Research on the stress corrosion and cathodic protection of API X80 steel under AC stray current interference

Purpose The corrosion of buried steel pipelines is becoming more serious because of stress corrosion, stray current corrosion and other reasons. This paper aims to study the various alternating current (AC) interference densities on the stress corrosion cracking behaviors of X80 steel samples under cathodic protection (CP) in the simulated soil electrolyte environment by using an electrochemical method. Design/methodology/approach The change of corrosion rate and surface morphology of the X80 steel samples at various AC current densities from 0 to 150 A/m2 or CP potential between −750 and −1,200 mV in the soil-simulating environment was revealed by the electrochemical methods and slow strain rate testing methods. Findings The results revealed that with the increase of interference density, the corrosion potential of the X80 steel samples shifted to the negative side, and the corrosion pitting was observed on the surface of the sample, this may cause a danger of energy leak. Moreover, the corrosion rate was found to follow a corresponding change with the stress–strain curve. Besides, with the introduction of the CP system, the corrosion rate of the X80 steel working electrode decreased at a low cathodic potential, while showed an opposite behavior at high cathodic potential. In this study, the correlation between AC stray current, cathodic potential and stress was established, which is beneficial to the protection of oil and gas pipeline. Originality/value Investigation results are of benefit to provide a new CP strategy under the interference of AC stray current corrosion and stress corrosion to reduce the corrosion rate of buried pipelines and improve the safety of pipeline transportation.

Electrochemical redox treatment of denitrification in coastal secondary effluent using Ti/IrO2 anode

In northern coastal industrial park, inlet of the wastewater treatment plant (WWTP) had the characteristics of low carbon source and high chloride ion concentration, which resulted in its poor biodegradability. In this case, the experiment explored an electrochemistral method to remove nitrogen. Cathodic potential, Ti/IrO2 was confirmed as the anode and − 1.6V was taken as the potential in order to remove nitrate-N. The findings include: when the initial chloride ion was 2000 and 3000 mg/L, the effect on the removal difference of nitrogen was slight. When the electrolysis time was 60 min, ammonia-N was removed completely, nitrite-N concentration kept 1mg/L approximately. The ammonia-N removal efficiency went up with the increasing cathodic potential, and was completely removed in different water samples, but nitrate-N removal showed an opposite result. The production amount of nitrite-N was the least at -1.6V. As the pH increased, ammonia-N and nitrate-N’s removal efficiency went up first and then down, the removal effect was the best at pH being 9, Nitrite-N was less influenced by pH. After optimizing the raw water sample, Nitrate-N and TN removal efficiency were significantly increased, but the nitrite-N almost kept constant.

Effect of Applied Cathodic Potential on Friction and Wear Behavior of CoCrMo Alloy in NaCl Solution

Most of the reported work on the effect of applied potential on tribocorrosion or corrosive wear of metallic alloys in a corrosive environment were conducted at anodic potentials. Limited tests have been conducted at cathodic potentials for comparison purposes or to derive the pure mechanical wear component in tribocorrosion. This work investigated the effect of cathodic potential on the friction and wear behaviour of an important biomedical alloy, CoCrMo, sliding against an Al2O3 slider in 0.9% NaCl solution at 37 °C. High friction was found at cathodic potentials close to the open circuit potential, where mechanical wear played a predominant role in material removal. At potentials more cathodic than the hydrogen charging potential, low friction and low wear were observed. The coefficient of friction (COF) and total material loss decreased with increasing cathodic potential, such that at −1000 mV (saturated calomel electrode, SCE), extremely low COF values, as low as 0.02, and negligible material loss were obtained. Such reductions in friction and wear at increasing cathodic potentials were accompanied with the formation of parallel lines in the sliding track and were gradually diminished with increasing applied contact load. It is believed that hydrogen charging and hydrogen segregated layer formation at the surface are responsible for such a phenomenon. It can also be concluded that it is difficult to derive the pure mechanical wear component in tribocorrosion by simply conducting a test at an arbitrary cathodic potential.

Parameters influencing the development of highly conductive and efficient biofilm during microbial electrosynthesis: the importance of applied potential and inorganic carbon source

Cathode-driven applications of bio-electrochemical systems (BESs) have the potential to transform CO2 into value-added chemicals using microorganisms. However, their commercialisation is limited as biocathodes in BESs are characterised by slow start-up and low efficiency. Understanding biosynthesis pathways, electron transfer mechanisms and the effect of operational variables on microbial electrosynthesis (MES) is of fundamental importance to advance these applications of a system that has the capacity to convert CO2 to organics and is potentially sustainable. In this work, we demonstrate that cathodic potential and inorganic carbon source are keys for the development of a dense and conductive biofilm that ensures high efficiency in the overall system. Applying the cathodic potential of −1.0 V vs. Ag/AgCl and providing only gaseous CO2 in our system, a dense biofilm dominated by Acetobacterium (ca. 50% of biofilm) was formed. The superior biofilm density was significantly correlated with a higher production yield of organic chemicals, particularly acetate. Together, a significant decrease in the H2 evolution overpotential (by 200 mV) and abundant nifH genes within the biofilm were observed. This can only be mechanistically explained if intracellular hydrogen production with direct electron uptake from the cathode via nitrogenase within bacterial cells is occurring in addition to the commonly observed extracellular H2 production. Indeed, the enzymatic activity within the biofilm accelerated the electron transfer. This was evidenced by an increase in the coulombic efficiency (ca. 69%) and a 10-fold decrease in the charge transfer resistance. This is the first report of such a significant decrease in the charge resistance via the development of a highly conductive biofilm during MES. The results highlight the fundamental importance of maintaining a highly active autotrophic Acetobacterium population through feeding CO2 in gaseous form, which its dominance in the biocathode leads to a higher efficiency of the system.