Marine Atmospheric Environment Research Articles

Effect of La on the Corrosion Behavior and Mechanism of 3Ni Weathering Steel in a Simulated Marine Atmospheric Environment

Effect of La on the Corrosion Behavior and Mechanism of 3Ni Weathering Steel in a Simulated Marine Atmospheric Environment

Synergistic Effects of Multiple Environmental Factors on Degradation of Silicone Rubber Seals under Marine Atmosphere.

In this research, the degradation behavior and failure mechanism of silicone rubber seal rings under the synergistic effects of multiple factors in the marine atmosphere are fully investigated. Firstly, four aging factors of air, temperature, compressive stress, and chemical medium were determined by analyzing the service environment profile of silicone rubber seal under a marine atmosphere environment. Secondly, to better simulate the actual service environment of silicone rubber and shorten the test period, an artificially accelerated aging test was designed and carried out in the laboratory. In this paper, temperature is utilized as the accelerating stress. According to the results of the pre-test, the accelerating stress level is finally determined to be 110-150 ∘C. In addition, the compression set applied is consistent with the constant compression permanent deformation value of 28% of the silicone rubber in the actual service process. Finally, through the macroscopic physical properties and microstructure analysis of the samples before and after aging, the corresponding test results are given, and the failure mechanism is analyzed and discussed in detail. Through the above test results and discussion, it can be concluded that the aging process of multi-factor coupling on the lower silicone rubber seal ring is uneven, and its aging process is not a simple superposition of multiple environmental factors. More importantly, the above test data and results are of great significance for evaluating the service life of silicone rubber seals, which can be utilized in the future to improve the reliability and durability of related equipment in the marine environment.

Potential change of failure modes and time-dependent behavior of RC beams under a marine atmospheric environment

Stirrups always corrode earlier than the longitudinal steel bars in RC beams, and the corrosion degree is higher. Stirrups will lose their bearing capacity due to corrosion, leading to a decrease in shear strength. Thus, the failure mode may change from bending to shear failure. Previous studies have proposed models to predict corroded RC beams' flexural and shear behavior, respectively. The missing link in these models was the absence of the change of failure modes on the structural behavior. This paper covers the authors' study of corroded RC beams, investigating the effects of reinforcement corrosion on the transformation of failure modes. A numerical simulation was performed to analyze RC beams' time-dependent behavior and failure modes. The effects of the concrete cover thickness, the corrosion initiation time, the concrete strength, and the reinforcement configuration were also investigated. The analysis showed that the stirrups corroded earlier than longitudinal steel bars, leading to potential shear failure rather than bending failure. The larger diameter of stirrups could be adopted in the design to delay the deterioration of structural behavior and the transformation of failure mode. Prolonging the corrosion initiation time using thicker concrete cover thickness and higher strength of concrete is also effective.

Comparative corrosion analysis of acrylic precoated aluminum foil under natural exposure and neutral salt-spray (NSS) testing

Conducting research on the corrosion behavior of condenser fins is of great significance for evaluating the performance of the air conditioner during service. The corrosion behavior of precoated aluminum foil for air conditioner condenser fins after natural exposure test and neuter salt-spray (NSS) test were investigated through surface morphology, chemical composition, contact angle and electrochemical analysis. The results showed that there were significant differences between the microenvironment surrounding air conditioner condenser fins and the natural atmospheric environment. The operating status, the air conditioner model, and the ambient atmospheric conditions will influence the microenvironment of the fins. The precoated aluminum foils exhibit the identical same corrosion characteristics in both natural exposure test and NSS test with corrosion mainly observed in the edge region. Compared with the sample after NSS test for 60 days, the sample after natural exposure test for 2 year had lager corrosion extension distance of edge area, smaller low-frequency impedance modulus and larger contact angle, which indicated more severe corrosion. The comparative analysis of results indicates that the NSS test recommended by standards for a duration of 500–1500 h cannot accurately evaluate the service performance of precoated aluminum foil used in air conditioner in marine atmospheric environment.

Study of short-term corrosion behavior of Q345 steel in marine atmospheric environment

This work studied the corrosion behavior law of Q345 steel exposed to 120 days in Qingdao marine atmospheric environment and the differences in corrosion behavior between the sunlit and shaded sides. The corrosion behavior law of Q345 steel was studied in detail by using weight loss method, electrochemical test, SEM, XRD and ultra-depth microscope. We found that the weight loss curve of Q345 steel under short exposure time still conforms to the power function form, and the corrosion rate increases in the early stage (15 d, 30 d) and decreases in the later stage. The change trend of polarization resistance (Rp) and corrosion current density (Icorr) obtained by electrochemical test corresponds to it. There are significant differences in the morphology and phase composition of the corrosion products of Q345 steel sunlit and shaded sides. On the one hand, the color of the rust layer is not the same, and the rust layer of the shaded side is loose and easy to fall off, and the corrosion is more serious. The three-dimensional morphology map after rust removal showed that Q345 steel had obvious local corrosion in the early stage of corrosion, and the depth of the corrosion pit on the shaded side was greater than that on the sunlit side. On the other hand, the ratio of (β + s)/γ * on the shaded side was greater than that on the sunlit side, and the protection ability of the rust layer on the shaded side was weak. The corrosion characteristics of Q345 steel are different between the sunlit side and the shaded side, and the corrosion of the shaded side is more serious. In engineering applications, we should consider the consequences of this phenomenon.

Corrosion of Copper with Nickel or Zinc Addition in a Typical Marine Atmospheric Environment

Corrosion of Copper with Nickel or Zinc Addition in a Typical Marine Atmospheric Environment

Mixed Bayesian Network for reliability assessment of RC structures subjected to environmental actions

Under environmental action, reinforced concrete (RC) structures might suffer from reinforcement corrosion caused by the surrounding environment, dramatically reducing structural reliability and threatening social development. However, most of the existing reliability assessment methods for RC structures only focused on the structural performance at the design stage given the original unchanged environment, ignoring the effects of realistic exposure conditions and inspection results on reliability evaluation. Thus, this paper develops a general reliability assessment framework based on a Mixed Bayesian network (MBN), incorporating three modules, i.e., durability assessment, load-bearing capacity analysis, and time-dependent reliability analysis. In MBN, separate sub-BNs are built based on different modules and connected by pinch point variables where probabilistic information is transmitted via soft evidence. Besides, this framework considers time-dependent environmental parameters and two-dimensional chloride transport and their effects on reliability. Meanwhile, adjustment coefficients are applied to improve the results of the analytical mechanical model with respect to different limit states through the finite element model (FEM). The proposed MBN framework is illustrated for a corroded RC beam under a marine atmospheric environment to investigate the effects of environmental modeling, chloride transport patterns, and concrete crack inspection on reliability assessment. The results indicate that under the assumed conditions in the case study, early inspection of large cracks may significantly overestimate the failure probability by about 500%. Besides, failure probability might be underestimated by about 95%, ignoring the time-variant environment and two-dimensional chloride transport.

Technical Note: Study on Accelerated Corrosion Behavior and Mechanism of X80 Pipeline Steel Welded Joint Under Cyclic Salt Spray Test

The corrosion behavior of X80 pipeline steel double-sided submerged arc welded joints in a marine atmospheric environment was simulated by cyclic salt spray accelerated corrosion test. The corrosion behavior and mechanism of X80 pipeline steel welded joints were studied by means of scanning electron microscopy, x-ray diffraction, and electrochemical test, and the current effect of welded joints was evaluated by means of macroscopic and microscopic morphology, corrosion weight loss, corrosion product composition, polarization curve, and impedance spectrum of samples with different cycles. The results show that with the extension of corrosion time, the corrosion morphology of each region of the welded joint changes from the initial uniform corrosion to a large difference. During the whole process, the surface fluctuation of the base-metal area is small, and no obvious pitting pits are observed. Cracks are gradually generated in the heat-affected zone and the weld metal, and as the cracks expand, the surface pits deepen. The corrosion rate of the three regions of the welded joint showed a trend of rapid increase-slow decrease-slow increase-slow decrease. It provides conditions for further research on the simulation and correlation of accelerated corrosion tests.

Influence of UV Illumination on the Corrosion Behavior of New 3Ni Weathering Steel in Marine Atmospheric Environments

We investigate the effect of pure darkness and UV illumination on the corrosion process of 3Ni weathering steels involved in both marine atmospheric environments. The corrosion behavior of 3Ni steel in both environments was assessed by cyclic acceleration experiments, electrochemical measurements, morphological analysis and physical phase analysis. The results show that UV illumination affects the corrosion process through the photovoltaic effect of the corrosion products, with photoelectrons and photo-vacancies participating in the redox reaction between the substrate and the atmospheric environment, thereby affecting the corrosion rate of 3Ni steel, the physical composition of the corrosion products and the denseness of the rust layer.

Effect of static elastic stress on the corrosion behavior of 7A04 aluminum alloy exposed to real marine atmospheric environment

Aluminum alloy structural materials are widely subjected to the interactive effect of atmospheric corrosion under thin liquid film and elastic stress during the actual service. This study utilized the real marine atmospheric environment as the corrosion environment of thin liquid film for 7A04 aluminum alloy, and the specially designed outdoor device was used to apply varying levels of static elastic tensile stress at the same time, and then the corrosion damage behavior of 7A04 alloy under the interactive effect was studied. The research indicates that the 7A04 alloy suffers from pitting and exfoliation corrosion under the test conditions. The applied elastic tensile stress can accelerate the corrosion damage process of 7A04 alloy, and the degree of acceleration increases with increasing stress levels and exposure time. Moreover, the applied stress can also significantly accelerate the deterioration of the mechanical properties of 7A04 alloy, which has a more prominent effect on the elongation after fracture. Additionally, the corrosion mechanism of 7A04 alloy under the interactive effect was also discussed in this paper.

Atmospheric chloride-induced corrosion of steel-reinforced concrete beam exposed to real marine-environment for 7 years

Steel-reinforced concrete structure easily suffers from chloride corrosion when exposed to a marine atmosphere environment. In this work, OPC/slag concrete beams combined with loading were naturally exposed to My Island (Qingdao, China) for 7-years and their chloride distributions were investigated as well as carbonation and corrosion-products. The results show that a concentration (Cs,%)-time (t,month) relationship was obtained as Cs=0.022t for concrete surface-chloride. With the increasing corrosion-depth, twice chloride accumulations occurred and were located near the carbonation depth and frontier, respectively. Slag increased the depth and height of the first accumulation peak-value while exacerbating its faster decrease of chloride concentration compared to the control. The chloride increment in the tensile zone was greater than its reduction in the compressive zone. The chloride corrosion mainly occurred in the stirrup bends, where the inner corrosion products mainly contained α-FeOOH and γ-FeOOH while further transforming into Fe3O4 in its outer layer.

High-performance amorphous carbon/PDMS flexible strain sensors by introducing low interfacial mismatch

It is important and challenging to develop environment-tolerant stretchable strain sensors under some harsh environments. Here, amorphous carbon (a-C)/Polydimethylsiloxane (PDMS) sensors were fabricated with the direct-current magnetron sputtering technology, their sensing performances were optimized by adjusting the elastic mismatch between the top a-C film and used PDMS substrate, and their application under a simulated marine atmospheric environment was evaluated. The results showed that the combination of low stress a-C and low elastic modulus PDMS was favorable to improve the sensing performance, the optimal sensor exhibited the maximum gauge factor (GF) of 3026.9, large tensile strain range to 50 %, rapid response (loading delay time 92.3 ms and unloading delay time 24.6 ms), as well as high durability (>5000 cycles). After 120 h salt spray test, the sensor was quite stable and can detect various human movements with both high sensitivity and stability, such as wrist pulse, wrist bending, and finger bending. This work pioneers the elastic mismatch strategy for high-performance a-C/PDMS sensors and confirms their great potential in the practical applications under harsh environments.

Inhibition resistance and mechanism of migrating corrosion inhibitor on reinforced concrete under coupled carbonation and chloride attack

Corrosion of steel bars in the marine environment is an important reason to reduce the service life of reinforced concrete structures. In this study, an amino alcohol migrating corrosion inhibitor (MCI) was coated on the concrete surface, which was then subjected to a simulated marine atmospheric environment by carbonation and salt spraying. The carbonation depth, chloride concentration of concrete, electrochemical performance of steel bars and mass loss rate of steel bar were determined to evaluate the corrosion inhibition performance of MCI. NELD-BS610 hardened concrete bubble spacing coefficient analyzer and scanning electron microscopy (SEM) were applied to analyze the pore structure parameters in concrete and the corrosion behavior of steel bar, respectively. The test results showed that MCI could alleviate the deterioration of concrete induced by accelerated carbonation and chloride attack, and delay the carbonation effect. After 7 days of accelerated carbonation and 35 days of chloride attack, the carbonation depth and chloride concentration of concrete coated with MCI were 16.07% and 16.93% lower than those of concrete uncoated with MCI, respectively. MCI could migrate to the steel bar surface of steel bar to form a protective film, significantly improving the electrochemical performance of the steel bar, and the inhibition efficiency of MCI was about 66.07 ∼ 97.91%. Besides, MCI could also reduce the mass loss rate of steel bars and porosity of concrete induced by carbonation and chloride attack. For the specimens coated with MCI, the mass loss rates of steel bar decreased by 20.31 ∼ 39.78%, and pores with sizes of 1.0 ∼ 0.2 μm in concrete reduced by 59.10 ∼ 76.38%. The results of this research are purposeful for alleviating the corrosion damage problems of reinforced concrete in marine areas.

Electrochemical Study on Corrosion Damage of 7B04 Aluminum Alloy/Anodic Film/Epoxy Coating System in a Simulated Marine Atmospheric Environment

This paper investigates the electrochemical characteristics of the 7B04 aluminum alloy/anodic film/epoxy coating system in a simulated marine atmosphere using electrochemical techniques and surface morphology measurements. The coating system underwent a periodic immersion test for 480 h to simulate the harsh service conditions in a marine environment. Three equivalent circuit models were proposed based on the analysis of the electrochemical failure mechanism of the coating system. Akaike information criterion and Bayesian information criterion were used to selectively choose models for different degradation stages of the coating system, revealing its electrochemical degradation characteristics. Two-stage aging kinetics and gamma models were proposed to describe the time-varying processes of electrochemical low-frequency impedance and corrosion trend, respectively. Ultimately, low-frequency impedance is identified as the most effective and rapid evaluation index for coating performance due to its strong correlation with corrosion trends. The aforementioned models and index provide a foundation for accurately identifying corrosion stages and effectively predicting the corrosion process.

Investigation of rare earth (RE) on improving the corrosion resistance of Zr-Ti deoxidized low alloy steel in the simulated tropic marine atmospheric environment

Rare earth (RE) decreased the initial corrosion susceptibility of Zr-Ti deoxidized low alloy steel in a simulated marine environment through modifying the properties of inclusion and pearlite. The localized acidification caused by the dissolution of (RE)2O2S and (RE)xSy inclusions suppressed the hydrolysis of Ca2+ from the environment, inhibiting the deposition of CaCO3 and its participation in the formation of rust layer, which improved the rust layer compactness at first. This inhibition effect was diminished with time, while, the improved inner rust layer by RE effectively blocked the invasion of Cl-, promoting the enrichment of Cl- in the outer rust layer.

Corrosion-Resistant Stainless-Steel Strands for Prestressed Bridge Piles in Marine Atmospheric Environments

This study demonstrated that stranded highly cold-worked 2205 stainless steel (SCW2205) exhibits superior corrosion resistance when compared to stranded cold-worked AISI 1080 (ASTM A416) steel and cold-worked modified austenitic stainless steel 201, making it a viable candidate for prestressing applications with extended service life. Laboratory and field testing were performed. The material microstructure was characterized using scanning electron microscopy/energy dispersive x-ray spectroscopy, transmission electron microscopy, and x-ray diffraction. Then, laboratory corrosion testing, including linear sweep voltammetry, pitting resistance exposure, and four-point bend stress corrosion cracking (SCC) testing, was performed under different conditions. These conditions included concrete pore solution saturated with chlorides, direct exposure to artificial seawater, various concentrations of NaCl and MgCl2, representative inland salt deposition conditions, and oxidizing conditions with high chloride concentrations. The laboratory studies were augmented with field testing (259 d), comprised of four-point bend SCC, U-bend SCC testing (ASTM G30), and atmospheric contaminant measurements. The pitting resistance results, corrosion morphology, stable pit safe range, SCC results in the lab and in the field, and hydrogen embrittlement (HE) testing by slow strain rate testing (SSRT) under cathodic polarization as a diagnostic showed that SCW2205 outperformed the other steels tested, in the case of marine atmospheric corrosive conditions. SCC in SCW2205 was characterized by a selective localized anodic dissolution of the ferrite matrix and environmentally assisted cracking in the austenite phase. However, SCC was only found in SCW2205 at or above 65°C. SSRTs confirmed susceptibility to hydrogen uptake and a hydrogen-assisted mechanism of HE given sufficient hydrogen. It is speculated that hydrogen uptake in pits or crevice sites might be a route to hydrogen absorption worth exploring further since the absence of cathodic polarization in application precludes hydrogen production and uptake.

Effect of Tropical Marine Atmospheric Environment on Corrosion Behaviour of the 7B04-T74 Aluminium Alloy

In this work, the effects of the tropical marine atmospheric environment on the corrosion behaviour of the 7B04-T74 aluminium alloy were systematically investigated by using accelerated testing, together with corrosion kinetic analysis, microstructure observation, product composition analysis, and potentiodynamic polarization curve tests. The weight loss method was used for the corrosion kinetics analysis. The surface morphology and corrosion products transformation law were investigated by OM, SEM, EDS, and XPS. The electrochemical characteristics were studied using potentiodynamic polarization curves. The research indicated that the 7B04-T74 aluminium alloy has eminent corrosion resistance in the tropical marine atmospheric environment. Localized pitting corrosion occurred rapidly in the tropical marine atmosphere. In the later stage of corrosion, the corrosion of aluminium alloy did not become serious. Specifically, no obvious intergranular corrosion was found, which is related to the thermal treatment method. Corrosion products included Al(OH)3, Al2O3, and AlCl3, of which Al(OH)3 is the most notable.

Corrosion behavior on carbon steel affected by iron-reducing bacteria via dissimilatory Fe(Ⅲ) reduction in simulated marine atmospheric environment

The corrosion behavior of carbon steel in simulated marine atmospheric environment combined with microorganisms was investigated. Results demonstrated that weight loss was increased, pitting corrosion was aggravated and the velocity of charge transfer and ionic migration were accelerated in media with bacteria. 16S rDNA sequencing revealed that iron-reducing bacteria (IRB) grew into a dominant population in the biofilm. The compact and protective corrosion product film in the inner layer was disrupted locally in presence of IRB. The corrosion mechanism of carbon steel in marine atmospheric environment influenced by IRB via dissimilatory Fe(Ⅲ) reduction had been discussed.

Influence of isothermal tempering on microstructures and hydrogen-environmentally embrittlement susceptibility of laser additively manufactured ultra-high strength AerMet100 steel

Good hydrogen-environmentally embrittlement (HEE) resistance is necessary for safe service of critical main load-bearing ultra-high strength steel (UHSS) components of advanced aircrafts in marine atmosphere environment. Controlling isothermal tempering time is one important heat treatment method to optimize HEE resistance of UHSS by designing microstructure. Influence of isothermal tempering time at 482 °C on microstructures and HEE susceptibilities of laser additively manufactured (LAM) AerMet100 steel was investigated by several material characterization methods and slow strain rate tensile (SSRT) tests in both of air and 3.5 wt% NaCl aqueous solution. Results mainly indicate that microstructure evolution behaviors of LAM AerMet100 steel successively include martensite and retained austenite decomposition, M2C carbide formation and coarsening, and film-like reverted austenite formation and thickening. Short-time tempering specimens of LAM AerMet100 steel has the highest strength-loss-index in all of the specimens due to the lowest austenite amount. The lower HEE susceptibility of LAM AerMet100 steel in long-time tempering condition is mainly corresponding to M2C carbide coarsening and film-like reverted austenite thickening. Furthermore, difference of hydrogen charging method strongly influences macro-fracture behaviors of the SSRT specimens, but micro-cracking modes of the steel in different conditions are predominantly martensite packet/plate boundary cracking. Under open-circuit potential condition, HEE cracking zone is prone to be origin from pitting corrosion sites, and the SSRT specimen in long-time tempering condition have a good ductility; in contrast, under cathodic polarization condition, HEE cracking zone is around the circumferential zones, and the tensile specimens are brittle fracture. These findings are important when considering achieving improved HEE resistance for LAM AerMet100 steel tempered at 482 °C of a longer isothermal tempering time at the strength level of interest.

Time-dependent reliability analysis of reinforced concrete beams considering marine environmental actions

Under marine atmospheric environments, reinforced concrete (RC) structures may suffer from structural deterioration induced by environmental actions, affecting structural performance and safety. Thus, it is essential to evaluate and predict the deterioration process of an RC structure subject to environmental actions. This paper proposes a novel and generic computational framework to assess the time-dependent reliability of an RC beam under environmental actions. This framework includes a comprehensive life-cycle performance assessment model that considers climate change, two-dimensional chloride transport, the coupling effects and corrosion non-uniformity of reinforcement, and the nonlinear behavior of RC beams, which is validated by experimental studies. Additionally, performance functions for an RC beam are established for different failure modes, and their time-dependent probabilistic information and reliability index are captured using the probability density function-informed method (PDFM). To demonstrate the computational processes of the developed framework under practical marine atmospheric conditions, illustrative cases are presented. The accuracy and efficiency of the proposed method are validated by traditional Monte Carlo Simulation (MCS). Results indicate that the proposed method is feasible and efficient, aiding the life-cycle design and maintenance of RC structures.