Corrosion Of Low Alloy Steel Research Articles

Effect of Mo and Sn co-regulation on low alloy steel corrosion in tropical marine atmosphere

The influence of co-regulating Mo and Sn on the corrosion resistance of low alloy steel in tropical marine atmospheric was investigated. The combined addition of Mo and Sn has been found to significantly improve the corrosion resistance of low alloy steel, augmenting the protective capabilities of the rust layer. This combined addition promotes the formation of protective compounds like α-FeOOH and FeCr2O4 within the alloy rust layer. Furthermore, it facilitates the conversion of Cr, Ni and Cu into corrosion-resistant oxides such as Cr2O3, NiFe2O4 and CuO, thereby enhancing the density of the rust layer. Additionally, as corrosion progresses over time, higher levels of Sn addition lead to increased Sn content within the inner rust layer, consequently bolstering the protective qualities of the rust layer. This comprehensive understanding sheds light on the synergistic effects of Mo and Sn in fortifying the corrosion resistance of low alloy steel, offering insights for the development of advanced corrosion-resistant materials in marine environments.

Data-driven atmospheric corrosion prediction model for alloys based on a two-stage machine learning approach

Alloy material corrosion is a comprehensive problem affected by multi-dimensional factors, including the time, environment, and material element. Its corrosion prediction has been facing the challenges of complex mechanism and small sample size. However, parametric methods are limited in terms of modeling accuracy and generalization performance for high-dimensional feature problems. Non-parametric machine learning algorithms, while having excellent modeling capabilities, need to be optimized in conjunction with the structure of the corrosion problem. Therefore, we develop a two-stage hybrid intelligent machine learning model for improving alloy corrosion prediction accuracy. The model takes the time, environment, and material information of the alloy corrosion process as inputs and the corrosion rate as output. The first stage of the model utilizes tree ensemble learning (TEL) models for initial prediction modeling and feature importance knowledge mining. In the second stage, the neural network (NN) is used to enhance the fusion of the multi-model prediction outputs, and it is optimized using feature importance modification (FIM). The proposed TEL-FIMNN model shows considerable performance improvement over the TEL and ANN models on real low-alloy steel corrosion dataset. Compared to other advanced multi-model fusion methods such as linear regression (LR), support vector regression (SVR), random forest (RF), and Bayesian model averaging (BMA), the proposed model also shows superior results. The TEL-FIMNN model provide a new structure from the perspectives of knowledge mining and fusion enhancement, which has good potential for multi-dimensional corrosion prediction.

Increased secretion of bacterial pyomelanin caused by light accelerates corrosion of low alloy steel

Microorganisms in the waterline zone can secrete pigments to avoid damage caused by ultraviolet radiation, some of which have corrosive effects. In this work, we found that the secretion of pyomelanin by P3 strain of Pseudoalteromonas lipolytica significantly increases under strong lighting conditions, accelerating the corrosion of the material. Molecular mechanisms indicate that strong light, as a stressful environmental factor, enhances the expression of melanin secretion-related genes to prevent bacteria from being damaged by ultraviolet radiation. Therefore, this work proposes a new corrosion mechanism in the waterline zone, pigment-producing microorganisms are also involved in the waterline corrosion process.

Investigation of microbiologically influenced corrosion of low alloy steels with different Cr contents in simulated oilfield produced water

Microbiologically influenced corrosion has become a predominant cause of pipeline and equipment failure in oil and gas fields. This research examines the corrosion behavior of steels with varying chromium contents in simulated shale gas formation water environments. Weight loss testing, Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectroscopy (EDS), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM), and x-ray Photoelectron Spectroscopy (XPS) were employed. The findings suggest that an elevated Cr content in steel results in a gradual reduction in its uniform corrosion rate in a CO2-SRB coexistence environment. This can be primarily attributed to the significant distribution of Cr content throughout the entire product film, including both biofilm and corrosion products, thereby enhancing the product film’s protectiveness. Additionally, the competitive corrosion between CO2 and SRB, as well as the influence mechanism of Cr on corrosion, were discussed.

Cracking time and prediction model of low-alloy steel reinforced seawater sea-sand concrete based on DIC technology

The cracking of seawater sea-sand concrete (SSC) cover due to the corrosion of low-alloy steel (LS) is a critical factor affecting its serviceability and durability. To analyze the cracking behavior of the SSC cover, a thick-walled cylinder model was developed in this study. The cylinder was divided into multiple coaxial rings of equal thickness, and damage variables were introduced to determine the extent of damage for each cracked ring based on the position of the rust expansion crack front. A predictive model for the cracking time of SSC cover was established by using the displacement compatibility equation at the interface of reinforcing steel and cover concrete, in combination with Faraday's law. To verify the accuracy of the model, the Digital Image Correlation (DIC) technique was utilized to determine the timings of two pivotal stages: the initial cracking and complete cracking of the cover. The comparison between the predictive outcomes and experimental results showed an error range of 4 %–10 %, indicating that the predictive model is relatively accurate.

Effect of splash amount on corrosion of low-alloy steel in marine splash zone

Splash corrosion of Q345D low-alloy steel was simulated using a simulation apparatus where in-situ electrochemical measurements were performed. In the early stage of splash corrosion, the corrosion rate in the low splash zone is far higher than that in the high splash zone, and in the later stage only slight difference in corrosion rate can be observed under different splash amounts. Compared to the high splash amount, the corrosion under the low splash amount is more localized. The densities of rust layers in the splash zone increase with time, and Fe3O4/γ-Fe2O3 phase dominates the composition of the rust layers apart from a small amount of α-FeOOH and γ-FeOOH. γ-FeOOH is mainly concentrated in the outer layer of corrosion products. Due to the obstruction of the denser rust layer in the low splash zone in the early stage to the transfer of Fe (II) species, the ratio of γ-FeOOH is higher in the rust layer under the high splash amount than under the low splash amount.

Effect of Local Fluid Disturbance Induced by Weld Reinforcement Height on the Corrosion of a Low Alloy Steel Weld

Weld corrosion exists widely in the petrochemical industry and attracts great attention. Most research proves that weld corrosion originates from the material factors introduced during the welding process. However, it is noted that local fluid turbulence due to the weld reinforcement height (WRH) plays an important role in the non-uniform corrosion of welds in flowing media. Accordingly, the individual effect of the local flow on the weld corrosion of low alloy steel was analyzed by experiments and simulation in this study. Electrochemical measurements and morphology observation were conducted, combined with flow field analyses. The results showed that local fluid turbulence due to WRH affected the non-uniform corrosion of low alloy steel welds. The upstream surface and the backflow surface had the highest and lowest corrosion rates, respectively. Interestingly, the high flow velocity surface region did not have a high-corrosion rate. This is due to the combined effects of mass transfer, charge transfer, and wall shear stress. The pitting corrosion was also discussed in view of the aspects above.

Effect of Small Amounts of Cr and Mo on Aqueous CO2 and H2S Corrosion of Low-Alloyed Steel

One of the important industrial issues is the corrosion of carbon and low-alloy steels exposed to a wet environment where CO2 and/or H2S are dissolved. In the case of carbon and low-alloy steels, mainly iron-based corrosion products such as iron carbonate and iron sulfides can form depending on the condition. Microalloys added in small amounts to carbon steel can change the water chemistry near the steel surface due to the dissolution of the microalloys, which may also alter the corrosion resistance of the steel and corrosion morphology. In this study, the individual microalloying effects of a small amount (1 mass%) of Cr and Mo added in carbon steel were investigated in a wet CO2 and H2S environment, where the formation of mackinawite (FeS) is considered to be the dominant iron-based corrosion product. The variation of corrosion rate and corrosion potential of the microalloyed steels was monitored in the NaCl solution aerated with CO2—10% H2S gas by linear polarization resistance measurements. The corrosion product formed on the steel surface was also analyzed by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. The experimental results show that the addition of a small amount of Cr improves corrosion resistance by forming a dense film of FeS on the surface, while the addition of a small amount of Mo delays the formation of FeS on the surface and the corrosion resistance behavior is similar to that of steel with no additions.

The effect of cooling rate-induced microstructural changes on CO2 corrosion of low alloy steel

The effect of cooling rate-induced microstructural changes on corrosion resistance in a CO2-saturated 3.5 wt% NaCl solution have been explored for the API L80–1Cr steel. The corroded layer majorly contains siderite, akagenite, and undissolved cementite. The amount of FeCO3 in this layer is larger for the water-cooled sample with a martensitic structure, whereas the furnace-cooled sample with a ferritic-pearlitic structure contains a larger amount of akagenite. The retained cementite and the microrough surface of the furnace-cooled sample provide greater anchoring to the scale. Comparing samples cooled at different rates, the furnace-cooled condition appears to provide better CO2 corrosion resistance.

Effect of hydrostatic pressure on galvanic corrosion of low-alloy steel in simulated deep-sea environments

ABSTRACT In order to study the effect of high hydrostatic pressure on the corrosion of low-alloy steels in deep-sea environments. The electrochemical corrosion behavior of single-metal system and triple-metal coupled system of 907A steel, 921A steel and 1# steel under different hydrostatic pressures were studied by electrochemical, weight loss and morphology observation methods. The results show that the high hydrostatic pressure promotes the corrosion of low-alloy steel by changing the composition and morphology of corrosion products. In addition, there was also severe galvanic corrosion between the couples with a low potential difference (< 60 mV),907A steel was used as the anode of the three-metal coupled system, and 921A steel and 1# steel as the cathode. The galvanic coupling effect accelerates the pitting corrosion of 907A steel as an anode metal. When using multi-metal couplers with low potential differences, they should be protected by both coating protection and cathodic protection.

Under Deposit Corrosion of Low Alloy Steel in Saturated CO2 Formation Water

Under Deposit Corrosion of Low Alloy Steel in Saturated CO2 Formation Water

Influence of dislocation on sour corrosion of carbon steel in a low H2S sour environment

AbstractThe influence of dislocation on corrosion of low alloy steel in a low H2S sour corrosion environment was investigated experimentally (immersion corrosion test and polarization measurement) and theoretically (ESM‐RISM simulation). The results showed that dislocation increases corrosion weight loss by promoting the anodic dissolution reaction. The Fe atom solubilities of two kinds of Fe slab models simulating conditions with/without lattice defects were evaluated, and the high Fe solubility of the model with lattice defects was clarified. Based on these experimental and theoretical findings, the mechanism by which dislocation influences anodic dissolution was discussed.

A study by electrochemical impedance spectroscopy and surface analysis of corrosion product layers formed during CO2 corrosion of low alloy steel

In the following research, electrochemical and surface analysis techniques are used to define the main contributing factor to the protectiveness offered by a scale formed at high temperature and pH under CO2 saturated conditions. At 80 °C and pH 6.6, trace amounts of a magnetite (Fe3O4) phase was identified at certain locations beneath a more dominant iron carbonate (FeCO3) film. Furthermore, over time, the evolution of the corrosion product layer towards a very low porosity results in a “diffusion barrier” that is indicated by a positive shift in the open circuit potential and is considered key to corrosion protection.

In-situ characterization of initial marine corrosion induced by rare-earth elements modified inclusions in Zr-Ti deoxidized low-alloy steels

In the present research, the effects of rare-earth (RE) elements modified inclusions on initial marine corrosion of Zr-Ti deoxidized low-alloy steels were studied by first principle modeling and a variety of analytical methods including in-situ scanning vibrating electrode technique (SVET), scanning electron microscopy with x-ray microanalysis (SEM/EDS), and confocal Raman microscopy (CRM). The obtained results revealed that two types of complex inclusions with intertwined components of RExZryOz-RE2O2S and RExZryOz-RE2O2S-TiN were formed. RE2O2S preferentially dissolved in 0.5wt% NaCl solution, whereas the dissolution of RExZryOz propagated from the periphery to the middle of the inclusions and subsequently, formed stable pits on the steel surface. TiN was stable in the marine environment and finally, became detached from the substrate. Moreover, in-situ SVET results demonstrated the local current density change during corrosion process was influenced by single and multiple inclusions, indicating that the dissolution of inclusions induced the electrochemical activities of pitting corrosion and further inhibited the propagation of local corrosion. Furthermore, the corrosion tendency of inclusions and the Fe matrix was examined by first principle modeling. Finally, two schematic models were proposed to demonstrate the effects of inclusions on initial marine corrosion of low-alloy steels.

Pseudoalteromonas lipolytica accelerated corrosion of low alloy steel by the endogenous electron mediator pyomelanin

Endogenous electron mediators are believed to be important bridges between microorganisms and electrodes, which influence the corrosion process. In this work, the genetically engineered P. lipolytica mutant strain with hmgA gene deletion, a hmgA restoration strain and a wild-type strain were used to investigate the impact of the pyomelanin on the corrosion of steel in marine broth. Weight loss and electrochemical data demonstrated that the corrosion rate of the steel increased when the hmgA deletion strain of P. lipolytica was inoculated in marine broth to produce pyomelanin, especially with the addition of L-tyrosine as a substrate.

The influence of KCl on biomass ash melting behaviour and high-temperature corrosion of low-alloy steel

The main aim of this work was to determine the influence of KCl-rich ash deposits on 10CrMo9-10 steel oxidation rate. Two agricultural biomass samples: oat and rye straw, clean and doped with KCl were tested in this study. The addition of KCl does not decrease the melting temperature of the ash when KCl is not incorporated with mineral matter components.Corrosion experiments were performed at 550 °C and 600 °C, with corrosion coupons covered with real and synthetic biomass ash under oxidising conditions. The nonuniform distribution of KCl in ash affected the results and the effect of potassium concentration on oxidation rate was not observed in all cases. More severe influence of ash rich in KCl was observed at lower temperature, the reason is lower protective oxide scale formation rate and higher influence of ashes on steel material and scale.The temperature increase by 50 °C doubled the corrosion rate. At 550 °C KCl was most aggressive salt, but at 600 °C the influence of eutectic mixture KCl+K2SO4 was the highest. Even at lower temperature thermal decomposition of K2CO3 was observed affecting the results. It might be concluded that temperature and eutectic mixture formation are essential parameters in corrosion prediction.

Corrosion of low alloy steel in stagnant artificial or stirred natural seawater: The role of Al and Cr

AbstractCarbon steel and low alloy (containing Al and Cr) steel coupons were immersed for 6–7 months in stagnant artificial seawater or in natural marine site. The corrosion processes were studied via the combination of electrochemical techniques and the analysis of corrosion product layers by µ‐Raman spectroscopy and X‐ray diffraction. In natural seawater, the low alloy steel showed better resistance to corrosion and the best results were obtained when the mill scale was removed from the steel surface. This shows that improved corrosion resistance is due to a protective layer that forms spontaneously in the environment. In stagnant artificial seawater, the behavior of low alloy steel coupons (without mill scale) was compared with that of carbon steel coupons. The polarization resistance of the carbon steel coupons remained approximately constant over time. The corrosion product layer proved to be mainly composed of magnetite, an electronic conductor that does not hinder oxygen reduction. In contrast, the polarization resistance of the low alloy steel coupons increased with time, as the growing corrosion product layer, enriched with insulating FeOOH compounds, hindered oxygen diffusion.

Effect of Chemical Composition and Microstructure Parameters on Carbon and Low-Alloy Steel Corrosion Resistance Under Oil Industry Pipeline Operation Conditions

The effect of chemical composition and microstructure parameters on corrosion resistance of carbon and low-alloy steels in neutral aqueous media, typical for oil-field pipeline operating conditions, is studied in order to develop requirements for the specified characteristics to improve steel equipment service life. It is shown that a large amount of interfacial nano-sized precipitates in steel, (even with sizes of 2–3 nm or less) mainly of vanadium carbide (carbonitride), and to a markedly lesser extent with niobium carbide, is present. A significant reduction in the corrosion resistance of steel due to the formation of such particles is observed with an increase in the vanadium content in steel more than 0.065–0.07%.

Interaction between Cu and Cr coadsorption on MnS inclusions in low alloy steels

Interaction between alloy elements Cu and Cr on MnS inclusions was studied by Scanning Transmission Electron Microscope (STEM)/X-ray energy-dispersive spectrometer (EDS) and the first principles calculation method. Assuming that the enrichments of Cu and Cr play a key role on pitting corrosion of low alloy steel, STEM/EDS were used to observe the enrichments of Cu and Cr on MnS inclusions in this study. The first-principles calculation, which is based on density functional theory was used to investigate the segregation behavior of Cu and Cr in the Fe matrix and the adsorption behavior of Cu and Cr on MnS surface. The atomic structures, electronic and energetic properties of clean and Cu or Cr adsorbed MnS surface were calculated. The results showed that both Cu and Cr tend to segregate on the Fe (1 1 0) surface rather than solid dissolved in the Fe bulk. MnS (1 0 0) is the most stable surface amongst the low-index surfaces, and H (hollow) is the most stable adsorption site for both Cu and Cr. Coadsorption of Cu and Cr on MnS (1 0 0) surface was also studied. The results showed that Cu and Cr promote the adsorption of each other on MnS (1 0 0) surface. However, this interaction is effective only within a certain distance between them. Overall, these findings will be helpful to understand the mechanism of pitting corrosion induced by MnS.

Investigations on the Effect of Impregnated WS2 on Corrosion of Low Alloy Steel (Distaloy AB)

Investigations on the Effect of Impregnated WS₂ on Corrosion of Low Alloy Steel (Distaloy AB)