This review critically examines calcareous deposits forming on metallic structures under cathodic protection, focusing on their formation mechanism, composition, characterization methods, and their impact on corrosion and hydrogen embrittlement. Unlike previous reviews, it systematically analyzes the interactions between environmental and electrochemical factors and examines how these interactions influence deposit formation, composition, and protectiveness. Given that the behavior of calcareous deposits toward corrosion and hydrogen embrittlement is highly morphology-dependent, this review provides a detailed overview of analytical techniques, quantitative parameters, and methodological considerations essential for accurate characterization. Their protective role against corrosion arises mainly from reducing oxygen diffusion, while their influence on hydrogen evolution and uptake remains controversial, with effects depending on deposit compactness, porosity, and mineral composition. It categorizes the individual and combined roles of Ca- and Mg-rich layers on hydrogen uptake and critically evaluates the inconsistencies reported across different studies. Variations in literature are linked to differences in experimental design, deposition time, and characterization techniques. By identifying gaps in experimental design and characterization, this review provides new insights into the conditions under which calcareous deposits are protective or detrimental, guiding future research toward more reliable assessment of corrosion protection and hydrogen uptake. This review highlights the importance of more controlled testing, comprehensive deposit characterization, and long-term studies in both natural and artificial seawater to bridge the gap between laboratory results and field performance.
Tavassolian et al. (Sun,) studied this question.