Synergistic inhibitory effects of free nitrous acid and imidazoline derivative on metal corrosion in a simulated water injection system

© 2020 Elsevier Ltd To maintain the integrity of the internal surfaces of the pipelines in oil and gas industry, chemicals, including corrosion inhibitors and biocides, are commonly dosed to prevent corrosion. Imidazoline and its derivatives are widely used corrosion inhibitors for the protection of oil pipelines, which have been shown effective in reducing general corrosion. As an effective biocide, free nitrous acid (FNA) is suitable to inhibit microbially influenced corrosion, induced by for example sulfate-reducing bacteria. In this paper, we hypothesize that the continuous addition of imidazoline and intermittent dosing of FNA, when used in combination, would yield effective control of both general and pitting corrosions. As a typical imidazoline derivative, N-b-hydroxyethyl oleyl imidazoline (HEI-17) was applied in conjunction with intermittent dosing of FNA in the experimental system, with the results compared with two control systems, one receiving HEI-17 only, and one receiving no chemical dosing. The corrosion properties were monitored with open circuit potential, electrochemical impedance spectroscopy, linear polarization resistance, 3D optical profiling, and weight-loss measurement. Following a single dose of FNA, the general corrosion rates in the experimental reactor dropped up to 50% of that in the reactor receiving continuous HEI-17 dosing (0.27 ± 0.04 vs. 0.54 ± 0.08 mm/y), but gradually recovered to 93.4% of that in 2.5 months. After the FNA treatment, the pitting corrosion was decreased by 64.6% compared with continuous HEI-17 dosing reactor for a month from measuring the cumulative distribution of the pitting depth. HEI-17 treatment alone showed moderate pitting corrosion inhibition effect (approx. 27%), and the FNA treatment inhibited the formation of deep pits effectively. The combined application of HEI-17 and FNA has shown synergistic effects and high efficiency in mitigating MIC in the simulated water injection system. This treatment strategy has strong potential to be applied in the practical oilfield operations

Decreasing microbially influenced metal corrosion using free nitrous acid in a simulated water injection system

Microbially influenced corrosion (MIC) is the main cause of metal corrosion in anoxic environments. Biocides are often dosed to the corrosive media to inhibit and kill the microbes which cause MIC. In this study, intermittent dosages of free nitrous acid (FNA), which was previously found to be a biocide, were applied to a simulated water injection system containing carbon steel coupons with mature biofilm, to study the effect of FNA on mitigation of metal corrosion. In each treatment, 0.49 mg-N/L FNA was dosed using 200 mg-N/L nitrite at pH 6 for 24\ua0h. The corrosion properties were monitored by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), 3D optical profiling, and direct weight measurement. The biofilm viability was monitored by measuring cellular ATP level. The general corrosion rate (calculated by weight-loss measurement) was decreased by up to 31%, which was supported by LPR tests and reduced ATP levels of the corrosion-inducing biofilm. The 3D optical profiling results showed that FNA decreased the average pitting corrosion rate by 59%, with 2 intermittent treatments and 82-day interval over 304 days. Intermittent dosing of FNA has strong potential to be an effective and efficient strategy for controlling MIC in oil recovery infrastructure

Evaluation of Mechanical Properties of Reinforced Poplar Laminated Veneer Lumber

Three types of reinforcement materials, a carbon fiber-reinforced polymer (CFRP) sheet, a glass fiber-reinforced polymer (GFRP) mesh, and a composite of the CFRP sheet and GFRP mesh, were used to reinforce poplar laminated veneer lumber (LVL), and the multi-step hot-pressing method was also applied. The mechanical properties, i.e., modulus of rupture (MOR), modulus of elasticity (MOE), and horizontal shear strength (HSS), of the reinforced LVL were investigated, as well as the effects of lay-up location of the CFRP sheet/GFRP mesh composite. The results indicated that applying the multi-step hot-pressing method and incorporating the CFRP sheet, GFRP mesh, and the CFRP sheet/GFRP mesh composite noticeably improved the MOR and MOE under horizontal and vertical loadings. Only the multi-step hot-pressing method was able to greatly improve the HSS of reinforced LVL under both loading modes. The improved effect of the three kinds of reinforcing materials on the mechanical properties was ordered as follows: CFRP sheet/GFRP mesh composite > CFRP sheet > GFRP mesh. Locating the CFRP sheet/GFRP mesh composite closer to the surface veneer layer yielded the best mechanical properties for the reinforced poplar LVL

Development of microbially influenced corrosion on carbon steel in a simulated water injection system

Microbially influenced corrosion (MIC) on internal pipeline surfaces has become a severe problem during the water injection process in secondary oil recovery. The formation of a biofilm, normally dominated by sulfate-reducing bacteria (SRB), is believed to be the critical step of the MIC process. A continuously fed biofilm simulating the water injection process was operated to investigate the influence of biofilm development on MIC behavior in the early phase of corrosion development. The development of the corrosion product film and biofilm was monitored for 5 months with electrochemical impedance spectroscopy, linear polarization resistance, scanning electron microscopy, 3D optical profiling, and direct weight measurement. MIC development was found to comprise three phases: initialization, transition, and stabilization. The initialization phase involved the formation of the corrosion product layer and the initial attachment of the sessile microbes on metal surface. In the transition phase, the MIC process gradually shifted from charge-transfer-controlled reaction to diffusion-controlled reaction. The stabilization phase featured mature and compact biofilm on the metal surface, and the general corrosion rate (CR) decreased due to the diffusional effect, while the pitting CR was enhanced at a lower carbon source level, which supported the mechanism of direct electron uptake from the metal surface by SRB

Free ammonia shock treatment eliminates nitrite-oxidizing bacterial activity for mainstream biofilm nitritation process

Nitritation (NH → NO ) is a critical step to provide nitrite for the followed anammox in a two-stage nitrogen removal system. In the mainstream line of wastewater treatment plants, the nitritation has not been applied to date, because of the significant difficulties in the suppression of nitrite-oxidizing bacteria (NOB), especially in biofilm systems. This study aims to systematically assess the effect of free ammonia (FA) shock treatment on the mainstream biofilm nitritation process through an integration of laboratory reactor operation, microbial community analysis, incubation tests, and kinetic model evaluation. In a laboratory nitrifying moving bed biofilm reactor (MBBR) fed with domestic-strength synthetic wastewater, it was shown that with the exposure of carrier-biofilms containing ammonia-oxidizing bacteria (AOB) Nitrosomonas and NOB Nitrospira to a high-level of FA (1068 mg NH-N/L) over two days, a much higher residual AOB level was retained in the biofilm in comparison to NOB. The higher residual AOB on biofilm led to much faster recovery of AOB over NOB after the shock treatment, when normal operation resumed with the dissolved oxygen (DO) controlled at around 0.2 mg/L. The faster recovery of AOB than NOB subsequently gave rise to a stable, high nitrite accumulation ratio (nearly 100%) over a long period (two months). Collectively, these results suggest that FA shock treatment in conjunction with limited DO control is effective in eliminating NOB for mainstream biofilm nitritation process. The chemical cost would be marginal given the intermittent nature of the FA shock strategy and the readily available ammonium in the anaerobic sludge digestion liquor

Corrosion of reinforcing steel in concrete sewers

Hydrogen sulfide is a controlling factor for concrete corrosion in sewers, although its impact on sewer rebar corrosion has not been investigated to date. This study determined the corrosion mechanism of rebar in sewers by elucidating the roles of chloride ions, apart from the effects of hydrogen sulfide and biogenic sulfuric acid. The nature and distribution of rusts at the steel/concrete interface were delineated using the advanced mineral analytical techniques, including mineral liberation analysis and micro X-ray diffraction which is the first-ever use in such studies. The corrosion products were found to be mainly iron oxides or oxy-hydroxides. HS and biogenic sulfuric acid did not directly participate in the product formation of steel partly covered by concrete or directly exposed to sewer atmosphere. Instead, chloride ions played an important role in initiating steel corrosion in sewers, supported by a thin chloride-enriched layer at the steel/rust interface. Away from the chloride-enriched layer, iron oxides accumulated on both sides of the mill-scale to form a corrosion layer and corrosion-filled paste respectively. The corrosion layer around rebar circumference was non-uniform and the rust thickness with respect to polar coordinates followed a Gaussian model. These findings support predictions of sewer service lifetime and developments of corrosion prevention strategies

Specific surface area of titanium dioxide (TiO2) particles influences cyto- and photo-toxicity

The aim of this study is to examine how different specific surface areas of similar-sized titanium dioxide (TiO2) particles could influence both cytotoxicity and phototoxicity. TiO2 particles of different specific surface areas were compared for their toxic effects on RAW264.7 cells in the absence and presence of UV light. From the results, TiO2 particles with larger specific surface area were found to induce higher cyto- (UV absent) and photo-toxicity (UV activated) to cells after 24 h incubation. The observed cytotoxicity from TiO2 particles with larger surface area could be explained from their interactions with biomolecules. Upon photoactivation, a larger number of hydroxyl radicals were detected from TiO2 particles with larger surface area, again suggesting a surface area dependent phototoxic effect. On the other hand, pre-adsorbing TiO2 particles with extracellular proteins were found to decrease toxicity effects.Accepted versio

Triboelectric Nanogenerator Driven Self-Powered Photoelectrochemical Water Splitting Based on Hematite Photoanodes

Hematite is one of the most promising photoanodes for photoelectrochemical (PEC) solar water splitting. However, due to the low conduction band position for water reduction, an external bias is necessarily required with the consumption of extra power. In this work, a titanium modified hematite (Ti-Fe₂O₃) photoanode-based self-powered PEC water splitting system in tandem with a rotatory disc-shaped triboelectric nanogenerator (RD-TENG) has been developed. It is a fantastic strategy to effectively drive the hematite-based PEC water splitting by using the environmental mechanical energy through a TENG. When the rotation speed is 65 rpm (water flowing rate ∼0.61 m/s), the peak current reaches to 0.12 mA under illumination contrast to that in the dark with almost zero. As for 80 rpm, the peak currents are 0.17 and 0.33 mA in the dark or under illumination, respectively, indicating the simultaneous occurrence of electrolysis and PEC water splitting. When higher than 120 rpm, the peak current in the dark is nearly equal to that under illumination, which can be attributed to the high enough peak voltage for direct electrolysis of water. Such a self-powered PEC water splitting system provides an alternative strategy that enables to convert both solar and mechanical energies into chemical energies

Triboelectric Nanogenerator Driven Self-Powered Photoelectrochemical Water Splitting Based on Hematite Photoanodes

Hematite is one of the most promising photoanodes for photoelectrochemical (PEC) solar water splitting. However, due to the low conduction band position for water reduction, an external bias is necessarily required with the consumption of extra power. In this work, a titanium modified hematite (Ti-Fe₂O₃) photoanode-based self-powered PEC water splitting system in tandem with a rotatory disc-shaped triboelectric nanogenerator (RD-TENG) has been developed. It is a fantastic strategy to effectively drive the hematite-based PEC water splitting by using the environmental mechanical energy through a TENG. When the rotation speed is 65 rpm (water flowing rate ∼0.61 m/s), the peak current reaches to 0.12 mA under illumination contrast to that in the dark with almost zero. As for 80 rpm, the peak currents are 0.17 and 0.33 mA in the dark or under illumination, respectively, indicating the simultaneous occurrence of electrolysis and PEC water splitting. When higher than 120 rpm, the peak current in the dark is nearly equal to that under illumination, which can be attributed to the high enough peak voltage for direct electrolysis of water. Such a self-powered PEC water splitting system provides an alternative strategy that enables to convert both solar and mechanical energies into chemical energies