AE signals generated by the reinforced concrete corrosion process are complex, and the threshold value of common commercial sensors in concrete corrosion monitoring is set high, resulting in the loss of a large number of AE signals. In this article, a homemade cement-based acoustic emission sensor is used to reduce the threshold value to 29 dB. By comparing the acoustic emission signals generated during the accelerated corrosion process of bare steel bars, cement mortar, and reinforced concrete. The research found that the amplitude of the acoustic emission signals caused by steel corrosion was approximately 35 dB, with a main frequency of 150 kHz. The amplitude of the bubble signals generated by corrosion was approximately 30 dB, with a main frequency of 30 kHz. The main frequency of the crack signals caused by the corrosion products of concrete decreased to 110 kHz. The cumulative energy and AE count rise significantly in the later corrosion stages, and the b -value drops below 1 as macro cracks develop. The related technologies have potential research value in identifying the corrosion stage of reinforced concrete and reducing maintenance costs.
Large language models (LLMs) have increasingly been applied as a novel and accessible alternative to traditional machine learning (ML). Their main advantage lies in the fact that they do not require model training or data pre-processing; instead, they are guided through natural language instructions. In this study, we evaluate the suitability of LLMs for corrosion-related tasks and introduce an approach that combines LLMs with hard-coded logic to enhance reliability and performance. The methodology was tested on three tasks: classifying images of organic coatings in ‘blister’/‘no blister’ classes, ranking specimens based on corrosion severity, and classifying images into severity classes. The results demonstrate performance comparable to that of trained ML models, with ‘blister’/‘no blister’ classification achieving accuracies up to 0.93. These findings highlight the potential of LLMs, when integrated with expert-driven strategies, as practical and scalable tools for corrosion assessment.
This study systematically investigates the time-dependent evolution of corrosion product layers on X80 steel during 120 days of seawater immersion and their effects on hydrogen transport and electrochemical corrosion behavior. The results show that the corrosion products mainly consist of Fe 3 O 4 , Fe 2 O 3 , and FeOOH, with the Fe 3 O 4 content progressively increasing and the Fe 2 O 3 content decreasing with prolonged immersion. A critical transition occurs between 60 and 75 days, during which the corrosion product film is proposed to develop a bilayer-like configuration, accompanied by an increase in the Fe 3 O 4 fraction to 43.64% and a subsequent reduction in both hydrogen permeation and anodic dissolution. Furthermore, a semi-empirical relationship, D = D 0 ·exp(-k·f), is established to correlate the Fe 3 O 4 fraction (f) with the hydrogen diffusion coefficient (D). Based on these observations, a three-stage evolution framework is proposed: (I) film formation and loosening (0–45 days), (II) compositional transition and enhanced hydrogen transport (45–75 days), and (III) film densification and inhibitory effects (75–120 days). Overall, this study provides a time-dependent and parameterizable description of the evolution of corrosion product layers and their coupled effects on hydrogen transport and electrochemical corrosion, extending the understanding of corrosion-film evolution beyond the qualitative trends reported in previous short-term studies.
Polyurethane is widely used coating to prevent corrosion. Incorporating nanoparticles into composite coatings has been explored to improve polyurethane barrier properties and prolong service life. In this study, an accelerated cyclic electrochemical technique (ACET) was developed and applied as a rapid evaluation method for evaluating the corrosion protection performance of nanoparticle-reinforced polyurethane coatings. Electrochemical characterization was conducted in 3.5 wt.% NaCl solution. TiO 2 /Polyurethane composite coatings with 1–5 wt% TiO 2 were evaluated. Coating performance was correlated with water contact angle measurements, scanning electron microscopy (SEM), and pull-off adhesion testing. Results showed that adding 1–3 wt% TiO 2 improved polyurethane barrier properties. The 3 wt.% TiO 2 composite exhibited the highest coating resistance and corrosion protection performance. The enhanced performance was attributed to the barrier effect of well-dispersed TiO 2 nanoparticles, which reduced coating porosity and improved coating hydrophobicity, thereby limiting water and electrolyte penetration. In contrast, the 4 −5 wt% composites showed little or no improvement because of the coating cracking and particle agglomeration caused by excessive TiO 2 loading. These findings demonstrate the effectiveness of ACET as a rapid screening tool for evaluating protective coating systems and identify an optimal TiO 2 loading range for improving the corrosion protection performance of polyurethane coatings.
The effect of tempering temperature on microstructure and Cl − corrosion resistance of 4Cr13 steel was investigated using XRD, SEM, electrochemical and immersion testing. The results showed that with increasing tempering temperature, the matrix evolved from tempered martensite to tempered troostite, and finally to tempered sorbite. The amount of retained austenite (RA) gradually decreased and became negligible after tempering at 500 °C. A small amount of primary carbides identified as M 23 C 6 carbides survived after quenching. Granular Cr-rich M 23 C 6 carbides were precipitated during tempering at 400 °C-600 °C. Electrochemical and immersion tests revealed that with increasing tempering temperature, both the corrosion potential and pitting potential initially decreased and then increased, whereas the corrosion current density exhibited the opposite trend. The average corrosion rate and the corrosion weight loss firstly increased and then decreased. The massive precipitation of Cr-rich M 23 C 6 carbides upon tempering at 500 °C-550 °C promoted the formation of Cr-depleted zones and markedly deteriorated the corrosion resistance. Tempering at 600 °C accelerated coarsening of the Cr-rich M 23 C 6 carbides and lowered their distribution density, which alleviated the Cr-depletion effect and partially restored the surface passivation capability. Tempering at 200 °C prevented the precipitation of Cr-rich carbides and yielded the highest corrosion resistance.
