The Interaction of Biofoulants and Calcareous Deposits on Corrosion Performance of Q235 in Seawater

Degradation and lifetime prediction of plastics in subsea and offshore infrastructures

Engineering and civil developments have relied on synthetic polymers and plastics (including polyethylene, polypropylene, polyamide, etc.) for decades, especially where their durability protects engineering structures against corrosion and other environmental stimuli. Offshore oil and gas infrastructure and renewable energy platforms are typical examples, where these plastics (100,000 s of metric tonnes worldwide) are used primarily as functional material to protect metallic flowlines and subsea equipment against seawater corrosion. Despite this, the current literature on polymers is limited to sea-surface environments, and a model for subsea degradation of plastics is needed. In this review, we collate relevant studies on the degradation of plastics and synthetic polymers in marine environments to gain insight into the fate of these materials when left in subsea conditions. We present a new mathematical model that accounts for various physicochemical changes in the oceanic environment as a function of depth to predict the lifespan of synthetic plastics and the possible formation of plastic debris, e.g., microplastics. We found that the degradation rate of the plastics decreases significantly as a function of water depth and can be estimated quantitatively by the mathematical model that accounts for the effect (and sensitivity) of geographical location, temperature, light intensity, hydrostatic pressure, and marine sediments. For instance, it takes a subsea polyethylene coating about 800 years to degrade on ocean floor (as opposed to <400 years in shallow coastal waters), generating 1000s of particles per g of degradation under certain conditions. Our results demonstrate how suspended sediments in the water column are likely to compensate for the decreasing depth-corrected degradation rates, resulting in surface abrasion and the formation of plastic debris such as microplastics. This review, and the complementing data, will be significant for the environmental impact assessment of plastics in subsea infrastructures. Moreover, as these infrastructures reach the end of their service life, the management of the plastic components becomes of great interest to environmental regulators, industry, and the community, considering the known sizeable impacts of plastics on global biogeochemical cycles.

From laboratory tests to field trials: a review of cathodic protection and microbially influenced corrosion

Cathodic protection (CP), an electrochemical method for managing corrosion, is widely used in many industries in both marine and buried environments. However, literature surrounding cathodic protection and its ability to prevent microbially influenced corrosion (MIC) is mixed. This review describes the mechanics of CP, how CP may influence MIC, and collates and summarises tests on CP and MIC reported in literature. The aim of the review is to identify any trends and knowledge gaps requiring further study. While the outcomes of CP testing are generally mixed, some trends can be seen and, overall, MIC is detrimental to the protective effects of CP, with CP being less effective when used according to current international standards. Tests conducted in the field or with mix communities of microbes showed that CP could be effective at preventing MIC, while tests with sulfate-reducing bacteria generally proved CP to be highly ineffective. It was commonly seen that the effectiveness of CP can be improved by increasing polarization, to potentials as low as -1000 mV (Ag/AgCl). However, a balance does need to be met via careful monitoring to ensure negative side effects of over protection do not become a major problem.