Studies of corrosion and stress corrosion cracking behaviour of x80 pipeline steel

Bibliography: p. 174-186Many pages are in colour.Corrosion and stress corrosion cracking (SCC) have been identified as essential threats to the integrity of pipelines. A research program was developed to investigate the fundamentals of corrosion and SCC of the high-strength X80 pipeline steel under conditions relevant to pipelines operation. The microstructure of X80 steel consists of polygonal ferrite and bainitic ferrite matrix, with martensite/austenite constituents distributing along grain boundaries. The inclusions existing in the steel include those enriched with Si, A b O3, Si-ferric carbide and Al-Mg-Ca-O mixture, respectively. The majority of inclusions are Si-enriched. Upon hydrogen-charging, cracks can initiate in the steel in the absence of external stress, which are primarily associated with the Si- and Al2O3-enriched inclusions. The diffusivity of hydrogen in X 80 steel at room temperature is 2.0x 10-11 m2/s, and the estimated hydrogen trapping density in the steel is as high as 3.33 x l027 /m3. Moreover, the effects of welding on corrosion and SCC of X80 steel were investigated. There is the smallest hydrogen permeation rate and hydrogen diffusive coefficient, but the highest hydrogen trapping density at heat-affected zone (HAZ), while the base steel has the highest hydrogen diffusivity and a low hydrogen concentration as well as the lowest hydrogen trapping density. These results are attributed to the typical microstructures of the individual zones of welded X80 steel. In near-neutral pH environn1ent, SCC of X80 steel is attributed to a synergistic effect of hydrogen and stress on the local dissolution of steel at the crack tip. The hydrogen and stress enhanced anodic dissolution of steel was characterized by an in-house photo-electrochemical measurement system, where the photocurrent density was measured on the steel. It is determined that, of the total photocurrent density measured at the crack tip of the charged steel, the photo-induced current density, hydrogen-enhanced dissolution current density and photo-oxidative current density of hydrogen atoms contribute approximately 65.8%, 12.8% and 21 .4%, respectively. A higher photocurrent density is measured at crack tip than the region ahead of the crack for both the charged and uncharged electrodes, demonstrating the high electrochemical activity at the crack tip, and the accumulation of hydrogen atoms locally. The passivity and pitting corrosion behaviour of the steel in a high pH carbonatebicarbonate solution were investigated. It is found that a stable passivity can be established in the absence and presence of chloride ions in the solution. Hydrogencharging does not alter the transpassive potential, but increases the passive current density. When chloride ions are introduced, pitting corrosion will initiate. Photo illumination can enhance the activity of the steel electrode, resulting in an increase of photo-induced anodic current density. Furthermore, the pitting corrosion of the steel under sand bed in COrcontaining systems was characterized and "visualized" in-situ by a localized electrochemical impedance spectroscopy technique. Moreover, the pitting growth rate was measured by monitoring the local current density through a scanning vibrating electrode. A galvanic effect model was proposed to illustrate the initiation and growth of corrosion pits. It also confirmed that the increases of the chloride concentration and flow velocity of the solution favored the growth of corrosion pits

A Century-Long Ex-Post Evaluation of a Countermeasure for a Serious Pollution Problem in Japan

Current environmental literature provides insufficient information and analysis on how today’s environmental state was shaped by countermeasures to pollution taken in the last century, which could be characterized as a century of environmental degradation. Such a look back is crucial to better understand and predict how policy and countermeasure choices today may shape the world in the future. Following this line of reasoning, the present work conducted a post audit on the long-term consequence of a countermeasure against a major heavy metal pollution case caused by the operation of the Ashio Copper Mine in Japan. It examined this issue from both environmental and societal perspectives by document analysis, field investigation on the heavy metal concentration in the soils of a heavy mental catchment area and questionnaire survey on the public knowledge with regard to the copper mining contamination case as well. It shed new light on how environment may evolve via the interaction with human activities by identifying drivers behind major changes. It also revealed a gap between the reality and the public perception towards the consequence of the copper contamination. Such insights will deepen the discussion on what is sustainability and motivate further study to pursue sustainable development

Convergence rate of overlapping domain decomposition methods for the Rudin-Osher-Fatemi model based on a dual formulation

This paper is concerned with overlapping domain decomposition methods (DDMs), based on successive subspace correction (SSC) and parallel subspace correction (PSC), for the Rudin--Osher--Fatemi (ROF) model in image restoration. In contrast to recent attempts, we work with a dual formulation of the ROF model, where one significant difficulty resides in the decomposition of the global constraint of the dual variable. We introduce a stable “unity decomposition” using a set of “partition of unity functions,” which naturally leads to overlapping DDMs based on the dual formulation. The main objective of this paper is to rigorously analyze the convergence of the SSC and PSC algorithms and derive the rate of convergence $O(n^{-1/2})$, where $n$ is the number of iterations. Moreover, we characterize the explicit dependence of the convergence rate on the subdomain overlapping size and other important parameters. To the best of our knowledge, such a convergence rate has not yet been claimed for domain decomposition related algorithms for the ROF model.Published versio

Transmission and refractive index sensing based on Fano resonance in MIM waveguide-coupled trapezoid cavity

A metal–insulator–metal (MIM) waveguide-coupled trapezoid cavity is presented, and the transmission properties are investigated by finite-element method. Results show that an asymmetric Fano profile emerged in the transmission spectrum, which was caused by the asymmetrical break of the MIM waveguide-coupled trapezoid cavity system. A refractive index sensitivity, Q-factor and FOM of approximately 750nm/RIU, 68.3 and 65.2 were measured based on the Fano resonance. The effect of the structural parameters on the transmission properties is also investigated. The results provide a new possibility for designing high-performance plasmonic devices

N-Amidation of Nitrogen-Containing Heterocyclic Compounds: Can We Apply Enzymatic Tools?

Amide bond is often seen in value-added nitrogen-containing heterocyclic compounds, which can present promising chemical, biological, and pharmaceutical significance. However, current synthesis methods in the preparation of amide-containing N-heterocyclic compounds have low specificity (large amount of by-products) and efficiency. In this study, we focused on reviewing the feasible enzymes (nitrogen acetyltransferase, carboxylic acid reductase, lipase, and cutinase) for the amidation of N-heterocyclic compounds; summarizing their advantages and weakness in the specific applications; and further predicting candidate enzymes through in silico structure-functional analysis. For future prospects, current enzymes demand further engineering and improving for practical industrial applications and more enzymatic tools need to be explored and developed for a broader range of N-heterocyclic substrates

N-Amidation of Nitrogen-Containing Heterocyclic Compounds: Can We Apply Enzymatic Tools?

Amide bond is often seen in value-added nitrogen-containing heterocyclic compounds, which can present promising chemical, biological, and pharmaceutical significance. However, current synthesis methods in the preparation of amide-containing N-heterocyclic compounds have low specificity (large amount of by-products) and efficiency. In this study, we focused on reviewing the feasible enzymes (nitrogen acetyltransferase, carboxylic acid reductase, lipase, and cutinase) for the amidation of N-heterocyclic compounds; summarizing their advantages and weakness in the specific applications; and further predicting candidate enzymes through in silico structure-functional analysis. For future prospects, current enzymes demand further engineering and improving for practical industrial applications and more enzymatic tools need to be explored and developed for a broader range of N-heterocyclic substrates