Lithium-ion batteries are widely used in electric mobility, renewable energy integration, portable electronics, and renewable–hydrogen hybrid energy systems. Despite significant advances in battery materials and design, long-term degradation remains a major challenge that affects system reliability, efficiency, and economic viability. In renewable–hydrogen hybrid architectures, battery degradation influences not only energy storage performance but also hydrogen production stability, electrolyzer operation, fuel cell utilization, and overall system efficiency. Major degradation mechanisms include solid electrolyte interphase (SEI) growth, electrolyte decomposition, lithium inventory loss, transition-metal dissolution, particle cracking, and structural phase transformations. This review provides a comprehensive assessment of degradation mechanisms affecting lithium-ion battery components and their implications for renewable–hydrogen hybrid systems. Advanced characterization techniques, including in situ and operando X-ray diffraction, electron microscopy, spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and differential capacity analysis, are examined for their ability to reveal chemical, structural, and morphological changes during battery operation. Particular emphasis is placed on the effects of dynamic load variations, partial state-of-charge cycling, temperature fluctuations, and intermittent renewable energy inputs that accelerate degradation in hybrid systems. The review further discusses mitigation strategies such as surface engineering, electrolyte optimization, material doping, thermal management, intelligent energy management systems, predictive maintenance, and machine learning-based prognostics. Key challenges associated with battery–hydrogen integration, including efficiency trade-offs, component ageing, hydrogen production stability, and lifecycle costs, are critically analysed. The adaptability of hybrid systems under varying operating conditions is also explored, highlighting the importance of degradation-aware control strategies, digital twins, and real-time diagnostics. Finally, future research directions are identified, including multiscale characterization, physics-informed machine learning, techno-economic optimization, and life-synergy modelling. These approaches are essential for developing reliable, adaptive, and cost-effective renewable–hydrogen hybrid energy systems capable of supporting long-term decarbonization objectives.
Improving gasoline octane quality is essential for modern spark-ignition engines, as increased knock resistance supports better efficiency, optimized combustion, and reduced fuel consumption. Environmental concerns have increased the demand for cleaner organic alternatives instead of conventional metallic octane boosters. This study evaluated selected organic octane improvers for commercial gasoline fuels, focusing on isopropanol (IPA), N-ethylaniline (NEA), and their binary blends. Fuel samples were prepared by controlled dosing of additives into base gasoline, followed by homogenization and determination of octane number using a portable fuel analyzer. Both additives increased gasoline octane rating, but their effectiveness depended on chemical type and dosage. NEA showed stronger octane-enhancing performance, whereas IPA provided a moderate improvement and potential combustion benefits associated with oxygenated fuel components. The investigated IPA–NEA binary blends increased the research octane number by up to 3.5 units at 3 vol.% additive concentration. Engine bench testing demonstrated reductions in CO emissions of up to 60%, in HC emissions of up to 40.8%, and in fuel consumption of up to 4.7% under selected operating conditions. Distillation characteristics remained within acceptable gasoline quality limits, indicating that the investigated additives did not adversely affect fuel volatility.
Child-well stimulation design has become a central challenge in mature unconventional reservoirs, where infill wells are commonly completed in reservoirs that have already been modified by parent-well production. Prior depletion changes pore pressure, stress distribution, and fracture-propagation pathways, causing child-well treatments to behave differently from parent-well completions. As a result, increasing fluid volume, proppant loading, stage density, or pump rate does not necessarily produce proportional gains in recovery. This review synthesizes the comprehensive literature on child-well stimulation intensity with emphasis on well performance, fracture-driven interactions, pad-scale economics, diagnostics, and resource-use considerations. The analysis shows that the production response is highly conditional: larger treatments can enhance reservoir contact when fractures access underdrained rock; however they may lose effectiveness when depletion-induced stress changes redirect fracture growth toward parent-well drainage areas or pre-existing fracture networks. In such cases, higher nominal intensity can increase interwell communication, reduce completion efficiency, impair parent-well performance, and weaken pad-level economic value. A key outcome of this review is the distinction between nominal stimulation intensity, represented by the treatment pumped, and effective stimulation intensity, represented by the fraction of that treatment that creates incremental productive fracture area. This distinction reframes child-well optimization from a treatment-size problem to a depletion-aware fracture-placement problem. Diagnostics, coupled modeling, production analysis, and mitigation strategies are therefore necessary to determine whether added stimulation intensity improves recovery or primarily redistributes production within the pad. From an economic perspective, the pad rather than the individual child well is the correct unit for evaluating stimulation-intensity decisions, since pad-level net present value integrates incremental child-well recovery, parent-well degradation, protection costs, spacing effects, and completion capital. Produced-water reuse and lifecycle emission benchmarking represent practical tools for reducing the environmental footprint of child-well development programs while simultaneously lowering freshwater demand and disposal volumes. These economic and environmental dimensions are inseparable from the technical optimization of stimulation intensity and are addressed explicitly in this review. This review concludes that child-well stimulation intensity should be optimized within a pad-scale framework that integrates depletion state, spacing, landing-zone selection, parent-well management, and long-term value rather than being uniformly maximized.
The standardized copper strip corrosion test is commonly used to assess the corrosive effects of automotive gasoline and diesel fuels on metallic materials. This test relies on visual evaluation of copper strip discoloration, which may introduce subjectivity and limit quantitative interpretation. The aim of this study was to compare the conventional visual evaluation with a colorimetric approach as a quantitative alternative. Copper strip corrosion tests were performed according to EN ISO 2160 using gasoline and diesel fuel samples. While all samples were visually classified within corrosion Class 1, colorimetric analysis revealed measurable differences in surface discoloration, with ΔE*ab values ranging from 0.4 to 11.1, and highest values observed for aged fuels. These results demonstrate that colorimetric evaluation provides additional quantitative information beyond conventional visual classification and enables differentiation between fuels within the same acceptance category.
Filter cake is a nutrient-rich solid byproduct generated during sugarcane juice clarification, representing both a challenge and an opportunity for the sugar–energy industry. This study presents a systematic bibliometric analysis of global research on filter cake valorization, with a particular focus on its potential for bioenergy and biofuel production. Data were retrieved from the Scopus database and analyzed using VOSviewer, resulting in a dataset of 530 publications up to 2024, of which 485 address recycling and reintegration pathways. The results identify Brazil and India as leading contributors, with research traditionally concentrated on agricultural applications. However, emerging trends highlight the growing interest in thermochemical and biochemical conversion routes, including its use as a substrate for biogas, bioethanol, and other biofuels. The findings demonstrate that filter cake is a promising feedstock for integrated biorefinery systems, contributing to renewable energy generation and resource recovery. Despite this potential, the transition toward advanced biofuel production and high-value energy applications remains limited. This review provides a comprehensive overview of research trends, identifies key gaps, and outlines strategic directions to support the shift from conventional waste management to energy-oriented valorization within a circular bioeconomy framework.
Traditional hypergolic propellants, such as hydrazine derivatives combined with nitrogen tetroxide, present severe toxicity, operational, and environmental hazards. High-test peroxide has emerged as a leading green oxidiser replacement due to its low volatility, high density, and benign decomposition products. This review comprehensively analyses recent advancements in HTP-based hypergolic fuel formulations, categorising them into three major emerging families: catalytically-promoted, reactive, and ionic liquid-based systems. By evaluating key parameters such as ignition delay times, specific impulse and toxicity, this work identifies a clear technological shift from fundamental chemical screening to increasingly more mature solutions. While historical targets defined hypergolicity below 100 ms, recent advanced formulations routinely achieve it under 10 ms requiring minimal additive concentrations (<5 wt%), directly competing with legacy systems. Furthermore, this review highlights critical open challenges that limit commercial adoption, including the long-term storage stability of catalytic blends, high toxicity of reactive systems, and the lifecycle toxicity and high cost of frequently employed ionic liquids. Ultimately, it is concluded that rather than a single universal replacement, the future of green hypergolic propulsion lies in a plurality of solution, where each family is tailored to specific niches defined by mission requirements and cost structures.
The growing demand for energy and emerging environmental concerns are making it necessary to look for more sustainable alternatives. To address the limitations of first-generation biofuels and reduce dependence on fossil fuels, this study focuses on second-generation bioethanol sourced from non-edible pomegranate waste. This study develops and analyses a supply chain optimization model for the sustainable production of biofuel from pomegranate waste and solves it using a genetic algorithm. The framework assesses key supply chain elements, including collection centres for pomegranate waste, processing plants, bio-refineries for conversion and distribution centres for final bioethanol. The primary objective of the optimization is to reduce the total cost of the biofuel production system and to maximize positive environmental impact through waste valorization. A numerical example validates the framework, and a sensitivity analysis further evaluates the economic viability of the supply chain under fluctuating market conditions, such as variations in the purchasing cost of waste, the production cost of bioethanol and the opening cost of plants. Biofuel production supports the Sustainable Development Goals (SDG-12 and -13) by transforming waste into renewable energy. This study aims to address gaps in biofuel research by focusing on the underutilized area of pomegranate-based biofuel through an integrated supply chain optimization framework. The findings offer practical values for researchers working on renewable energy solutions, policymakers and business leaders.
In the Philippines’ agricultural setup, pre-harvest cacao (Theobroma cacao) fruits are wrapped with low-density polyethylene (LDPE) for moisture retention and damage protection. Responding to the growing concern for its waste volume and scarcity of treatment, this research explores the co-hydrothermal carbonization (co-HTC) of cacao shells (CS) and LDPE as a method to convert agricultural waste with plastic into hydrochar for potential energy applications. Thus, observations on the thermal, physicochemical, and morphological changes from feedstocks to hydrochar are carried out. Optimal conditions of 200 °C for 60 min resulted in hydrochar with 21.11 MJ/kg and appreciable thermal properties. SEM micrographs show that hydrochar had increased surface area, a good fuel characteristic, and surface flaking on oversized LDPE film, suggesting relative LDPE degradation. EDX analysis reveals C, K, Ca, and Zn metals that affect chemical pathways. FTIR analysis further supports chemical synergy by preservation of functional groups innate from both parent materials. Kinetic and thermal evolutions are also investigated to reveal the influence of pretreatment on the stability of cacao shell-dominated hydrochar and the effectivity of biomass integration to facilitate relatively easier cracking of LDPE. The findings support co-HTC as a viable technology to enhance the circular economy by valorizing LDPE and cacao shells while promoting energy recovery and solid fuel production.
The transition towards alternative marine fuels introduces new safety challenges related to onboard storage, distribution, and fuel management, due to the markedly different physical and chemical properties of methane, methanol, ammonia, and hydrogen. While numerous studies address the risks of individual fuels, there is a lack of structured and comparable risk-assessment methodologies to support early-stage fuel selection and preliminary system design under a unified framework. This study introduces the Methodology to Alternative-fuels Hazardous Identification, a hybrid framework that integrates HAZOP-based deviation analysis with HAZID-style risk classification to enable a consistent qualitative–quantitative comparison of alternative marine fuel systems. The methodology is applied to representative storage and distribution architectures for methane, methanol, ammonia, compressed hydrogen, and liquefied hydrogen, allowing the identification of dominant risk drivers and system-level vulnerabilities across fuel options. The results reveal distinct fuel-specific risk profiles. Methane and methanol are mainly associated with moderate risks linked to operational temperature deviations and system controllability. Ammonia exhibits the most severe risk profile due to the high consequences of toxic releases, particularly under pressure-related failures. Compressed hydrogen is dominated by high-risk scenarios driven by extreme storage pressures, while liquefied hydrogen presents a mixed profile governed by the interaction between cryogenic temperature control and pressure regulation. By providing a comparative and scalable risk-assessment framework, the Methodology to Alternative-fuels Hazardous Identification (MAHI) supports informed decision-making in early design phases and complements existing regulatory safety analyses, contributing to a safer energy transition in maritime transport.
Fossil fuel depletion has increased interest in renewable alternatives such as biodiesel derived from non-edible plant oils. Droplet evaporation is a key process influencing fuel–air mixing and combustion efficiency in diesel engines. In this study, the evaporation characteristics of diesel and two non-edible biofuels, Jatropha and Castor, are investigated using computational fluid dynamics (CFD) under high-temperature and high-pressure conditions representative of engine environments. The numerical model incorporates the conservation equations of mass, momentum, and energy, together with the k–ε turbulence model and a discrete phase model to simulate droplet heating, motion, and mass transfer during evaporation. A comparative CFD analysis is performed to examine how fuel properties, ambient temperature, and droplet size affect the evaporation behaviour of diesel, Jatropha, and Castor droplets under identical engine-like conditions. The evolution of droplet diameter, temperature, velocity, and lifetime is analysed, and the applicability of the classical D2-law is evaluated under different operating conditions. The results indicate that biofuel droplets generally evaporate faster than diesel droplets at lower temperatures, while evaporation trends become similar at higher temperatures. These findings provide insight into the evaporation behaviour of Jatropha and Castor fuels and their potential application in diesel engines.
This study investigates improving the flowability of heavy crude oil using non-ionic surfactants that modify interfacial properties, thereby enhancing emulsification and dispersion. A mixture of Span 85 (HLB = 1.8) and Tween 20 (HLB = 16.7) was selected to meet the affinity requirements of both oil and water phases. Experiments were conducted on five different densities of heavy crude oil, evaluating viscosity reduction, emulsion droplet size distribution, and interfacial tension. Notably, this work presents the first systematic examination of interactions between various heavy crude oil densities and mixed emulsifiers. Results show that aligning the HLB value of the mixed emulsifier with that of the heavy crude oil enhances electrostatic repulsion between droplets, reducing droplet size and optimizing surfactant arrangement at the interface. The optimal HLB value for viscosity reduction was determined to be 8.0, at which a viscosity reduction rate of over 89% was achieved for high-density heavy crude oil. A quantitative relationship between emulsion droplet size and viscosity reduction rate was also established, leading to improved emulsion stability and significant viscosity reduction. These findings provide a theoretical framework for applying non-ionic mixed surfactants to enhance heavy crude oil flowability, and deliver experimental data to support field applications in petroleum engineering.
This study evaluates the impact of long-term storage on aviation fuel blends composed of Jet A and camelina-derived biodiesel. The physicochemical properties of the pure biodiesel were assessed according to EN 14214 and ASTM D6751 standards, while the resulting Jet A–biodiesel blends were evaluated against ASTM D1655 aviation fuel specifications. Particular attention was given to the evolution of density during storage as an indicator of fuel stability. The results show that camelina methyl esters exhibit generally satisfactory physicochemical characteristics; however, the iodine value remains a critical limitation. The measured value of approximately 155 significantly exceeds the maximum limit of 120 established by European standards, reflecting the high degree of unsaturation of the feedstock. Long-term monitoring of the blends revealed a clear relationship between biodiesel concentration and the rate of fuel degradation. Increasing the biodiesel fraction led to more pronounced variations in density during storage, indicating reduced stability of the fuel system. Consequently, instability risks increase proportionally with the biodiesel-to-Jet A ratio, highlighting the need for appropriate storage strategies and technological optimization when considering higher concentrations of camelina-derived biodiesel in aviation fuel blends.
This work presents a mechanistic modeling approach for simulating methane emissions from triethylene glycol (TEG) dehydrators used in oil & gas (O&G) operations. The model was developed as a modular component of the Mechanistic Air Emissions Simulator (MAES) tool, incorporating species-specific absorption and emission dynamics through two-level, second-order polynomial regression (PR) models trained on ProMax simulation data: (1) species-level regression models that track the transfer rates of individual gas species within the dehydrator unit streams, and (2) outlet flow stream regression models that predict the fraction of inlet gas distributed among the outlet streams of the dehydrator unit. These behaviors were characterized over a range of glycol circulation ratios, wet gas pressures, and temperatures. The model was validated using root mean square error (RMSE) analysis. The species-level PR achieved low root mean square error (RMSE) values (<0.03) for light hydrocarbon species across all dehydrator components, ranging from 0.0009 for methane to 0.029 for normal pentane. Similarly, the outlet-level PR yielded RMSE values below 0.002 for the dry gas fraction, 0.001 for the flash tank fraction, and 0.002 for the still vent fraction, demonstrating strong agreement between predicted and reference ProMax values. When deployed at field facilities, the model significantly improved MAES-simulated dehydrator emissions, revealing that gas-assisted glycol pump emissions are the dominant contributors to both dehydrator-level and site-level methane emissions under uncontrolled conditions. Further analysis of the 154 dehydrator units reported by operators under the AMI 2024 project showed that 54 units (31%) used gas-driven glycol pumps, of which 6 units (11%) operated with uncontrolled flash tanks, and 22 units (40.7%) were identified as potentially oversized. Of the six dehydrator units with uncontrolled gas-assisted pumps, pump emissions accounted for 90.25% of total dehydrator emissions and 63.10% of total site-level emissions. These findings highlight substantial opportunities for emissions mitigation through equipment upgrades.
Bioenergy production from agro-industrial waste has the potential to contribute to climate change mitigation. In Brazil, the pequi (Caryocar brasiliense Camb.) production chain makes an economic, environmental, and social contribution. However, the collection and processing of the fruit produce large amounts of waste, such as the peel, whose improper disposal leads to significant environmental impacts. This study evaluated how moisture and carbonization temperature influence the energy properties of charcoal briquettes made from pequi peel waste. Carbonization was performed at two final temperatures (360 °C/480 °C) with a heating rate of 1.5 °C min−1 and residence times of 4 h and 5 h 20 min, respectively. Carbonization yields were calculated based on dry mass. Briquettes were produced from pequi peel at moisture contents of 5%, 7.5%, and 10% (wet basis). After carbonization, the charcoal briquette samples were characterized by proximate analysis, higher heating value (HHV), bulk density, energy density, and mechanical durability. Carbonization temperature exerted a more pronounced effect on the properties of the carbonized briquettes than the initial moisture content. Carbonization at 480 °C increased the fixed carbon content (76.38%, 74.25%, and 75.10% for treatments 1, 2, and 3) and the HHV (25.10–25.31 MJ kg−1), while reducing the gravimetric yield (32.84–33.25%). The influence of moisture content was more evident in carbonizations carried out at 360 °C, indicating a temperature-dependent interaction. The use of pequi peel for solid biofuel production promotes the valorization of agro-industrial residues and supports strategies aimed at the circular bioeconomy and the decarbonization of the energy matrix.
This study investigates whether countries converge toward common long-run paths in renewable energy consumption and examines the implications for global fuel transition dynamics. Using a balanced panel of 108 countries over the period 1990–2022, we implement an integrated econometric framework that combines stochastic convergence tests, β- and σ-convergence analysis, the Phillips–Sul club convergence methodology, ordered logit modelling, and heterogeneous panel causality tests. The results reject global stochastic convergence, indicating that countries do not share a common transition trajectory. However, evidence of β- and σ-convergence suggests the presence of partial and bounded catch-up dynamics. The Phillips–Sul approach identifies four distinct convergence regimes, implying multiple steady-state equilibria in global energy systems. Structural analysis shows that income and governance quality increase the probability of belonging to higher-renewable-energy regimes, while carbon intensity constrains upward transitions. Regime-specific causality results further reveal that the drivers of renewable energy dynamics differ across structural contexts. Overall, the findings demonstrate that global energy transitions are characterized by persistent heterogeneity and regime-dependent adjustment processes rather than uniform convergence. This study contributes by integrating convergence analysis with structural modelling and regime-based interpretation, offering a more comprehensive framework for understanding differentiated decarbonization pathways. The results carry important policy implications, highlighting that effective energy transition strategies must be tailored to regime-specific conditions rather than relying on uniform policy approaches.
The energy utilization of residual woody biomass is a relevant strategy for the decentralized energy transition and local waste management in rural areas. The objective of this study was to characterize (physically, chemically, and energetically) five types of residual biomass: pine branches, huinumo (this material refers to the long, thin pine needles that, after drying and falling, form a layer on the forest floor), cherry branches and leaves, and grass waste generated in the community of San Francisco Pichátaro, Michoacán, Mexico, in order to evaluate its viability for the production of densified solid biofuels. A comprehensive analysis was conducted, including moisture content, higher heating value, proximate characterization, structural chemical analysis (using the Van Soest method), elemental CHONS analysis, ash microanalysis (by ICP-OES), and a multicriteria analysis with normalized energy and compositional indicators. The results showed that huinumo and cherry leaves were the most outstanding biomasses, presenting the highest heating values (20.7 MJ/kg) and low moisture and ash contents. Pine branches obtained the most balanced results, characterized by their equilibrium in fixed carbon and lignin, as well as their low potassium content. The multicriteria analysis showed that there is no absolute optimal biomass; however, it indicates that pine branches and huinumo are the most robust feedstocks for the production of briquettes or pellets. The results confirm the significant technical and environmental potential of local lignocellulosic residues for the production of solid biofuels and for contributing to sustainable energy solutions at the local scale.
The International Maritime Organization’s (IMO) greenhouse gas (GHG) strategy aims for a 40% reduction in carbon intensity by 2030 and a 70% reduction by 2050, relative to 2008 levels. Attainment of these objectives necessitates an integrated strategy encompassing technological advancements, operational optimization, and the adoption of innovative practices to curtail fuel consumption and enhance vessel performance. The Ship Energy Efficiency Management Plan (SEEMP), mandated by MEPC 62 in 2011, establishes a systematic framework for the continual enhancement of energy efficiency. SEEMP is intrinsically associated with reductions in fuel consumption, enabling maritime organizations to systematically monitor and control energy performance via the Energy Efficiency Operational Indicator (EEOI). This metric enables operators to assess operational energy performance and implement measures such as optimized voyage planning and fuel-saving technologies. However, the effectiveness of SEEMP varies widely across companies and vessel types, often due to limited crew awareness. To enhance daily implementation, it is essential to improve crew training and streamline SEEMP documentation. Simplifying SEEMP structures within ship management companies can further facilitate usability and compliance. By focusing on these areas, the maritime industry can better align with IMO’s GHG reduction targets and promote more sustainable operations and fuel-saving technologies.
Vibration-assisted water flooding (VA-WF) can improve sweep efficiency. However, unclear macro-scale mechanisms limit its wider adoption in heavy oil reservoirs. This study combines previous sandpack experiments with two-dimensional Volume-of-Fluid (VOF) simulations to show how vibrations reshape permeability fields and, in turn, pressure and production behaviour. Heavy oil sandpacks were water-flooded under conditions of no vibration and 2 Hz and 5 Hz axial excitation. Measured injection pressure histories and oil production were used to calibrate a VOF model in which absolute permeability follows a log-normal distribution with directional anisotropy. Only when axial and radial permeabilities were assigned a negative local correlation did the model reproduce key observations: secondary pressure spikes, irregular viscous-fingering morphologies, delayed production drops, and variability in cumulative recovery. Parameter sweeps quantify the sensitivity of VA-WF performance to the variance and correlation of the permeability field, and multiple runs estimate the variability in outcomes introduced by stochastic heterogeneity. This study proposes a transferable workflow—comprising sample testing, parameter inference, and probabilistic simulation—to screen excitation conditions and forecast VA-WF performance prior to field implementation, enabling operators to optimize vibration frequency based on reservoir-specific permeability characteristics and to anticipate production variability under uncertainty. These results highlight the dominant factors affecting swept volume and oil recovery, supporting data-driven decision making in VA-WF projects.
To investigate the synergistic effect of hydraulic fracturing and hot water injection on enhancing methane extraction from low-permeability coalbeds and elucidate the underlying thermal-hydraulic coupling mechanism, methane desorption experiments were conducted in coal samples with varying fracture networks using a self-developed multi-field coupling experimental system. Tests were performed under different injection pressures and temperatures to analyze coal temperature evolution and methane desorption-seepage characteristics. The results demonstrate that hydraulic fracturing significantly improves pore structure and connectivity, thereby optimizing methane desorption behavior. The methane migration in the samples is influenced by water injection, exhibiting an initial promotion followed by inhibition. The combined fracturing-thermal injection approach effectively reduces the dynamic viscosity of water, mitigates the water lock effect, and enhances the desorption capacity. The hydraulic fracturing and the hot water injection complement each other, achieving synergistic production enhancement. The optimal injection pressure and water temperature can be selected according to specific reservoir conditions to balance the production increase and cost efficiency. This laboratory-scale study provides theoretical support for optimizing hydraulic measures and thermal injection techniques in coalbed methane extraction, revealing complementary synergies between these two methods and offering new insights into multi-field coupling enhancement mechanisms with practical application guidelines.
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.
