ALBERT

Description: Microbiologically influenced corrosion (MIC) is a major concern in a wide range of industries, with claims that it contributes 20% of the total annual corrosion cost. The focus of this present work is to review critically the most recent proposals for MIC mechanisms, with particular emphasis on whether or not these make sense in terms of their electrochemistry. It is determined that, despite the long history of investigating MIC, we are still a long way from really understanding its fundamental mechanisms, especially in relation to non-sulphate reducing bacterial (SRB) anaerobes. Nevertheless, we do know that both the cathodic polarization theory and direct electron transfer from the metal into the cell are incorrect. Electrically conducting pili also do not appear to play a role in direct electron transfer, although these could still play a role in aiding the mass transport of redox mediators. However, it is not clear if the microorganisms are just altering the local chemistry or if they are participating directly in the electrochemical corrosion process, albeit via the generation of redox mediators. The review finishes with suggestions on what needs to be done to further our understanding of MIC.

Description: For infrastructure applications in marine environments, the eventual initiation of corrosion (and pitting) of steels (and other metals and alloys) often is assumed an inescapable fact, and practical interest then centres on the rate at which corrosion damage is likely to occur in the future. This demands models with a reasonable degree of accuracy, preferably anchored in corrosion theory and calibrated to actual observations under realistic exposure conditions. Recent developments in the understanding of the development of corrosion loss and of maximum pit depth in particular are reviewed in light of modern techniques that permit much closer examination of pitted and corroded surfaces. From these observations, and from sometimes forgotten or ignored observations in the literature, it is proposed that pitting (and crevice corrosion) plays an important role in the overall corrosion process, but that longer term pitting behaviour is considerably more complex than usually considered. In turn, this explains much of the, often high, variability in maximum depths of pits observed at any point in time. The practical implications are outlined.

Description: Common concretes use considerable amounts of fresh water and river sand, and their excessive use is already seriously implicating the environment. In this respect, seawater and sea sand concrete (SWSSC) is a very attractive alternative, since it addresses the increasing shortage of fresh water and dredging of river sand. A major concern with reinforced SWSSC is the severe corrosion of the steel reinforcements by seawater (that has a very high content of chloride which is very corrosive), thereby seriously impairing the strength of such concrete. Fibre reinforced polymer (FRP) can be a suitable alternative to replace steels as reinforcement. However, there has been little systematic work to understand the degradation kinetics and mechanisms of FRP in the chloride-containing alkaline SWSSC environment. This review first provides an overview of the degradation of FRP composites in normal concrete and chloride-containing alkaline SWSSC environments, and then presents an example of a recent study using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) that may provide a pathway to systematic experimental approach to understanding such degradation. The review also makes a comprehensive assessment of the influence of environment-assisted degradation on mechanical properties of FRPs.

Description: The influence of hydrogen on the mechanical properties of four, medium-strength, commercial, quenched-and-temped steels has been studied using the linearly increasing stress test (LIST) combined with cathodic hydrogen charging. The relationship was established between the equivalent hydrogen pressure and the hydrogen charging overpotential during cathodic hydrogen charging, though the use of electrochemical permeation experiments and thermal desorption spectroscopy. The cathodic hydrogen charging conditions were equivalent to testing in gaseous hydrogen at hydrogen fugacities of over a thousand bar. Under these hydrogen-charging conditions, there was no effect of hydrogen up to the yield stress. There was an influence of hydrogen on the final fracture, which occurred at the same stress as for the steels tested in air. The influence of hydrogen was on the details of the final fracture. In some cases, brittle fractures initiated by hydrogen, or DHF: Decohesive hydrogen fracture, initiated the final fracture of the specimen, which was largely by ductile micro-void coalescence (MVC), but did include some brittle fisheye fractures. Each fisheye was surrounded by MVC. This corresponds to MF: Mixed fracture, wherein a hydrogen microfracture mechanism (i.e., that producing the fisheyes) competed with the ductile MVC fracture. The fisheyes were associated with alumina oxide inclusion, which indicated that these features would be less for a cleaner steel. There was no subcritical crack growth. There was essentially no influence of hydrogen on ductility for the hydrogen conditions studied. At applied stress amplitudes above the threshold stress, fatigue initiation, for low cycle fatigue, occurred at a lower number of cycles with increasing hydrogen fugacity and increasing stress amplitude. This was caused by a decrease in the fatigue initiation period, and by an increase in the crack growth rate. In the presence of hydrogen, there was flat transgranular fracture with vague striations with some intergranular fracture at lower stresses. Mechanical overload occurred when the fatigue crack reached the critical length. There was no significant influence of hydrogen on the final fracture.

Description: Corrosion is among the most common forms of materials degradation which poses enormous challenges across industries, and can even impact our health [...]