High temperature oxidation of ultra-high purity Fe-Cr-Al model alloys

A field emission gun scanning electron microscope (FEGSEM), equipped with an EDX analysis system was used to investigate the oxidation behaviour of Fe-20Cr-5Al based ultra-high purity alloys, which were specifically prepared with controlled levels of Zr, Ti, Hf, La, Si, and Y additions. The oxidation temperature was up to 1200°C for 3000 hours. Numerous studies dedicated to this field have shown that impurities and additions strongly affect the oxidation/spallation behaviour in many different ways. In this pilot study, the effect of carefully controlled combinations of the added elements on α-alumina scale formation, growth and spallation have been examined. The model alloy which contained approx. 300-450 ppm Hf, Ti and Y behaved the best with respect to scale spallation, whereas, the alloy containing only 250 ppm of La spalled the most. Another interesting finding is that in the case of the alloys which contain Hf+Ti, Zr+Ti and Zr+Hf in addition to Y, the scale fractured/spalled in a cohesive manner, whereas in the case of the alloys containing Si +Y and La the scale spalled at the scale/metal interface (adhesive failure). Also a “sunflower” type oxide grain structure was observed in the spalled regions in the case of the commercial alloy YHfAl and the model alloys containing Zr+Hf, and Zr+Ti in addition to Y.In this paper the different oxidation behaviour of the alloys will be discussed, in order to shed light on the influence of the various selected combinations of additional elements

Laboratory study on efficiency of three calcium carbonate scale inhibitors in the presence of EOR chemicals

Chemical flooding has been widely used in the oil industry since the 1980s for enhanced oil recovery (EOR) process. Previous studies have shown that the effectiveness of calcium carbonate scale inhibitors is affected by many factors, such as water composition, system pressure, temperature, production rates, pH etc. The breakthrough of the EOR chemicals in the production well could also affect scale formation process and interfere with the scale treatment program as well. However, the studies on the impacts of injected EOR chemicals to scale inhibitor performances are very limited. This paper presents the comprehensive laboratory study on the impacts of the EOR chemicals on CaCO3 scale formation and prevention using static bottle and dynamic tube blocking methods. The EOR chemicals used in this study are a combination of surfactants and polymers. Three different types of inhibitors were evaluated: tri-phosphonate, penta-phosphonate, and polyacrylate based chemicals. Inhibition (%) from the bottle test and minimum effective dose (MED) based on the tube blocking method were determined for each inhibitor at 160 °F. Scale precipitates from the bottle tests were also characterized for morphology and polymorphs using environmental scanning electron (ESEM) and X-ray diffraction (XRD) techniques. Results suggest that the performance of scale inhibitors could be substantially affected by the EOR chemicals. In dynamic tube blocking tests, the MED values of inhibitors were increased roughly 10 times with the EOR chemicals. The static bottle tests showed considerable changes under the test conditions. The impact of EOR chemicals were also demonstrated by the remarkable ranges of crystal morphologies, changing from simple aragonite columns to nanorod, distorted spheroid, and flower-like superstructure in the presence of EOR chemicals and inhibitors. Keywords: Calcium carbonate, Scaling, Inhibitor, Chemical flooding, Enhanced oil recover