Corrosion Pits Research Articles

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.

Failure Analysis of Corrosion Pit on Outer Wall of Membrane Wall Pipe

Abstract Flue gas pipework is a critical component of a flue gas treatment system, mainly transporting the flue gases produced by a combustion plant from the source to the vent. Flue gas pipework is vital in all applications, such as thermal storage gas stoves, heaters, and gas water heaters. However, due to negligent management during the use of piping. Corrosion pits were created in several places on the outer wall of a membrane wall pipe located on the flue gas side of the membrane wall pipe. The external circulation medium of the membrane wall pipe is mainly high-temperature flue gas, and the internal circulation medium is water. This paper determines the causes of the corrosion pits by macroscopic observation, metallographic microstructure analysis, scanning electron microscopy, and energy dispersive spectroscopy (EDS). It was found that the outer wall of the flue gas sidewall pipe of the failed part was covered with reddish-brown rust, wide and shallow corrosion pits were observed, and the detection area of the inner surface of the pits had a high ‘S’ content. To reiterate, it was concluded that the cause of the corrosion pits was the flue gas dew-point corrosion.

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 pH on the controlled release of benzotriazole from halloysite clay nanotubes for corrosion protection of mild steel

Due to the increase in severe consequences of mild steel corrosion, the development of coatings with improvement in corrosion-resistant properties has become very essential. In this work, benzotriazole (BTA) was encapsulated into halloysite nanotubes (HNTs) for inhibiting the corrosion of mild steel surface. The BTA-encapsulated HNT exhibits pH-responsive properties over a wide range of pH. It was found that a large amount of BTA was released at pH 3 (48 %), followed by pH 7 (30 %) and least in the case of pH 10 (20 %). At neutral pH, a rapid release of BTA was observed during initial exposure, reaching a steady-state later, with no significant release further. A salt immersion test was carried out after immersing mild steel (MS) substrates in BTA-HNT nanopowder dispersion in 3.5 wt% NaCl at different pH. SEM images and EDS maps confirmed that corrosion product formation on MS surface at pH 3 was significantly more with corrosion pits along with HNTs throughout the surface. At pH 7 and 10, corrosion pits were observed with very few halloysite nanotubes on the surface. An optimum amount of BTA is required to inhibit corrosion, excessive release may cause more Cl− ions to penetrate, leading to more corrosion. Electrochemical data also reveals the same trend, where the icorr value was maximum for pH 3 (1.09 × 10−5 A/cm2) > pH 7 (4.74 × 10−6 A/cm2) > pH 10 (3.43 × 10−6 A/cm2). Therefore, results suggest that BTA-encapsulated HNT can be efficiently incorporated into the coating matrix for their controlled release to provide corrosion protection under varying neutral and alkaline marine environments.

Improving optical and electrical stabilities of fluorine-doped tin oxide films in sweat solutions with O2 addition in plasma

Abstract Recently, the use of wearable smart devices has significantly increased; however, sweat can corrode the outer-layer films, thereby decreasing their transmittance, conductivity, and overall functionality. In this study, fluorine-doped tin oxide (FTO) films for wearable smart devices were prepared via magnetron sputtering. The effects and mechanism of O2 gas flow in plasma on the properties of the fabricated films were investigated. Minor changes were observed in the film morphologies, with the preferred orientations shifting from polar (101) to nonpolar (110) and standard positions. As the O2 flow rate increased from 0 to 2 sccm, the transmittance of the film within the visible spectrum increased from 83% to 89%, with sheet resistance values in the order of 102–106 Ω·sq–1. Following immersion in an acidic sweat solution, the film without O2 peeled off, whereas several corrosion pits were observed in the films with 1 or 2 sccm O2. Conversely, following immersion in an alkaline sweat solution, several pits were observed in the films without O2, while the other films exhibited excellent corrosion resistance. The transmittance of the films immersed in different solutions did not significantly differ. Notably, the sheet resistances of the films treated with 1 sccm O2 met the industrial requirement of 3000 Ω. Moreover, the coexistence of polar and nonpolar planes provided transparency and conductive stability to the FTO films treated with 1 sccm O2. Our study aimed to not only enhance the transmittance and sweat-corrosion resistance but maintain the conductivity of the outer screen layer of a wearable smart electronic device.

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.

Effect of shaft voltage on electric damage of GCr15 bearing material

Electrical erosion pit is a fundamental manifestation of electrical bearing damage. As the shaft voltage increased, the degree of electrical damage became more severe, and the residual compressive stress and hardness of bearing surface decreased. The transition of martensite into ferrite induced by high discharge temperature was found at the edge of the erosion pit using a transmission electron microscopy. This phenomenon has not been observed below the mechanically rolled surface under the same conditions. Electrical penetration harmed the bearing through surface erosion, lubrication deterioration and martensite decomposition. The electrical pit could be observed when current density exceeded 0.95 A/mm2. The results can help understand bearing failure in the fields of railways, wind turbines, and new-energy vehicles.

Comparison of Corrosion Behavior of a-C Coatings Deposited by Cathode Vacuum Arc and Filter Cathode Vacuum Arc Techniques

This study explores the utilization of cathodic vacuum arc (CVA) technology to address the limitations of magnetron sputtering technology in preparing amorphous carbon (a-C) coatings, such as having a low ionization rate, low deposition rate, and insufficiently dense structure. Specifically, a-C coatings were prepared by the cathodic vacuum arc (CVA)and the filtered cathodic vacuum arc (FCVA) technology,, one with embedded carbon particles and one without, both having closely related carbon structures. Research is currently underway on bipolar plate coatings for fuel cells. The corrosion behavior of the prepared a-C coatings was examined through Tafel polarization analysis under simulated fuel cell operating conditions as well as potentiostatic analysis at 0.6 V under normal conditions and 1.6 V under start–stop conditions for 7200 s. The coatings before and after corrosion are characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and infrared spectroscopy. The results reveal that the incorporation of conductive graphite-like particles in the coatings reduces their contact resistance. However, the gaps between these particles and the coatings act as pathways for corrosive solution, exacerbating the corrosion of the coatings. After corrosion at 0.6 V, both sets of coatings with sp2-hybridized carbon structures are contaminated by elements such as hydrogen and oxygen, leading to an increase in their contact resistance. Under high potential conditions (1.6 V), large corrosion pits and defects appear at the locations of graphite-like carbon particles. Furthermore, both sets of samples exhibit more severe oxygen contamination and a transformation of broken carbon bonds from sp3- to sp2-hybridized forms, irrespective of whether embedded graphite particles are present.

The Influence of Microstructure Evolution on the Mechanical and Electrochemical Properties of Dissimilar Welds from Aluminum Alloys Manufactured Via Friction Stir Welding

The present study investigated a new configuration of friction stir welded joints from two aluminum alloys. Dissimilar welds AA6082/AA1350 were examined, whereas, for AA1350, two states were investigated—coarse-grained (CG) and ultrafine-grained (UFG). Changes in the mechanical and electrochemical properties regarding the microstructure evolution across the welds were discussed. The average grain size in the stir zone (SZ) for all materials equaled 4 to 5 µm with a fraction of high-angle grain boundaries of about 77 pct, indicating the occurrence of continuous dynamic recrystallization. Changes in the microhardness across the welds were connected with differences in grain size (AA1350) and dissolution of β″ precipitates in the SZ of AA6082. As a result, the tensile strength of the welds decreased compared to base materials AA6082 and AA1350 UFG; however, there was an increase when compared to the base material AA1350 CG. Electrochemical experiments revealed that pitting corrosion occurred for AA1350, while for AA6082, it was a combination of pitting and intergranular corrosion. The depth of corrosion attack was higher for AA1350, with a maximum value of ~ 70 µm for base materials, while in the SZ, a depth decreased to 50 µm. For the AA6082, the maximum depth was measured in the SZ and did not exceed 30 µm.

Substantial Improvement in Mechanical Properties and Anti‐corrosion Properties of Rolled Zn–Mg–Sr Alloys as an Orthopedic Implant

This study investigates a Zn–Mg alloy, enhanced for biodegradability and biocompatibility, by introducing trace amounts of Sr and subjecting it to hot‐rolling. The resulting Zn–Mg–Sr alloy shows a reduced average grain size to 3.35 μm and a transformed Mg2Zn11 phase from lamellar to finely dispersed particles, while maintaining a uniform SrZn13 phase distribution. The as‐rolled alloy exhibits significantly improved mechanical properties, with a tensile strength of 340 MPa and 40% of elongation, attributed to grain‐boundary strengthening, reinforcement by second‐phase particles, and the presence of intragranular dislocations and nanoscale precipitates. This microstructural refinement enhances the elongation by hindering crack propagation. Corrosion resistance tests reveal the superior performance of the as‐rolled alloy, owing to the finely distributed eutectic particles, which mitigated localized corrosion and altered the corrosion morphology from localized to finer corrosion pits. In vitro biocompatibility assessments show over 80% cell viability in C3H10 cultures with 50% Zn–Mg–Sr alloy extract, indicating low cytotoxicity. Furthermore, the alloy exhibits promising bone‐promoting properties, highlighting its potential for biomedical applications.

The Role of Nitrogen Gas and PWHT on Pitting Corrosion Behavior of Duplex Stainless-Steel Joint Made by GTAW

The Role of Nitrogen Gas and PWHT on Pitting Corrosion Behavior of Duplex Stainless-Steel Joint Made by GTAW

Insights into the biocorrosion of Q235A steel influenced by the electron transfer process between iron and methanogenic microbiota

Anaerobic microbiologically influenced corrosion (MIC) of Fe (0) metals causes great harm to the environment and economy, which depends on the key electron transfer process between anaerobic microorganisms and Fe (0) metals. However, the key electron transfer process in microbiota dominating MIC remains unclear, especially for methanogenic microbiota wildly distributed in the environment. Herein, three different methanogenic microbiota (Methanothrix, Methanospirillum, and Methanobacterium) were acclimated to systematically investigate electron transfer pathways on corroding Q235A steel coupons. Results indicated that microbiota dominated by Methanothrix, Methanospirillum, or Methanobacterium accelerated the steel corrosion mainly through direct electron transfer (DET) pathway, H2 mediated electron transfer (HMET) pathway, and combined DET and HMET pathways, respectively. Compared with Methanospirillum dominant microbiota, Methanothrix or Methanobacterium dominant microbiota caused more methane production, higher weight loss, corrosion pits with larger areas, higher corrosion depth, and smaller corrosion pits density. Such results reflected that the DET process between microbiota and Fe (0) metals decided the biocorrosion degree and behavior of Fe (0) metals. This study insightfully elucidates the mechanisms of methanogenic microbiota on corroding steels, in turn providing new insights for anti-corrosion motives.

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.

Hierarchical Significance of Environment Impact Factor on the Sand Erosion Performance of Lightweight Alloys.

This paper addresses the challenge of ranking the factors that affect the erosion resistance of lightweight alloys, with a specific focus on aluminum alloys. A three-factor, four-level orthogonal experimental design was employed to examine the influence of various sand particle sizes, erosion speeds, and sand concentrations on the abrasion qualities of these alloys. Parameters such as mass loss, depth, residual stresses, and failure mechanisms were assessed to determine erosion performance. Analysis of variance (ANOVA) and regression analysis of the three key factors were performed. Our findings resulted in an erosion rate formula: erosion rate = 0.679 sand particle size +0.067 sand concentration -0.002 erosion velocity +0.285. Our findings indicate that particle size is the most significant factor affecting erosion rate, with sand concentration and erosion velocity being secondary factors. The failure mechanism reveals that larger sand particles tend to produce deeper slides, and higher sand concentrations result in an increased number of slides. A lower concentration leads to the appearance of erosion pits. And the test conditions of high concentration and low velocity lead to more serious brittle fractures of the substrate, often accompanied by the appearance of cracks.

Failure assessment of deteriorated steel light poles

Steel poles are extensively used as street light posts and various other applications within the power distribution network. For partially buried pole, the effect of corrosion below and at the ground level significantly controls the overall load capacity. In this study, number of in-service steel pole specimens extracted from field were assessed for the corrosion damage. The level of corrosion was estimated by remaining wall thickness measured using ultrasonic testing and the surface corrosion was estimated using 3D laser scanning to adopt an appropriate existing model for buried steel structures. A relationship between maximum and average corrosion pit depth and loss of embedment depth was then developed. Finally, the corrosion parameters, combined with uncertainty in loading and soil properties were employed to perform time-dependent reliability assessment for steel light poles which can be used to assist the asset maintenance team in planning the replacement or strengthening works for steel pole.

Dynamic Simulation Model and Performance Optimization of a Pressurized Pulsed Water Jet Device

Pulsed water jet technology has broad application prospects in the field of rock breaking. The pressurized pulsed water jet (PPWJ) is a new type of pulsed jet that offers high-amplitude pressurization, variable pulse pressure and frequency, and a high energy usage rate. To achieve a more destructive and powerful pulsed water jet, a dynamic simulation model of the device was established by using the AMESim software (v1400) based on the operational principle of PPWJs, and the simulation model was validated against the experimental results. The relationships between the key structural parameters of the PPWJ device and the pulse parameters were quantitatively investigated. The pulse pressure and frequency can be increased by appropriately increasing the nozzle diameter or boost ratio, and the pulse pressure will drop if the nozzle diameter or boost ratio exceeds a threshold value. Increasing the maximum displacement or action area of the piston will increase pulse length while decreasing pulse frequency; a proper match of the maximum displacement or action area of the piston will assure pulse peak pressure. The maximum outer diameter of the piston only affects the pulse frequency. The key structural parameters of the device were optimized on that foundation. Compared to the original device, the optimized device resulted in an increase in pulse frequency and jet output energy, leading to larger diameter and volume of erosion pits at the same stand-off distance and erosion time. The findings of this study offer valuable scientific insights for achieving efficient rock breaking with PPWJ.

A 2-D Reaction-Transport Model for Investigating Pit Morphology Under the Influence of a Salt Film

A 2-D reaction transport model with the phase field method was employed here to simulate the propagation stage of corrosion pitting in stainless steels in a chloride environment. The influence of the salt film on pitting dissolution kinetics was incorporated into the model to study its effect on the pit morphology under various settings. In potentiostatic conditions, the pit morphology tends toward a dish-like shape due to the presence of the salt film inside a corrosion pit. This leads to diffusion-controlled dissolution at the pit bottom and active dissolution near the pit mouth. On the contrary, in galvanostatic conditions and at a high applied current, although the salt film was initially present, its effect diminished as the chemistry inside the pit became diluted and the pit growth transitioned into active dissolution near the repassivation current. This effect is attributed to the limited resources to support the enlargement of a corrosion pit under constant applied current. As a result, the pit morphology in galvanostatic conditions is likely to be hemispherical and can transition into complex morphology, as discussed in a previous paper.

Experimental Investigation of Nonlinear Cyclic Behavior of Circular Concrete Bridge Piers with Pitting Corrosion

Experimental Investigation of Nonlinear Cyclic Behavior of Circular Concrete Bridge Piers with Pitting Corrosion

Comparison of Performance of NiCr2O4 and Cr2O3 Formed on the Ni-Based Superalloy RR1000 Under Corrosive Conditions

AbstractSamples of the Ni-based superalloy, RR1000, were exposed to 98% Na2SO4/2% NaCl salts at 700 °C with a flux of 1.5 µg cm−2 h−1 in flowing air + 300 ppm SO2 for a total of 250 h. Three pre-exposure conditions were studied: a bare reference alloy; fast heating to the test temperature followed by a 100 h hold; heating at a rate of 5 °C min−1 to the test temperature following by a 100 h hold. The surface oxide formed under the latter two conditions were Cr2O3 or NiCr2O4, respectively. The results show corrosion pit formation on the surface of the base, reference sample, and no pits present on the sample with the preformed Cr2O3. Some protection was found for the sample heated at 5 °C min−1 with a delay in the progression to accelerated corrosion attack. Additional testing under moisture containing air was also conducted. This showed no obvious difference in surface oxide morphology under the two tested heating rates for the short-term exposures examined but a difference was noted to be dependent on the moisture content of the air.

Influence of heat treatment on the microstructure evolution and corrosion performance of biodegradable Zn-Mg alloys

Zinc and zinc-based alloys have garnered increasing attention as biodegradable materials due to their excellent mechanical properties, lower degradation rates compared to magnesium, and favorable biocompatibility. This study investigates the impact of homogenization treatment on the microstructure and corrosion behavior of Zn-Mg alloys using scanning electron microscopy, X-ray diffraction, hardness testing, and accelerated corrosion immersion tests. The results reveal that homogenization treatment induces the fusion of eutectic cells within the alloys, causing significant morphological alternations in the eutectic structure and varying proportions of the Mg2Zn11 phase, These changes notably affect material properties. The raised content of Mg2Zn11 phase in the eutectic structure correlates with higher hardness but reduced corrosion resistance, whereas the reduced Mg2Zn11 phase content leads to enhanced corrosion resistance. Furthermore, in-situ corrosion observations demonstrate that corrosion initiates at the eutectic phase, with corrosion pits forming due to the ion release as corrosion progresses, leading to gradual enlargement of the corrosion pits. In summary, this study provides comprehensive insights into the microstructural changes in Zn-Mg alloys and their impact on corrosion resistance, offering valuable references for their engineering applications.