Volume 38, Issue 3

Nuclear steam generators (NSGs) are key components of nuclear power plants (NPPs) since their reliability affects the overall plant performance. Corrosion control of steam generators under operation and during plant outages is attained by proper design, adequate material selection and control of water chemistry in the entire secondary cooling circuit. This article reviews the types of steam generators, the materials used for their construction (with a special focus on tubing alloys), the corrosion processes that may occur under operation and the strategies to preserve steam generators and other components of the secondary cooling system from corrosion during plant outages.

Buried pipelines are essential for the delivery of potable water around the world. A key cause of leaks and bursts in these pipelines, particularly those fabricated from carbon steel, is the accelerated localized corrosion due to the influence of microbes in soil. Here, studies conducted on soil corrosion of pipelines' external surface both in the field and the laboratory are reviewed with a focus on scientific approaches, particularly the techniques used to determine the action and contribution of microbiologically influenced corrosion (MIC). The review encompasses water pipeline studies, as well as oil and gas pipeline studies with similar corrosion mechanisms but significantly higher risks of failure. Significant insight into how MIC progresses in soil has been obtained. However, several limitations to the current breadth of studies are raised. Suggestions based on techniques from other fields of work are made for future research, including the need for a more systematic methodology for such studies.

A nickel-rich conductive anti-corrosive coating (CACC) was fabricated to improve the corrosion resistance of the carbon steel grounding materials. The coating was tested using surface contact resistance measurement, electrochemical impedance spectroscopy (EIS) and surface characterization. The results indicate that the increase of the nickel powder content in the coating induces its electrical conductivity enhancement; the surface contact resistance is as low as 0.05 Ω/cm 2 when the nickel powder content is 20%. The EIS data show that the anti-corrosive performance of the coating with 20% nickel powder content in three soil saline-alkali solutions (mild, moderate and severe) is higher than that with 40% nickel powder content, and the impedance of the coating decreases with the increase of the salt concentration. It is detected that 20% nickel powder content can achieve a good balance between low surface contact resistance and high corrosion resistance of the coating.

Microstructural changes that result in relevant improvements in mechanical properties and electrochemical behavior can be induced using different sintering conditions of ASTM F75 cobalt alloys during their processing using powder metallurgy technique. It has been observed that the increase in carbon and nitrogen content improves corrosion resistance and mechanical properties as long as the precipitation of carbides and nitrides is avoided, thanks to the use of rapid cooling in water after the sintering stage. In addition, the reduction of the particle size of the powder improves hardness and resistance to corrosion in both acid medium with chlorides and phosphate-buffered medium that simulates the physiological conditions for its use as a biomaterial. These results lead to increased knowledge of the role of carbon and nitrogen content in the behavior displayed by the different alloys studied.

The wastewater of petroleum refineries consists of various corrosive pollutants that are harmful not only for human and living organisms but also for the equipment and materials exposed to it. The galvanic corrosion of carbon steel in MgCl 2 solution as a pollutant in petroleum refinery wastewater was studied under concentration cell formation. The influence of different operating parameters on the galvanic corrosion established by concentration cell was studied, and the concept of concentration cell corrosion was examined and discussed versus experimental results. The effects of some operating conditions on the galvanic behavior, such as the concentration of MgCl 2 (0–2500 ppm) and solution flow velocity (150–1000 rpm), on corrosion rate, corrosion potentials, and corrosion current were investigated. New findings regarding the effect of corrosive substance concentration and the hydrodynamics on the corrosion rate of each electrode and the galvanic current were reported. It was found that the corrosion rate of carbon steel in both cell poles increases with increasing MgCl 2 concentration in both free and galvanic corrosion. Increasing MgCl 2 concentration also led to an increase in the galvanic currents and the corrosion rate of the two electrodes. The flow velocity in either cell terminal considerably influences the potentials, corrosion rates of both electrodes, and the galvanic current passing in the cell. A high flow velocity in the compartment with the more negative potential caused polarity reversal on some occasions.