During the 2000s, the concept of cathodic protection (CP) shielding was first raised in open literature and remains debated between coatings professionals. The mechanism of CP shielding, and its understanding continue to be studied for different coatings with different approaches and using various techniques. From the CP shielding factors to the assessment methods, the published literature merits a deep analysis to capture the established knowledge and identify the research gaps to further tackle the issue for reliable coated buried structures. A holistic approach to this topic seems necessary where coatings ageing, cathodic protection, electrochemistry, and transport processes should be considered. In the first part of the present review, the recent works related to the understanding of CP shielding, coatings properties were considered before discussing the mechanisms involved underneath coatings. Transport phenomena and their relationship with cathodic protection performance in the presence of chemical and microbiological processes are discussed in the second part. Finally, CP shielding assessment methods and modeling works are presented and discussed from different perspectives. 

Crevice corrosion is one of the main corrosion problems for metallic alloys used in reverse osmosis (RO) desalination plants. This type of corrosion depends on many factors, that is, alloy composition and/or metallurgy, seawater location, biofilm, temperature, service conditions and crevice geometry. Corrosivity of gulf seawater was compared with the heated Brest seawater (France) for different stainless steels and nickel-based alloy. Maintaining the same experimental conditions, similarity of crevice corrosion performance in both sites relied on the tested alloys. Both crevice corrosion initiation and propagation were evaluated and compared with previous studies. Duplex S32205 and nickel-based N06625 suffered from crevice corrosion contrary to the superaustenitic S31266. However, corrosion results of superduplex S32750 and superaustenitic S31254 were reported very randomly, confirming the “borderline” behavior of these grades in some seawater applications. The impact of the results on the RO plants materials selection is outlined. 

Water diffusion through natural fibers represents an important aspect with regard to the integrity of biocomposites. Usually, diffusion model is defined assuming circular fiber cross-sections, while microscopic analysis findings revealed other geometries. This was found to affect the modeling of water transport through fibers and provide a gap versus experimental data. This work aims to present a numerical approach using finite element method to overcome the limits of use of analytical approaches relating to the morphological shape of vegetal fibers. The cross-section of the Diss fibers was observed by an optical microscope and simulated at an ellipsoidal shape after processing the images. Then, the average morphological parameters were determined. A numerical finite element model was implemented based on the observed geometry in order to determine the diffusion coefficient by an inverse approach compared to experimental results. The results showed that the numerical approach made it possible to raise the effect of fiber morphology, often assumed to be circular for plant fibers in analytical approaches, on the diffusion coefficient value, which was defined by a unique diffusion coefficient. 

Abstract: Long-term protectiveness of zinc coatings remains challenging where conversion surface pre-treatments are suggested such as the promising cerium oxide-based coatings. In the present work, the effect of acetic acid addition and of temperature of the bath on the ceria-based coatings produced by cathodic electrodeposition on electrogalvanized steel are investigated. The electrochemical, surface chemistry, and topographical properties are characterized and their corrosion performance is evaluated in NaCl solution. The results show that the coatings prepared from equimolar mixture of cerium chloride and acetic acid at pH 8 and room temperature were less cracked, had a smaller grain size, and offered a three-fold increase of the corrosion resistance when compared with those prepared in cerium chloride solution at pH 6. From X-ray diffraction patterns, it seems that the deposits obtained at pH 8 are free from corrosion products. Moreover, the porosity of the coatings obtained at pH 8 increases with increasing the bath temperatures indicating that at high bath temperature the deposits become heterogeneous and do not cover the whole surface of the substrate. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s)