Abdelkader Meroufel

Bimetallic corrosion results in accelerated deterioration of the less noble metal due to the galvanic coupling. Electrochemical reactions between metals lead to one metal acting as an anode, corroding more rapidly, while the other acts as a cathode, experiencing reduced corrosion. This process impacts various industries, from defense structures to electronics. A bimetallic composite comprising iron rods and a copper matrix was prepared by casting. Most bimetallic corrosion studies have focused on the effects of environmental conditions and the cathode/anode area ratio on coating layers in bimetallic joints. However, the present work introduces an innovation by investigating the influence of the interfacial microstructure between the two metals, as determined by different casting parameters, on the bimetallic corrosion of iron/copper composites. The casting parameters subject to variation were the steel rod numbers and preheat temperatures, as well as the cast composite’s cooling conditions. The different bimetallic composites, inside the mold, were cooled at three different rates. The interfacial zone microstructure was investigated by scanning electron microscopy, and electrochemical methods were used to assess its impact on the corrosion process in a 3.5 wt.% stagnant solution at ambient temperature. The obtained results indicated that the width of the interference region in bimetallic systems is directly proportional to the corrosion rate, as influenced by the galvanic cell effect. Therefore, when the width of the interference region increased from 2.5 µm to 6.3 µm, the corrosion current density increased from 35 µA/cm ² to 54 µA/cm ² , respectively. Beyond the interference zone, the corrosion rate decreased, indicating a shift toward pure metal pitting corrosion behavior. Furthermore, it was found that both the cathode-to-anode area ratio and the grain size exhibit a direct proportional relationship with the corrosion rate. This directly improves the durability of components used in electrical connections, thermocouples, and military applications, where Cu–Fe systems are widely implemented.

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.

Glass fiber-reinforced polymer (GFRP) composite pipelines are used by many industries for fluids transport including seawater for cooling. The durability of these pipes can be affected where the loss of their strength is due to the occurrence of several internal irreversible micro-damages. One of the challenges facing the integrity of these pipelines is the presence of surface defects. The present research aims to determine the critical size of osmotic blister affecting a 30- year-old seawater handling GFRP pipe. Osmotic blisters were simulated through surface notches with two different geometries and sizes. Longitudinal pipe mechanical strength was studied through tensile tests to study the effect of the surface notch size. At a certain surface notch depth, the strength of the pipe wall decreased with increasing the notch surface depth. This represents the critical value of the damage size called maximum undamaged defect size and noted d _max. Damage with size below d _max does not affect the strength of the pipe wall. To simulate the progressive failure of this aged composite, a 3-D finite element model was employed based on Hashin’s failure criteria.

Microbial activity involvement on soil corrosion of old ductile iron was studied through electrochemical tests and microscopic analysis. Immersion test was conducted at room temperature under stagnant conditions during 62 days where sterilization and oxygen parameters were considered. Mechanisms were investigated through DC and AC electrochemical measurements combined to microscopic observation of surface products by SEM. The results showed an accelerated corrosion in the case of aerated biotic condition with evidence of oxygen promoting bacterial activity. However, corrosion inhibition was observed under deareated biotic condition. The results imply clearly the role of burying depth and soil compactness on ductile iron water pipe life time.