Growth Of Corrosion Pits Research Articles

Investigation of microstructure and corrosion resistance of an Al-Zn-Mg-Cu alloy under various ageing conditions

In this study, transmission electron microscopy and 3D optical profilometer were employed to investigate the effects of single-stage ageing and regression re-ageing treatments on the microstructure and corrosion resistance of Al-Zn-Mg-Cu alloy. The results indicate the intergranular corrosion resistance is increased by 36% with the regression re-ageing. Based on the semi-elliptical damage model, a 3D expansion model for pits is established. Meanwhile forms a systematic study of the formation mechanism, nucleation and growth of corrosion pits. This will contribute to the systematic and in-depth study of the corrosion resistance of Al-Zn-Mg-Cu alloy in aviation applications.

Corrosion behaviours of a LaB6/TiC/TiB/ti composite in neutral or acidic electrolytes

LaB6/TiC/TiB was incorporated into a Ti–Al–Zr–Sn alloy to achieve an efficient improvement in acid-resistance. The incorporation of LaB6/TiC/TiB deteriorated the performance of the passive layer, but impeded the penetration of the corrosive medium into Ti matrix. The incorporation of the conductive reinforcements promoted galvanic corrosion, leading to a decrease in barrier effect of the passive film. Delayed passivation in less aggressive media was achieved by controlling the formation and growth of corrosion pits. The distribution of LaB6/TiC/TiB determined the corrosion properties after complete failure of the passive layer. An appropriate approach for enhancing the acid-resistance of Ti-based materials was suggested.

REVIEW: INVESTIGATION OF PROCESSES OF DAMAGE TO THE HEAT TRANSFER TUBE OF WWER-1000 STEAM GENERATORS

The analysis of operational damages of heat transfer tubes (HTT) in steam generators (SG) of WWER-1000 power units was carried out. The processes of contamination of the surfaces of HTT of SG PGV-1000M are considered. The processes of formation and growth of corrosion pits on the surface of heat transfer tubes are analyzed. The process for the initiation of corrosion pits and the development of cracks in the heat transfer tubes metal, which includes the combined action of a corrosive environment and non-metallic inclusions in heat transfer tubes, was proposed.

Pitting corrosion behavior and mechanism of 316L stainless steel induced by marine fungal extracellular polymeric substances

In this study, effect of extracellular polymeric substances (EPS) secreted by fungus Aspergillus terreus on the pitting corrosion of 316L stainless steels (SS) was deeply investigated by electrochemical measurements and surface analysis. Results demonstrated that adsorption of EPS can change surface wettability of 316L SS leading to a much more hydrophilic steel–water interface. EPS not only accelerates uniform corrosion but enhances pitting corrosion of 316L SS. EPS can promote the formation of metastable pitting corrosion and the subsequent growth of corrosion pits. The density of corrosion pits (>2 µm) reach (5.6 ± 0.5)× 103 pits/cm2 when EPS is 400 mg/L.

Improving the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating by vacuum sealing with silicone resin

The properties of thermal sprayed WC based cermet coatings are limited by their structural defects, especially corrosion resistance. This article studied the influence of vacuum sealing with silicone resin on the long-term corrosion resistance of HVOF sprayed WC-Cr3C2-Ni coating in 3.5 wt.% NaCl solution. The surface morphologies of the unsealed and sealed coatings show the high compatibility between sealant and WC-Cr3C2-Ni coating. Benefiting from the block of sealant in defects, the sealed coating presents lower corrosion current density (5.843 × 10−8 A cm−2) after long-term corrosion than the unsealed coating (1.776 × 10−7 A cm−2). Owing to the vacuum treatment, sealant adequately penetrates and remains inside the WC-Cr3C2-Ni coating, and inhibits the growth of corrosion pits on the sealed coating surface. The vacuum sealing with silicone resin effectively hinders the diffusion of corrosion solution, and provides practicable strategy to improve the corrosion resistance of the coatings.

Corrosion test and three-dimensional cellular machine simulation of Q235 steel by ion diffusion in different soil environments

In the actual soil environment, due to the unpredictable characteristics of metal pitting corrosion. Therefore, in this study, soil composed of different concentrations of corrosion medium was used for the mental corrosion test, and the experimental results of single ion and multiple ions were compared. At the same time, the corrosion behavior of metals is introduced in combination with the mathematical model of unsteady diffusion. In addition, the cellular automata model verification method is used to study the comparison and verification of the diffusion growth model of the model corrosion pit in different iteration steps under the discrete mathematical model. The results show that the growth and diffusion trend of corrosion pits controlled by the concentration of SO42-, HCO3–, and Cl- is consistent basically with the law reflected by cellular automata.

Improving corrosion resistance of Ti alloy in hydrochloric acid by embedding TiC/TiB and Y2O3 ceramic nano-particles

A TiC/TiB/Ti composite was fabricated and Y2O3 nanoparticles were introduced to improve the corrosion resistance in HCl solution. When the HCl concentration exceeded 5 wt%, the passive film on the Ti alloy lost efficacy and the alloy suffered from severe exfoliation corrosion. Incorporating reinforcements and Y2O3 refined the grains, leading to an increased frequency of corrosion pits. The homogeneous distribution of reinforcements and Y2O3 in composites inhibited corrosion pit growth and exfoliation corrosion, resulting in increased corrosion resistance in HCl solutions. An innovative Y2O3 reinforced Ti/TiC+TiB composite with high resistance to concentrated acid is proposed for application in extreme environments.

Influence of load frequency and corrosive environments on fatigue behavior of as-extruded Mg–Zn–Zr–Nd alloy

Fatigue resistance is a key criterion for new material that would be applied as an implant. As a “smart” implant material with good biodegradability and high strength, Mg–2Zn–0.5Zr–0.5Nd alloy has been recognized as a promising candidate for bone implant. A series of tests on fatigue properties of extruded Mg–2Zn–0.5Zr–0.5Nd alloy are carried out in this study. Alternating cyclic dynamic loads at frequencies of 5 Hz and 10 Hz both in air and in 0.9 wt% NaCl solution were loaded on extruded Mg–2Zn–0.5Zr–0.5Nd alloy respectively. In air condition, the fatigue life variational trends of Mg–2Zn–0.5Zr–0.5Nd alloy at different frequencies are similar according to the stress-life (S–N) curves. However, under high fatigue cycles, the lower loading frequency prolongs the loading time of repetitive stresses and reduces the fatigue life of the samples. In 0.9 wt% NaCl solution, the S–N curves under different frequencies show different changing trends due to the synergistic effect of corrosion environment and loading frequency. It is also found that the fatigue resistance of the alloy in 0.9 wt% NaCl solution is poorer than that in air due to the significant promotion of the formation and growth of corrosion pits by the NaCl environment. In addition, according to the fatigue fracture morphology analysis, it can be found that the failed samples show different fracture patterns in air and 0.9 wt% NaCl solution.

Verification, validation, and parameter study of a computational model for corrosion pit growth adopting the level-set method. Part I: Corrosion

Corrosion is a phenomenon observed in structural components in corrosive environments such as pipelines, bridges, aircrafts, turbines, etc. The computational model of corrosion should enjoy two features: a) accurately considering the electrochemistry of corrosion and b) properly dealing with the moving interface between solid and electrolyte. There are several approaches to model corrosion such as using FEM with mesh refinement algorithms, combining FEM and level-set method, employing finite volume methods, adopting peridynamic formulation, and utilizing phase field models. Because of its accuracy, lower computational cost, and robust dealing with multiple pit merging, the model which combines FEM with level-set method is selected to be more extensively assessed in this paper. Part I focuses on demonstrating the model’s capabilities of simulating pitting corrosion through a set of numerical examples which include numerical solution verification, experimental validation, and uncertainty quantification of model parameters and properties.

Quantitative 3D Characterization for Kinetics of Corrosion Initiation and Propagation in Additively Manufactured Austenitic Stainless Steel.

In situ X-ray computed tomography (X-ray CT) is used to investigate the effects of characteristic microstructural features on the pitting initiation and propagation in austenitic stainless steel specimens prepared with laser powder bed fusion (LPBF) additive manufacturing. In situ X-ray CT in probing the mechanism and kinetics of localized corrosion is demonstrated by immersing two LPBF specimens with different porosities in an aggressive ferric chloride solution for the evaluation of corrosion. X-ray CT images are acquired from the specimens after every 8hours of immersion over an extended period of time (216hours). Corrosion pit growth is then quantitatively analyzed with a data-constrained modeling method. The pitting growth mechanism of LPBF stainless steel is found to be different from that of conventional stainless steels. More specifically, the mechanism of corrosion pit initiation is closely correlated with the original lack of fusion porosity (LOF) distribution on the surface of the specimens and preferential pit propagation through the LOF pores inside the specimens. Pit growth kinetics are derived from pit volume changes determined through 3D data analysis. The pit growth kinetics in LPBF specimens are found to vary in the initial pit formation, competitive pit propagation, and the dominant pit growth stages.

Modeling of Corrosion Pit Growth in Buried Steel Pipes

A review of the published literature shows that although intensive research has been conducted on corrosion of steel in soils, accurate prediction of corrosion pit growth remains a serious challenge. This study aimed to develop a new model for predicting the maximum pit depth in buried steel pipes and verify it with data obtained from actual corrosion measurements in the field. A method was developed that integrates advanced data mining techniques, shape descriptive modeling, and evolutionary polynomial regression in deriving the underlying relationships between corrosion-influencing factors and model parameters. It was found that the area effect ψ is closely related to the ion content of the soil (Na+,K+, Mg2+, Cl−, and SO42−) and that the correlation between model parameter Ku and soil properties varies among soils with different aeration. It was also found that the developed predictive model exhibits superiority over existing models in quantifying multiple-phase corrosion growth. The proposed method can effectively correlate model parameters with the main contributing factors, which enables researchers and practitioners to accurately predict the maximum corrosion pit depth in buried steel pipes.

The Effects of Pits Size and Shape on Fatigue Crack Initiation

Generate and monitor the growth of corrosion pits on the surface of 316L stainless steel using the scanning droplet cell technique and assess the effects of varies factors such as pits size, pits shape, flow rate, and applied stress on pit initiation and growth. Configure of a test system to measure the pit and short fatigue crack growth behaviour, to investigate each stage of the corrosion fatigue damage process occurring at the material surface and compare this with the modified film surface using alternating voltage passivation process (AVPP). Understand the effects of corrosion on cracking behaviour during the different stages of fatigue crack growth.

Time-Dependent Reliability Analysis of Buried Water Distribution Network: Combined Finite-Element and Probabilistic Approach

Corrosion deterioration is the predominant factor for a large number of cast iron (CI) water main breaks. The reliability of CI pipelines decreases overtime as corrosion growth on pipe walls significantly reduces the strength of pipeline materials. To predict the reliability of water pipelines accurately, this study used a finite-element analysis (FEA) approach to determine the maximum pipeline stress at various stages of the pipeline’s life. A series of FEAs was performed to consider uncertainties in parameters associated with stress analysis. The circumferential stress was found to be the most critical stress for pipelines. Time-variant circumferential stress was obtained by accounting for the time-dependent corrosion pit growth on the pipeline wall. The time-variant failure probability of pipelines was determined by comparing the circumferential stress and the tensile failure strength of the pipeline at the burst limit state. The FEA model developed in this study was validated with the results obtained from previous studies. Monte Carlo simulation was performed to generate the fragility curves in a probabilistic manner. This study also compared the fragility curves obtained utilizing FEA and conventional equations (elastic ring theory and the Spangler formula). The results showed that analytical equations are too conservative and provide a higher failure probability of pipeline. A sensitivity analysis was performed to identify the relative importance of parameters contributing to the pipeline’s performance. Additionally, the reliability of the water distribution network (WDN) was calculated based on the minimum cut set (MCS) and graph decomposition methods. The results showed that the two methods provide similar outcomes, however, MCS provides a greater safety margin. The proposed approach was illustrated for an example WDN.

Modeling of Corrosion Pit Growth for Buried Pipeline Considering Spatial and Temporal Variability

Corrosion of metal in soils has been intensively investigated in the past. However, a review of the published literature shows that there are challenges for researchers to accurately predict the corrosion growth of buried pipes with spatial and temporal variations. This paper intends to develop a methodology to predict the corrosion pit growth for buried pipelines by thoroughly considering the spatial and temporal variability of corrosion processes. The developed method integrates the corrosion science, conditional random field theory, stochastic process, and copula method into an interrelated simulation algorithm for generating corrosion pit growth fields. It is found in the paper that the shape parameter and rate parameter of the gamma process, as well as the correlation structure of corrosion processes, are not only time-variant but also exhibit spatial variability with time. It is also found that the developed method is much superior to other methods in terms of accuracy and effectiveness. The proposed method considers the correlation between corrosion processes in a long pipeline, which is more practical. It can be concluded that generating an accurate corrosion growth field fully requires consideration of the spatial and temporal variability of model parameters.

Quantitative Characterization of the Spatial Distribution of Corrosion Pits Based on Nearest Neighbor Analysis

Nearest neighbor analysis (NNA)-based procedures are proposed for the quantitative characterization of the spatial distribution of corrosion pits in metals. After the exposure of a carbon steel to a 3.5% NaCl solution mist, the results derived from observation of corrosion pit initiation and growth were used to justify the applicability of this approach. The pits initially comprised clusters that were superimposed on a randomly distributed background set. The clustered pits subsequently coalesced, evolving into a more random pit arrangement. Furthermore, it was revealed that in the early stages, the spatial pit distribution can be predicted via inspection of surface inclusions prior to the corrosion process.

Pitting corrosion modelling of X80 steel utilized in offshore petroleum pipelines

High strength steels such as X80 steels have recently been used more frequently in production of offshore structures. However, they may still be subject to degradation processes such as corrosion considering the conditions in marine environment. Pitting corrosion is a destructive form of corrosion which reduces the material resistance and may result in failure accidents with severe financial, human life and environmental consequences. The process of pitting corrosion is inconsistent and largely stochastic being influenced by a number of parameters with a high level of uncertainty. This makes it very difficult to predict corrosion in terms of its initiation time and spatial behavior. Therefore, it is vital to investigate pitting corrosion phenomena in offshore structures using a probabilistic approach for the assessment of structural reliability and operational safety. In this study, an in-situ experiment has been conducted on X80 steel in an NaCl solution in a laboratory environment to observe the generation and growth of corrosion pits. A probabilistic model based on Hierarchical Bayesian Approach (HBA) is developed for predicting the pitting corrosion growth rate using experimental results. In order to model the process more realistically, the proposed methodology considers the degradation process to be consisting of the time needed for pit initiation and propagation. The results indicate that the proposed methodology is capable of predicting the time required to reach a specific pit size. The methodology developed in this study can be applied to estimate the remaining useful life of subsea structures.

Probabilistic Life Prediction for Reinforced Concrete Structures Subjected to Seasonal Corrosion-Fatigue Damage

The coupled effect of corrosion and fatigue deteriorates the performance of reinforced concrete (RC) structures. This paper proposes a novel framework for the probabilistic life prediction of aging RC structures under seasonal corrosion-fatigue damage based on the fracture mechanics and equivalent initial flaw size concept. A series of fatigue crack growth tests of steel bars in air and solution environments are conducted to simulate the fatigue crack growth behavior of rebar in different seasons. The framework includes three critical deterioration stages: corrosion initiation–pure fatigue crack growth, competition between corrosion pit growth and fatigue crack propagation, and structural failure. The chloride ingress, cyclic load, corrosion pit growth, concrete cracking, seasonal environmental variation, and corrosion pit-induced stress concentration are considered. Following that, an uncertainty model is established to incorporate various uncertainties associated with the load and environment. The characteristics of different stages are discussed. A parametric analysis is also performed to illustrate the influence of stress concentration, concrete severe cracking, and seasonal environmental variation on the life prediction results. Several conclusions are drawn and future work is discussed based on the proposed study.

Mechanical and Electrochemical Coupled Pitting Behavior of 2219 Aluminum Alloy: A Theoretical and Experimental Study

Abstract This study attempts to provide a theoretical estimate coupled with an analysis of the measured data to predict pitting damage of an aluminum alloy 2219 under the conjoint influence of mechanical load and corrosive environment. In accordance with the basic principle of crater growth coupled with the synergistic influences of mechanical and chemical effects, the law governing the presence and growth of corrosion pits was studied. Based on the concept of microscopic damage mechanics, porosity as a damage variable was introduced and the resulting model for estimating the reduction in elastic modulus of the material that has experienced observable damage due to pitting was established. Accelerated corrosion tests and uniaxial tensile tests are carried out, and a research-grade microscope coupled with a laser range finder was used to study the formation, presence, and growth of the pits with time. It was found that the corrosion pit in the chosen aluminum alloy can be simulated as a semi-ellipsoid, and the relationship between the depth of the pit and applied stress is an exponential function. This enabled in establishing the influence of alloy chemistry on nature, extent, and severity of damage due to pitting. The macroscopic morphology of the damaged specimens after corrosion was carefully observed and analyzed. The influence of time of exposure to the environment and applied load on damage due to pitting was verified. A comparison between the calculated results and experimental data reveals an overall correctness of the method developed and discussed in this paper.

Modelling guidelines for corrosion-fatigue life prediction of concrete bridges: Considering corrosion pit as a notch or crack

Corrosion accelerates the fatigue damage accumulation and decreases the fatigue life of reinforced concrete bridges. A critical issue in the corrosion-fatigue life prediction is to deal with the relationship between fatigue crack and corrosion propagation. This paper proposes two modelling methods for fatigue life prediction of reinforced concrete bridges subjected to coupled corrosion-fatigue effect: model I considers the corrosion pit as a notch and model II treats the corrosion pit as a surface crack. The chloride ingress, cyclic load, corrosion pit growth, fatigue crack growth and concrete severe cracking are systematically considered. Following that, a probabilistic analysis is also performed to include various uncertainties in the two models, and the effects of environment aggressiveness level and traffic frequency on the prediction results are investigated. The results show that corrosion pit-induced stress concentration has a significant effect on the fatigue behavior, and modelling the corrosion pit as a notch is the preferred method for theoretical prediction. For the extreme aggressiveness environment and low traffic frequency conditions, considering the corrosion pit as a crack is an alternative modelling method for the fast assessment of aging reinforced concrete bridges due to its simplicity.

An Experimental Method to Evaluate the Effect of Welding Residual Stress on Corrosion Fatigue Properties of Structural Steel in Synthetic Seawater

Tensile residual stress can cause a reduction in the fatigue strength of steel not only in air but also in corrosive environments. In air, for example, the effect of residual stress on fatigue strength can be estimated by using relations between fatigue strength and mean stress such as the modified Goodman diagram. However, it is not clear whether a sort of fatigue strength estimation can be applicable to corrosion fatigue properties. This paper presents an experimental method to evaluate the effect of welding residual stress on corrosion fatigue properties quantitatively, where corrosion fatigue tests were conducted in synthetic seawater by using characteristic fatigue specimens that have two parts, a tensile residual stress part and the other supporting part. Bead-on-plate welding was performed for applying welding residual stress in the tensile residual stress part. Residual stress relaxation was measured using the X-ray diffraction method in the midst of fatigue testing. Effects of tensile residual stress on corrosion pit growth and S-N curves were discussed.