Search Results (578)

The topology optimization of reinforced-concrete (RC) building frames is relatively underexplored compared to steel structures, partly due to the lack of a systematic approach to generate and select ground structures (GS). Existing methods often use less systematic GS strategies, limiting efficient exploration of the vast and sparse design space shaped by large bay widths and story heights. This work addresses this gap by providing a comprehensive and systematic pipeline tailored for RC frames. The key contributions are: (1) development of a GS generation framework that systematically enumerates all feasible RC frame configurations within user-defined constraints, (2) introduction of a candidate GS selection map, a surrogate-based tool employing graph-based Latin hypercube sampling (LHS) and sparse Gaussian Process (GP) models, which predicts compliance early and strategically guides candidate selection, reducing computational cost by limiting full finite-element evaluations to the order of ${10}^3$ out of up to ${10}^5$ generated frames while serving as a reference for understanding design-parameter influences; and (3) implementation of an integrated topology-optimization pipeline applying particle swarm optimization (PSO) to selected candidates, achieving efficient compliance minimization with reduced computational effort. The complete workflow—which spans GS generation, surrogate-based candidate selection, and iterative optimization—is implemented and validated in two design domains with width-to-height aspect ratios of 1:1 and 1:1.5 and generates 438,984 and 104,032 different frame configurations, respectively. These selected candidates undergo PSO-based optimization, yielding designs with volume fractions below 0.55 and preserving critical floor beams, demonstrating the framework’s ability to identify structurally efficient stiffness-driven RC frame topologies for early-stage screening. The framework is designed as an extensible foundation that can be coupled with more detailed member-level design checks and nonlinear RC analysis in future work, rather than replacing full reinforced-concrete design procedures. Full article

The article deals with the study of stress corrosion cracking (SCC) of X70 steel using corrosion-mechanical testing that simulates the operating conditions of underground pipelines. The tests were carried out under cyclic four-point bending at stresses close to the yield point, in electrolytes with various hydrogen charging capacities. The following model environments were used: NS4 solution and citrate buffer (pH 5.5). Hydrogen charging was controlled by the addition of thiourea and by varying the potential. It was shown that microcracks initiated at corrosion defects (pits) and then emerged at the surface to form narrow cracks. The incubation period depends on the environment: under corrosive conditions it is approximately two times shorter than in the air. The size and nature of stress concentrators play a significant role: natural pits (~hundreds of μm) lead to crack formation within 24–28 days, whereas artificial holes (0.6–1 mm) lead to crack formation within 5–7 days. The effect of hydrogen was established: the acceleration is insignificant under moderate hydrogen charging, whereas the incubation period decreases sharply at high hydrogen charging. Critical hydrogen concentrations where its effect becomes significant were determined. Methods for inhibiting stress corrosion cracking by means of organosilicon films (vinyl- and aminosilanes, as well as their mixtures with inhibitors—benzotriazole and amines) were considered. The most effective composition is vinylsilane + benzotriazole: the time to crack initiation increases from 5 to 36 days, and the crack growth rate decreases. Full article

The demand for efficient combustion in boilers drives the development of ultra-supercritical power plants. P92 steel pressure, and pipelines operate in high-temperature and high-pressure environments and are prone to high-temperature creep damage. Non-destructive testing is a key method to ensure the safety of the pipe. However, existing non-destructive testing methods are difficult to achieve non-destructive detection of creep damage. Creep damage affects magnetic Barkhausen noise (MBN) and magneto-acoustic emission (MAE) signals; therefore, it is possible to evaluate creep damage using these signals. This article first establishes a theoretical model for MBN and MAE. Afterward, the influence of magnetizing waveform, amplitude, and frequency on MBN and MAE signals was studied through experiments. Finally, by analyzing the characteristics of MBN and MAE signals, the optimal magnetization conditions and signal characteristic parameters for detecting creep damage using MBN and MAE signals were determined. The experimental results also confirmed the correctness of the theoretical model. Full article

This study investigates pulsed gas metal arc welding (pGMAW) of API 5L X65 pipeline steel for sour service applications where H₂S exposure is anticipated. Mechanized pGMAW in the 5G downhill position was employed to fabricate girth welds using ER70S-6 filler wire with Ar-20%CO₂ shielding. Comprehensive characterization, including optical microscopy, tensile testing, fractography, EBSD, and fracture toughness evaluation via SENT specimens, was conducted on specimens tested in both air and H₂S-precharged sour conditions. Microstructural analysis revealed ferritic–pearlitic base metal, weld metal with acicular ferrite and bainitic constituents, and a transformed HAZ gradient. Tensile testing demonstrated severe hydrogen embrittlement in sour conditions, with elongation dropping from 22% in air to 4% after H₂S exposure, accompanied by a transition from ductile cup–cone fracture to quasi-cleavage morphology. EBSD showed texture sharpening toward ⟨101⟩ fiber post-deformation, with a broader orientation spread under sour conditions, indicating heterogeneous strain localization. Fracture toughness testing revealed approximately a 50% reduction in CTOD values under sour exposure, with the weld centerline exhibiting greater degradation (0.50 mm to 0.27 mm) compared to the HAZ (0.92 mm to 0.47 mm). Fractography confirmed hydrogen-assisted cracking features, including shallow dimples, cleavage facets, and secondary cracking. These findings establish critical baseline data for engineering a critical assessment of pGMAW-welded X65 pipelines in sour service. Full article

To investigate the effect of crack geometry on tensile deformation and strain localization in X46 pipeline steel thin-walled tubes, uniaxial tensile tests were conducted on specimens containing prefabricated cracks with different sizes, types, and orientations, and full-field strain evolution was characterized by digital image correlation. The material exhibited a favorable strength-ductility balance, with an average yield strength of 324 MPa, an ultimate tensile strength of 553.5 MPa, and an elongation of 27%. Non-cracked specimens showed three deformation stages: uniform deformation, strain localization, and necking instability. In cracked specimens, strain localization initiated at the crack tips and expanded with increasing displacement. Larger cracks significantly intensified crack-tip strain concentration and enlarged the high-strain zone. Through-wall cracks caused stronger localization and earlier local instability than surface cracks because of the loss of wall continuity, whereas small surface cracks had a limited effect on the final localization path. Crack orientation also affected deformation behavior, and the 45° inclined crack produced the most severe X-shaped localization under combined normal and shear stresses. Full article

This study investigates hydrogen embrittlement in welded joints of X52 (L360) pipeline steel obtained from an operating natural gas transmission network after 31 years of service, with particular emphasis on production (longitudinal) and girth (circumferential) welds. The aim is to elucidate the influence of microstructural heterogeneity across the pipe wall and within different welded joint types on hydrogen transport, trapping behavior, and fracture mechanisms. The investigation combines X-ray diffraction, electrochemical hydrogen permeation testing, fractographic analysis, and transmission electron microscopy. X-ray diffraction results show that the base metal and girth weld consist predominantly of body-centered cubic ferrite, whereas the production weld additionally contains retained austenite associated with an elevated manganese content. These phase-related differences are consistent with transmission electron microscopy observations of martensite–austenite constituents within the weld microstructure. Electrochemical hydrogen permeation measurements reveal pronounced microstructure-dependent hydrogen transport behavior. The production weld exhibits a significantly lower apparent diffusion coefficient and a markedly higher hydrogen trap density, approximately five times greater than those of the base metal and girth weld, providing a mechanistic explanation for the observed differences in hydrogen uptake behavior. Fractographic analysis demonstrates a transition from ductile microvoid coalescence in the uncharged condition to predominantly brittle fracture following hydrogen charging. This transition is accompanied by a substantial increase in the fraction of brittle fracture zones, reaching approximately 53% in hydrogen-charged specimens. A pronounced gradient in hydrogen embrittlement susceptibility is observed across the pipe wall thickness, with outer-wall specimens consistently exhibiting greater susceptibility than inner-wall specimens. This behavior reflects the combined influence of long-term soil corrosion and hydrogen-assisted degradation. Transmission electron microscopy reveals that plastic deformation governs dislocation generation, while hydrogen significantly modifies dislocation behavior by promoting dislocation pile-ups near martensite–austenite constituents and non-metallic inclusions. These observations indicate strong interactions between hydrogen, dislocations, and microstructural heterogeneities. A clear size-dependent role of non-metallic inclusions is identified. Sub-micron inclusions act primarily as irreversible hydrogen trapping sites that contribute to hydrogen redistribution within the microstructure, whereas larger inclusions serve as preferential crack initiation sites under hydrogen charging conditions. Overall, the results demonstrate that hydrogen embrittlement behavior is governed by the combined effects of microstructural state, welded joint type, and long-term service-induced degradation, resulting in distinct hydrogen transport characteristics and fracture responses across the pipe wall. Full article

The modernization of global energy infrastructure within the Industry 5.0 framework requires the use of high-strength steels and reliable joining technologies to ensure safe, sustainable pipeline transport. This study focuses on the analysis of heterogeneous welded joints formed between high-strength alloy steel (34KhN2MA/EN 34CrNiMo6) and an austenitic welded seam (ER 307). While austenitic welds mitigate the risk of cold cracking, they introduce significant structural and mechanical heterogeneity. To address this, the research proposes and validates a material homogeneity criterion (MHC) derived from the LM-hardness methodology. By analyzing the statistical dispersion of macrohardness (HRC) through indicators such as the Weibull homogeneity coefficient (m) and the coefficient of variation (ν), the study establishes a quantitative approach to assess material degradation and structural uniformity across key weld zones. Results demonstrate that macrohardness profiling effectively distinguishes between structurally heterogeneous regions near the weld axis characterized by low homogeneity coefficients (m = 4.04 < 10, A_m = 0.742 < 0.878), elevated variability (ν = 29.68% > 11.6%), and high technological damageability (D = 0.92 > 0.81, j_D = 11.87 > 4.38) with pronounced step-like variation in macrohardness (HRC ∈ [12.6; 47]), on the one hand, and stabilized homogeneous zones in the base material, where m = 24.89 > 10, A_m = 0.947 > 0.878, ν = 4.39% < 11.6%, D = 0.52 ⟶ 0, j_D = 1.09 ⟶ 0, and characteristic range of HRC = 47–55, on the other hand. This methodology provides a robust, quasi-non-destructive tool for enhancing predictive maintenance, digital twins, and the overall integrity management of “smart” pipeline systems. Full article

In the present work, eleven self-shielded flux-cored wires with nickel (Ni) contents ranging from 1.42 wt.% to 4.02 wt.% were designed for the semi-automatic welding of X80 pipeline steel. The effects of Ni on the microstructural evolution and mechanical properties of the weld metal were investigated. The results indicate that when the Ni content is below 2.06 wt.%, the microstructures of both the solidification zone and the inter-pass reheating zone are dominated by coarse granular bainite and martensite/austenite (M/A) constituents. As the Ni content increases from 2.06 wt.% to 3.73 wt.%, the microstructure transforms to fine lath bainite with M/A constituents characterized by low content, small size, and uniform distribution. When the Ni content reaches 3.73 wt.%, the microstructure becomes almost fully bainite. Furthermore, with increasing the Ni content, both the yield strength and tensile strength of the weld metal increase from ~600 MPa to ~700 MPa and from ~660 MPa to ~730 MPa, respectively. However, the impact energy at −20 °C of the weld metal initially increases and then decreases, reaching a peak of ~110 J with the lowest degree of dispersion at a Ni content of approximately 3.73 wt.%. When the Ni content exceeds 3.73 wt.%, the ductility decreases slightly. Further analyses indicate that the synergistic effects of Ni in refining the microstructure and reducing the activity coefficient and solubility of nitrogen (N) jointly contribute to the impact toughness of the weld metal. Full article

Corrosion and scaling critically threaten the safety and efficiency of oil–gas gathering stations. Through field inspections, water chemistry analysis, scale characterization, and corrosion simulation in Yanchang oilfield, this study identifies severe localized damage in key components—such as valves, bends, and injection pipelines—with service lives of only 1–2 years. Analysis of over 200 scale samples revealed that CaCO₃ (42 wt%) and CaSO₄ (23 wt%) were the predominant scale types. High salinity >56,000 mg/L, Cl⁻ >31,000 mg/L, and Ca²⁺ promote under-deposit pitting, galvanic corrosion (e.g., Cu–steel couples), and erosion-corrosion at high-velocity zones. Simulations based on OLI Analyzer Studio (a professional thermodynamic simulation software for electrolyte solution and high-salinity brine systems) reveal that the carbon steel (the primary material for the process pipelines and water injection pipelines in the studied oil–gas gathering and transportation stations) has a corrosion rate rising from 0.078 mm/year at 25 °C to 1.94 mm/year at 90 °C. Despite common use of coatings and cathodic protection, these measures often fail to address site-specific failure mechanisms. The study advocates a tailored mitigation strategy combining material compatibility, real-time water monitoring, optimized filtration, and component-level design. This integrated approach enhances asset reliability and operational safety in onshore oilfields. Full article

Hydrogen embrittlement is a critical degradation mechanism in microalloyed and pipeline steels used in hydrogen-economy infrastructure. We present a physics-informed neural network (PINN) framework that embeds Fick’s second law and the Arrhenius temperature dependence directly into the loss function, trained on 22 temperature-dependent data points spanning pure α-Fe and API X65 pipeline steels (modern and vintage microstructures). The PINN recovered the pure-iron activation energy (4.2 kJ mol⁻¹ vs. literature 4.15 kJ mol⁻¹, R² = 1.00) and yielded Arrhenius activation energies of 28.5 and 45.2 kJ mol⁻¹ for modern and vintage X65, respectively, indicating substantially stronger trapping in older microstructures. McNabb–Foster analysis of ten ternary Fe–Me–C,N alloys revealed flat-trap binding enthalpies of 19 ± 2 kJ mol⁻¹ and deep-trap free energies of 57 ± 2 kJ mol⁻¹, with effective diffusivities spanning three orders of magnitude governed primarily by flat-trap density. The framework provides a computationally efficient and physically consistent tool for hydrogen transport prediction, with a clear roadmap for multi-feature extension incorporating compositional and microstructural descriptors. Full article

Forecasting scrap steel prices is crucial for the economic sustainability of recycling operations, yet it remains challenging due to inherent volatility and non-stationary behavior. In this study, we develop and evaluate a delta-targeted Hybrid forecasting pipeline for short horizons of 1, 3, and 7 days. We benchmark classical baselines (Naive, Seasonal Autoregressive Integrated Moving Average (SARIMA), and Exponential Smoothing (ETS)) against recurrent deep learning models (Simple Recurrent Neural Network (RNN), Gated Recurrent Unit (GRU), and Long Short-Term Memory (LSTM)) and recent neural forecasting baselines, including Decomposition-Linear (DLinear), Convolutional Kolmogorov–Arnold Network (C-KAN), and Neural Basis Expansion Analysis for Time Series (N-BEATS), using real-world daily scrap steel price data. The results indicate that delta-targeting generally yields more stable predictive performance than direct raw-price forecasting as the prediction horizon increases. For example, at the 7-day horizon, the predictive fit improves from approximately $R^2\approx 0.87$ for raw-price LSTM to around $R^2\approx 0.90$ for delta-trained recurrent models. At the same horizon, a delta-based RNN achieves the lowest Mean Absolute Percentage Error (MAPE) among the evaluated models (approximately $1.39\%$), while the proposed Hybrid model remains competitive across all tested horizons and maintains a goodness-of-fit of approximately $R^2\approx 0.90$ without uniformly minimizing point error relative to the best-performing recurrent baseline. Attention profiling and permutation-based feature importance analyses indicate that the model places relatively higher weight on calendar-related inputs, consistent with the presence of weekly patterns in the data; these results should be interpreted as sensitivity diagnostics rather than causal evidence. Overall, the findings suggest that delta-transformed targets provide a more suitable prediction space than raw-price targets for short-horizon scrap steel forecasting, while the Hybrid design offers a balanced combination of predictive performance and diagnostic interpretability for operational decision support. Full article

Carbon capture and storage (CCS) is widely recognized as a key technology for reducing carbon dioxide (CO₂) emissions from large industrial sources. Among the stages of the CCS chain, CO₂ transportation plays a decisive role in determining overall system safety, reliability, and economic viability. CO₂ transportation through pipelines is generally preferred for large-scale, long-distance applications and is commonly operated under dense or supercritical conditions to maximize efficiency. However, internal corrosion of pipeline steels remains a major integrity concern, with corrosion accounting for approximately 45% of reported CO₂ pipeline failures. This review provides a comprehensive assessment of internal uniform and localized corrosion phenomena in CO₂ pipelines operating under supercritical CO₂ environments. The influence of key CO₂ stream impurities, including H₂O, O₂, H₂S, SO_x, and NO₂, is examined, considering their individual and synergistic effects on corrosion mechanisms, corrosion morphology, corrosion products, and severity ranking. In addition, an in-depth analysis of operating parameters such as temperature, pressure, flow conditions, and exposure time is presented alongside material-related factors, including steel grade, internal surface roughness, and welded regions. Corrosion mitigation approaches are also reviewed, with particular emphasis on organic, inorganic, and composite corrosion inhibitors. The review concludes by identifying key knowledge gaps and outlining future perspectives for improving corrosion control in CO₂ transport systems supporting large-scale CCS deployment. Full article

Ensuring the integrity of weld seams in pipeline components is critical for the safe and reliable transportation of oil and natural gas. This paper presents a systematic failure investigation of a cracked weld in a reducer located at a natural gas transmission station in Western China, aiming to identify the failure mechanism and assess its implications for pipeline safety management. A comprehensive analysis was conducted using macroscopic examination, chemical composition analysis, mechanical property testing, metallographic observation, and microscopic fracture characterization. The results reveal that the heat-affected zone (HAZ) exhibited abnormally high hardness (up to 588 HV0.1), indicating insufficient toughness that made it susceptible to cracking. The base metal showed a high carbon equivalent (CEV), placing it in the “difficult-to-weld” category and increasing its sensitivity to improper welding thermal cycles. On-site investigation further identified significant deficiencies in welding process control, including inadequate preheating, improper interpass temperature management, and insufficient post-weld heat treatment (PWHT). These deficiencies allowed welding residual stresses to persist and failed to mitigate the hardened HAZ microstructure. The combination of poor material weldability and inadequate on-site welding practices ultimately led to brittle fracture under service conditions. This failure highlights a critical vulnerability in pipeline transportation infrastructure and underscores the necessity of strict adherence to qualified welding procedures for high-carbon-equivalent steels. The findings provide practical guidance for enhancing welding quality control and ensuring the long-term operational safety of natural gas pipeline systems. Full article

In response to corrosion challenges encountered during the gathering and transportation of wet natural gas, this study systematically investigates the corrosion behavior of L245NCS steel in environments containing O₂, H₂S, CO₂ and simulated oilfield-produced water. The research employs a combined approach involving high-pressure autoclave experiments and transparent flow loop simulations. Autoclave tests reproduce gas phase, liquid phase, and gas–liquid interface conditions under a controlled O₂-H₂S-CO₂ mixture, while a visual flow loop equipped with elbows and undulating sections is used to examine liquid accumulation behavior and flow characteristics under dynamic, real-world operating conditions. Results indicate that corrosion is most severe at the gas–liquid interface. H₂S is identified as the primary corrosive agent, exerting a stronger influence than CO₂ or O₂. Liquid accumulation is the main factor leading to non-uniform corrosion distribution, and its formation is influenced by water content, pressure, temperature difference, and pipeline shutdown and restart operations. Critical areas such as low-lying sections, downhill bottoms, and the beginning of uphill sections exhibit localized corrosion rates up to 61.4% higher than areas without liquid accumulation. This integrated methodology bridges mechanistic understanding with engineering practice, providing a basis for corrosion risk assessment, optimal monitoring point placement, and integrity management of wet gas pipelines. Full article