Search Results (55)

Microbiologically influenced corrosion induced by sulfate-reducing bacteria (SRB) poses a significant threat to shale gas pipeline integrity. This study investigates an integrated control strategy combining the biocide glutaraldehyde with denitrifying bacteria (DNB) to synergistically inhibit SRB activity and corrosion. The efficacy and mechanisms were systematically evaluated using electrochemical measurements (EIS, LPR), weight-loss analysis, surface characterization (SEM, maximum pit depth), and microbial community profiling (16S rDNA sequencing). Compared to the SRB-inoculated system, the combined treatment reduced the average corrosion rate of L245 steel by 44.2% (to 0.01608 mm/a) and the maximum pit depth by 84.3% (to 1.53 μm). EIS results further confirmed the superior inhibition effect, showing the largest capacitive arc diameter and the highest polarization resistance in the combined system. Microbial community analysis indicated a substantial decline in SRB abundance from 62.7% (day 1) to 11.9% (day 14). This synergistic strategy presents an effective and more sustainable approach by reducing chemical dosage and leveraging the bio-competitive exclusion by DNB. Full article

Pipeline steels under cyclic loading in corrosive environments are prone to wear and corrosion–wear synergy. Low-dilution, high-reliability Ni-based Cold Metal Transfer (CMT) overlays are therefore required to ensure structural integrity. In this work, three overlay architectures were deposited on L415QS pipeline steel: a single-layer ERNiFeCr-1 coating, a double-layer ERNiFeCr-1/ERNiFeCr-1 coating, and an ERNiCrMo-3 interlayer plus ERNiFeCr-1 working layer. The microstructure, interfacial composition gradients, and dry sliding wear behavior were systematically characterized to clarify the role of interlayer design. The single-layer ERNiFeCr-1 coating shows a graded transition from epitaxial columnar grains to cellular/dendritic and fine equiaxed grains, with smooth Fe dilution, Ni–Cr enrichment, and a high fraction of high-angle grain boundaries, resulting in sound metallurgical bonding and good crack resistance. The double-layer ERNiFeCr-1 coating contains coarse, strongly textured columnar grains and pronounced interdendritic segregation in the upper layer, which promotes adhesive fatigue and brittle spalling and degrades wear resistance and friction stability. The ERNiCrMo-3 interlayer introduces continuous Fe-decreasing and Ni-Cr/Mo-increasing gradients, refines grains, suppresses continuous brittle phases, and generates dispersed second phases that assist crack deflection and load redistribution. Under dry sliding, the tribological performance ranks as follows: interlayer + overlay > single-layer > double-layer. The ERNiCrMo-3 interlayer system maintains the lowest and most stable friction coefficient due to the formation of a dense tribo-oxidative glaze layer. These results demonstrate an effective hierarchical alloy-process design strategy for optimizing Ni-based CMT overlays on pipeline steels. Full article

L360QS pipeline steel, due to its high toughness, high strength, resistance to sulfide stress cracking, and resistance to hydrogen-induced cracking, is increasingly being used in pipeline network construction. Its fracture behavior is a critical factor for safe operation in mountainous steep-slope environments, but it has not yet been widely studied. Therefore, this paper conducts extensive experiments on the ductile fracture of L360QS pipeline steel. The tests employed standard tensile, notched tensile, shear, and compression specimens, covering a stress triaxiality range from approximately −0.33 to 0.92. The study combined Ling’s iterative method to establish an elastoplastic constitutive model considering post-necking behavior, and incorporated it into finite element models to extract the average stress triaxiality and equivalent plastic strain at the moment of fracture initiation for each type of specimen. Based on the extracted data, a piecewise ductile fracture model was established: a simplified Johnson–Cook criterion is used in the high triaxiality range, while an empirical function is used to describe fracture behavior in the medium, low, and negative triaxiality ranges. The model was validated using a train–test split approach, predicting fracture displacements for an independent test set of specimens. The results showed all prediction errors were within 5%, demonstrating the model’s high accuracy. Furthermore, a Spearman correlation analysis quantified the influence of geometric factors, revealing that notch curvature has the strongest monotonic relationship in controlling average stress triaxiality and fracture strain. The fracture model established in this paper can accurately predict the fracture behavior of L360QS pipeline steel and provides a reliable basis for failure prediction and safety assessment under complex service conditions (such as mountainous steep slopes). Full article

The operational integrity of L415 pipeline steel, a critical component of China’s energy network, is severely threatened by the unique acidic red soil environments prevalent in Southern China. A significant knowledge gap exists regarding its specific failure mechanisms, particularly the interplay between Anodic Dissolution (AD) and Hydrogen Embrittlement (HE) in driving Stress Corrosion Cracking (SCC). This study systematically investigates the corrosion and SCC behavior of L415 steel in a simulated environment that replicates the typical soil chemistry of the Gannan region in Southern China. Results revealed that corrosion kinetics are highly dependent on environmental chemistry, with corrosion rates escalating nearly four-fold from 0.0505 mm/a to a severe 0.1949 mm/a, driven by the synergy of low pH and high SO₄²⁻ concentration. This behavior is governed by the integrity of the corrosion product film, where aggressive environments form porous, unprotective layers with low charge transfer resistance. Slow strain rate tensile (SSRT) tests confirmed that the steel’s susceptibility to SCC is strongly promoted by acidity. Critically, the dominant SCC mechanism was environment-dependent, transitioning from Hydrogen Embrittlement (HE) to intergranular cracking in the most acidic environment, and a mixed AD-HE mechanism causing transgranular cracking in high-chloride conditions. These findings provide a direct mechanistic link between soil chemistry and failure mode, offering a crucial scientific basis for developing environment-specific integrity management strategies for pipelines in these challenging terrains. Full article

The laser-directed energy deposition (L-DED) technique, with its excellent environmental adaptability and superior repair capability, shows great potential for the repair of damaged X70 pipeline steel. In this work, the microstructure and mechanical properties of L-DED repaired X70 steel were systematically investigated. The deposited material exhibited inhomogeneity along the building direction. From the bottom to the top, the grains gradually coarsened, and the proportion of polygonal ferrite increased. This was mainly attributed to increasing thermal accumulation with deposition height, which reduced the cooling rate and promoted solid-state transformations at higher temperatures. Meanwhile, the heat accumulation and intrinsic heat treatment reduced the dislocation density and promoted Fe₃C precipitation within grains and along boundaries. Microhardness was highest in the bottom region and decreased along the building direction due to the gradual coarsening of microstructure and decreasing in dislocation density. The L-DED X70 showed lower yield strength (435 MPa) and ultimate tensile strength (513 MPa) compared to the base material and API 5L requirements. The elongation of the L-DED X70 was 42.9%, which was 58% higher than that of the base material, indicating excellent ductility. These results revealed a thermal history-dependent strength–ductility trade-off in the L-DED repaired X70 steel. Therefore, more efforts are needed to control the L-DED thermal process, tailor the microstructure, enhance strength, and meet the service requirements of harsh environments. Full article

Hydrogen-assisted fatigue cracking presents a critical challenge to the structural integrity of legacy carbon steel natural gas pipelines being repurposed for hydrogen transport, posing a major barrier to the deployment of hydrogen infrastructure. This study systematically evaluates the fatigue crack growth (FCG) behavior of API 5L X60 pipeline steel under varying hydrogen–natural gas (H₂–NG) blending conditions to assess its suitability for long-term hydrogen service. Experiments are conducted using a custom-designed autoclave to replicate field-relevant environmental conditions. Gas mixtures range from 0% to 100% hydrogen by volume, with tests performed at a constant pressure of 6.9 MPa and a temperature of 25 °C. A fixed loading frequency of 8.8 Hz and load ratio (R) of 0.60 ± 0.1 are applied to simulate operational fatigue loading. The test matrix is designed to capture FCG behavior across a broad range of stress intensity factor values (ΔK), spanning from near-threshold to moderate levels consistent with real-world pipeline pressure fluctuations. The results demonstrate a clear correlation between increasing hydrogen concentration and elevated FCG rates. Notably, at 100% hydrogen, API X60 specimens exhibit crack propagation rates up to two orders of magnitude higher than those in 0% hydrogen (natural gas) conditions, particularly within the Paris regime. In the lower threshold region (ΔK ≈ 10 MPa·√m), the FCG rate (da/dN) increased nonlinearly with hydrogen concentration, indicating early crack activation and reduced crack initiation resistance. In the upper Paris regime (ΔK ≈ 20 MPa·√m), da/dNs remained significantly elevated but exhibited signs of saturation, suggesting a potential limiting effect of hydrogen concentration on crack propagation kinetics. Fatigue life declined substantially with hydrogen addition, decreasing by ~33% at 50% H₂ and more than 55% in pure hydrogen. To complement the experimental investigation and enable predictive capability, a modular machine learning (ML) framework was developed and validated. The framework integrates sequential models for predicting hydrogen-induced reduction of area (RA), fracture toughness (FT), and FCG rate (da/dN), using CatBoost regression algorithms. This approach allows upstream degradation effects to be propagated through nested model layers, enhancing predictive accuracy. The ML models accurately captured nonlinear trends in fatigue behavior across varying hydrogen concentrations and environmental conditions, offering a transferable tool for integrity assessment of hydrogen-compatible pipeline steels. These findings confirm that even low-to-moderate hydrogen blends significantly reduce fatigue resistance, underscoring the importance of data-driven approaches in guiding material selection and infrastructure retrofitting for future hydrogen energy systems. Full article

Traditional natural gas transportation pipeline steels, such as API 5L X42 grade and the higher grades, are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However, the microstructural constitution of steels with a ferrite phase and the presence of welds, with their non-polyhedral “sharp” microstructures acting as structural notches, make these steels prone to hydrogen embrittlement (HE). In this work, the notch tensile properties of copper- or nickel–phosphorus-coated API 5L X42 grade pipeline steel were studied in both the non-hydrogenated and electrochemically hydrogen-charged conditions in order to estimate anticipated protective effects of the coatings against HE. Both the Cu and Ni–P coatings were produced using conventional coating solutions for electroless plating. To study the material systems’ HE sensitivity, electrochemical hydrogenation of cylindrical, circumferentially V-notched tensile specimens was performed in a solution of hydrochloric acid with the addition of hydrazine sulfate. Notch tensile tests were carried out for the uncoated steel, Cu-coated steel, and Ni–P-coated steel at room temperature. The HE resistance was evaluated by determination of the hydrogen embrittlement index (HEI) in terms of relative changes in notch tensile properties related to the non-hydrogenated and hydrogen-charged material conditions. The results showed that pure electroless deposition of both coatings induced some degree of HE, likely due to the presence of hydrogen ions in the coating solutions used and the lower surface quality of the coatings. However, after the electrochemical hydrogen charging, the coated systems showed improved HE resistance (lower HEI_RA values) compared with the uncoated material. This behavior was accompanied by the hydrogen-induced coatings’ deterioration, including the occurrence of superficial defects, such as bubbling, flocks, and spallation. Thus, further continuing research is needed to improve the coatings’ surface quality and long-term durability, including examination of their performance under pressurized hydrogen gas charging conditions. Full article

Microbiologically influenced corrosion (MIC) poses significant challenges in oilfield water injection environments, leading to substantial socioeconomic losses. L245 steel, a low-alloy steel widely used in oil and gas pipelines due to its excellent mechanical properties and cost-effectiveness, remains highly vulnerable to MIC during long-term service. This study uses surface characterization and electrochemical techniques to investigate the corrosion behavior of L245 pipeline steel under short-cycle conditions in a symbiotic environment of iron-oxidizing bacteria (IOB) and Shewanella algae (S. algae). Key findings revealed that localized corrosion of L245 steel was markedly exacerbated under coexisting IOB and S. algae conditions compared to monoculture systems. However, the uniform corrosion rate under symbiosis fell between the rates observed in the individual IOB and S. algae systems. Mechanistically, the enhanced corrosion under symbiotic conditions was attributed to the synergistic electron transfer interaction: IOB exploited electron carriers secreted by S. algae during extracellular electron transfer (EET), which amplified the microbial consortium’s capacity to harvest electrons from the steel substrate. These results emphasize the critical role of interspecies electron exchange in accelerating localized degradation of carbon steel under complex microbial consortia, with implications for developing targeted mitigation strategies in industrial pipelines exposed to similar microbiological environments. Full article

For over five decades, blending hydrogen into existing natural gas pipelines has been explored as a potential solution to reduce greenhouse gas emissions. Despite its promise, implementing this approach has been slow due to concerns about hydrogen embrittlement (HE) and its interactions with various metals. Stainless steel alloys like 316L are commonly used in hydrogen service due to their superior resistance to HE. However, the impact of additive manufacturing (AM) on 316L’s susceptibility to HE when subjected to gas charging has not been thoroughly investigated. To fill this knowledge gap, we created conventionally manufactured and AM 316L tensile bars and solubility specimens, which were then exposed to hydrogen-blended natural gas at 10 MPa with a 50% blend and 100% pure H₂. Both conventionally manufactured and additively manufactured specimens had as-received/printed samples that were used as controls. The samples underwent mechanical evaluation through tensile testing and hot chemical extraction to assess hydrogen solubility. Further analysis revealed significant changes in the microstructure near the fracture area of the soaked samples using scanning electron microscope fractography and metallography. These findings were compared with our previous work on traditionally produced 316L bar stock, which demonstrated that AM processing conditions can yield superior performance in terms of resistance to HE. Notably, this study provides valuable insights into the effects of AM on 316L’s susceptibility to HE when subjected to gas charging. The results have significant implications for the development and implementation of AM 316L for hydrogen/natural gas applications in pressure regulators when AM processing conditions are well-controlled. This article is a revised and expanded version of a paper entitled “Effect of Hydrogen-Blended Natural Gas on Additive Manufactured 316L Stainless Steel in Pressure Regulator Environments”, which was presented at TMS in Las Vegas, March 2025. Full article

This study presents a systematic optimization of GTAW welding parameters to achieve a pipe-to-pipe butt weld with a root height consistently below 2 mm when joining stainless-steel 316L material, employing the Taguchi design of experiments. To the authors’ knowledge, no similar studies have been conducted to explore the optimization of welding parameters specifically aimed at minimizing weld root height under 2 mm in stainless-steel EO pipeline welding applications. This gap in the existing literature highlights the innovative aspect of the current study, which seeks to address these challenges and improve welding precision and joint reliability. Root height, also referred to as weld root reinforcement, is defined as the excess weld metal protruding beyond the inner surface root side of a butt-welded joint. The input parameters considered are the welding current, voltage, speed, and root gap configurations of 1, 1.5, and 2 mm. Welding was performed according to the Taguchi L-09 experimental design. Nine weld samples were evaluated using liquid penetrant testing to detect surface-breaking defects, such as porosity, laps, and cracks; X-ray radiography to identify internal defects; and profile radiography to assess erosion, corrosion, and root height. Among the nine welded plate samples, the optimal root height (less than 2 mm) was selected and further validated through the welding of a one-pipe sample. An additional macro examination was conducted to confirm the root height and assess the overall root weld integrity and quality. Full article

Fatigue endurance anisotropic behavior was evaluated for an API 5L X42 pipeline steel through axial force-controlled fatigue tests amongst Longitudinal, Diagonal, and Circumferential directions. This study shows that fatigue life anisotropy is mainly controlled by pearlite banding degree (A_i) and ferritic grain orientation (Ω₁₂). Also, it is foreseen that the observed behavior can be related to the dislocation arrays generated by the cyclic loading in relation to microstructure orientation, and the interactions of the fatigue crack tip with the microstructure during the crack propagation stage. Full article

In the extraction of shale gas, Cl⁻ and S₂O₃²⁻ are one of the important factors causing severe corrosion and failure of equipment and pipelines. Addressing the Cl⁻/S₂O₃²⁻ corrosion challenge in shale gas exploitation pipeline steels, this study evaluates the corrosion rates of L245 steels under diverse conditions, including S₂O₃²⁻ concentration and exposure time, utilizing the weight loss method. The microstructural, elemental, and phase compositions of the corrosion products were examined, and the electrochemical behavior of L245 steel was scrutinized under various conditions. Findings indicate that S₂O₃²⁻ addition intensifies localized corrosion on L245 steel, with the corrosion nature being contingent upon S₂O₃²⁻ concentration in the Cl⁻-containing solution. Concurrently, an escalation in S₂O₃²⁻ concentration correlates with a reduction in capacitive arc diameter and a significant decrease in film resistance, culminating in an accelerated corrosion rate. Full article

Sodium hypochlorite is a commonly used disinfectant in reclaimed water, and the decay law of its free chlorine directly affects the disinfection effect and the safety of reclaimed water. Currently, most of the decay studies have been carried out on the temperature, pH value, and concentration of organic matter in water, without fully considering the differences between fresh and corroded pipeline materials and their effects. This study aims to compare the influences of fresh and corroded carbon steels on the decay law of sodium hypochlorite through dynamic reaction devices and static flask experiments, based on simulations using uncorroded and pre-corroded carbon steel hanging plates. The effects of Fe⁰ and corrosion products on sodium hypochlorite decay are investigated to provide data support for disinfection strategies in reclaimed water distribution networks. By integrating DPD spectrophotometry, ATP detection, XRD analysis, and corrosion weight loss analysis, the microbial control efficacy and corrosion of sodium hypochlorite under the effects of fresh and corroded carbon steels are compared. The differences in decay kinetics are quantified using the restricted first-order decay model, and the dominant mechanisms of sodium hypochlorite consumption that cause differences in the effectiveness of the action are explored. The influences of fresh and corroded carbon steels on the decay are evaluated. Additionally, the percentages of consumption are also analyzed. The results show that in order to effectively kill microorganisms while reducing corrosion, it is recommended to add sodium hypochlorite under simulated conditions for fresh and corroded carbon steels to achieve free chlorine concentrations of 5 mg/L and 9 mg/L in the water, respectively. The effective control time of sodium chlorate on microorganisms in the bulk of the water under the fresh carbon steel conditions can be maintained for up to 48 h. However, under the corroded carbon steel conditions, the activity of microorganisms in the bulk of the water is relatively high, with an effective action time of only 8 h. The decay coefficient of sodium chlorate under the corroded carbon steel conditions is 2.61~6.94 times that of the fresh carbon steel. The additional average consumption of sodium hypochlorite under the corroded carbon steel conditions is 13.91~26.57% compared to the fresh carbon steel. Both Fe⁰ and corrosion products accelerate the decay of sodium hypochlorite in the initial stage, with an average consumption increase rate of 18.9% for Fe⁰ and 17.4% for corrosion products. The bulk decay coefficient is 0.073 h⁻¹, and the wall decay coefficient represented by Fe⁰ is 0.204 h⁻¹, which is higher than the wall decay coefficient represented by corrosion products, which is 0.077 h⁻¹. Full article

Accurate mechanical property parameters constitute an indispensable guarantee for the accuracy of finite element simulations. Traditionally, uniaxial tensile tests are instrumental in acquiring the stress–strain data of materials during elongation, thereby facilitating the determination of the materials’ mechanical property parameters. By capitalizing on the digital image correlation (DIC) non-contact optical measurement technique, the entire test can be comprehensively documented using high-speed cameras. Subsequently, through in-depth analysis and meticulous numerical computations enabled by computer vision technology, the complete strain evolution of the specimen throughout the test can be precisely obtained. In this study, a comparison was made between the application of strain gauges and DIC testing systems for measuring the strain alterations during the tensile testing of 316L stainless steel, which serves as the material for the primary circuit pipelines of pressurized water reactor (PWR) nuclear power plants (NPPs). The data procured from these two methods were utilized as material mechanical parameters for finite element simulations, and a numerical simulation of the uniaxial tensile test was executed. The results reveal that, within the measuring range of the strain gauge, the DIC method generates measurement outcomes that are virtually identical to those obtained by strain gauges. Given its wider measurement range, the DIC method can be effectively adopted in the process of obtaining material mechanical parameters for finite element simulations. Full article

Microorganisms are often observed in the produced medium during the oil and gas extraction process. Corrosion caused by CO₂ and microorganisms is found on the inner wall of the metal gathering pipelines during the production process. In order to explore the corrosion characteristics of L245 materials under the combined action of sulfate-reducing bacteria (SRB) and CO₂, a CO₂-SRB corrosion system was established in this paper. Experimental research on corrosion rate, surface morphology, and corrosion products analysis was conducted. The effect of temperature on the corrosion of SRB while CO₂ is saturated and the partial pressure is 0.06 MPa was investigated. It was observed that the corrosion is more serious in the CO₂-SRB corrosion system than that in the single CO₂ corrosion system. At 40 °C, the corrosion caused by CO₂ is 0.0597 mm/a, and the corrosion caused by SRB is 0.0766 mm/a. So, more attention should be paid to the corrosion status of gathering pipelines with microorganisms. Further, the activity of SRB is stronger when the temperature of the medium is 40 °C, and corrosion on L245 samples is more obvious under the experimental conditions in this article. In order to reduce the corrosion damage of metal pipelines with microorganisms, the temperature should be well controlled to reduce the activity of SRB during the production process. Full article