Simulated Pit Research Articles

Beneficial effect of copper on pitting resistance of Ni-Cr-Fe alloys

This study examines the effect of copper alloying on pitting resistance in a model solid solution FCC Ni-13%Cr-10%Fe alloy through potentiodynamic and potentiostatic polarization in 0.1 M NaCl in conjunction with an analysis using first-principles competitive electro-chemisorption modeling. The pitting potential increased with increasing Cu content in the alloy. Furthermore, the extent of metastable pit growth was suppressed and the incubation time for metastable to stable pit transition increased with Cu content. The first-principles competitive adsorption calculations suggested that Cu alloying suppresses chloride ion adsorption on the alloy surface in a simulated pit environment, which inhibits active dissolution at the pit bottom, enhances proton adsorption, and thereby increases the local pH at the pit bottom. We propose that these two effects of Cu in solid solution combine to reduce pit stability and may act in addition to the enrichment of Cu on the corroding pit surface.

Function and safety evaluation of Staphylococcus epidermidis with high esterase activity isolated from strong flavor Daqu

This study was aimed at evaluating the safety of Staphylococcus epidermidis YTPW-4 isolated from strong flavor Daqu and its beneficial functional characteristics in Baijiu-making. The content of ethyl caproate catalyzed by crude enzyme solution of Staphylococcus epidermidis YTPW-140 was 583.09 mg/100 mL, and the activity of esterase was 2.13 U/mL. Vancomycin, erythromycin, and gentam were sensitive to the strain, which was negative for the causative gene, hemolytic activity, and biofilm formation capacity. In addition, the strain was selected for laboratory-scale fermentation using HS-SPME-GCMS and statistical analysis to confirm its role in the production of flavor compounds. Propyl-3-methylbutyrate, hexanoic acid, and ethyl acetate had higher contents after fermentation than other flavor compounds, at 530.40 μg/L, 471.07 μg/L, and 297.33 μg/L, respectively. There was also a small amount of ethyl hexanoate in these products. Esterase could increase the levels of short-chain free fatty acids, which were precursors of flavor compounds. Most importantly, the isolate maintained viability under simulated pit conditions, and was resistant to pH 3.5 and 8% ethanol. These results indicated that the strain had the potential to be used as a starter to improve the quality of Nongxiangxing baijiu.

Simulation on coupling effects between surface wear and fatigue in spur gear

A surface wear prediction method is used to determine the wear rate of the tooth surface. This method employs the Archard’s wear model together with the gear contact mechanics model. An equivalent calculation model based on Hertzian contact theory and fracture mechanics is used to investigate crack initiation and crack propagation. The virtual crack extension (VCE) method is employed to analyze the propagation process from the initial crack to occurrences of tooth surface pitting. A life prediction method on the wear-fatigue coupling is developed. The crack propagation process and pit shapes are determined by the iterative analysis. The relationship between service life and the remaining distance from the crack tips to the tooth surface is determined. The damage mechanism of wear-fatigue coupling is explored. The results of the comparative analysis show that the wear of tooth surface affects the cracks propagation characteristics, reduces the service life and even can change the failure mode. The simulated pit shapes and crack propagation process are in good agreement with the results of other literature. The analysis method of wear-fatigue coupling damage can well simulate the damage process and predict service life in spur gear.

Study of pitting corrosion under actual operating conditions of a first stage compressor blade

In this study, pitting corrosion was investigated numerically and experimentally under actual operational conditions of a gas turbine compressor. First, the samples cut from a blade made of Custom 450 stainless steel were exposed to different corrosion times in a 3.5 wt% NaCl solution. After the creation of pits in the samples, the dimensions of the corrosion pits were measured using a 3D profilometer device. The stoichiometry equations governing the corrosion of the Custom 450 alloy in a chloride solution were extracted and applied to the models. The results of this simulation were validated by comparing the depth of the simulated pits and the experimental samples. Subsequently, simulation was conducted for 48 months on a compressor having pits. There is a good agreement between the simulation results and the results obtained from the Turbo machine laboratory of the Texas A&M University. In addition, pits grew under the influence of corrosion, joined together, and made an equivalent pit.

Critical pitting temperature of selective laser melted 316L stainless steel: A mechanistic approach

The critical pitting temperature (CPT) of selective laser melted (SLM) 316 L stainless steel in 1.0 M NaCl was measured and compared with a commercial wrought alloy. Potentiostatic measurements determined a mean CPT value of 16 ± 0.7 °C, 27.5 ± 0.8 °C and 31 ± 1 °C for the wrought alloy, the SLM alloy normal to the build direction and parallel to the build direction, respectively. The lead-in pencil electrode technique was used to study the pit chemistry of the two alloys and to explain the higher CPT values observed for the SLM alloy. A lower critical current density required for passivation in a simulated pit solution was measured for the SLM alloy. Moreover, the ratio of the critical concentration to saturated concentration of dissolving metal cations was found to be higher for the SLM alloy, which was related to its different salt film properties, possibly as a result of the SLM’s distinct microstructure.

A Monte Carlo Model for Pitting Corrosion in Phosphor Bronze Tape Used in Underground Power Transmission Cables

Life of underground oil-filled power transmission cables used with phosphor bronze tapes is greatly reduced by pitting corrosion and hence accurate prediction of the pit growth in these tapes becomes essential. In the present work, the probability distribution of corrosion pit depth on phosphor bronze tapes is calculated using probabilistic Monte Carlo simulations and compared with the measured pit depth distribution on samples of broken tapes which have been in service for about 50 y. This Monte Carlo simulation is performed on every stable pit that nucleates, propagates, and repassivates on the metal surface. Due to the random nature of pitting corrosion, the probability of failure of this class of cables can be simulated based on the Monte Carlo model. This paper shows that the simulated pit depth distribution is very similar to the experimental data. The results demonstrate that the Monte Carlo model by Engelhardt and Macdonald can be effectively applied to long-term field data of phosphor bronze tapes, even over 50 y. In addition, the probability of failure due to pitting corrosion can be evaluated analytically, without need of conducting expensive and time-consuming experimental campaigns. Therefore, this probabilistic pit depth distribution model will be a powerful tool in the decision-making strategy for the replacement of underground power transmission cables near their end of life.

Comparison of thromboelastography versus conventional coagulation tests in simulated Crotalus atrox envenomation using human blood

IntroductionPit viper bites are a source of significant morbidity and mortality. Pit viper bites can cause venom-induced consumptive coagulopathy (VICC), typically evaluated with laboratory-based conventional coagulation tests (CCTs). However, CCTs require a laboratory and average 1 h to conduct. Thromboelastography (TEG) provides real-time, point-of-care tests of coagulation that are fast and require no separate laboratory facilities, which could be advantageous in both hospital and austere settings. However, the relative efficacy of TEG versus CCTs was unclear, particularly at low venom concentrations. Therefore, the objectives of this study were to test human blood with various concentrations of pit viper venom using CCTs and TEG to determine dose-dependent changes, lowest observed effect concentration (LOEC), and sensitivity to detecting samples out of normal diagnostic range. MethodsBlood samples from 20 volunteers were mixed with varying concentrations of western diamond back rattlesnake (Crotalus atrox) venom based on the mouse LD50IV (none, 0.5%, 1%, 2%, 33%, 66%, and 100% LD50IV). Samples were split and assessed with both CCTs including prothrombin time (PT), international normalized ratio (INR), partial thromboplastin time (PTT), fibrinogen, and D-dimer, along with TEG measures of reaction time (R), kinetic time (K), rate of clot formation (α-angle), and clot strength (MA). Data were analyzed as dose-dependent concentration-based changes in raw values and in percent of samples exceeding diagnostic thresholds using ANOVA and nonparametric statistics at the p < .05 threshold. ResultsAll evaluations showed significant concentration-dependent changes, and 100% of samples exceeded diagnostic thresholds at 33%LD50IV and above, save D-dimer. At 0.5%LD50IV, R, K, α-angle, PT, and INR were significantly different from controls, and at 1%LD50IV, mean values exceeded diagnostic thresholds for R, K, α-angle, MA, PT, and INR, but not for PTT, D-dimer, or fibrinogen. At 2%LD50IV, 100% of samples were out of normal range for K, α-angle, and PT. ConclusionTEG is effective in coagulopathy evaluations of in vitro simulated pit viper envenomation. At low venom concentrations, TEG performed as well or better than the majority of CCTs. These findings provide empirical evidence supporting the use of TEG to rapidly and accurately evaluate VICC.

22 Thromboelastography Detects Coagulopathy Faster than Standard Coagulation Studies in Simulated Pit Viper Envenomation

Venomous snakebites pose a significant risk of morbidity and mortality in rural and austere environments, so it is not surprising that the World Health Organization recently set a goal of reducing snakebite deaths by half by 2030. Many of these envenomations are due to pit vipers, leading to severe hematologic derangements, such as venom-induced consumptive coagulopathy (VICC). Immediacy in detection of envenomations is crucial for ameliorating morbidity and mortality, but diagnosis of envenomization can be challenging, requiring access to clinical laboratory facilities. Further, the laboratory-based evaluations of coagulation function take more than an hour to conduct. In contrast, thromboelastography (TEG) is promising as a rapid, portable, bedside test of coagulation that produces meaningful results in less than 15 minutes. Therefore, the primary objective of this study was to assess the efficacy of TEG compared to standard lab tests in detecting pit viper venom at increasing concentrations. Blood samples drawn from 19 healthy adult volunteers were mixed with varying concentrations of western diamond back rattlesnake (Crotalus atrox) venom (none, 0.5%, 1%, 2%, 33%, 66%, and 100% of LD50), then assessed with standard laboratory-based tests of coagulation function (labs), including prothrombin time (PT), partial thromboplastin time (PTT), international normalized ratio (INR), D-dimer, and Fibrinogen, as well as with TEG measures of reaction time (R), amplification (K), rate of clot formation (Angle), and clot strength (MA). Data were analyzed as changes from baseline and categorized as percent of samples out of normal physiologic range, then analyzed using ANOVA and binomial statistics at the p<.05 threshold for statistical significance. TEG and standard labs were both excellent (100%) at detecting higher concentrations of venom (33%, 66%, 100%), save D-dimer. Importantly, at low venom concentration levels (0.5%, 1%, 2%), the TEG measures of R, K, alpha, and MA were similar to laboratory-based evaluations of PT and INR at detecting venom, and were significantly superior to PTT, D-dimer, and Fibrinogen. TEG provides a sensitive, real-time quantitative evaluation of coagulation derangements during simulated pit viper envenomation that is faster than standard laboratory tests. TEG was sensitive at low venom concentrations, outperforming multiple traditional laboratory evaluations of VICC. While the present study was limited to in vitro analyses, our findings suggest that TEG is a fast, effective, and portable point-of-care testing modality to assist the emergency physician community to rapidly and accurately diagnose patients stricken with venomous snake bites.

Effects of digging by a native and introduced ecosystem engineer on soil physical and chemical properties in temperate grassy woodland.

Temperate grasslands and woodlands are the focus of extensive restoration efforts worldwide. Reintroduction of locally extinct soil-foraging and burrowing animals has been suggested as a means to restore soil function in these ecosystems. Yet little is known about the physical and chemical effects of digging on soil over time and how these effects differ between species of digging animal, vegetation types or ecosystems. We compared foraging pits of a native reintroduced marsupial, the eastern bettong (Bettongia gaimardi) and that of the exotic European rabbit (Oryctolagus cuniculus). We simulated pits of these animals and measured pit dimensions and soil chemical properties over a period of 2 years. We showed that bettong and rabbit pits differed in their morphology and longevity, and that pits had a strong moderating effect on soil surface temperatures. Over 75% of the simulated pits were still visible after 2 years, and bettong pits infilled faster than rabbit pits. Bettong pits reduced diurnal temperature range by up to 25 °C compared to the soil surface. We did not find any effects of digging on soil chemistry that were consistent across vegetation types, between bettong and rabbit pits, and with time since digging, which is contrary to studies conducted in arid biomes. Our findings show that animal foraging pits in temperate ecosystems cause physical alteration of the soil surface and microclimatic conditions rather than nutrient changes often observed in arid areas.

Mechanistic Investigation on the Effect of Molybdate on the Critical Pitting Temperature of 2205 Duplex Stainless Steel

In this research, a mechanistic approach was used to investigate the effect of molybdate ion on the critical pitting temperature (CPT) of 2205 duplex stainless steel. Firstly, the CPT of 2205 DSS was measured using potentiodynamic and potentiostatic polarization. It was found that with addition of 0.0005, 0.005 and 0.05 M Na2MoO4 to 0.5 M NaCl solution, the CPT increases approximately 4, 9, and 14°C, respectively. Using the lead-in pencil electrode technique, the mechanism by which molybdate ion influences the CPT was interpreted using the CPT model proposed by Salinas-Bravo and Newman. The results showed that molybdate has a negligible effect on the pit solution chemistry, resulting in a slight change in the diffusion-limited current density. However, it reduces the rate of alloy dissolution within the simulated pit solution, which was found as a reduced maximum current density.

Efficiency of additives and internal physical chemical factors for pit latrine lifetime extension

Pit latrines are the most common form of on-site sanitation, but are blighted by the problem of pit fill-up. Little is known about what factors and conditions affect decomposition of pit content and thus govern pit filling, but the liquid–mass balance is the key factor. Under laboratory conditions the effect of inorganic and biological additives and the effect of physical chemical factors on solids hydrolysis of black water and human faeces were investigated to establish the potential of these to extend pit latrine lifetime. Additives did little or nothing to enhance net solids hydrolysis in batch tests or to reduce pit fill height in miniature simulated pit latrines. Physical chemical factors such as redox condition and initial pH increased solids hydrolysis, whereas temperature and substrate moisture did little. Since additives need contact with the substrate to act, measurements on faeces crust formation speed and strength were performed and showed that crusts formed within three hours and persisted af...

Investigation of Local Hydrogen Uptake in Rescaled Model Occluded Sites Using Crevice Scaling Laws

A major challenge in the quantification of hydrogen (H) assisted cracking is the determination of local H contents in pits and cracks and subsequently the environment assisted cracking behavior as a function of H concentration for the given metallurgical condition. Moreover, the lack of insight on these issues makes it difficult to computational design improved alloys for resistance to H assisted cracking. One difficulty in understanding H uptake at cracks and pits stems from the occluded chemistry and the local current and potential distribution due to ohmic potential drop. The effects of occluded site geometry and applied potential leading to depassivation/activation, and potential drop on H production and uptake in a martensitic precipitation/age hardened stainless steel PH 13-8Mo (Fe-13Cr-8Ni-2Mo-1Al) were explored. A potential (E)-pH diagram for PH 13-8Mo was calculated using the CALPHAD approach which illustrates the H/H+ equilibrium line and the oxide stability regions. On planar electrode surfaces, the total H concentration was found to increase exponentially with H overpotential in simulated acidified pit solutions. Comparison of CALPHAD and experimental findings indicated that the potential and pH range expected in acidified pit bottoms that H production would be thermodynamically possible on metal surfaces without a stable oxide film. This data could later be used to quantify H uptake in pits as a function of potential and pH. The x2/gap scaling law, where x is the pit/crevice depth and “gap” is the pit/crevice width, was computationally determined and used to rescale model pits from micrometer to millimeter dimensions using E-log current density (i) data as a boundary condition for finite element analysis. Such rescaling enabled local H measurements by thermal desorption as a function of pit depth in rescaled pits. Two values of critical depth (xcrit) were identified. Significant local H uptake was observed at x > xcrit under conditions where external surfaces were in a passive state and above the H electrode potential (EH/H+). The local potential drops below EH/H+ at a depth, xcrit1= xHER and reaches the primary passivation potential (EPass) of the stainless steel at a depth, xcrit2 = xPass. Thus, at x>xcrit1, the stainless steel experiences H production and uptake at/near the pit bottom but remains passivated. At x>xcrit2, H absorbs on actively dissolving pit surfaces since the local potential drops below EPass. Concurrent metal dissolution and H uptake lead to significant amounts of local H absorption at simulated pit surfaces. The ability of this rescaled approach to provide insight on the development of crack tip conditions that negatively impact environment assisted fracture are further discussed. Acknowledgments: This work was supported in part as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584. Finite element analysis, CALPHAD calculation and assessments of environment assisted cracking were conducted under the auspices of this grant while corrosion electrochemistry and hydrogen analysis was conducted under funding from NSF.

Experimental support for new electro active repair method for reinforced concrete

This paper, describes experiments that form the basis of an invention that aims at improving the durability of conventional (mechanical) repairs to concrete structures suffering from chloride induced corrosion of reinforcing steel. The invention comprises application of a short term, low voltage, DC current before or after concrete is broken out and before repair material is applied. It is an additional step in conventional concrete repair. The application of current will last typically 24 h at a current density of typically 5 A/m2 of steel surface area. In laboratory experiments corrosion pits are simulated by placing highly concentrated iron(II)chloride solution in contact with a mortar surface, after which current is applied. The results indicate that this treatment is able to remove 90% or more of the chloride from the simulated pit solutions. Furthermore, the pH has increased from about 3 to more than 12. The combined reduction of chloride content and increase of pH strongly reduces the chloride to hydroxyl ratio of the pore solution and thus the aggressive conditions at the reinforcing steel. After applying alkaline chloride free repair material, this will result in a longer life of the repair, thus reducing the life cycle costs of repaired structures. The process is named EAR, electro active repair.

Experiments Based on One-Dimensional Diffusion Modeling to Determine Critical Factors in Pitting

Critical conditions for stable pitting were first formulated by Galvele1, considering mass transport in a one-dimensional pit, with the parameter (i*x) (pit stability product2) describing steady-state kinetics. Beck3, Alkire and coworkers4, and Newman and coworkers5,6 established artificial pits as the experimental tool to examine these kinetics. An associated descriptor of critical conditions is the critical potential1,7–9. Given the quasi-steady state obtained under a salt film6,10,11 for a corroding pit, this potential was taken as the potential at which this film was first stable, the transition potential ET 6. However, pitting was observed to proceed stably at potentials below ET 12–14, calling into question its validity as the critical potential as well as the salt film as a critical surface condition. Long-term experiments oriented towards establishing a potential lower bound for propagating pits showed that the repassivation potential Erp 15–18 below which no new pits nucleate and any existing pits repassivate, could be a critical potential. Erp would describe the same conditions as the critical pit stability product (i*x)crit, a fraction of (i*x) measured under a salt film. Studies to date have focused on determining either the critical potential15,18–20 or the critical pit stability product2,13,21,22, and have not provided a definitive quantitative connection between the two and to other associated critical factors like surface concentration (CS 12) and pH. This work presents a combined experimental and modeling framework that relates these factors. Artificial pit experiments were performed using 316L stainless steel wires in sodium chloride solution. Experimental estimates related to the critical factors include (i*x)saltfilm and Erp. Experimental results were fed into a one-dimensional diffusion model. A graphical method for determining CS at the transition between pitting stability and repassivation was developed, comparing a) Δt, the difference between tact (time taken to scan to Erp from ET) and tf (time taken for the CS to dilute to different fractions of saturation), and b) Erp (Fig. 1). Experiments were also designed to obtain anodic kinetics at different CS. The time required for a corroding surface under a salt film to dilute to various CS values was calculated from the mass transport model developed. Pits were grown under a salt film to predetermined depths and then allowed to dilute under open circuit to various CS. Rapid scanning to anodic potentials was subsequently carried out once each CS was achieved, so that the anodic kinetics at that particular CS could be determined, removing the need for separate experiments in simulated pit chemistries. Results showed that there was a change in type of behavior and not merely in degree for CS < 50% of saturation (Fig. 2), indicating that the critical CS is lower than previously considered estimates, which has implications on damage estimation models based on anodic stability. Estimates of the critical pH associated with this transition was also obtained based on the influence of local cathodic reactions23,24. A single quantitative framework was therefore developed relating key parameters describing pitting stability and repassivation.

Investigation of the effect of solution annealing temperature on critical pitting temperature of 2205 duplex stainless steel by measuring pit solution chemistry

In this research, the effect of solution annealing temperature on critical pitting temperature of DSS 2205 in 3.5wt.% NaCl solution and also the pit chemistry is studied using electrochemical methods and mechanistic analyses. Pencil electrode studies revealed that in comparison to samples solution annealed at 1050°C and 1150°C, maximum current density in simulated pit solution is increased and limiting current density in presence of salt film is decreased for alloy solution annealed at 1250°C. Based on these results and microscopic observations, lower CPT of DSS 2205 solution annealed at 1250°C is explained.

The effect of dichromate ion on the pitting corrosion of AISI 316 stainless steel. Part I: Critical pitting temperature

This article provides a better understanding of dichromate effect on the critical pitting temperature (CPT) of 316 SS in chloride solution. Potentiostatic measurements revealed that dichromate effectively improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution in simulated pit environment and a slight decrease in the saturation concentration of cations in pit solution were defined in pencil electrode experiments. Scanning electron microscopy showed that, in compare with pure chloride solution, the pits formed on the metal surface in dichromate containing solution, have finer lacy covers.

Effect of Thiosulfate on Pitting Corrosion of 316SS: I. Critical Pitting Temperature and Pit Chemistry

In this research, the effect of thiosulfate ion on pitting corrosion behavior of 316 stainless steel was studied. Part I of this work deals with the influence of thiosulfate on the critical pitting temperature of 316 SS in 0.1 M chloride solution and studies the effect of this ion on the pit chemistry. Electrochemical experiments performed in absence and presence of 0.01 M thiosulfate ion revealed that thiosulfate deteriorates the CPT. Pencil electrode studies showed that thiosulfate addition decreases both saturation concentration of metal cations necessary to metal salt precipitate at the pit bottom (CS) (the value of diffusion controlled limiting current density (iLim) was decreased) and the ratio of C*/CS (where C* is the critical concentration of metal cations in pit solution essential for a pit to remain stable) while it increases the anodic dissolution rate in a simulated pit solution. Furthermore, scanning electron microscopy showed that the lacy cover formed over the pits mouth has coarser pore structure in the presence of thiosulfate ion.

Stochastic modeling of pitting corrosion in aluminum alloys

The stochastic theory of pitting corrosion has been successfully used to analyze the statistical nature of pitting. In this paper a Monte Carlo model is used to predict the extent of damage accumulation in aluminum alloys. This model uses experimental parameters obtained by electrochemical noise measurements on electrodes arrays. The algorithm is based on the random occurrence of the metastable pit birth/death or the stable pit growth. Simulated pit depth distributions are compared to experimental data obtained by Optical Profilometry (OP), leading to an improvement of the model and challenging the existence of a metastable/stable transition in free corrosion conditions.

Simulating the interface morphology of silver thick film contacts on n-type Si-(100) and Si-(111)

Silver crystals at the interface of silver thick film contacts carry the current across such contacts and therefore govern the contact resistance. The crystals grow nearly exclusively in pits in the silicon surface, which form during contact formation before the crystals and hence determine the amount and size of crystals. We simulate the mechanism of pit formation at such contact interfaces by using a model based on the removal probability of silicon surface atoms. The model leads to good agreement between experimentally observed and simulated pits. The results enable the prediction of pit formation in dependence of contact processing parameters.

Ultimate open pit stochastic optimization

Classical open pit optimization (maximum closure problem) is made on block estimates, without directly considering the block grades uncertainty. We propose an alternative approach of stochastic optimization. The stochastic optimization is taken as the optimal pit computed on the block expected profits, rather than expected grades, computed from a series of conditional simulations. The stochastic optimization generates, by construction, larger ore and waste tonnages than the classical optimization. Contrary to the classical approach, the stochastic optimization is conditionally unbiased for the realized profit given the predicted profit. A series of simulated deposits with different variograms are used to compare the stochastic approach, the classical approach and the simulated approach that maximizes expected profit among simulated designs. Profits obtained with the stochastic optimization are generally larger than the classical or simulated pit. The main factor controlling the relative gain of stochastic optimization compared to classical approach and simulated pit is shown to be the information level as measured by the boreholes spacing/range ratio. The relative gains of the stochastic approach over the classical approach increase with the treatment costs but decrease with mining costs. The relative gains of the stochastic approach over the simulated pit approach increase both with the treatment and mining costs. At early stages of an open pit project, when uncertainty is large, the stochastic optimization approach appears preferable to the classical approach or the simulated pit approach for fair comparison of the values of alternative projects and for the initial design and planning of the open pit.