This study aims to evaluate the corrosion behavior of ductile cast iron (FCD-500) under simulated marine engine operating conditions and to determine the optimal corrosion inhibitor conditions under chloride contamination. Experiments were conducted at 50 °C and 80 °C, with different Cl⁻ concentrations (0–500 ppm) and sodium nitrite (NaNO₂)-based inhibitor concentrations (0; 9000; 15,000; 17,000 ppm). Immersion and electrochemical tests were performed to analyze the microstructural corrosion characteristics and inhibitor efficiency. The results indicated that as the Cl⁻ concentration increased, proportionally higher levels of inhibitor were required to maintain surface stability. The maximum inhibition efficiency, approximately 97.3%, was achieved with an inhibitor concentration of 17,000 ppm, at a Cl⁻ concentration of 100 ppm.

In this study, cavitation erosion tests were conducted to investigate the effects of the presence of coolant additives and chlorides on the corrosion and cavitation erosion of cylinder liners in marine diesel engines. Electrochemical experiments were conducted to evaluate the corrosion characteristics of ductile cast iron (DCI), and the corrosion potential and corrosion current density were measured. In addition, weight loss, surface roughness, and maximum surface damage depth were quantified as a function of cavitation exposure time. Furthermore, to investigate the erosion and erosion–corrosion characteristics induced by cavitation attack, the damaged surface morphology was closely examined using a scanning electron microscope (SEM) after the cavitation erosion tests. The results revealed that the coolant additive effectively protected the DCI from corrosion caused by aggressive chlorides. In particular, when an appropriate amount of additive was added to a coolant containing 100 ppm of chloride, the corrosion current density of DCI was reduced by approximately 31.7 times, significantly improving corrosion resistance. Therefore, different surface damage mechanisms corresponding to cavitation erosion and cavitation erosion–corrosion were identified depending on the presence or absence of the coolant additive during the cavitation erosion tests.

Marine selective catalytic reduction (SCR) systems are widely used to comply with stringent NO_x emission limits, yet the long-term deterioration of catalysts under traceable real-world ship operation remains insufficiently documented. In this study, V-based SCR catalysts were recovered from the generator-engine SCR system of the training ship T/S SEGERO after approximately 1000 and 3600 h of actual vessel operation and compared with a fresh reference. The field-aged catalysts were evaluated by visual inspection, pressure-drop measurements, SEM–EDS, ICP-OES, N₂ physisorption, and laboratory NH₃-SCR activity testing. After 3600 h, localized carbonaceous and inorganic deposits were observed together with an approximately 9–18% increase in pressure drop relative to the fresh catalyst. Ca, P, and Zn accumulation increased with field exposure, while Ca and S showed spatial co-localization at the catalyst surface. The BET surface area decreased by approximately 10% after 1000 h and 35% after 3600 h. Relative DeNO_x activity remained close to that of the corresponding fresh reference after 1000 h but was lower after 3600 h, with mean reductions of 8.3–13.3% in the first layer and 2.0–5.9% in the second layer across 300–400 °C. These results demonstrate the value of a training vessel as a traceable longitudinal platform for linking marine operating history with catalyst deterioration.

This study investigates the degradation characteristics of turbocharger nozzle rings in marine diesel engines by conducting numerical analysis and solid particle erosion (SPE) tests to examine their structural stability and morphological surface damage trends. The fatigue analysis was conducted under a load condition corresponding to 100% output of the main engine, using ANSYS software. The SPE test was conducted in accordance with ASTM G76-05 standards, and the weight loss and erosion rate were calculated. Surface damage was closely examined through 3D analysis and scanning electron microscopy (SEM). The flow analysis revealed that the loads were highly concentrated at the nozzle ring inlet and the leading edge of the blades, with a maximum pressure coefficient of 0.07678 MPa. The load decreased toward the trailing edge of the nozzle ring, and the surface pressure coefficients of the flange, inner hoop, and outer hoop—where the nozzle ring blades are fixed—were found to be nearly identical. The fatigue life of the nozzle ring under 100% engine load was calculated as 1.377e⁺⁷ cycles, with a fatigue damage value of 1.32e⁺³². Notably, the fatigue life in the regions near the inner and outer hoops of the nozzle ring approached zero. The results of the SPE test using spherical SiO₂ particles confirmed that the surface damage of the nozzle ring material, 316L stainless steel, followed a typical ductile material damage mechanism. In addition, the surface damage characteristics were significantly influenced by SPE test parameters such as the shape of solid particles, nozzle diameter, and impact angle.

The performance of the turbocharger nozzle ring is a key factor in the overall operation of the main engine of the ship. Minimizing failure and damage caused by high exhaust gas temperature and pressure is essential. As a first step toward improving turbocharger safety, this study performed 3D scanning of an aged nozzle ring to obtain its precise geometry and developed a corresponding numerical model. The boundary conditions of the numerical model were defined by the exhaust gas temperature and pressure at various engine output loads. Structural safety was assessed using static structural and stress-life fatigue analyses. A sharp increase in maximum equivalent stress and strain was observed at output loads of 85% and higher. At 25% load, the maximum fatigue life indicated $1.76{ \times 10}^8$ cycles, while at 100% load, the maximum damage index reached 1. A field performance test conducted at 85% of the main engine’s output load revealed severe damage under high-load conditions. Specifically, damage occurred at the contact area between the outer hoop and the tip of the blade’s trailing edge. This observed damage pattern closely aligned with the results predicted by the fatigue life analysis. The validity of the present study was confirmed through a comparative analysis of the fatigue life predictions and the field test results.