Investigation of corrosion resistance property of cold deformed (bended) duplex and super duplex stainless steel tubes

Master's thesis in Environmental technologyCold deformation (bending) of stainless steel tubes is one of the efficient and cost effective methods to gain the required shapes of the tube that can be useful for different practical applications. Different mechanical properties can change after the plastic deformation of the material. The purpose of this study is to investigate the corrosion (basically pitting) resistant property of cold deformed Duplex and Super Duplex materials namely UNS S32205 and UNS S32750 respectively. The bended tubes 2.5ND and 5ND were studied and compared with the straight tubes of same materials. Accelerated coupon testing (ASTM G48) and electrochemical method (ASTM G61) were followed to accomplish the objective of this study. ASTM G48 Test method was performed to know about the pitting corrosion behaviour of material at different temperatures. Weight loss per unit area was measured after exposure at acidic environment at different temperature for different exposure duration. ASTM G61 method was adopted to determine the pitting potential for each specimens and also to find the crevice/pitting susceptibility for each specimen. The results show that the corrosion resistant property of material decreases with temperature. The pitting and crevice resistant properties of cold deformed duplex and super duplex tubes were found to be similar to that of straight tubes. No specific patterns were observed in weight loss of straight and bended parts. The specimens’ weight loss per unit area was found to be under the acceptance criteria according to NORSOK Standard MDS-630. Similarly, the pitting potential of straight and bended parts for both duplex and super duplex were found to be in the similar range of about 1 V. The hardness of bended material was observed to be higher than straight one but the hardness decreased slightly after accelerated coupon testing

The Effects of Acidic, Alkaline, and Neutral Anolytes on Electrochemical Seawater Deoxygenation

Electrochemical deoxygenation of seawater has advantages over available chemical and physical methods. For seawater deoxygenation, acidic, neutral, or alkaline anolytes can be used. The effects of acidic, alkaline, and neutral buffered and non-buffered anolytes were studied in two compartment deoxygenation cells. The pH, conductivity, H2O2 production, and current were measured throughout the experiments. The optimum applied potentials for oxygen reduction were between 1.9 V⁻2.2 V, giving water as product; reducing the applied potential also resulted in the formation of H2O2. Analysis after the experiments using a scanning electron microscope with electron-dispersive X-ray spectroscopy showed that both the silver mesh and the cation exchange membrane remained stable during the experiments. The use of alkaline anolytes resulted in the maximum oxygen removal with minimal side reactions in the cell

Nitrogen doped Carbon Nanotubes as Electrocatalyst for Oxygen Reduction Reaction

The oxygen reduction reaction on nitrogen doped multiwalled carbon nanotubes (N-MCNTs) is studied for its application for deoxygenation of seawater. N-MCNTs were synthesized using commercial MCNTs and polyaniline as nitrogen precursor and annealing at a high temperature. The ORR was studied on N-MCNTs in 0.5 M sodium chloride solution using a rotating disk electrode, and physical characterization of the electrocatalysts was performed using X-ray diffraction, mass spectroscopy and transmission electron microscope techniques. The material showed high activity for the ORR in the chloride electrolyte. The onset potential for N-MCNTs was 0.94 V vs RHE. Koutecky-Levich analysis showed that the electrons transfer mainly followed the four-electron pathway, and the electrocatalyst showed good stability during a 15-h stability test.Peer reviewe