To accurately simulate engineering service conditions and evaluate the impact of corrosive environments on crack propagation in a steel box girder structure, this study conducted material- and structural-scale corrosion-environment and mechanical performance tests.

Material-level compact tension (CT) specimens and a steel box girder model were fabricated, with initial cracks introduced via artificial defects and fatigue loading. Corrosion tests were then conducted separately: CT specimens were exposed to a coastal field environment for three months to simulate marine atmospheric corrosion, whereas the box girder model underwent accelerated corrosion in a laboratory chamber for one month. Fracture toughness tests were performed on CT specimens before and after corrosion, and crack propagation tests were conducted on the box girder under cyclic fatigue loading.

Key findings include the following: (1) At the material scale, fracture toughness of the uncorroded welded CT specimens was $237.4\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m}}^{\frac{1}{2}}$, which increased to $380.0\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m}}^{\frac{1}{2}}$ (~60% increase) after three months of coastal exposure. This is attributed to corrosion-induced blunting of the sharp crack tip, which raised the energy required for crack re-initiation. (2) At the structural scale, after accelerated corrosion, only two of three pre-existing cracks on the box girder (at the #4 support point) propagated under cyclic loading, with a significant delay in crack initiation that further supports the crack-tip-blunting effect. Propagation paths traversed corrosion pits, where the crack rate slowed or briefly halted until a new sharp tip formed on the opposite side, rendering the paths more complex and discontinuous. (3) The two propagating cracks at the #4 support point grew essentially perpendicular to the primary load-bearing direction, predominantly as Mode Ⅰ (opening mode); the fastest crack (#4-V-b) propagated at 2.06×10^–3 mm/cycle along a largely linear a–N curve, indicating stable fatigue crack growth.

This study reveals dual effects of corrosive environments on crack propagation in steel box girder structures. Corrosion enhances fracture toughness by blunting the crack tip, inhibiting crack initiation. However, pre-existing corrosion pits can act as preferential propagation paths and cause growth fluctuations, increasing the risk of local failure.

The deposition of Cl-containing harmful salts on the surface of service materials critically influences their corrosion process. The Qinshan Nuclear Power Station, located near the sea, has encountered corrosion issues due to the deposition of these harmful salts. Although researchers have conducted numerous in-depth studies on the corrosion behavior and mechanisms of materials in nuclear power plants, only limited literature addresses the deposition patterns of harmful salts on the surfaces of nuclear-grade materials.

A field environmental investigation was conducted to understand nuclear material corrosion in salty environments, and then a harmful salt solution for salt spray deposition experiments was formulated based on the investigation results following the ASTM standard. To investigate the deposition patterns of harmful salts on the surface of spent fuel storage canister materials, this solution was used for salt spray deposition on nuclear-grade materials. Tests were conducted at 90 ℃ to simulate the coastal service environment of the Qinshan Nuclear Power Station.

The analysis of seawater composition revealed that the seawater near the Qinshan Nuclear Power Station is diluted by freshwater, as it is located near the Yangtze River estuary. Despite this dilution, a comparison with the global average sodium content of seawater indicated that the seawater near the Qinshan Nuclear Power Station retains the typical characteristics of normal seawater. The design results for the harmful salt solution indicated that, based on the total chloride content of substitute ocean water according to the ASTM D1141-98 standard (2021 edition), the concentration of each compound in the seawater near the Qinshan Nuclear Power Station must be multiplied by 4.075 26 for amplification. This adjustment allows the formulation of a harmful salt simulation solution for salt spray deposition that complies with ASTM standards. The experimental results of harmful salt deposition on the surface of nuclear-grade material at 90 ℃ indicated the following: By setting the sedimentation rate of the salt spray at 1.75 mL/(h·80 cm²) and establishing a single salt spray period as “1 min of salt spray followed by 15 min of standing,” one salt spray period was necessary for the average harmful salt concentration on the surface of the sample to reach 0.1 g/m² (using thin slice samples measuring 100 mm×100 mm× 0.1 mm). To achieve a concentration of 1.0 g/m², 12 salt spray cycles were required (using flat samples measuring 50 mm×25 mm×2 mm). Finally, 112 salt spray cycles were needed to reach a concentration of 10.0 g/m² (also using flat samples measuring 50 mm×25 mm×2 mm).

The seawater near the Qinshan Nuclear Power Station retains the characteristics of normal seawater. This paper proposes a laboratory design concept and serves as a reference for evaluating the service life and performance of materials used in nuclear power plants operating in actual service environments.

Deviations caused by current (I) and resistance (R), known as IR drops, are prevalent in various engineering and industrial applications, such as cathodic protection of buried pipelines, electrocatalytic CO₂ reduction reaction, and water electrolysis. These IR drops substantially affect the field of electrochemical characterization. During the evaluation of the performance and service life of engineering materials, IR drops are an influential factor. This is especially crucial in high-impedance pure water systems used in nuclear power, in which the resistance of the pure water solution amplifies the impact of IR drops.

We constructed an electrochemical three-electrode system to study IR drops and utilized well-polished samples of nuclear-grade 304L stainless steel and pure water as the working electrode and cell electrolytes. Before the electrochemical tests, conventional X-ray diffraction (XRD) measurement was utilized to analyze the phase of the matrix composition of the nuclear-grade 304L stainless steel samples. Then, grazing incidence X-ray diffraction (GIXRD) was employed to investigate the passive film phase on the surface of these samples. Subsequently, a series of electrochemical tests, including electrochemical impedance spectroscopy (EIS) and polarization curve tests, were carried out.

XRD characterization results showed that the matrix of the nuclear-grade 304L stainless steel sample mainly comprised the austenite phase with a small amount of ferrite phase. The GIXRD results revealed a passivation film on the sample surface composed of multivalent oxides such as Cr₂O_2.4, Cr₃O, FeCr, and FeO, in addition to a matrix austenite phase. This passivation film was considered while selecting the electrochemical fitting circuit. Based on the GIXRD phase analysis, a reasonable equivalent circuit shaped as “R(RQ)(RQ)(RQ)” in the series mode was selected to fit the EIS spectroscopy data for nuclear-grade 304L stainless steel in pure water solution. Electrochemical parameters were obtained from this model, with the resistance R_s of the pure water solution measured at 3.319 × 10⁴ Ω. This value could easily be confused with the passivation film resistance and charge transfer resistance. To verify whether the 3.319 × 10⁴ Ω value was indeed the solution resistance, we assumed that the high-impedance pure water solution behaved like a “pure water coating” with a response of the parallel plate capacitor. By analyzing and comparing the theoretically calculated capacitance value of this “pure water coating” with the actual measured values, we validated the proposed hypothesis. This promoted further research on IR drop control in high-impedance pure water systems within the nuclear power field. The IR drop compensation calculation for the polarization curve further confirmed the presence of solution resistance for the “pure water coating” and ensured the accuracy of related measurements.

For high-impedance pure water systems in the nuclear power field, the “pure water coating” exhibited characteristics akin to a flat plate capacitor response. After the IR drop compensation, the polarization curve of the nuclear-grade 304L stainless steel in a pure water system accurately reflects the actual conditions. Therefore, timely IR drop compensation is crucial for electrochemical systems with high solution resistance.