Localized Pitting Research Articles

Effects of Ta on the strengthening mechanism of microstructure and corrosion resistance of underwater wet laser cladding 17-4PH coating

Underwater wet laser cladding has gradually become the key technology for online repair of marine engineering materials. This work successfully prepared a Ta-reinforced 17-4PH coating on a 20Cr substrate using this technique. The study primarily examined how varying levels of tantalum (Ta) influence the microstructure, phase composition, microhardness, immersion corrosion, and electrochemical properties of underwater cladding coatings. Additionally, a detailed analysis of the corrosion mechanism was conducted. The experimental findings demonstrated that incorporating Ta can greatly enhance the forming quality and overall performance of coatings. When the Ta addition was 10 %, the forming quality was the best, and there were no porosity or depressions. The 10 % Ta coating had the best densification with a minimum porosity of 0.05 %. The average microhardness of the T10 coating was 594.1 ± 5.9 HV0.2, an increase of about 13 % over the original T0 coating. Additionally, when the Ta content reached 10 %, the formation of Ta2O5 on the surface played a crucial role in enhancing the coating's resistance to immersion corrosion. The T10 coating demonstrates the highest polarization resistance and superior corrosion resistance among the coatings tested. The corrosion mechanism of the original unadded Ta coating involved severe intergranular corrosion and pitting; The corrosion mechanism observed in the T10 coating involved local crevice corrosion and minor pitting. This study reveals the strengthening mechanism of Ta on the organizational properties of the underwater laser cladding layer, which can provide meaningful guidance for the future development of underwater laser cladding technology.

Corrosion and wear performance and mechanism study of ZrB2/AA6016

Abstract This study involved the fabrication of aluminum matrix composites reinforced with ZrB2/AA6016 particles using the KBF4-Al-K2ZrF6 reaction system， the composites were then subjected to T6 heat treatment. An investigation was conducted to examine the impact of varying friction speeds on the corrosion and wear characteristics of ZrB2/AA6016. An investigation was conducted to study the frictional wear behavior of ZrB2/AA6016 in the presence of 3.5wt. % NaCl, both before and after T6 heat treatment. The study also aimed to understand the underlying mechanism of this behavior. The results indicate that the T6 heat treatment mitigates the impact of thermal stresses and strains caused by thermal mismatch, hence enhancing the material's wear resistance. The coefficient of friction (COF) for heat-treated ZrB2/AA6016 is lower than that for unheated-treated ZrB2/AA6016. As friction increases, the pace at which the material wears down tends to decrease. At a friction wear velocity of 50 mm/s, the wear rate of the material is minimized both before and after heat treatment, measuring 0.23×10-2mm3/Nm and 0.22×10-2mm3/Nm, respectively. Through the utilization of XRD, SEM, EBSD, TEM, and XPS analytical techniques, it has been determined that the ZrB2 particles exhibit strong bonding with the Al matrix. Additionally, the particle diameters range from 50~150nm. Following the T6 heat treatment, the grain size measured 40.53μm, while the proportion of large-angle grain boundaries was found to be 66.4%. The accumulation of Cl- resulted in the formation of localized corrosion pits on the surface undergoing wear, hence hastening the deterioration of the material. The primary causes of wear failure are corrosive wear, abrasive wear, and oxidative wear.

Effect of pre-exposure to chloride environment on the tensile deformation of SS 304HCu at 973 K

304HCu austenitic stainless steel (SS 304HCu) with 3 % copper content is utilized as the tubing material for advanced ultra-supercritical boilers, which operate at temperatures around 973 K and a pressure of 31 MPa. The current investigation aimed to examine the influence of prior exposure to an acidic chloride environment on the tensile characteristics of SS 304HCu at 973 K with the nominal strain rate of 1× 10−3 s−1 in solution annealed as well as thermally aged (973 K/10000 h) conditions. In the prior exposure condition, both the solution annealed and aged specimens were subjected to a pre-determined potential of −0.14 V (Ag/AgCl) for 48 h in 5 M NaCl + 0.15 M Na2SO4 + 2 ml HCl solutions. Thermally aged SS 304HCu showed lower strength in both true UTS and true yield strength compared to the solution annealed specimen tested at 973 K. Exposure to an acidic environment resulted in a considerable reduction in tensile strength and uniform plastic strain. For all the conditions, saturation-stress-based relationship was employed to describe the flow behaviour of the alloy. The relationship adequately fits the true stress-true strain data of SS 304HCu. A systematic variation in strain hardening parameters with respect to different test conditions is noticed. In the case of the aged alloy, the observed microstructure revealed the presence of M23C6 at grain boundaries and copper precipitates in the grain interior. The increased chromium depletion and the higher degree of sensitization led to the formation of localized pits in pre-exposed aged specimen conditions. Consequently, the synergistic influence of precipitation and pitting corrosion significantly affected the tensile deformation behaviour of SS 304HCu alloy in the aged and pre-exposed condition compared to the solution annealed condition.

Accelerated corrosion by nitrate-reducing bacteria and gaseous hydrogen permeation of X80 steel

Effects of hydrogen gas and Nitrate-Reducing Bacteria (NRB) on the corrosion and hydrogen permeation dynamics of X80 steel in simulated pipeline condensate water was investigated. Weight-loss analysis and electrochemical tests show a direct correlation between NRB-induced corrosion of X80 steel and the presence of hydrogen gas, particularly evident with escalating hydrogen blending ratios. Notably, corrosion primarily manifested through the formation of localized pitting, exhibiting a positive correlation with hydrogen blending ratios. Furthermore, the hydrogen permeating results show there is a synergistic enhancement of hydrogen permeating facilitated by the coexistence of hydrogen gas and NRB. Quantitative assessments of hydrogen permeability parameters highlighted significant amplifications in hydrogen diffusion flux (J) and apparent hydrogen concentration (Capp) under the combined influence of hydrogen and NRB, underscoring the complex interplay between these factors.

Corrosion behavior of additively manufactured M300-CuCr1Zr by multi-material laser-based powder bed fusion

Additive manufactured parts of thermally-conductive CuCr1Zr and high-hardness M300 tool steel were fabricated via a single step multi-material Laser-based Powder Bed Fusion (PBF-LB). The corrosion properties of two interface configurations, CuCr1Zr built on M300 and M300 on CuCr1Zr, were evaluated using the electrochemical polarization resistance measurement, weight loss method and galvanic corrosion current measurement via a Zero Resistance Ammeter. The interface microstructure of the dissimilar bi-metallic parts fabricated by multi-material PBF-LB is tunable. The printing configuration influences the defect size and density and interface microstructure, which affect the global corrosion rate of the fabricated parts. Electrochemical measurements were performed on the fabricated parts in oxygen-saturated and chloride-containing water at elevated temperature, complimented by post-mortem characterizations. The interface configuration with M300 on CuCr1Zr has a slightly lower corrosion rate than that of CuCr1Zr on M300. Unexpectedly, galvanic corrosion occurred only locally in the interface region between M300 and CuCr1Zr materials. Beyond the interface regions, there is no clear sign of galvanic corrosion. Pitting and intergranular corrosion in CuCr1Zr material is the dominant corrosion mechanism. Both base materials beyond the interface region underwent localized pitting, particular in CuCr1Zr. Intergranular corrosion in CuCr1Zr is governed by sub-surface defects like pores and microcracks formed during printing.

Enhanced Joule heat release at surface irregularities

The heat release that occurs in a cylindrical conductor carrying an alternating current is analyzed for the cases when the conductor has axisymmetric surface irregularities of one of three types: local bumps, local pits, and sequences of alternating bumps and pits (wavy irregularities). The magnetic field and current density distributions over the conductor cross section have been simulated. The simulation parameters were chosen to match the conditions of experiments on the generation of strong magnetic fields. However, due to the analysis of the initial heating stage, the problem is solved neglecting the temperature dependence of the resistivity of the material. A multiple increase in heat release power in the vicinity of a surface irregularity has been revealed for the three types of irregularities.

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.

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.

Effect of air pressure and flow on steels materials in simulated wet fire drives

The corrosion behaviour of N80, 3Cr, and 5Cr steels were investigated under wet fire drive conditions using a high-temperature and high-pressure autoclave, weight-loss method, and scanning electron microscopy analysis. The findings indicated that elevated air pressure (4–6 MPa) and flow rates (0.5–1.5 m/s) significantly exacerbated corrosion, leading to both localised pitting and general corrosion on the steel samples. Predominant components of the corrosion product scales were identified as FeCO3 and Cr2O3. Notably, N80 steel exhibited higher pitting sensitivity compared to 3Cr and 5Cr steel, whereas 5Cr steel demonstrated superior corrosion resistance under the experimental conditions. Consequently, it is recommended to use cost-effective pipes with adequate corrosion resistance, such as various low-alloy pipes with differing chromium (Cr) contents, in oilfield applications. This study underscores the importance of selecting corrosion-resistant pipes as a primary means of corrosion prevention in oil and gas operations. Furthermore, it provides valuable insights into the corrosion performance of diverse steel materials in wet fire drive environments, offering pertinent implications for corrosion mitigation strategies within the industry.

The corrosion behavior of carbon steel under coexistence of carbon dioxide and SRB.

The corrosion behavior of carbon steel under the coexistence of carbon dioxide and SRB was studied by means of corrosion weight loss, SEM, EDS, in situ pH test, and other methods. The results showed that Chloride ions, temperature, pH, and oxygen coexist with iron bacteria will affect the corrosion under the coexistence of CO2 and SRB, and SRB tends to grow in a favorable environment for itself, and the corrosion rate of X52N at 42days is slightly higher than that at 21days. However, the pitting depth increased sharply from 21.20µm in 21days to 39.79µm in 42days. So that the corrosion can be divided into two stages. First, SRB catalyze the dissolution of FeCO3, leading to local uniform corrosion. Second, SRB directly obtain electrons from the metal surface, resulting in local pitting. In addition, the environment under the stable mineralized biofilm was found to be slightly alkaline.

Intermetallic particles distribution in 7010-T7451 and 7175-T6 aluminium alloys substrate impacts cathodic stability of silicate sealed anodic oxide film

Effect of silicate sealing on tartaric sulphuric acid anodized 7010-T7451 and 7175-T6 alloys with different distributions of intermetallics (IMPs) in aluminum substrates was studied. Surface characterisations evidenced similar morphology and chemical composition of the sealed layers on both substrates. Electrochemistry and time-lapse microscopy demonstrated the layer’s stability under anodic polarization and its localized pitting under cathodic polarization in NaCl electrolyte. No chemical or morphological modifications were detected outside of the pits. The number and size of the pits depended on the IMPs distribution in the alloy, buried under 6 µm thick oxide. A degradation mechanism explaining these observations was proposed.

Microstructure characterization and corrosion resistance in soil of Mg-2Zn-xCe-yCu alloy for light agricultural machinery

The microstructure, mechanical properties, corrosion behavior, and potential for lightweight applications of Mg-2Zn alloys enhanced with Cu and Ce were investigated. It was observed that the Ce and Cu-containing phases displayed various morphologies in the as-cast and extruded conditions. The extruded alloy, containing 0.8 wt% Ce and 0.5 wt% Cu, exhibited optimal mechanical properties, with the yield strength of 289 MPa, ultimate tensile strength of 336 MPa, and elongation of 15.8 %. Grain boundary and precipitation strengthening significantly contributed to the increase in yield strength. After four months of soil burial, the specimen surface showed localized pits and cracks, likely serving as anodes in the areas including Ce and Cu-containing phases. The corrosion rates in different soil environments paddy, vegetable, orchard, and corn fields were 2.029, 2.293, 2.133, and 1.986 mg·cm−2·d−1, respectively indicating variations due to complex soil conditions. The corrosion products included Mg(OH)2 and Mg5(CO3)4(OH)2·4 H2O, among others, throughout the burial period. Furthermore, model assembly in SolidWorks and static structural simulation with ANSYS confirmed the alloy's reliable load-bearing capacity, safety, and potential as the material for lightweight agricultural machinery.

Helical Gearbox Defect Detection with Machine Learning Using Regular Mesh Components and Sidebands.

The current paper presents helical gearbox defect detection models built from raw vibration signals measured using a triaxial accelerometer. Gear faults, such as localized pitting, localized wear on helical pinion tooth flanks, and low lubricant level, are under observation for three rotating velocities of the actuator and three load levels at the speed reducer output. The emphasis is on the strong connection between the gear faults and the fundamental meshing frequency GMF, its harmonics, and the sidebands found in the vibration spectrum as an effect of the amplitude modulation (AM) and phase modulation (PM). Several sets of features representing powers on selected frequency bands or/and associated peak amplitudes from the vibration spectrum, and also, for comparison, time-domain and frequency-domain statistical feature sets, are proposed as predictors in the defect detection task. The best performing detection model, with a testing accuracy of 99.73%, is based on SVM (Support Vector Machine) with a cubic kernel, and the features used are the band powers associated with six GMF harmonics and two sideband pairs for all three accelerometer axes, regardless of the rotation velocities and the load levels.

Research on the Multifactor Synergistic Corrosion of N80 and P110 Steel Tubing in Shale Gas Wells in Sichuan Basin

We aimed to investigate the corrosion patterns and the main controlling factors of N80 steel and P110 steel tubing under different sections. Conducting weight loss corrosion experiments for 168 h using high-temperature and high-pressure autoclaves to simulate the corrosion behavior of two types of casing materials, N80 steel and P110 steel, in different well sections under specific conditions of CO2 content, chloride ion concentration, temperature, pressure, and sulfate-reducing bacteria population in highly mineralized formation water. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the corrosion products, surface morphology, and elemental composition of the two steel pipes. Additionally, 3D microscopy was employed to observe the morphology and measure the dimensions of localized corrosion pits. Under different well sections, the corrosion products formed on N80 steel and P110 steel mainly consist of FeCO3, and crystalline salts of chlorides present in the solution medium. Under low-water-cut conditions, narrow and deep corrosion defects were observed, while narrow and shallow corrosion defects were found under high-water-cut conditions. In the upper wellbore section, both steel pipes exhibited dispersed and thin corrosion product films that suffered from rupture and detachment, resulting in severe localized corrosion. In the middle wellbore section, the corrosion product film on N80 steel comprised irregularly arranged polygonal grains, some of which exhibited significant gaps, leading to extremely severe corrosion. For P110 steel, the corrosion product film was also dispersed and thin, with extensive detachment and extremely severe corrosion. In the lower wellbore section, both steel pipes were covered with a dense layer of grains, with smaller gaps between them, effectively protecting the metal matrix from corrosion. Consequently, the corrosion rate decreased compared to the middle section but still exhibited severe corrosion. In low-water-cut conditions, attention should be given to the risk of column safety due to corrosion from condensate water and CO2, as well as the size of narrow and deep corrosion defects in the middle wellbore section. In high-water-cut conditions, it is recommended to use corrosion inhibitors in combination while focusing on SRB bacteria corrosion in the upper wellbore section, condensate water in the middle section, CO2 content and chloride ion coupling in the lower section, and the size of narrow and shallow corrosion defects causing column safety risks.

Stainless steels as a solution for corrosion and erosion problems involving grains in agribusiness sector applications

Agricultural activities such as grain processing play a crucial role in Brazil's economy, contributing significantly to its gross domestic product (27.4% in 2021). The use of carbon steel equipment leads to considerable environmental and economic losses in agribusiness due to corrosion. This study explores the erosion-corrosion behavior of a dual-phase 11Cr and an 18Cr8Ni stainless steel (SS), compared to a mild (ASTM A36) and a high-strength carbon (AHSS) steel under conditions close to the agribusiness reality. The impact of corn particles as erosive component associated to pure water and chloride-containing environments was studied using a fog chamber, a topic until now unexplored in the literature. The methodology adopted is novel and explores the erosion-corrosion synergy in cumulative steps, aiming to shed light on the mechanisms of corrosion and wear that affect the materials in the agribusiness industry. The findings reveal that corn particles, despite their soft nature, can easily remove non-adherent corrosion products from the steel surface. In the deionized water medium, the impact of the soft particles can also shift the corrosion pattern of advanced high-strength steels from general corrosion to localized pitting damage reduzing the corrosion rates. The carbon and 11Cr steels showed the highest corrosion rates under the pure corrosion condition in both media. The erosion-corrosion process considerably reduced the corrosion rate, mainly in the deionized water medium for the carbon steels. An exception to this behavior was 18Cr8Ni steel, whose corrosion rates, however, were the lowest among the materials. Low-chromium stainless steel emerges as a cost-effective solution to erosion-corrosion challenges in the agribusiness segment.

Impact of intermetallic phases on the localised pitting corrosion and high-temperature tensile strength of Al–Si[sbnd]Mg[sbnd]Cu[sbnd]Ni alloys

The influence of Ni-rich intermetallic particles (IMPs) on the microstructure, high-temperature mechanical properties, and corrosion behaviour of Al–Si–Mg–Cu–Ni alloys was investigated. The presence of coarse block-like γ-Al7Cu4Ni and thin needle-like δ-Al3NiCu IMPs contributed to low-temperature alloy strengthening during tensile tests. However, void nucleation and coalescence within the IMPs facilitated ductile fracture and alloy rupture, resulting in a lower tensile strength at high temperatures. Although both IMP phases had a cathodic electrochemical nature, resulting in strong galvanic corrosion, the γ-Al7Cu4Ni phase acted as the primary cathode, amplifying localised pitting while reducing the overall alloy corrosion resistance.

High fidelity ultrasonic measurements for defect detection and characterisation

Repeatable measurements with detachable transducers such as phased arrays have much potential for enhancing the sensitivity of nondestructive evaluation (NDE), as baseline subtraction can be employed. This paper aims to develop post-processing methods to overcome the variation between inspections which leads to poor subtraction performance. In this paper, ultrasonic immersion inspections are performed on a brass sample and a steel sample with a corroded backwall. Reference measurements are taken, and then small defects are machined to simulate defect growth in industrial applications. Defect types include two 1 mm diameter flat bottom holes (FBH) extending from 15 mm to 17 mm in the brass sample and two 2 mm diameter holes drilled to 1 mm depth from the corroded surface of the steel sample to represent the growth of localised pits. Although FMC/TFM is used in this paper, the defects have similar response amplitudes to the structural noise, and they cannot be detected or characterised directly from the images by the conventional 6 dB drop method. This paper demonstrates the utilisation of ultrasonic measurements, together with cross-correlation, to obtain inspection variables which include array position and couplant wave velocity. By knowing the variations between inspection conditions, compensation is made in post-processing to improve image repeatability, and hence the performance of baseline subtraction. The SNR is improved by approximately 10–25 dB depending on how great the actual variations are. It is shown that these previously undetectable defects can be seen and accurately sized after conducting baseline subtraction with compensation.

Surface Adaptive Dual‐Layer Protection of Li‐metal Anode for Extending Cycle‐Life of Li–Sulfur Batteries with Lean Electrolyte

AbstractBuilding a lithium–sulfur (Li–S) battery with lean electrolytes is essential to far exceed the energy density of today's Li‐ion. However, earlier electrolyte depletion triggered by Li‐metal anodes (LMAs) causes sluggish Li–S redox kinetics and poor S utilization, resulting in a short cycle lifespan. To retard the electrolyte loss effectively, sustainable protection of LMAs is necessary against the dynamic interfacial evolution between LMA and protective layers (PLs). This study elucidates two critical parameters in securing the interfacial adaptivity of PLs upon local Li pitting: surface free energy (SFE) and Young's modulus through solid‐mechanic simulations and experiments using three different PL models. To alleviate the PL delamination at the early stage, a dual‐layer structured, adaptive protective layer (APL) is introduced to adapt the Li pitting‐driven structural evolution of the PL|LMA interfaces. The APL consists of a high‐ SFE polymer as an inner layer, reducing the interfacial energy in contact with LMA surface, and a highly stretchable polymer for outer shield, serving as a physical barrier for the electrolyte and Li polysulfides. APL‐coated LMA demonstrates stable cycling of Li–S cells, achieving a twofold extension of cycle‐life compared to unprotected LMA, even superior to other single‐layer PLs.

Study on hydrogen permeation and stress corrosion cracking behaviors of AISI 4135 high-strength steel with macrofouling adhesion in marine immersion zone

A field exposure test was set up to study the effect of macrofouling adhesion on hydrogen permeation and stress corrosion cracking (SCC) behaviors of a high-strength steel in marine immersion zone, and the results were further verified by laboratory electrochemical simulation tests. The results indicated that the crevices formed by macrofouling adhesion can promote localized corrosion pits and change the local chemical environment. More severe localized corrosion can increase the hydrogen permeation current density and promote the SCC of high-strength steel. As a comparison, the hydrogen permeation current density of steel under cathodic protection state was slightly decreased owing to the shielding effect of macrofouling.

Effect of B. subtilis in simulated acid red soil on the corrosion behavior of X80 pipeline steel

The eastern section of China's West-east gas transmission project is laid in acidic red soil. NRB are widespread in soils and play an important role in metal corrosion. In this article, the corrosion failure behavior and mechanism of X80 pipeline steel under the action of NRB in simulated acidic soil were studied. It was found that the biofilm of B. subtilis had significant inhibitory on the overall corrosion of X80 steel. Electrochemical results prove that the corrosion rate of the sterile group after 14 days of immersion was about 4.5 times that of the bacterial group. However, the biofilm promotes the formation of local corrosion pits. Confocal laser scanning microscopy images indicate that that the corrosion pit depth of the bacterial group (46.1 μm) was three times that of the bacterial-free group (15.7 μm) after 14 days. The pH of the acidic environment was slightly improved by B. subtilis. XPS results proved that B. subtilis complicates the corrosion products of X80 steel through its nitrate reduction ability and metabolism.