Electrochemical Testing for Pitting Corrosion Above Ambient Temperatures Using the Syringe Cell

The syringe cell method has been further developed to evaluate the temperature dependence of pitting corrosion in passive alloys having critical pitting temperature above ambient without artifacts associated with crevice corrosion. The pitting potential of commercially available duplex stainless steel type 2205 was measured at different temperatures by using a hot plate to heat the specimen. Breakdown potentials decreased by about 1 V at test temperatures above 50 °C. The critical pitting temperature (CPT) of the alloy was determined to be between 54 °C and 59 °C by scanning the temperature of the specimen surface during a constant potential hold. In all experiments, pits were observed in the area defined by the electrolyte droplet in contact with the specimen surface. The CPT of the alloy determined using a more conventional approach mentioned in ASTM Standard G48 Method C was 55 °C.

CO2 Corrosion of Carbon Steel: The Synergy of Chloride Ion Concentration and Temperature on Metal Penetration

This paper investigates the synergy of chloride ion concentration and temperature on the general and pitting corrosion of carbon steel in CO2-saturated environments. Experiments were conducted over 168 h in different concentrations of NaCl brines (1 wt%, 3.5 wt%, and 10 wt%) and temperatures (30°C, 50°C, and 80°C) with the aim of elucidating the combined effect of changes in chloride ion concentration and temperature on overall metal degradation, taking into consideration general and pitting corrosion. This also includes a correlation with the formation and properties of FeCO3 corrosion products. Linear polarization resistance was implemented to monitor the electrochemical responses. Corrosion product characteristics and morphologies were studied through a combination of scanning electron microscopy and x-ray diffraction. Pitting corrosion evaluation was conducted through the application of 3D surface profilometry to study pit geometries such as the depth and diameter. The results show that general and pitting corrosion are strongly correlated to the synergistic effects of changing chloride ion concentration and temperature in carbon steel as a result of their combined influence on ferrite (Fe) dissolution and FeCO3 formation. This represents a paradigm shift from the already established mechanisms on chloride ion and temperature effects on passive alloys such as stainless steel. Increasing chloride ion concentration and temperature up to 10 wt% NaCl and 50°C to 80°C, respectively, is observed to increase the rate of Fe dissolution and formation of semiprotective FeCO3 corrosion products, leading to the increased manifestation and severity of pitting corrosion. The results also show that a “threshold chloride concentration” exists at 30°C, above which there is no significant increase in corrosion rate. However, such “threshold effects” were not observed at higher temperatures evaluated in the range of chloride concentration considered in this study.

Factors in the Selection of Container Materials for the Disposal of HLW/SF

ABSTRACTThe container is the only absolute barrier in the multi-barrier system that forms the basis of all nuclear waste disposal strategies. The selection of an appropriate container material is therefore of utmost importance. Some of the factors that underlay the choice of container material are discussed, ranging from the properties of the near-field and host rock to the desired or expected containment period.There has been a trend towards the specification of container materials that will corrode actively under repository conditions, such as copper and carbon steel. Passive materials, such as titanium and nickel alloys and the various stainless steels, have found less acceptance and the reasons for this emphasis on active materials are also discussed.In selecting an appropriate container material, it is essential to understand the nature of the corrosive environment and how it evolves over time. The evolution of environmental conditions will also cause the corrosion behaviour of the container to change with time. For repositories in saturated environments, it will be argued that passive alloys can provide long container lifetimes without some of the disadvantages of some active materials such as gas generation and other adverse impacts on other barriers.Finally, areas of future development and areas requiring additional study will be discussed.

Electrochemical Grinding for Unclosed Internal Cylinder Surface

The electro discharge machining (EDM) process is widely applied to produces surfaces of difficult-to-machine materials that require some form of grinding or finishing operation. This is conducted so as to improve the surface texture and appearance of the component’s surface. However, it is also desirable to remove the white uppermost recast layer or damaged surface layer (produced by the EDM process) in order to improve the functional performance of the surface. The finishing of the surface by traditional manual methods, especially in the operation of small and long internal cylinder surface, is both tedious and time-consuming. A novel electrically conductive diamond mounted point electrochemical grinding (DMP-ECG) process is being developed for hard passive alloys unclosed internal cylinder surface grinding. The process mechanism of DMP-ECG is introduced; the influence parameters of the surface roughness, machining accuracy, and diamond tool wear are investigated experimentally for nickel-based super alloys materials. An application of the DMP-ECG to aircraft engine component is verified in term of the optimized process parameters.