Localized Corrosion Research Articles

Effects of H2S content on the corrosion behavior of gas storage reservoir injection and production pipeline steel in CO2-H2S environment

The effects of H2S content on the corrosion behavior of gas storage reservoir injection and extraction pipeline steel in a CO2-H2S environment were investigated by surface characterization and ultrasonic thickness measurement. The results show that the corrosion products of gas injection and extraction pipelines under real conditions are more complex. In the CO2-H2S environment, with the increase of H2S content, the corrosion rate of gas storage reservoir gas injection and extraction pipeline steel firstly increases and then decreases. At a partial pressure ratio of CO2 to H2S of 550, corrosion resulted mainly in the formation of FeCO3, FeS2, and Fe3O4, with limited generation of stabilizing protective films. This led to severe localized corrosion, mainly driven by CO2. In contrast, when the CO2 to H2S partial pressure ratio was reduced to 5.2, the corrosion mainly produced Fe7S8, FeS2, and BaSO4, which promoted the formation of a more stable protective film on the inner wall of the tube, while the presence of gums reduced the severity of the localized corrosion and shifted the corrosion control to H2S.

CAVITATION EROSION IN FRANCIS TURBINES

The phenomenon of secondary flow is a global problem that causes cavitation erosion in hydraulic equipment. Cavitation is a phenomenon of localised corrosion of the metal surface leading to instability and highly uneven flow behaviour with a consequent excessive noise, vibration, and decreased efficiency in Francis, Kaplan, and other turbines. Both Kaplan and Francis turbines are reaction turbines. Francis turbines (FT) are used worldwide due to their relatively compact design, high efficiency, and operation underwater at heights ranging from 100 to 300 m with an efficiency ranging from 90% to 95%. The article analyses the latest relevant research conducted by various researchers on different turbine components. The analysis shows that this type of erosion depends on flow characteristics, surface, and properties of the material eroding. Tools for design optimisation, cavitation erosion, and well-conducted experiments will provide results for identifying and reducing erosion. Although some researchers conducted experimental work to study the effect of cavitation erosion, literature on computational fluid dynamics (CFD) is very scarce. Over the past two decades, experts have been applying CFD methods to detect cavitation by examining areas where the pressure is below the vapour pressure with a single-phase model. Most studies do not consider the impact of cavitation bubbles on the flow field. However, these methods cannot provide detailed information, such as the impact of cavitation on efficiency or a more accurate prediction of the cavitation bubble size. Some researchers use cavitation inducers and some of the latest visualisation methods as experimental tools to study cavitation phenomena. In the last decade, a numerical methodology has been widely used in research and experiments, yielding significant results. Studying cavitation erosion in hydroelectric turbine systems presents a complex challenge for future research. Many parameters and features still require further investigation. All the discussed studies have established that cavitation phenomena require state-of-the-art equipment for their detection and visualisation. Moreover, more work is necessary for the numerical assessment of cavitation. Keywords: hydroelectric turbine, cavitation erosion, computational fluid dynamics.

Prediction of quantitative in-situ local corrosion via deep learning

A deep understanding of corrosion behavior is critical for improving steel durability and reliability. Typically, it requires significant experimental effort and extensive measurements over a long period of time. Therefore, exploring the time-dependent corrosion at an early stage to predict its progress at a later stage can effectively understand it. In this study, we quantitatively predicted later stages of local corrosion behavior using deep learning methods based on the early stage topographical information. Furthermore, we predicted and visualized the formation, growth, and accumulation of the particle-like oxides. Our proposed method can be extended to other types of corrosion-resistant electrochemical materials.

Synergistic effects of mixed microorganisms on the corrosion of X65 carbon steel in actual reinjection water

Complex microbiological interactions in reinjection water can lead to severe corrosion of pipelines. In this study, X65 specimen was used for corrosion simulation experiments to explore the microbiologically influenced corrosion (MIC) and mechanism in actual oilfield reinjection water. The results of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) showed that the X65 carbon steel was severely corroded by microorganisms, with the maximum localized corrosion pit depth of 15.04 μm after 28 days of immersion. Electrochemical analysis and weight loss measurement further confirmed that the mixed microorganisms caused serious corrosion of X65 carbon steel, and the maximum corrosion rate was 0.249 mm/y. Furthermore, microbial community structure determination showed that mixed microorganisms in the actual reinjection water formed a corrosive biofilm on the surface of X65 steel, inducing severe pitting corrosion, which was mainly attributed to the synergistic effect of Pseudomonas, sulfur-oxidizing bacteria (SOB), sulfate-reducing bacteria (SRB) and methanogenic archaea. The results of this study have important guiding significance for the identification of MIC process for actual water samples of the oilfield and the timely adjustment of MIC control measures.

Spatially Resolved Assessment and Analysis of Al-Zn, Mg, and Mg/Al-Zn Metal-Rich Primers Applied to AA 7075-T651 in Full Immersion

The scanning vibrating electrode technique (SVET) was utilized to monitor localized corrosion and substrate protection of three metal-rich primers (MRP). The ability to suppress localized corrosion and provide widespread cathodic polarization to enable sacrificial anode-based cathodic protection of a AA 7075-T651 substrate with either an aluminum-rich primer (AlRP), magnesium-rich primer (MgRP), or a composite magnesium + aluminum-rich primer (MgAlRP) in a polyamide-based epoxy primer coatings fully immersed in 1 mM NaCl was investigated. Pigments did not activate uniformly in each MRP. The notion of throwing power polarizing the bare substrate and uniform current and potential distributions at scratch sites does not describe the behavior observed. In cases where activation occurred, protection was noticed in the form of suppression of local anodes on bare AA 7075-T651. Local corrosion was suppressed on heterogeneously corroding AA 7075-T651 with strong local anodes and cathodes. Widespread cathodic polarization was absent. The MgRP and MgAlRP were shown to provide superior local corrosion suppression associated with pitting on AA 7075-T651 compared to the AlRP.

Corrosion behavior of 2A97 Al−Cu−Li alloys in different thermomechanical conditions by quasi-in-situ analysis

As a promising material in the aircraft industry, 2A97 Al−Cu−Li alloy exhibits high corrosion susceptibility that may limit its application. In the present work, to illustrate the influences of precipitate and grain-stored energy on localized corrosion evolution in 2A97 Al−Cu−Li alloy, cold working and artificial aging were carried out to produce 2A97 Al−Cu−Li alloys under different thermomechanical conditions. Quasi-in-situ analysis, traditional immersion test and electrochemical measurement were then conducted to examine the corrosion behavior of 2A97 alloys. It is revealed that precipitate significantly affects Cu enrichment at corrosion fronts, which determines corrosion susceptibility of alloys, whereas grain-stored energy distribution is closely associated with localized corrosion propagation. It is also indicated that quasi-in-situ analysis exhibits a consistent corrosion evolution with traditional immersion tests, which is regarded as a proper method to explore localized corrosion mechanisms by providing local microstructural information with enhanced time and spatial resolutions.

Study on the Destruction Law and Main Controlling Factors of Corrosion Product Film in H2S-CO2 Coexistence System

Abstract The failure law and main controlling factors of corrosion product film in this corrosion environment were studied according to the characteristics of H2S-CO2 coexistence in a gas field pipeline, so as to provide guidance for corrosion prevention and control of gas field pipeline. Sediment effects of sand particles in the pipeline on corrosion, the influence of flow rate, dissolved oxygen and sediment on corrosion products were analyzed by conducting corrosion experiments at 0.5m/s, 1m/s and 2m/s, corrosion experiments without oxygen and aerobic conditions. The destruction law of corrosion product film in pipeline and the main controlling factors of corrosion product film in single well pipeline and gathering and transportation line were determined. The results show that high flow rate will cause local damage of corrosion product film and promote pitting corrosion, dissolved oxygen will destroy the integrity of corrosion product film, and sediment is one of the factors causing local corrosion and perforation of pipeline inner wall. The corrosion product film structure of the gas field pipeline will be destroyed and pitting corrosion under the condition of high flow rate, oxygen and sand deposition. Meanwhile, the main control factor affecting the corrosion product film destruction of the gas field single well pipeline is dissolved oxygen, and the main control factor affecting the corrosion product film destruction of the gas field gathering and transportation main line is sediment.

Micro-galvanic corrosion behaviour of Mg−(7,9)Al−1Fe−xNd alloys

The localized micro-galvanic corrosion process and the kinetic information of Mg−(7,9)Al−1Fe−xNd alloys were investigated by in situ observation under electrochemical control and in situ atomic force microscopy (AFM) in an electrolyte environment. The results revealed that the formation of the Nd-rich phase in alloys resulted in a decrease in the Volta potential difference from ~400 mV (AlFe3/α-Mg) to ~220 mV (Nd-rich/α-Mg), reducing the corrosion products around the cathodic phase and corrosion current density of the microscale area. The addition of Nd significantly improved the corrosion resistance, mainly due to the suppression of the micro-galvanic corrosion between the second phases and substrate. Finally, the corrosion mechanism of Mg−(7,9)Al−1Fe−xNd alloys was discussed based on in situ observations and electrochemical results.

Exploration on the corrosion inhibition performance of Salvia miltiorrhiza extract as a green corrosion inhibitor for Q235 steel in HCl environment

Salvia Miltiorrhiza, extensively distributed and commonly employed as a traditional Chinese medicinal herb, has garnered significant attention. In this study, the Salvia Miltiorrhiza extract (SME) was prepared by one-step water extraction method, and was firstly used as a novel corrosion inhibitor for Q235 steel in 1 mol/L HCl solution. As identified via liquid chromatography-mass spectrometry, the findings reveal that Salvianic acid A, tanshinone II A, danshenxinkun D, dihydrotanshinone, and methylene tanshinquinone are the primary constituents of SME. The optimum corrosion inhibition efficiency reached 92.8 % at 200 mg/L and maintained at 90.4 % after 72 h. Based on in-situ scanning vibration electrode technology (SVET) monitoring, the adsorption of inhibitor molecules on metal surface greatly retarded the propagation of localized corrosion. AFM examination of the corroded surface reveals that the samples supplemented with SME exhibit a smoother surface compared to the blank group. The force curve graph for the SME-added group demonstrates a more evenly distributed point array and an elevated average adhesion force, indicating that the addition of SME improves the corrosion resistance of the metal surface. XPS characterization illustrated that SME interacted with iron ions to form insoluble precipitate. This work investigated the application of SME as an eco-friendly corrosion inhibitor for carbon steel in acidic medium, providing a new approach for the high value-added utilization of Salvia Milliorrhiza.

A coupling method for CRUD mass calculation based on Eulerian-Eulerian two-fluid model

Abstract The corrosion products occur in the pressure boundary in the pressurized water reactor primary loop which is known as CRUD. CRUD could increase the risks of crud induced power shift and crud induced localized corrosion. The mechanism of CRUD production depends on nucleate boiling. Eulerian-Eulerian two-fluid model has been currently proved as effective means to understand flow boiling character. In this research, the input data of thermo-hydraulic parameter is obtained by CFD method. The CRUD mass has been calculated based on thermo-hydraulic and chemical coupled model. The main calculation code in this article is FLUENT and CAMPSIS. The calculation results show that the CRUD does most likely occur the 3rd grid mixing vanes from the top of the fuel rod. The maximum CRUD mass is closer to the position of onset of nucleate boiling.

Achieving balanced uniform and local corrosion performance of SS 316L/IN625 hybrid alloy manufactured by directed energy deposition

This study investigates hybrid stainless steel (SS) 316L/Inconel 625 (IN625) materials via DED for hydrofluoric acid (HF) corrosion resistance. 20% SS 316L + 80% IN625 (20% 316L) exhibits low uniform corrosion (0.35 mm/y) and improved local corrosion performance. High Cr2O3 content in its passive film ensures uniform corrosion resistance. The thermodynamic analysis combined with microstructure observation shows reduced Nb content in 20% 316L's Laves phase, enhancing resistance to micro-galvanic local corrosion. This study provides insights into the design and manufacturing technology of corrosion-resistant materials in harsh corrosive environments.

Research on eccentric-compressive behavior of steel stub columns with localized corrosion

To explore the impact of localized corrosion on the mechanical properties of hollow steel columns under eccentric loads, a specialized localized immersion-accelerated corrosion apparatus was developed. This device facilitated the creation of 17 locally corroded specimens, all subjected to eccentric loading. A systematic examination was conducted on various corrosion parameters including corrosion length, corrosion angle, localized corrosion rate, and corrosion location as well as loading conditions, which encompassed eccentricity and loading angle. Surface corrosion morphology and statistical parameters of the specimens were obtained using a 3D scanner. Subsequently, a nonuniform corrosion model, based on element displacement, was formulated through finite element analysis. Both experimental findings and numerical simulations indicate that localized corrosion does not alter the failure mode of locally corroded circular steel tubes (LCCSTs), which predominantly undergo local buckling in the compressed region. However, it was noted that localized corrosion leads to the elimination of the ascending segment in the load-displacement curve of the LCCSTs, thereby reducing both the ultimate load and ductility. Interestingly, the ultimate load of the LCCSTs was found to be relatively unaffected by variations in corrosion length and location but significantly influenced by factors such as localized corrosion rate, corrosion angle, eccentricity, and loading angle. Furthermore, through a comparative analysis of existing calculation models for the ultimate load of LCCSTs in major specifications, a practical model that accounts for localized corrosion is proposed. This model demonstrates high accuracy and is expected to enhance the understanding and prediction of the ultimate load capacity of LCCSTs in real-world applications.

Study on the corrosion and damage behaviours of P110 tubing of deep shale gas wells

This study conducts weight loss corrosion experiments by a high-temperature autoclave to investigate the corrosion behaviours and the damage rules of mechanical properties of P110 tubing under coupling working conditions of multiple factors (temperature 50–155 °C, CO2 content 1%–2%, Cl− content 10,000–20,000 mg/L). It analyses the characteristics of corrosion products of P110 steel using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (EDS). In addition, the 3D morphology and size of local corrosion pits are measured microscopically. The mechanical properties’ damage behaviours at different tubing positions are analysed by constant-load tensile stress corrosion tests. The results showed that the average corrosion rate of the tubing reaches the maximum value of 1.627 mm/a at the middle section of the shale gas well. With an increase in temperature and CO2 partial pressure, the depth of the local corrosion pits on the tubing rises from 3.8 to 25.0 μm. The yield strength and tensile strength of the tubing at the bottom-hole section reduced by less than 8%, and the coupling damage effect of stress and corrosive mediums is serious. The tubing shows a sensitivity to stress corrosion cracking at the bottom-hole section. It was recommended that corrosion inhibitors should be cyclically added to inhibit CO2 corrosion to control the corrosion rate of the tubing within the range of medium-degree corrosion, thus ensuring that the strength reduction of P110 tubing under the corrosion working conditions containing CO2 and sulphate-reducing bacteria coupled with tensile stress is within the controllable range of safety factor.

Study on mechanical properties of locally corroded square steel tube short column

To investigate the axial compressive properties and failure modes of 18 locally corroded square steel tube short columns, salt spray corrosion tests were conducted. The findings indicate that local corrosion in the horizontal direction significantly impacts the ultimate bearing capacity of the specimens, with all failures occurring in the corroded areas. However, the influence of the corrosion area on the ultimate bearing capacity and ductility of the specimens is not evident. A local corrosion model for square steel tube short columns was developed using the finite element method. The ultimate bearing capacity determined through finite element simulation closely aligns with experimental results, validating the reliability of the simulation approach. Moreover, a comparison is made between the prediction models of the BP neural network and the GA-BP neural network, with the prediction effectiveness of each model evaluated using the leave-one-out method. The verification results indicate that the GA-BP neural network model demonstrates superior predictive performance, with an average error of 3.14%.

Corrosion at Top-of-the-Line in High Pressure and Dense CO2 Environments

This study presents unique data on top-of-the-line corrosion (TLC) occurring in high-pressure environments where CO2 was in the gaseous, liquid, or supercritical state. While CO2 is traditionally in a gaseous phase, this form of degradation is referred to as TLC. In this study, similar phenomena with different mechanisms were observed in liquid CO2 and supercritical states all of which are referred to as TLC due to the location of specimens and ease of comprehension. Experiments were conducted to investigate the effect of CO2 partial pressure (ranging from 20 bar to 100 bar) with temperatures (30°C to 50°C) relating to different water condensation rates (0.001 mL/m2/s to 0.1 mL/m2/s). Uniform and localized TLC rates increased with a higher water condensation rate and surface temperature. As long as CO2 remained gaseous, its partial pressure (pCO2) showed a negligible influence on both uniform and localized TLC rates. At the highest gaseous CO2 content tested, the formation of a protective iron carbonate (FeCO3) layer decreased the TLC rate, with this effect being more pronounced at lower water condensation rates. The risk of localized corrosion for specimens exposed to this environment at high and medium water condensation rates remained an issue. In the dense phase CO2 environment, the difference in temperature between the bulk environment and the specimen’s surface caused a similar phenomenon to water condensation, termed water drop-out, which resulted in corrosion. The rate of water drop-out could not be measured experimentally or estimated theoretically but is a complex function of temperature, pCO2, and CO2 physical state. The interplay between high pCO2 and low pH of the dropped-out water led to elevated uniform and localized corrosion rates. The depth of localized corrosion, at the high and medium water drop-out conditions, reached its maximum at the surface temperature of ca. 45°C. At a lower surface temperature of ca. 25°C and a higher surface temperature of ca. 65°C, the maximum penetration rate was decreased due to slower kinetics of reactions and the formation of a more protective FeCO3 layer, respectively. The results presented in this study highlight the significant difference between corrosion rates, especially in the form of localized damage, in gaseous and dense-phase CO2 environments.

Gradient textures induce micro-galvanic corrosion on Mg

In this study, the reason for the non-basal-plane-rich area more corrosion resistant than the basal-plane area on pure Mg in NaCl electrolyte was demonstrated based on quasi-in-situ EBSD observations. Due to the higher concentration of dissimilar crystallography orientations in the basal-plane-rich area, the gradient textures and ‘micro-texture’ galvanic couples were promoted. This exacerbates the progression of localized corrosion in basal-plane-rich area, ultimately deteriorating the overall corrosion performance of Mg. Randomizing the gradient texture diminishes the tendency towards micro-galvanic corrosion and enhances the corrosion resistance of Mg. These findings shed light on yet another facet of complex mechanism of Mg corrosion.

Mechanism of alteration in passivity of additively manufactured Ni-Fe-Cr Alloy 718 caused by minor carbon variation

Unlike conventional alloys, where carbon content typically promotes carbide compound formation and reduces localized corrosion resistance, the impact of carbon in additively manufactured materials remains largely unexplored due to rapid cooling rates inhibiting carbide formation. This study addresses the novel question of whether reducing carbon content benefits corrosion performance and its underlying mechanisms in Ni-Fe-Cr-based alloy 718. Employing high-resolution techniques and microcapillary electrochemical methods, it was revealed that higher carbon content increases dislocation density at cell boundaries. This increased dislocation density facilitates the enhanced ejection of nickel and iron from the protective chromium oxide layer on the surface, leading to the formation of a defective outer Ni-Fe oxide layer. This compromised layer subsequently diminishes the alloy's corrosion resistance, particularly under tensile stress conditions.

Effect of Fatigue and Precorrosion Fatigue on Fatigue Crack Propagation and Fracture Failure Behavior of 5B70 Aluminum Alloy

Aluminum alloys are ideal lightweight structural materials for spacecraft, but they are susceptible to local corrosion during service. Herein, a systematic investigation is carried out to determine the fatigue behavior of 5B70 aluminum alloy under salt spray precorrosion. The mechanism of salt spray corrosion, fatigue life, crack propagation, and failure fracture mechanism of 5B70 aluminum alloy are studied. Under the salt spray corrosion, 5B70 aluminum alloy mainly undergoes pitting corrosion via a galvanic corrosion mechanism. After precorrosion, the formation of macroscopic fatigue cracks is accelerated, which significantly reduces its fatigue life. Fracture occurs due to single crack initiation and propagation under fatigue conditions. The fatigue crack tip undergoes a mixture of intergranular and transgranular modes, but mainly transgranular mode. Multiple strain localization phenomena occur during precorrosion fatigue, and corrosion pits on the surface provide a tortuous crack propagation path; the fatigue crack tip is mainly transgranular mode.

Behavior of eccentrically loaded slender concrete-filled steel tubes with defect representing random local corrosion

This paper focuses on the eccentric compression behavior of slender concrete-filled steel tubes (CFSTs) subjected to random localized corrosion and the localized corrosion was represented by a local defect. The randomness of corrosion includes the random locations and the random geometric characteristics that involve irregular corrosion profiles and uneven surfaces. Corrosion on the steel tube was represented by a defect in the experiment. The influence of spatial characteristics of local corrosion was investigated by seven CFST beam-column specimens, each featuring the defect in different locations along both height and circumferential directions. It was indicated through test results that both dimensions and locations of the defect considerably affected the failure mode and ultimate strength of the CFSTs. A numerical analysis was performed to confirm that local corrosion with irregular shape and uneven surface on a CFST beam-column can be approximated by a constant-depth circumscribed rectangular defect. Subsequently, a parametric analysis was conducted to find out how the corrosion dimensions, locations, and other critical parameters such as steel ratio, slenderness ratio, and material strengths influence the eccentric compression behavior of CFST. It revealed that negligible effects from local corrosion were observed in cases where slight corrosion was located near the column end. Finally, a calculation method was introduced to predict the ultimate strength of randomly localized corroded CFST beam-columns, with high precision.

Enhancing corrosion resistance of AZ31B magnesium alloy substrate in 3.5 % NaCl solution with Al-Si coating prepared by cold metal transfer-based wire arc additive manufacturing

In this study, we explored an innovative approach to enhance the corrosion resistance of AZ31B magnesium alloy in 3.5 wt% NaCl solution by applying an Al-Si coating using cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM) technology. The findings indicate that the Al-Si coating improved the alloy’s corrosion performance, with a more noble self-corrosion potential (- 0.97 VSCE) and lower self-corrosion current density (3.68 μA/cm2) compared to untreated AZ31B. Long-term immersion tests demonstrated that AZ31B suffered from severe localized corrosion, while Al-Si coating maintained a uniform corrosion profile. Analysis of the corrosion products showed that the Al-Si coating primarily comprised oxidized Mg and hydroxide Al, with minimal oxidized Al and Si, in contrast to the mainly metallic and hydroxide Mg on AZ31B. By reducing the electrochemical activity and enhancing the stability of corrosion products, the Al-Si coating significantly improved the corrosion resistance of AZ31B substrate. This study suggests a promising avenue for advancing the durability of magnesium alloys in corrosive environments.