Simulated Soil Solution Research Articles

Effect of temperature on the electrochemical corrosion behavior of X52 pipeline steel in NS4 simulated solution

In this study, the electrochemical corrosion performance of both the base material and welded joint of X52 pipeline steel was analyzed at various temperatures (room temperature-RT, 30 °C, 50 °C, and 80 °C) using microscopic characterization techniques and electrochemical methods in a simulated soil solution (NS4). Additionally, the influence of temperatures on the electrochemical corrosion behavior of the X52 pipeline steel base material and welded joint was examined. The findings indicate that the open circuit potential (Eocp) of the base material and welded joint shifts in the negative direction with increasing temperature. The corrosion current density increased from 30.7 to 110.2 μA∕cm2 and from 19.5 to 100.2 μA∕cm2, respectively, while the polarization resistance dropped from 637.3 to 272.6 Ω•cm2 and from 961.3 to 360.7 Ω•cm2. Notably, anodic dissolution controls the corrosion process of the base material and welded joint of X52 pipeline steel at room temperature. Furthermore, the charge transfer resistance (Rt) of the base material and welded joint gradually decreases with increasing temperature, and the corrosion process transforms into cathodic diffusion control. Additionally, the welded joint of X52 pipeline steel exhibits superior corrosion resistance to that of the base material at the same temperature.

Effect of cathodic current density on hydrogen embrittlement susceptibility of X70 steel girth weld in different soil simulation solutions

PurposeIn this paper, the authors aim to study the relationship between hydrogen embrittlement (HE) susceptibility and cathodic current density applied on the X70 steel girth welds.Design/methodology/approachThe HE susceptibility of X70 steel girth welds were investigated through slow strain rate tensile test and observed and analyzed by optical microscope and scanning electron microscope methods.FindingsThe results show that HE susceptibility of X70 girth weld was basically unchanged with increasing of ion concentration while gradually increased and maintain at a specific value with the increase of cathodic current density. As for same ion content, a dense calcareous deposit layer generated on the sample surface in soil simulation solution with Ca2+ and Mg2+ resulted a decreased HE susceptibility while the porous calcareous deposit layer resulted a increased HE susceptibility.Originality/valueA logistic regression model was established to describe the correlation between HE index and the cathodic current density.

Insight into the effect of oxygen content on the corrosion behavior of X70 pipeline steel in a typical simulated soil solution by dissolution-diffusion-deposition model

In this work, traditional experimental methods were employed to investigate the effect of dissolved oxygen (DO) on the corrosion behavior of X70 pipeline steel in a low-temperature acidic-bentonite simulation soil solution. A novel model was utilized to describe the complex dissolution-diffusion-deposition process at the metal/solution interface. This model aims to enhance comprehension of the dynamics of the corrosion product layer of X70 pipeline steel under varying oxygen concentrations, as well as the effects of alloying elements (Fe, Cr and Cu) on the corrosion resistance. By integrating traditional experimental methods with calculation models, the results reveal a positive correlation between DO levels and the corrosion rate X70 pipeline steel. This relationship is attributed to the distinct characteristics of the corrosion product layers formed under different DO conditions. At low DO levels, the nucleation and growth rates of oxide/hydroxide are slower, leading to the formation of a denser, more protective corrosion product layer. Conversely, at high DO levels, the accelerated nucleation and growth rates produce larger oxide/hydroxide particles, resulting in a porous and less protective corrosion product layer. Furthermore, the variation in the protective qualities of the corrosion product layers under different DO conditions causes differences in corrosion morphology: X70 pipeline steel exhibits localized corrosion in low DO environments and more uniform corrosion under high DO conditions.

Corrosion behavior of Q345 and Q235 steels in simulated neutral soil solution

Abstract Q345 and Q235 steels are widely used in infrastructure and manufacturing. Examining the corrosion behavior of two types of steel in a neutral soil environment can facilitate the assessment of the service life of the steel machinery, thereby mitigating potential corrosion failures. In order to investigate the corrosion and mechanism of Q345 and Q235 steels in the neutral soil solution, an electrochemical test, scanning electron microscopy, and X-ray diffraction were employed to analyze the corrosion morphology, corrosion product, and electrochemical polarization curves. The results showed that no visible pitting pits were observed on the surfaces of Q345 steel and Q235 steel. The corrosion types were mainly overall corrosion in the simulated neutral soil solution. The microstructure of Q235’s corrosion product exhibits greater compactness, facilitating the formation of Fe3O4. This compound demonstrates excellent binding ability with the metal matrix and hinders the continuous corrosion of the steel. Q235 steel has better corrosion resistance with a lower corrosion rate than Q345 steel in the simulated neutral soil solution. These findings contribute valuable information for material selection considerations in manufacturing machinery in neutral soil environments.

Application of voltammetry as a technique to monitor cathodic protection performance of steel in simulated soil solution

Cathodic protection (CP) in combination with organic coating is applied as a secondary technique to mitigate corrosion of buried steel in an effort to prolong the lifespan of the buried steel pipeline. This study was aimed at developing and applying an adequate technique for monitoring the electrochemical behaviour of buried steel in the presence of CP. A modified voltammetry procedure was applied on carbon steel immersed in simulated soil solution for four days under open circuit potential (OCP) before applying CP for further ten days. Electrochemical impedance spectroscopy (EIS) was also applied at various time intervals to investigate the electrochemistry at the steel/solution interface. The voltammetry experiments revealed that the corrosion rate peaked at 680 µm/yr after three days of being subjected to OCP and then decreased to 411 µm/yr on day four as a result of a passive layer development on the steel surface. The corrosion rate was reduced from 411 µm/yr to 8 µm/yr as result of CP application before fluctuating between 21 and 40 µm/yr. The examination of steel surface via x-ray diffraction revealed the presence of calcareous deposit which resulted due to the application of cathodic protection.

Synergistic effect of microorganisms and a direct current electric field on X70 steel corrosion in a near-neutral solution

In this paper, the corrosion behavior of X70 steel in the near-neutral simulated soil solution (NS4 solution) under the synergistic effect of sulfate reducing bacteria (SRB) and a direct current electric field (DCEF) were explored. The corrosion rate was determined with the electrochemical technique and the corrosion morphology and corrosion products were respectively characterized by SEM and XPS. In the sterile solution, corrosion morphology of X70 steel was pitting and the corrosion rate increased with the increase in DCEF intensity and exposure time. When DCEF was absent, the corrosion rate of X70 steel in bacterial NS4 solution was faster than that in the sterile solution and the corrosion morphology was general corrosion. The acceleration effect of DCEF on corrosion was more significant than that of SRB. Under the synergistic effect of SRB and DCEF, when DCEF intensity increased below 500 V/m, the metabolic activity of SRB was gradually enhanced and the corrosion rate of X70 steel decreased. The protective effect of biofilm weakened the acceleration effect of DCEF on corrosion and the corrosion behavior was controlled by SRB corrosion. When DCEF intensity increased above 1000 V/m, SRB cells were inactivated and the corrosion rate of X70 steel increased. The corrosion behavior of X70 steel was controlled by DCEF. Based on the above research results, preventative actions were proposed.

Electrochemical study characterizations of pyrite weathering in simulated acidic soil: Iron transformation, sulfur conversion and environmental implications

Pyrite in natural environments is susceptible to weathering, which results in acid mine drainage (AMD) and heavy metal pollution-related environmental problems. The increase in mining activities has led to a large amount of pyrite entering surroundings, which may aggravate soil acidification and heavy metal pollution. In situ electrochemical techniques were used to investigate the weathering behavior of pyrite in simulated acidic soil solutions, which is conducive to understanding the weathering mechanism and environmental impact. In this study, the polarization curves and electrochemical impedance spectroscopy reveal that a higher soil solution concentration, temperature and/or acidity accelerate pyrite weathering rate, with an activation energy of 21.21 kJ·mol-1. Further investigations reveal that the pyrite is initially oxidized to initially oxidized to S0 and released Fe(II), the Fe(II) is easily transformed into Fe(III), and part of the Fe species ultimately transforms into goethite γ-FeOOH and hematite α-Fe2O3. The S0 ultimately transform into sulfate, accompanied by the release of hydrogen ions (H+), resulting in serious soil acidification. These results specifically reveal the mechanism of pyrite weathering, especially the process of iron transformation and sulfur conversion, and they also quantitatively identify the pyrite weathering rate and the quantities of heavy metal ions released, providing an experimental basis for the risk assessment of pyrite in acid soils.

Corrosion of API 5L X60 Pipeline Steel in Soil and Surface Defects Detection by Ultrasonic Analysis

The corrosion steels phenomenon is one of the main problems in the oil industry, such as in buried transmission pipelines used for high gas pressure for long distances. Steels are protected from the external soil corrosion through a bituminous coating, whose action is coupled with a cathodic protection system, which aims to maintain steel in its protection field and thus to avoid any corrosion risk. However, steels in service may experience external surface defects like corrosion pitting and cracking due to electrochemical or mechanical interactions of bare steel with an aggressive soil solution after steel protection failure. These are concerning phenomena and are the major threats of the pipeline transmission system’s reliability and ecological safety. Corrosion mechanisms are varied and can be evaluated by different methods, such as electrochemical measurements, which are influenced by various factors like temperature, pH, soil characteristics, resistivity, water content, and as well mechanical stresses. Corrosion results from simulated artificial soil solutions showed that steel is sensitive to corrosion by soil. Surface defects detection was carried out using an ultrasonic non-destructive method such as C-Scan Emission testing and the time of flight diffraction technique (TOFD) ultrasonic non-contact testing method. After propagation of the ultrasonic waves, the diffracted ultrasonic reflected wave occurring at the edges of the defects appears due to the presence of a corrosion defect by generating defect echoes. The C-Scan ultrasonic image shows surface reflection, including corrosion defects on interfaces with varying acoustic impedances. The cross-transverse speed ultrasonic propagation through the plate including defect is modified, revealing more surface defects, and cross-transverse speed is shown to increase ultrasonic detection presents some advantages, such as precision and speed of detection without alteration to the structure. This method can be used in the industrial context as an intelligent industrial robotics technique.

Effect of post-weld heat treatment on corrosion resistance of X90 pipeline steel joints

Abstract In order to improve the corrosion resistance of welded joints, X90 pipeline steel joints were subjected to post-weld heat treatment at 610 °C, 640 °C, and 670 °C (holding time was 1 h). Through electrochemical corrosion and full immersion corrosion experiments, the corrosion resistance of welded joints under various conditions was tested, and the surface morphology and corrosion products of the corroded samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. The experimental results show that the corrosion products of X90 pipeline steel welded joints in simulated soil solution mainly include Fe(OH)3, γ-FeOOH, α-Fe2O3, γ-Fe2O3, and a small amount of Fe3O4, FeCl3 and Fe. After heat treatment at 610 °C, the corrosion current density of the parent metal, heat-affected zone, and weld metal of the joint changes from 1.081, 2.889, 2.079 (×10−5 A cm−2) to 0.977, 2.211, 1.810 (×10−5 A cm−2), respectively, the corrosion resistance is improved.

Corrosion Behavior of X80 Steel in a Simulated Soil Solution Under Square-Wave Current Interference

The buried pipeline is disturbed by the dynamic direct current (DC) stray current with the subway as the main leakage source, which has the safety risk of accelerating corrosion, resulting in pipeline failure, which not only causes economic losses but also threatens personal safety. Therefore, it is necessary to study the corrosion behavior of pipeline steel under dynamic DC interference. The corrosion behavior of X80 steel under dynamic DC interference were studied by a mass loss test, alternating current impedance, circuit simulation, x-ray diffraction, and a Pourbaix diagram. Combined with the corrosion efficiency and Pourbaix diagram of the Fe-H2O system, the reversible process and reduction process mechanism in the Faraday process are proposed. The reason why the corrosion efficiency slows down in the process of non-Faraday is analyzed by the electric double-layer model of equivalent circuit calculation. In addition, based on the above corrosion process, the corresponding conceptual model of the corrosion mechanism is proposed. The experimental results show that with the asymmetry of positive and negative half-cycle interference duration and the increase of current density, the corrosion efficiency, and current corrosion efficiency of X80 steel decrease, and local corrosion intensifies. The length of the negative half-cycle interference affects the capacitive charge-discharge effect at the metal/solution interface and the reduction reaction process of corrosion products, resulting in corrosion slowing down and corrosion efficiency reduction. This is also an important reason for the reduction of corrosion mass loss observed in the experiment compared with steady-state DC.

Effect of laser power on microstructure and properties of laser assisted cold sprayed copper coatings on steel

Laser assisted cold spraying (LACS) is a promising technology for preparing high performance copper-steel composite materials for grounding electrode applications. Laser power is a critical LACS parameter, however, in literature there is a lack of studies on the influence of laser power on coatings. In this study, the effect of laser power on microstructure and properties of LACS copper coatings on steel is investigated. The results show that with the increase of laser power, the copper coating generally shows reduced porosity and microhardness, as well as increased bonding strength. However, the grains are first refined and then coarsened, while the electrical conductivity and corrosion resistance both increased and then decreased. This is because when the laser power exceeds 4 kW, the grain is coarsened and the amount of large angular grain boundaries (HAGBs) increases because excessive temperature increases the recrystallization driving force, ultimately leading to decrease in coating electrical conductivity and corrosion resistance. 4.0 kW, 5 MPa, 800 °C is considered as optimal LACS parameters for preparation of pure copper coatings on Q235 steel. The coating has a porosity of <0.04 %, grain size of 0.634 μm, microhardness of 99.4HV0.1, bonding strength exceeds 62 MPa, electrical conductivity of 99 % IACS, and corrosion current density of 6.092 × 10−8 A/cm2. In addition, mechanisms of LACS particle deposition and corrosion of copper coatings in simulated soil solution were discussed. With the increase of laser power, more heat absorbed by the powder and the substrate promotes thermal softening and plastic deformation, resulting in stronger mechanical bonding. The corrosion mechanism gradually changes from pitting corrosion to uniform corrosion due to the reduced porosity and tighter grain boundaries, and finally to intergranular corrosion due to grain coarsening and high HAGBs content. Overall, this study provides guidance and reference for the practical application of LACS.

Electrochemistry Numerical Study of Stress Corrosion Cracking under Near-Neutral Soil Solution

Stress Corrosion Cracking (SCC) is a phenomenon in which cracks develop in certain materials due to a combination of stress and corrosion. This process is commonly observed in low-alloy steels with a ferritic-pearlitic structure, such as X70, which are often used in buried pipeline applications within the oil and gas industry. These materials are particularly susceptible to SCC failure in dilute solutions. To simulate SCC conditions, the Near-neutral simulated soil solution (NS4) has been established as a widely accepted industry standard for conducting crack growth experiments in many laboratories. This paper aims to investigate the role of electrochemistry in SCC under near-neutral soil solution conditions by presenting a numerical study using COMSOL on the effects of applied potential on corrosion rate in near-neutral soil solutions. According to the findings, the electrode thickness, current density, and corrosion rates were mostly affected by an applied potential of -1.2 V. This implies that slight modifications in the applied voltage can greatly influence the corrosion rate of the electrode. This outcome aligns with prior research on the influence of potential on electrode performance and emphasizes the crucial role of precise control of the applied potential in electrochemical systems.

Experimental Study on Stress Corrosion of Q235 Buried Old Pipeline Steel Welded Joints

The stress corrosion susceptibility of Q235 buried old pipeline steel welded joint was studied by slow strain rate tensile test. The results showed that the mechanical properties of Q235 steel samples in J6A soil simulation solution were lower than those in the air. The quasi-cleavage fracture morphology was observed on the fracture surface of the samples, and clear stress corrosion cracks were also observed on the side of SSRT samples, indicating that Q235 steel has a certain SCC sensitivity in J6A solution. The corrosion effect of the test medium will be strengthened in the areas with various stress concentrations such as defects and cracks on the surface of Q235 steel, and the effect of external stress will cause non-uniformity of corrosion and strengthen local corrosion.

Biochar Promotes Arsenopyrite Weathering in Simulated Alkaline Soils: Electrochemical Mechanism and Environmental Implications.

Oxidation dissolution of arsenopyrite (FeAsS) is one of the important sources of arsenic contamination in soil and groundwater. Biochar, a commonly used soil amendment and environmental remediation agent, is widespread in ecosystems, where it participates in and influences the redox-active geochemical processes of sulfide minerals associated with arsenic and iron. This study investigated the critical role of biochar on the oxidation process of arsenopyrite in simulated alkaline soil solutions by a combination of electrochemical techniques, immersion tests, and solid characterizations. Polarization curves indicated that the elevated temperature (5-45 °C) and biochar concentration (0-1.2 g·L-1) accelerated arsenopyrite oxidation. This is further confirmed by electrochemical impedance spectroscopy, which showed that biochar substantially reduced the charge transfer resistance in the double layer, resulting in smaller activation energy (Ea = 37.38-29.56 kJ·mol-1) and activation enthalpy (ΔH* = 34.91-27.09 kJ·mol-1). These observations are likely attributed to the abundance of aromatic and quinoid groups in biochar, which could reduce Fe(III) and As(V) as well as adsorb or complex with Fe(III). This hinders the formation of passivation films consisting of iron arsenate and iron (oxyhydr)oxide. Further observation found that the presence of biochar exacerbates acidic drainage and arsenic contamination in areas containing arsenopyrite. This study highlighted the possible negative impact of biochar on soil and water, suggesting that the different physicochemical properties of biochar produced from different feedstock and under different pyrolysis conditions should be taken into account before large-scale applications to prevent potential risks to ecology and agriculture.

Mechanism of incipient annular corrosion of high-tin bronze in simulated soil solution

ABSTRACT The mechanism of Cu–Sn–Pb bronze (18.2 wt-% Sn) in a simulated soil solution was examined using optical microscopy, scanning electron microscopy, scanning Kelvin probe, X-ray photoelectron spectroscopy, X-ray diffraction and electrochemical techniques. The findings demonstrated that the α-phase possessed a more negative corrosion potential, and the central annular position was more active owing to the difference in the solid-solution tin content during casting. Cl− was not directly involved in the production of corrosive products in the early stage of corrosion, but it damaged the copper oxide layer and promoted the loss of copper ions. Subsequently, the tin oxide was gradually produced on the surface, and the selective copper dissolution led to abundant tin compounds on the surface.

Pitting corrosion behavior of X70 steel in weakly alkaline solution under dynamic DC interference

Stray current discharged into the soil when subway trains operate will lead to fluctuation in the pipe-soil potential, which causes severe corrosion. In this work, the pitting corrosion behavior of X70 steel in a weakly alkaline simulated soil solution under different potential fluctuation ranges was studied. The influence of the fluctuation of the pipe-to-soil potential on the passivation film and pitting corrosion was studied using electrochemical measurement and surface characterization. X70 steel has passivation characteristics in the weakly alkaline solution. The passivation film is in a dynamic process of continuous growth or growth-dissolution due to the alternating polarization. The critical factor in inducing pitting corrosion is the failure to produce stable and dense passivation film or the instantaneous polarization potential exceeding the range of passivation potential. The passivation film's density determines the pitting's initiation and development trend. It is preliminarily found that the charge transfer resistance at the initiation stage of pitting has a good exponential function relationship with the pitting rate at the stable development stage, which is of great significance for the qualitative evaluation of the pitting rate.

Stress-based hydrogen damage model of X80 pipeline steel and its damage risk assessment under cathodic interference

In this paper, the crack propagation behaviors of X80 pipeline steel under different cathodic current conditions were investigated by constant displacement loading experiment of double cantilever beam (DCB) samples, and the subsurface hydrogen concentration rules were obtained by hydrogen permeation test. A hydrogen damage model based on the threshold stress intensity factor of hydrogen-induced cracking arrest was established for X80 pipeline steel. The hydrogen permeation data showed that in 0.5 mol/L H2SO4 + 0.2 g/L CH4N2S solution, the relationship between subsurface hydrogen concentration C0 and applied current density i satisfied the expression of C0/L∝ i when the current density was 1–10 mA/cm2. The relationship between the threshold stress intensity factor of hydrogen-induced cracking arrest KHSC and the subsurface hydrogen concentration C0 satisfied the expression of KHSC ∝ -lnC0. An analytical model of KHSC = -0.4648lnC0-1.5040 was proposed for the API X80 steel pipe used in the experimental. The KHSC value under cathodic interference was calculated according to the C0 value in the soil simulation solution, and the risk of crack growth was analyzed under service conditions.

Corrosion behavior and kinetics model of rare earth low‐alloy steel in a soil simulation solution

AbstractThe corrosion behavior of rare earth (RE) low‐alloy steel in soil simulation solution was investigated by immersion test, electrochemical experiment, scanning electron microscopy, and X‐ray diffraction, compared with Q450 weathering steel. The kinetics model of all steels in soil simulation solution was established. The pitting corrosion mechanism of nonmetallic and RE inclusions was discussed. The results revealed that the RE improved the corrosion resistance of low‐alloy steel by modifying inclusions and promoting the formation of a dense protective film. The steel containing 0.0047% RE achieved the best corrosion resistance. The corrosion product layers were mainly composed of γ‐FeOOH, α‐FeOOH, Fe3O4, and Fe(OH)3. The results of the kinetic model showed that the dissolution of the anode was the restricted link of the whole process. The lowest apparent corrosion rate constant k of the sample containing 0.0047% RE was 2.359 × 10−4 μm/h in the soil simulation solution. The kinetic model could serve as a method to predict the service life of steel parts.

Nanoscale Interactions of Humic Acid and Minerals Reveal Mechanisms of Carbon Protection in Soil.

The concentrations of terrestrially sourced dissolved organic matter (DOM) have expanded throughout aquatic ecosystems in recent decades. Although sorption to minerals in soils is one major pathway to sequestrate soil organic matter, the mechanisms of organic matter-mineral interactions are not thoroughly understood. Here, we investigated the effect of calcium phosphate mineralization on humic acid (HA) fixation in simulated soil solutions, either with or without clay mineral montmorillonite (Mt). We found that Mt in solution promoted nucleation and crystallization of calcium phosphate (CaP) due to amorphous calcium phosphate clustering and coalescence on Mt surface, which contributed to the long-term persistence and accumulation of HA. Organic ligands with specific chemical groups on HA have higher binding energies to CaP-Mt than to CaP/Mt, according to dynamic force spectroscopy observations. Moreover, CaP-Mt formed in solution showed a great capacity for HA adsorption with a maximum adsorption quantity of 156.89 mg/g. Our findings directly support that Mt is crucial for DOM sequestration by facilitating CaP precipitation/transformation. This has an impact on how effectively we understand the long-term turnover of DOM and highlights knowledge gaps that might assist in resolving essential soil C sequestration issues.

Effect of Heat Treatment and Passivation on Corrosion Behavior of Electroless Ni-P Coating on 20# Steel in Simulated Soil Solution

Effect of Heat Treatment and Passivation on Corrosion Behavior of Electroless Ni-P Coating on 20# Steel in Simulated Soil Solution