH≈10). The AS is prepared according to ASTM D1141-98, and SCPS is obtained by adding 2 g/L Ca(OH)2 to AS. EIS, potentiodynamic polarization, weight-loss measurements, and localized corrosion-depth analysis, are employed to evaluate the electrochemical response and corrosion rate of the samples. In addition, surface morphology, corrosion products, and microstructural characterization are investigated by SEM, EDS, XPS, and XRD. The results show that in AS at 25 ℃, when NaClO concentration increases from 0 to 100 mg/L, the charge transfer resistance and corrosion product film resistance (Rct + Rf) decrease from 2 266 to 1 207 Ω·cm2, while the corrosion current density (Jcorr) increases from 11.48 to 18.29 μA/cm2. The weight-loss corrosion rate remains 0.108 mm/a at 0 and 1 mg/L NaClO. It increases slightly to 0.123 mm/a at 10 mg/L, and then increases sharply to 0.202 mm/a at 100 mg/L. This corresponds to increases of 13% and 87% at 10 and 100 mg/L, respectively. With increasing NaClO concentration, the corrosion morphology in AS changes from localized corrosion to more uniform corrosion, and the average pit depth decreases. In contrast, SCPS at 25 ℃, the alkaline environment significantly inhibits NaClO-induced corrosion. The Rct + Rf decreases from 2 922 to 2 266 Ω·cm2 as NaClO concentration increases, and Jcorr increases less significantly than in AS. The corrosion rate in SCPS is 0.086 5 mm/a (0 mg/L), unchanged at 1 mg/L, rises to 0.093 7 mm/a at 10 mg/L (8% increase), and reaches 0.108 mm/a at 100 mg/L (25% increase), respectively. Unlike in AS, the localized corrosion depth in SCPS increases significantly with NaClO concentration, indicating that high NaClO concentration induces deeper pitting in alkaline media. Temperature also plays an important role in controlling the corrosion process. When temperature is reduced from 25 to 10 ℃, in both AS and SCPS, the Nyquist arc radius increases, the fitted Rct + Rf values rises, and Jcorr decreases. Meanwhile, the corrosion rate and pit depth both are effectively suppressed. EDS results show that the chlorine content in the corrosion products increases after adding 100 mg/L NaClO in both media. XPS and XRD analyses further confirm that the main corrosion products are FeOOH, Fe2O3, CaCO3, and residual NaCl. The addition of NaClO does not change the surface corrosion product composition. The mechanism is as follows: in near-neutral AS, NaClO hydrolyzes to form strongly oxidizing HClO, which participates in cathodic reduction, accelerating cathodic depolarization and anodic dissolution. In alkaline SCPS (pH≈10), the equilibrium shifts toward less oxidizing ClO-, so corrosion acceleration is weakened. However, local acidification at anodic sites can regenerate HClO from ClO-, explaining why high NaClO still causes deep pitting in SCPS. Low temperature (10 ℃) suppresses NaClO decomposition, slows electrode kinetics, and reduces ion diffusion, leading to lower corrosion rates and shallower pits. Overall, this study provides a clearer understanding of the corrosion behavior of 45# steel under the combined effects of NaClO concentration and temperature. The pH-dependent oxidizing ability of chlorine species, the transition from uniform to pitting corrosion depending on the medium, and the inhibitory effect of low temperature are the main factors governing the corrosion response. These results provide a theoretical and experimental basis for anti-corrosion design and maintenance of steel and reinforced concrete structures in LNG terminals and marine engineering.
关键词
腐蚀 /
碳钢 /
海水 /
温差 /
次氯酸钠
Key words
corrosion /
carbon steel /
seawater /
temperature difference /
sodium hypochlorite
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基金
国家自然科学基金（52250710159,51731008,51671163）; 中国博士后科学基金（2024M751292）
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