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ABSTRACT Ethanol (C2H5OH) is used as a gasoline additive, serving both as an octane enhancer and an oxygenate to promote complete combustion and reduce harmful emissions. The specifications and procedures for handling fuel ethanol have been described in a document published by the Renewable Fuels Association (RFA).1 The RFA-recommended standard for fuel ethanol is governed by ASTM D 4806.2 The ethanol quality specification under ASTM D 4806 is given in Table 1. ASTM D 4806 also restricts the type of denaturant to be natural gasoline, gasoline components, or unleaded gasoline. The purpose of the denaturant is to render the ethanol undrinkable. For this study, unleaded gasoline was used as the denaturant. Furthermore, ASTM D 4806 cites California and Federal ethanol requirements that limit the ethanol sulfur content to 10 ppm, benzene (C6H6) to 10 vol%, olefins (CnH2n) to 0.5 vol%, and aromatics to 1.7 vol%. Somewhat similar fuel ethanol standards exist in other countries with either more or less restricted water contents.3 It must be noted that the pHe is a measured value using the specific procedure described in ASTM D 6423.2 The value measured using this procedure is time-dependent and does not correspond to equilibrium or even a steady-state hydrogen activity. The RFA fuel ethanol guidelines1 further recommend the addition of one of a number of corrosion inhibitors. Among the nonaqueous environments, the stress corrosion cracking (SCC) of steel in anhydrous ammonia (NH3) and methanol (CH3OH) are well known. The
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Renewable > Biofuel > Ethanol (1.00)
ABSTRACT For economic reasons, the United Kingdom power industry is now operating its 500-MW coal-fired plants on a two-shift cycle in which the turbines are on-load for 16 h per day and off-load overnight and weekends. The concern with "two-shifting" is the impact on environment-assisted cracking of the associated transients in stress, water chemistry, and temperature.1 On-load, with well-controlled water chemistry, the condensate on the low-pressure turbines will be free of oxygen, with chloride and sulfate levels both up to about 300 ppb. Off-load, with the steam fully condensed, the condensate would tend to reflect the inlet water chemistry, with only a few ppb of chloride and of sulfate, but aerated unless there is nitrogen blanketing. The stress off-load would be zero. Ideally, to fully simulate two-shifting in laboratory testing, the combined influence of transient stress and water chemistry would be evaluated, but there are technical difficulties in synchronizing the changes in the stress, temperature, oxygen, and anion (chloride and sulfate) concentrations. For the purpose of assessing the impact of transient stress on crack propagation, the environment was held constant. In previous work using a 3NiCrMoV disc steel, a very severe environment--aerated 1.5-ppm Cl solution at 90°C2--was adopted. In the present study, a more relevant environment for the on-load simulation of de2 aerated 300 ppb Cl + 300 ppb SO4 solution at 90°C was used. EXPERIMENTAL PROCEDURES Materials The material used was a disc steel (3% NiCrMoV), cut from an ex-service steam turbine disc. The chemical composition is listed in Table 1. Specimens Compact tension (CT) specimens were made in accordance with ISO 7539-6.3 The thickness (B) and
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.69)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.69)
- Facilities Design, Construction and Operation > Processing Systems and Design > Compressors, engines and turbines (0.62)
INTRODUCTION ABSTRACT Field experiments designed to evaluate deoxygenation of natural seawater as a corrosion control measure for unprotected carbon steel seawater ballast tanks demonstrated decreased corrosion in hypoxic (<0.2 ppm O2) seawater using linear polarization measurements. They also demonstrated the diffi - culty of maintaining hypoxic seawater. Using a gas mixture it was possible to displace dissolved oxygen. However, aerobic respiration and corrosion reactions consumed oxygen and produced totally anaerobic conditions within the fi rst days of hypoxia. When gaskets and seals failed, oxygen was inadvertently introduced. The impact of oxygen ingress on corrosion depends on the amount of oxygen in the system at the time oxygen is introduced. Carbon steel exposed to cycles of hypoxic seawater and oxygenated atmosphere had higher corrosion rates than coupons exposed to cycles of either consistently aerobic or deoxygenated conditions. The deoxygenation of seawater has been demonstrated as an environmentally friendly ballast water treatment to control the introduction of nonnative aquatic species.1 Investigators have proposed that the same treatment provides a low-cost, effective corrosion control measure for uncoated carbon steel ballast tanks based on the concept that reducing oxygen from the ballast tanks will limit oxidation.1-2 Matsuda, et al.,2 conducted shipboard trials by sealing a ballast tank at the deck and installing vertical pipes into the headspace. They reported that pumping pure nitrogen gas into the headspace for 1.5 h reduced oxygen levels in the seawater to approximately 0.2 ppm and decreased the rate of uniform corrosion of carbon steel by 90% as determined by weight loss. Previous laboratory experiments3-4 comparing corrosion resulting from stagnant aerobic natural seawater with corrosion resulting from stagnant anaerobic natural seawater over a 1-year period demonstrated the following: ?Corrosion was more aggressive under totally anaerobic conditions as measured by instantaneous corrosion rates (1/Rp) and weight loss. ?Under aerobic conditions corrosion was uniform and the surface was covered with hydrous iron oxides (lepidocrocite [?-FeO(OH)] and goethite [?-FeO(OH)]). ?Under anaerobic conditions the corrosion was localized pitting and the corrosion products were an iron/nickel sulfide (mackinawite [(Fe,Ni)S] and an iron sulfide (pyrrothite [Fe1-xS]). Several investigators5-7 have suggested that the most corrosive operating condition is one in which carbon steel is exposed to alternating oxygenated/ deoxygenated seawater. Under constant oxygenation an oxide will form that provides corrosion resistance.
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.46)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT In previous work, crevice corrosion of pure chromium was modeled by coupling polarization curves with the waterhydrogen-chromium-chloride heterogeneous phase diagram. Assuming equilibrium conditions in the crevice, the time stepwise-calculated development of the critical crevice solution was quantitatively shown to initiate crevice corrosion through a breakdown of the passive layer, which was followed by the formation of chromium chloride and the subsequent acidification of the crevice solution. In the present paper, the same principles are applied to pure nickel with the main emphasis on the determination of the effects of bulk levels of pH, chlorides, and oxygen, at constant crevice geometry frequently applied in experimental work with a remote crevice assembly (RCA). As a result, increasing chloride contents, bulk oxygen levels, and decreasing pH reduce the calculated initiation times for passive layer nickel hydroxide (Ni[OH]2) breakdown, representing the crevice corrosion start as well as the times for total dissolution of the passive layer. At the same time the mean crevice corrosion currents are reduced by increasing chloride contents and pH as well as by decreasing bulk oxygen levels. Although these results are qualitatively in accordance with the behavior of chromium previously reported, the incubation times for nickel are shorter because of its specific properties at respective conditions. The goal of this paper is to convey a basic understanding of the crevice corrosion process with the participation of nickel in respective alloys. In previous papers1-2 the masses of passivating chromium hydroxide and depassivating chromium chloride, which precipitated from various crevice solution compositions, were calculated from the tentative four-phase equilibrium water-chromium-chromium hydroxide-chromium chloride. These masses have then been coupled to the Tafel slopes of the anodic polarization curves inside the crevice, thus establishing a time stepwise calculation loop for both the electrochemical and the chemical crevice reaction. The Tafel slope of the cathodic reaction was assumed from literature results and depended on pH and bulk oxygen contents. As an important result for the lifetime assessment of corroding components, the model calculated times at which the chromium hydroxide mass became zero in the four-phase equilibrium with chromium, chromium chloride, and water. At this time the crevice corrosion currents reached a final level representing respective local thickness reduction rates. As another obvious consequence of the calculated crevice solution concentration process, it was demonstrated that the often-discussed acidification during crevice corrosion can only start after the complete dissolution of the buffering chromium hydroxide in equilibrium with chromium chloride, chromium, and water. The resulting local pH levels would decrease
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The impedance properties (resistance and capacitance) of oxide scales on the martensitic/ferritic steel HT-9 and austenitic stainless steel Type 316L (UNS S31603) were examined during immersion in lead-bismuth eutectic (LBE) using a technique similar to electrochemical impedance spectroscopy. These scales were created by preoxidizing the samples in an air/ water vapor environment at 800°C for various times prior to immersion in LBE. Calculation of oxide conductivity for samples immersed in LBE at 200°C for 200 h yielded HT9 4 × 107 ( × cm)1 while 316 3 × 108 ( × cm)1. The influence of temperature alone gave the anticipated Arrhenius behavior with Ea equal to 0.12 eV, which is consistent with an electron hopping in ferrites close to the magnetite composition (such as Fex+1Cr2xO4). The influence of temperature during immersion in LBE deviated from Arrhenius behavior (irreversible). Oxide conductivity data for HT-9 were also used to calculate the corrosion rate using Wagner's oxidation theory. Values of corrosion rate for HT-9 in LBE at 200°C (oxygen saturated) decreased with increasing preoxidation time from 0.97 µm/h (preoxidation time = 36 h) to 0.55 µm/h (preoxidation time = 63 h). The structural components proposed for liquid leadbismuth eutectic (LBE)-based reactor coolant systems include austenitic and martensitic/ferritic steels. These materials, such as HT-9 (martensitic/ferritic) and Type 316L (UNS S31603)(1) stainless steel (SS) (austenitic), suffer from degradation in the form of dissolution owing to the relative high solubilities of Fe, Ni, and Cr in Pb, as well as oxidation. Traditionally, investigators have used immersion testing to characterize the oxidation rate in LBE.1-3 In these studies, the post-immersion oxide thickness has been used to calculate the oxidation rate. While immersion studies may provide useful information on oxide scale formation, corrosion rates calculated from immersion experiments may be misleading for any number of reasons, including nonlinear oxidation rates (the Parabolic Rate Law) and metal dissolution at the oxide/LBE interface that is lattice conservative, i.e., no oxide thinning is apparent. In this investigation, we have characterized the impedance properties of oxide films on austenitic and martensitic/ferritic steel during immersion in static LBE. Researchers have known for some time that
- North America > United States (0.68)
- Europe (0.68)
ABSTRACT The geographical variation in the corrosivity of natural seawater results from the variations in the salinity, microbiological activity, dissolved oxygen concentration, and temperature.1 Discounting the inland seas, such as the Dead Sea, the chloride (Cl) concentration of seawater varies from about 5.8 g/kg to about 2 24 g/kg, the sulfate (SO4 ) concentration varies from 0.8 g/kg to 3.4 g/kg, and the bicarbonate (HCO3) con1 centration varies from 0.01 g/kg to 0.2 g/kg. Except in the case of Dead Sea, the sodium to magnesium weight ratio (Na/Mg) remains about 8 in these waters and the sodium to calcium weight ratio (Na/Ca) remains about 26.1 Natural seawater is more aggressive than artificially made seawater (by mixing the appropriate compounds found in seawater) or seawater that has been sterilized. It has been argued that the microbial organisms in natural seawater increase the open-circuit potential, a process called ennoblement.2-3 More recently, Salvago and Magagnin4-5 observed that the corrosion potential of stainless steel (SS) in seawater had a broad distribution, spanning a range of about 500 mV, although the distribution of the corrosion potential narrowed considerably after prolonged exposure with a mean value of about 400 mV vs saturated calomel electrode (SCE).4 The mechanism of ennoblement is still under some debate,4 and recent experiments by Salvago and Magagnin5 argue that the ennoblement may not necessarily be explained by cathodic depolarization arising from microorganisms, but may involve lowering of passive dissolution kinetics. Lacking a sound theoretical basis for the anodic and cathodic kinetics in natural seawater, calculation of the corrosion potential must use of necessity "apparent" anodic and cathodic parameters. Temperature and chlorination level can determine the corrosion behavior of SS. In natural seawater, the 915
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The elemental depth profiling of tarnish films were analyzed at the early stages of atmospheric copper corrosion by glow discharge optical emission spectroscopy (GDOES), where the tarnish films had been formed by exposing copper plates to various outdoor environments, i.e., urban, rural/coastal, and hot-spring sites, for 1 month. Since GDOES probed a large surface area, on the order of millimeters, the depth profiles reflected macroscopic-averaged characteristics over this area, which are representative of real corroded surfaces. GDOES complemented previous analyses, i.e., Auger electron spectroscopy (AES), x-ray diffraction, field-emission scanning electron microscopy (FE-SEM), coulometric reduction, and x-ray photoelectron spectroscopy, and provided a better understanding of these tarnish films. In particular, the previous findings from microscopic FE-SEM observation and AES depth profiling were well supported by the GDOES results. With GDOES we observed the generation and distribution of cuprite [Cu2O] and posnjakite (Cu4SO4[OH]6·H2O), which had formed through the influence of sea salt at the urban site. The posnjakite was mostly located on the top of cuprite particles in the tarnish film. The tarnish film extended over 2 µm in depth at the rural/coastal site due to the higher atmospheric sea-salt concentration and humidity. In addition, chlorine, which promotes copper corrosion, was incorporated into the tarnish film with the growth of the oxide. Sulfide and oxides were generated at the hot-spring site, and the tarnish film extended to >5 µm, where a part of sulfide was oxidized to become sulfate. The tarnish film formed on copper that has been exposed outdoors generally has a complex structure. Many studies have provided analytical details for this tarnish film.1-10 X-ray diffraction (XRD), which can identify crystalline corrosion products, has frequently been used.4,7-10 Nassau, et al., revealed the existence of cuprite (Cu2O), brochantite (Cu4SO4[OH]6), antlerite (Cu3SO4[OH]4), posnjakite (Cu4SO4[OH]6·H2O), and atacamite (Cu2Cl[OH]3) in natural patinas.4 X-ray photoelectron spectroscopy (XPS) also has been used to analyze the chemical state.9-10 Patinas formed over decades also have been studied,11-15 where a doublelayer structure of a blue/green brochantite layer on a cuprite layer has been observed. The authors recently proposed a monitoring method of atmospheric corrosiveness that involved exposing a copper plate to the atmosphere for a short time (1 month) and measuring the amounts of elements such as chlorine and sulfur in the tarnish film with x-ray fluorescence (XRF) analysis.16 We found that the chlorine and sulfur content in the tarnish film reflected the degree of corrosion progress.10,16-17 Both elements exist in sea salt, and sulfur also can originate from other sources such as sulfur dioxide (SO2) and hydrogen sulfide (H2S). To evaluate the feasibility of this monitoring method, tarnish films formed during short-term exposure to the atmosphere have been studied extensively,10,16-18 while previous works of other researchers 729
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.91)
ABSTRACT In a recent paper, a crevice corrosion model for pure chromium was presented aiming at basic understanding of the local corrosion mechanism in an already deoxygenated crevice with a given geometry. The time stepwise calculation of chromium dissolution was based on arbitrarily selected levels of initial corrosion potential and slopes of the cathodic polarization curve at the open surface in contact with the bulk liquid. As a basic feature, the anodic polarization slopes inside the crevice were controlled by the mass of the precipitated chromium hydroxide phase, which was thermodynamically calculated from the resulting crevice solution composition using the tentative quaternary phase diagram: water--chromium--chromium hydroxide--chromium chloride. The present paper applies additional oxygen diffusion calculation steps and demonstrates the effects of various crevice widths, chloride contents, and bulk oxygen contents diffusing into the crevices at pH = 6. The calculations are based on the assumption of chemical equilibrium conditions as well as on rather short electromigration times of the chromiumcontrolled chloride ions complementary to the OH ions resulting from oxygen diffusion and reduction during the individual time steps. Considering total oxygen consumption and its respective corrosion currents inside the crevice, it is shown that increasing bulk oxygen levels and decreasing crevice widths are reducing the start times for dissolution as well as the final breakdown times of the passivating chromium hydroxide. Increasing chloride ion contents also reduce the hy- During crevice corrosion, the electrochemical dissolution process of the metal is assumed to be controlled mainly by the cathodic reaction at the open surface in contact with the bulk liquid, by electromigration of chloride ions and by diffusion of oxygen from the bulk liquid into the crevice. The positive charges of the produced chromium ions are balanced by respective negative charges of OH ions from the cathodic oxygen reduction, leading to formation of a passivating chromium oxide or hydroxide layer. Without sufficient oxygen inside a crevice, the positive metal ion charges are balanced by negative charges of accumulated chloride ions resulting from electromigration from the bulk liquid. Such chloride ions again may create crevice solution concentrations, which are positioned inside constitutional limits for the dissolution of the passivating chromium oxide or hydroxide that create conditions for depassivation and crevice corrosion. In previous papers,1-2 as an example, the mass of chro-
- North America > United States (0.47)
- Europe (0.46)
ABSTRACT New golden, yellow-colored cerium chemical conversion coatings on aluminum alloy 2024-T3 (AA2024-T3 [UNS A92024]) surface at room temperature were obtained by immersing the alloy into a cerium solution containing zinc chloride (ZnCl2) and hydrogen peroxide (H2O2). Electrochemical methods and immersion tests were used to study the dynamics of the coatings formation and their corrosion resistance in 3.5% sodium chloride (NaCl) solution. The morphologies of the coatings were recorded by scanning electronic microscopy (SEM). Energy-dispersive x-ray (EDX) analysis and x-ray photoelectron spectroscopy (XPS) were used to analyze the chemical composition and the oxidation state of the elements in the coatings. Polarization experiments and immersion tests in 3.5% NaCl solution showed that the sensitivity to pitting corrosion for the conversion-coated AA2024-T3 was greatly lower than that of the untreated specimens, and the corrosion resistance improved markedly. SEM photographs showed that the coatings consisted of a lot of spherical particles. EDX and XPS experimental results showed that the coatings were made up of oxygen, cerium, and aluminum, and the spherical particles contained higher contents of cerium and oxygen than the other sites. Cerium was mainly in the form of Ce4+. The mechanisms of conversion coatings formation and improvement on corrosion resistance also are discussed. Aluminum and its alloys are applied extensively in modern industry, especially in the aerospace industry. But, these materials have a tendency to pitting corrosion or other local corrosion in Cl-containing media. To improve their corrosion resistance, they usually are passivated or treated by chemical techniques. The traditional chemical techniques mainly involve chromate passivation.1-3 However, these processes endanger human health and pollute the environment, owing to the extreme toxicity of chromate.4 Chromate will be prohibited from being used in the near future. Developing a nontoxic and environmentally benign process to displace chromate conversion process for aluminum alloys has become an objective for researchers. Since Australian scientists discovered the inhibitive effect of rare earth metal (REM) on aluminum alloys and other metals,5 many studies have taken this approach to improve corrosion resistance on metals.6-11 These research indicated that it is possible to displace chromate by REM to improve material corrosion resistance. Furthermore, REMs are nontoxic or low toxic, so they cannot result in pollution nor can they generate cancer. But, almost all of these techniques remain at the laboratory stage. Most of the techniques were complex and required higher temperatures or longer treating times.6,12-15 Now, researchers working in this field are focused on
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- Materials > Metals & Mining > Aluminum (1.00)
- Materials > Chemicals > Commodity Chemicals (0.68)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Some rivers in China such as the Yellow River and Talimu River contain high concentrations of salt (up to 31.7 g/L).1 This causes a serious problem for flow-handling components of hydraulic turbines and pumps, which suffer the combined damage of cavitation erosion and electrochemical corrosion. Numerous studies on cavitation have been made and show that both mechanical and electrochemical factors are involved. In a large number of systems, the conjoint action of electrochemical and mechanical factors produce far more damage than if each acted separately.2-5 The erosion and corrosion of cast iron owing to cavitation attack have been discussed in terms of components of the cavitation damage. In a range of cast irons in various metallurgical conditions, it was seen that typically less than a fraction (0.05) of the damage arose from electrochemical corrosion and that typically a fraction (0.70 to 0.85) of the damage was from corrosion-induced erosion.4 The methods to successfully improve cavitation resistance, from a corrosion viewpoint, includes the addition of inhibitor and cathodic protection,5-7 which also indicate clearly the presence of a large chemical component of cavitation damage under certain circumstances. In some cases, the interaction may produce diverse and complex effects. For example, cavitation decreases the probability of pitting of the stainless steel (SS), i.e., one component may inhibit the harmful effect of the other.8 Kwok, et al., also found that corrosion and corrosion/cavitation erosion synergism plays a negligible role for SS in