Pit Growth Rate Research Articles

Durolon® polymer as a nuclear track detector: Characterization by chemical etching

This paper presents the properties of alpha particle tracks in a polymer, known as Durolon®. The study involves measurements of the time-dependent evolution of etch pit diameters and areal densities for low-energy alpha particles under various etching conditions, including different temperatures and solutions. A time-dependent model was successfully employed to describe the etch pit growth rates. Additionally, optical absorption and Raman spectroscopy techniques were applied to the samples under investigation, complementing the traditional results obtained through optical microscopy. The suitability of Durolon® polymer as a nuclear track detector is discussed based on the results obtained from the aforementioned complementary techniques. In summary, this research represents a critical step toward establishing Durolon® polymer as a viable nuclear track detector.

Mathematical modeling and prediction of pit to crack transition under cyclic thermal load using artificial neural network

The formation of pitting is a major problem in most metals, which is caused by extremely localized corrosion that creates small holes in metal and subsequently, it changes into cracks under mechanical load, thermo-mechanical stress, and corrosion process factors. This research aims to study pit to crack transition phenomenon of steel boiler heat tubes under cyclic thermal load, and mathematical modeling as well as Artificial Neural Networks (ANN) used to estimate the cycles takes to initiate a crack. In this study, the pit-to-crack transition model is developed mathematically, and the effects of stress intensity factor on the number of cycles to initiate crack and pit size are studied for steam tubes under thermal stress at 500℃. The ANN model is designed to predict the number of cycles required for the transition from pit to crack. The novelty of the approach lies in the use of ANN model for the complex behavior of materials under cyclic thermal loading. The stress intensity factor is a parameter that amplifies the magnitude of applied stress that includes the geometric parameter. In-pit-to-crack transition stage stress intensity factor-based approach and volumetric pit growth rate used. The fit regression of all R-values of the output pit size and number of cycles is 0.99195 and 0.9954 respectively showing good agreement for the obtained results using ANN. In addition, the comparison of mathematical model predicted results using equations and ANN predicted outputs using MATLAB® for pit size, and number of cycles shows good agreement in results. In addition, the comparison of mathematical model predicted results using equations and ANN predicted outputs using MATLAB® for pit size, and number of cycles shows good agreement in results. Hence, the formation of pitting problems in most of the metals can be effectively analyzed and reduced by using this research study.

Pit growth kinetics in aluminum: effects of salt loading and relative humidity

The growth kinetics of localized corrosion, e.g. pits, in corrosive environments often controls the service life of metallic components. Yet, our understanding of these kinetics is largely based on coupon-level, e.g. mass-loss, studies which provide limited insights into the evolution of individual damage events. It is critical to relate observed cumulative loss trends, such as links between changing humidity and mass loss rates, to the growth kinetics of individual pits. Towards this goal, we leverage in-situ X-ray computed tomography to measure the growth rates of over sixty pits in aluminum in four different humid, chloride environments over ≈3 days of exposure. Pit growth rates and final volumes increased with increasing droplet volume, which was observed to increase with increasing humidity and salt loading. Two factors, droplet spreading and oxide jacking, dramatically increased pit growth rates and final volumes.

The evolution of pit morphology and growth kinetics in aluminum during atmospheric corrosion

Assessing the lifetimes of alloys in humid, corrosive environments requires growth kinetic information regarding individual instances of damage, e.g. pit growth rates. Corrosion rates measured at the continuum scale using mass change convolute the rate of pit nucleation and growth, providing limited information on local kinetics. The current study used in-situ X-ray computed tomography to measure growth rates of individual pits in aluminum over 100 h of exposure in a humid, chloride environment. While pits grew at relatively constant rates over the first hours after nucleation, significant growth-rate nonlinearities subsequently occurred. These were linked to both droplet spreading, which altered the cathode size, and changes in the mode of pit growth. Pit morphology appeared to influence the dominant growth mode and the duration of pit growth. Post-mortem serial sectioning revealed pits preferentially attacked grain-boundary triple junctions and dislocation boundaries.

Dependence of Pit Growth Rate on Applied Potential and Chloride Concentration under Conditions with and without Fluid Flow

Pitting corrosion on stainless steel is one of the most serious problems caused by seawater intrusion into power plants because it possibly perforates boundary structures, such as piping or containers, and leads to solution leakage. Although the evaluation of the pit growth rate in accordance with the corrosion condition is required to secure the plant’s safety, the dependence of the pit growth rate on various corrosion conditions is not fully understood. In this study, the effects of applied potential and chloride concentration on the pit growth rate on Type 304L stainless steel were assessed with and without fluid flow by performing the pit penetration test with in situ observations of pit initiation and penetration. An artificial one-dimensional pit experiment was performed to obtain a fundamental understanding of pit growth with and without fluid flow. In addition, three-dimensional pit growth behavior was further analyzed by measuring a dissolution current of a single three-dimensional pit. In the pit penetration test, the effects of applied potential and chloride concentration on the pit growth rate differed depending on the fluid flow condition; the pit growth rate is almost independent of the applied potential and chloride concentration without fluid flow, whereas the growth rate was decreased by decreasing the potential and chloride concentration with fluid flow. For the results of the artificial one-dimensional pit experiment, regardless of the fluid flow condition, stable pit growth in the depth direction was suggested to be diffusion-controlled. Measuring the time variation of the dissolution current of a single three-dimensional pit indicated that the three-dimensional pit growth involves temporary passivation and reactivation, which depend on the fluid flow condition and applied potential. This suggested pit growth in the pit penetration test proceeded discontinuously depending on the corrosion conditions, resulting in a dependence of the pit growth rate on the corrosion conditions.

Investigation of the effect of pitting corrosion on the fatigue strength degradation of structural steel using a short crack model

Steel support structures of offshore wind turbines (jackets and monopiles) undergo both fatigue and corrosion damage, impacting their lifetime. This paper investigates how pitting corrosion, caused by being exposed to the marine environment, affects the fatigue strength of structural steel. A short fatigue crack model is used to estimate the minimum required applied load amplitude which causes a growing crack emanating from the bottom of a semi-elliptical pit. Pit growth rate data, reported in literature, is employed to update the pit size and its sharpness at each time step. The modelling results show the fatigue strength degradation as a function of the exposure time to the corrosive environment. As exposure time increases, it is observed that degradation happens more quickly in the early years followed by a gradually decreasing degradation rate of the fatigue strength in the following years.

On the Importance of Geometry in Open Bipolar Electrochemistry Configurations for Corrosion Studies

This work aims to optimize cell geometry with finite element modeling to ameliorate open Bipolar electrochemistry (BPE) and split BPE setups, increase the faradaic current through the bipolar electrode to trigger localized corrosion on the anodic region, and study the corrosion behavior of anodic films when activated as bipolar electrodes under thermostatic condition.The advent of Bipolar electrochemistry (BPE) stems from a series of investigations on fluidized bed electrodes conducted by Fleischmann et al. in the 1970s.[1] Since then, and mainly in the recent decade, BPE has been profoundly scrutinized and exploited in disparate fields such as electrodeposition[2,3], synthesis of Janus particles, propulsion of microparticles, corrosion of stainless steel[4,5], anodizing[6], biosensors, and water treatment. Additionally, it has been studied in miscellaneous formats including split BPE, 2D BPE, and array BPE. Fundamentally, BPE is performed by applying an electric field between two inducing electrodes through an electrolytic medium in which an electronic conductor is immersed. The electronic conductor is indirectly polarized such that one end becomes anodic and the other cathodic thus creating two poles of charge.Due to lack of direct contact to the bipolar electrode, direct monitoring of the current and potential of the bipolar electrode is not viable. However, indirect measurement of current and potential through the integration of BPE with electrogenerated chemiluminescence (ECL), surface plasmon resonance imaging (SPRi), and scanning vibrating electrode technique (SVET) have been proven feasible. In studies that coupled BPE and ECL as well as in corrosion studies of a stainless-steel bipolar electrode, an apparent curvature of the equipotential lines, specifically near the extremities of the bipolar electrode, is noticed[7,8], although it has not been addressed to date. This nonlinearity of potential can be related to the non-uniform electric field in the electrolyte and can be precluded via manipulation of cell geometry.The major benefit of using BPE for corrosion studies compared to traditional three-electrode techniques with direct polarization is the presence of a continuum of applied potentials distributed along the length of the bipolar electrode in the direction of the electric field. The distribution of potential results in distinct corrosion behaviors that may be analyzed along the length of the metal. Nevertheless, the challenge is to configure the experimental setup in a way that promotes a one-dimensional distribution of applied potential on a 2d surface while ensuring the polarization is high enough to produce the necessary corrosion response. Doing so allows one to study pitting characteristics such as pit initiation rates and distribution as well as pit growth rate from post-analysis of pit size distributions. References R. Backhurst, J. M. Coulson, F. Goodridge, R. E. Plimley, and M. Fleischmann. A preliminary investigation of fluidized bed electrodes. Journal of the Electrochemical Society, 116 197 (11):1600, 1969Braun, T. M., and D. T. Schwartz. "Localized electrodeposition and patterning using bipolar electrochemistry." Journal of The Electrochemical Society162, no. 4 (2015): D180.Rahul Dhopeshwarkar, Dzmitry Hlushkou, Mark Nguyen, Ulrich Tallarek, and Richard M. Crooks. Electrokinetics in microfluidic channels containing a floating electrode. Journal of the American Chemical Society, 130(32):10480–10481, 2008Yiqi Zhou and Dirk Lars Engelberg. Application of a modified bi-polar electrochemistry approach to determine pitting corrosion characteristics. Electrochemistry Communications, 220 93:158–161, 2018.Sara Munktell, Leif Nyholm, and Fredrik Bjorefors. Towards high throughput corrosion screening using arrays of bipolar electrodes. Journal of Electroanalytical Chemistry, 747: 239 77–82, 2015.Ryo Takeuchi and Hidetaka Asoh. Effects of size and position of an unconnected aluminum electrode on bipolar anodization in an AC electric field. Scientific reports, 11(1):1–7, 2021Vera Eßmann, Jan Clausmeyer, and Wolfgang Schuhmann. Alternating current-bipolar electrochemistry. Electrochemistry Communications, 75:82–85, 2017Gwendoline Tisserant, Zahra Fattah, Ce´dric Ayela, Je´roˆme Roche, Bernard Plano, Dodzi Zigah, Bertrand Goudeau, Alexander Kuhn, and Laurent Bouffier. Generation of metal composition gradients by means of bipolar electrodeposition. Electrochimica Acta, 179:276–281, 2015. Figure 1

Carbon fiber damage evolution under flame attack and the role of impurities

AbstractCarbon fibers (CFs) are prone to extensive oxidation under fire attack, for instance, in an aircraft fire scenario. This work addresses the damage mechanisms observed on polyacrylonitrile (PAN)‐based CFs with different microstructure exposed to open flames. A fixed‐point technique was developed to follow‐up individual CFs by means of time‐controlled insertion into premixed methane/air flames, followed by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS) analyses. Besides diameter reduction, three localized damage mechanisms were discerned in the presence of impurities, which were quantified by neutron activation analysis (NAA). Severe pitting was ascribed to catalytic oxidation mainly caused by alkali and alkaline earth metals. After an initial period where catalytic reactions between impurities and the carbon surface dominate, the flame stoichiometry governed the CF gasification process, with lean flames being much more aggressive than rich ones. A second mechanism, channeling, was caused by mobile metallic impurities. Some impurities showed an opposite effect, lowering reactivity and thus preventing further catalysis. Amorphous damage with a skin‐peeling effect is believed to be the result of localized impurities at high concentrations and microstructural variations. Hindrance or synergistic effects between impurities are discussed. Finally, apparent axial pit growth rates were determined and compared with other carbonaceous materials, revealing a strong influence of impurities and the flame reactive atmosphere on CF oxidation.

Effect of HAc on the Metastable Pitting Corrosion of 304 SS in NaCl Solution.

Stainless steels (SSs) easily suffer localized corrosion damage, such as pitting corrosion, in mixed solutions of acetic acid and sodium chloride. Currently, few works have been focused on the early stages of the pitting corrosion (metastable pitting corrosion) process of SSs in a chloride-HAc mixture solution. In this work, the effects of acetic acid (HAc) and its concentration on metastable pitting corrosion and the uniform corrosion of 304 SS in 0.6 mol/L NaCl solution were investigated by a slow-scanning potentiodynamic polarization test, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that the uniform corrosion rate of 304 SS increases after HAc addition but, with an increase in HAc concentration, the corrosion rate decreases. In the presence of HAc, the metastable pitting potential (Em) and stable pitting potential (Eb) move negatively, but the number of metastable pits notably decreases. HAc has a promoting action on the growth rate of the metastable pits and facilitates the transition from metastable pits to stable pits. The influence of HAc is related to a decrease in solution pH and the chemical adsorption of HAc.

Corrosion-fatigue life prediction of reinforced concrete square piles in marine environments

In this paper, a three-stage model of the corrosion-fatigue life prediction of reinforced concrete square piles in marine environments is established. First, a two-dimensional diffusion equation of chloride ions is presented. A simplified corrosion pit model is given to estimate the pit nucleation time. Second, according to the principle of competition between the growth rate of corrosion pits and the growth rate of cracks, a rate competition model is proposed. Third, a crack growth model is established based on the Paris-Erdogan equation. Finally, an example is illustrated to verify the validity of the model, and a parametric analysis of the main influencing factors is conducted. The analysis results show that the corrosion-fatigue life decreases with increasing surface chloride concentration, chloride diffusion coefficient, concrete compressive strength, reinforcement stress range, reinforcement diameter and cyclic load frequency. The corrosion-fatigue life increases as the critical chloride concentration and concrete protective layer thickness increase.

Investigation of the metal dusting attack on the temperature range 500−700 °C using X-ray tomography

A test rig consisting of a quartz tube placed in a horizontal furnace made of five independently regulated heating zones allowed the evaluation of the metal dusting attack of a FeNiCr alloy. Fifteen samples were exposed in a temperature gradient from 504° to 704°C, 1.1 bar, to a highly carburizing atmosphere for 1500 h. Below 561 °C the high density of pits led to uniform corrosion whereas localized pits developed at higher temperatures. In depth pit growth rate raised to a maximum at 632 °C, then decreased showing that it depends both on temperature and on the carbon activity gradient.

Effect of Stress Magnitude on Pit Growth Rate of 304 Austenitic Stainless Steel in Chloride Environments

In this study, a corrosion pit test using notched bar specimens was conducted to investigate the effect of stress magnitude on the pit growth rate. To produce the notched bar specimens, 304 austenitic stainless steel was used, which is a material used for spent nuclear fuel canisters. Furthermore, three levels of stresses were generated using different notch radii. The corrosion pits were quantitatively measured through scanning electron microscopy and analyzed by finite element analysis. Based on experimental data, the pit growth rate model is suggested in terms of the stress and exposure time.

Application of bipolar electrochemistry to assess the ambient temperature corrosion resistance of solution annealed type 2205 duplex stainless steel

The corrosion resistance of solution annealing heat-treated type 2205 duplex stainless steel microstructures was assessed with a bipolar electrochemistry technique. Chemical element partitioning in both crystallographic phases was correlated to simulations of critical pitting temperatures. The as-received microstructure had the highest pit nucleation resistance, with high-temperature solution annealing treatment revealing reduced pit growth rates. Pit nucleation occurred either within the ferrite phase or at ferrite-austenite interfaces, with the resulting pit shape affected by the microstructure characteristics. The results of this study are discussed in the framework of microstructure design for enhanced corrosion resistance in duplex stainless steels.

Corrosion of Steel Rebars in Anoxic Environments. Part II: Pit Growth Rate and Mechanical Strength.

Reinforced concrete may corrode in anoxic environments such as offshore structures. Under such conditions the reinforcement fails to passivate completely, irrespective of chloride content, and the corrosion taking place locally induces the growth of discrete pits. This study characterised such pits and simulated their growth from experimentally determined electrochemical parameters. Pit morphology was assessed with an optical profilometer. A finite element model was developed to simulate pit growth based on electrochemical parameters for different cathode areas. The model was able to predict long-term pit growth by deformed geometry set up. Simulations showed that pit growth-related corrosion tends to maximise as cathode area declines, which lower the pitting factor. The mechanical strength developed by the passive and prestressed rebar throughout its service life was also estimated. Passive rebar strength may drop by nearly 20% over 100 years, whilst in the presence of cracking from the base of the pit steel strength may decline by over 40%.

Modeling and Finite Element Method Analysis of Fatigue Failure of 8.72Cr-0.9Mo Steel Boiler Heat Tube

In power plant heat tube is the main component where the water is changed to high-pressure steam, it operates under corrosive and high temperature environment. Corrosive environment and cyclic temperature fluctuation cause fatigue on boiler heater tube, and which degrade life of the component. This paper presents corrosion rate by volumetric pit growth, crack initiation and crack propagation of boiler heat tube for power plant under cyclic thermal load. 8.72Cr-0.9Mo steel is one of the steel type which mostly used nowadays as boiler heat tube. Volumetric pit growth rate approach used for crack initiation and energy release rate approach (J-integral) used to find crack propagation phenomenon. Temperature is taken in the interval of 25 , and it has a significant effect on rate of chemical reaction (corrosion rate) and material properties. The results show 906Mpa and 895Mpa thermal stress induced at crack tip at from analytical and FEM respectively. And also energy release rate results are from analytical and FEM respectively. From the result, material reach fatigue limit in the range of low cycle fatigue having the value less than cycles. The existence of corrosion reduces crack initiation cycles since crack initiation is speed up by the presence of corrosion.

A level set model for stress‐dependent corrosion pit propagation

AbstractA numerical model for corrosion pit propagation under mechanical loading is presented. The level set method is used for corrosion front tracking and also enables the domain to be split into a solid and a pit domain. In the pit the diffusion of atoms originating from the dissolution process occurring at the pit front is simulated. The model is capable of automatically capturing lacy cover formation due to the inclusion of activation control, diffusion control, and passivation. In the solid static equilibrium is solved to obtain strains and stresses. A parameter, dependent on the signs of the plastic strain increment and the back stress, is introduced to define the influence of plasticity on the corrosion rate. The model is used to study pit growth under electrochemical and mechanical loading. Under activation control combined with an elastic material response, pits propagate faster under constant loading than under cyclic loading. When plastic deformation occurs, cyclic loading can significantly increase the pit growth rate. Increasing the cyclic load frequency results in faster propagation due to kinematic hardening. Under diffusion control, mechanical loading does not influence the pit growth rate, given that the salt layer leading to diffusion control remains intact.

A Review of Data-Driven Oil and Gas Pipeline Pitting Corrosion Growth Models Applicable for Prognostic and Health Management

Pitting corrosion is a primary and most severe failure mechanism of oil and gas pipelines. To implement a prognostic and health management (PHM) for oil and gas pipelines corroded by internal pitting, an appropriate degradation model is required. An appropriate and highly reliable pitting corrosion degradation assessment model should consider, in addition to epistemic uncertainty, the temporal aspects, the spatial heterogeneity, and inspection errors. It should also take into account the two well-known characteristics of pitting corrosion growing behavior: depth and time dependency of pit growth rate. Analysis of these different levels of uncertainties in the amount of corrosion damage over time should be performed for continuous and failure-free operation of the pipelines. This paper reviews some of the leading probabilistic data-driven prediction models for PHM analysis for oil and gas pipelines corroded by internal pitting. These models categorized as random variable-based and stochastic process-based models are reviewed and the appropriateness of each category is discussed. Since stochastic process-based models are more versatile to predict the behavior of internal pitting corrosion in oil and gas pipelines, the capabilities of the two popular stochastic process-based models, Markov process-based and gamma process-based, are discussed in more detail.

Effect of pH on the corrosion and crack growth behavior of the ZK60 magnesium alloy

To investigate the effect of pH on corrosion and fatigue crack growth of ZK60 magnesium alloy, the corrosion and fatigue crack growth experiments with cyclic sinusoidal waveform in PBS with pH 5.2, 7.4 and 9.0 were performed. With the increase of pH, the integrity and compactness of the protective layer increased as well as Mg3(PO4)2, reducing the channels for Cl− and hydrogen to contact the magnesium matrix which inhibited pitting and crack growth rate in LI stage. In LII stage, the effect of pH was weakened and the slope of crack propagation curve decreased.

Effects of U‐Bending on Pitting Corrosion of 304L Stainless Steel

The influence of cold U‐bending on pitting corrosion of 304L stainless steel in an acidic NaCl solution is investigated using surface analyses and electrochemical measurements. The pitting behavior of the exterior and interior surfaces of U‐bended specimen exhibiting tensile and compressive residual stress respectively are both considered. The results show that microstructural modification by U‐bending promotes the pit nucleation. Considering the passive film properties after U‐bending, no significant change in both the thickness and Cr/Fe ratios of the passive films formed on the two deformed surfaces can be found. The accompanying residual stresses after U‐bending, especially the tensile residual stress, exhibits a remarkable acceleration of the metastable pit growth rate. Therefore, the pitting potential declines significantly for the exterior surface of U‐bended specimen. However, the compressive residual stress in the interior surface facilitates the repassivation of the metastable pit, can nullify the negative effect of microdefects for the pitting corrosion resistance, so that the pitting potential of the interior surface of U‐bended specimen does not decrease.

EIS Characteristics of Galvanic Couple of Aluminum Alloy and High-strength Steel under Thin Solution Films

Galvanic corrosion of 6061-T6 (AA) coupled with high-strength steel (HSS) under 2 M NaCl solution films was investigated by electrochemical impedance spectroscopy (EIS). The AA is passivated in a 2 M NaCl solution and suffered pitting corrosion by galvanic coupling with HSS of the same surface area. Impedance of the AA/HSS couple was successfully measured under thin solution films (25–100 μm) using a potentiostat as a zero-resistance ammeter. The obtained impedance data shows a typical transmission line behavior above 1 kHz, owing to a nonuniform current distribution. Impedances for the AA and HSS were separately measured in the frequency domain. The average growth rate of pits on the AA surface, estimated from the charge transfer resistance for AA, increased with decreasing solution film thickness.