The cathodic protection provided by epoxy coating/epoxy zinc-rich coatings on defective areas under atmospheric and immersion conditions was studied via a Q235 wire beam electrode (WBE), scanning electron microscopy, X-ray diffraction, and surface morphology analysis. The results showed that the cathodic protection processes under the two test conditions displayed significant differences. The effective protection time of the defective area under the atmospheric condition was 1.7 times that under the immersion condition. Compared with the immersion condition, zinc particles in zinc-rich coatings under the atmospheric condition exhibited higher cathodic protection efficiency. The possible activation mechanism of zinc particles under the two conditions was elucidated.

Corrosion brings serious losses to the economy annually. Therefore, various corrosion protection and detection techniques are widely used in the daily maintenance of large metal engineering structures. The emergence of image recognition technology has brought a more convenient and faster way for nondestructive testing. Existing image recognition technology can be divided into two categories according to the algorithm: traditional image recognition technology and image recognition technology based on deep learning. These two types of technologies have been widely used in the three fields of metal, coating, and electrochemical data images. A large amount of work has been carried out to identify defects in metals and coatings, and deep learning-based methods also show potential for identifying electrochemical data images. Matching electrochemical images with the detection of defect morphology will bring a deeper understanding of image recognition techniques for metals and coatings. A database of accumulated morphology and electrochemical parameters will make it possible to predict the life of steel and coatings using image recognition techniques.

Calcareous deposits are a consequential outcome of cathodic protection in marine environments, exerting significant influence on the cathodic protection process and current density prerequisites. This study investigates the process of calcium deposition and its impact on the cathodic protection current density of carbon steel under the influence of a rust layer in different corrosion periods. This was investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results demonstrate that the formation processes of calcareous deposits vary after exposure to the corrosive environment for 0, 7, and 30 days. While a longer corrosion period leads to thicker rust layers on the metal surface and a higher initial cathodic protection current, the presence of these rust layers facilitates the deposition of calcium and magnesium ions, resulting in a rapid decrease in cathodic protection current density after a certain period. Meanwhile, long-term cathodic protection facilitates the thickening and densification of the oxide layer, thereby enhancing its protective efficacy, effectively reducing the corrosion rate of the metal surface and stabilizing the cathodic protection current density at a lower level. This study provides theoretical data and experimental evidence to support the maintenance of corroded marine engineering equipment.

This study investigated the degradation of aluminum-based sacrificial anodes caused by sulfate-reducing bacteria (SRB) in marine mud. Through self-discharge tests simulating real cathodic protection conditions, alongside macroscopic observations, electrochemical analysis, and microscopic characterization, we systematically elucidated the corrosion behavior and mechanisms of the anodes with and without SRB. The results showed that the electrochemical capacity of anodes in SRB-inoculated mud was only 1281.28 Ah·kg⁻¹ (efficiency: 44.82%), failing to meet the design requirement of ≥1500 Ah·kg⁻¹. In contrast, in sterile mud, the capacity was 1972.84 Ah·kg⁻¹ (efficiency: 69.01%), which met the standard. SRB promoted the formation of discrete corrosion pits with depths reaching up to 0.43 mm, 3.07 times deeper than those observed under sterile conditions. The local pH within the pits dropped to 3–4, accelerating the selective dissolution of active elements such as Al and Zn. Mechanistic analysis revealed that the sulfides produced by SRB not only disrupt the passive film but also exacerbate the inefficient consumption of the anode through a positive feedback loop involving “acidic corrosion and electron consumption”. This led to a reduction in the protective current density, accompanied by significant fluctuations. This study provides the underlying mechanisms by which SRB degrade the performance of sacrificial anodes and valuable insights for optimizing the design of cathodic protection systems for steel structures in marine mud environments.