Effective monitoring of internal corrosion risk is crucial to ensuring the safety and longevity of natural gas pipeline infrastructure. While electrochemical sensors are commonly used to assess corrosion rates and corrosion indicators in aqueous fluids, they are rarely used in gas pipelines as these fluids lack the ionic conductivity needed for electrochemical measurements. The inclusion of ion-conductive membranes into electrochemical sensors can extend their functionality into humidified gas streams, providing critical information about emerging corrosion events that are common during withdrawal season in pipeline systems downstream from underground storage facilities. In parallel, new protective films, like those obtained through cold spray coating, are being developed to protect oil and gas pipelines and recover losses in structural integrity due to corrosion damage. Herein, we demonstrate how membrane-based electrochemical sensors (MBES) can be used to monitor fluid corrosivity by examining their response to changes in water content for a wide range of fluid compositions. It was found that MBES readings were highly sensitive to water content changes with membrane conductivity measurements varying from 10-6 to 10-1 S cm-1, and corrosion rate measurements which varied from 10-7 to 1 mm y1. Electron microscopy confirmed that the self-healing characteristics of metal coating films were still active despite their inclusion into an MBES probe. These findings indicate that membrane-based corrosion monitoring can be expanded to monitor coated-pipeline materials and provide early detection of emerging corrosion upsets relevant to underground gas storage facilities.

Silicon carbide-based ceramic matrix composites protected by environmental barrier coatings (EBCs) present a promising materials solution for next-generation gas turbines. Developing more robust and efficient EBCs is therefore of significant technological importance. During the service in high-temperature oxidative environments, there is a thermally grown oxide (TGO) layer, spontaneously formed in the EBC system. TGO is recognized as a critical factor for the degradation and failure of EBCs, yet the detailed mechanisms of TGO growth and its effect on EBC failure remain unclear. In this study we develop a comprehensive chemo-mechano-phase-field model to simulate growth of the TGO in EBCs, factoring in creep and deformation, and especially the cracking behaviors. The volume expansion due to TGO growth and the resulting large inelastic deformation are addressed by using our recently developed, so-called incremental realization of inelastic deformation (IRID) algorithm, in combination with an adapted Hu-Chen spectral solver for elasticity. Simulations of TGO growth are performed considering different growth modes of TGOs determined mainly by the ratio of oxidant permeability in the topcoat to that in the TGO itself. Large-scale three-dimensional (3D) simulations are performed to model the formation of interconnecting vertical/channel cracks (often called 'mud cracks'). The simulated crack morphology are in excellent agreement with the experimental observations from the literature. The simulations also provide insights into the cracking of EBCs and its dependence on the structure and constituent properties of the coating system. These results demonstrate the developed damage model can be a useful tool for design of more durable EBCs.

Environmental barrier coatings (EBC) are crucial for the use of SiC-based ceramic matrix composites in high-temperature combustion environments, yet knowledge of oxygen diffusion in these coatings is limited. This study investigates oxygen diffusion dynamics in the β-RE2Si2O7 system to minimize oxygen penetration in rare earth disilicates. We analyze defect formation energy under varying oxygen conditions, identifying key diffusion mechanisms. In oxygen-rich environments, the most favorable neutral interstitial oxygen diffuses along the [110] direction. In oxygen-poor conditions, neutral oxygen vacancies rotate around Y and Si atoms, exhibiting a diffusivity of 6.59×10−22 m2/s at 1500 K for β-Yb2Si2O7. Under intermediate oxygen levels, charged interstitial oxygen diffuses via concerted interstitialcy along the [001] direction with a diffusivity of 6.21×10−17 m2/s. Additionally, alloying rare earth Y with Er and Yb increases diffusion barriers, contributing to improved EBC performance in extreme environments. The insights gained provides valuable guidance for designing robust coatings tailored to withstand extreme operational environments.

This research advances the field of additive manufacturing (AM) of silicon carbide (SiC) ceramics by integrating spark plasma sintering (SPS) to enhance material density, mechanical strength, and thermal properties. Traditional AM techniques struggle to achieve the high-density SiC required for demanding applications, such as aerospace engineering, where high thermal conductivity and mechanical strength are paramount. Our study addresses these challenges by incorporating SPS as a post-processing step, achieving near-theoretical maximum densities and significantly reducing porosity, thereby resulting in outstanding thermal conductivity in SiC ceramics. We developed a specialized SiC ink optimized for 3D printing, ensuring structural integrity after deposition through tailored rheological properties. The application of SPS facilitates rapid, uniform sintering, essential for attaining superior density, mechanical properties, and thermal performance. Our experimental results, confirmed through scanning electron microscopy analysis, demonstrate significant microstructural properties, mechanical strength, and thermal conductivity, showcasing the effectiveness of integrating SPS in AM processes. This innovative approach not only expands the capabilities of AM in producing complex, high-density ceramic structures but also broadens the potential applications of SiC in demanding environments.

Herein, the effect of Ce additions ranging from 57 to 263 ppm is evaluated for an experimental pipeline steel. Compared to the Ce‐free steel, progressive Ce additions result in a slightly refined microstructure, significantly improve transverse impact properties, and slightly increase strength. All these observations can be attributed to the gradual transformation of Mn sulfide and Mn–Si–Al oxide inclusions to Ce‐containing oxide/sulfides. In particular, the inclusions consist exclusively of sub‐5 μm spherical Ce 2 O 2 S particles upon near‐stoichiometric additions of Ce, considering the oxygen and sulfur impurity level of the steel. The results suggest that Ce is a potentially promising alloying addition for next‐generation pipeline steels by replacing overtly deleterious inclusions with potentially beneficial ones.

To enhance the protection of Ni-based superalloys in gas turbine engines' high-temperature environments, it is crucial to develop advanced thermal/environmental barrier coating (T/EBC) materials with a balanced combination of thermal, environmental, and mechanical properties. This optimization is essential to safeguard against chemical and thermal challenges at high temperatures. In this study, we harness the power of density functional theory (DFT) in conjunction with combinatorial chemistry methodologies to engineer high-performance, high-entropy rare earth aluminum garnets of the R 3 Al 5 O 12 family (where R denotes Y, Gd, Er, and Yb). These materials are meticulously designed to exhibit superior phase stability, a targeted coefficient of thermal expansion (CTE), low lattice thermal conductivity, and robust mechanical properties. The determination of CTE values is accomplished through phonon calculations at various volume settings within the quasiharmonic approximation, while lattice thermal conductivities are rigorously assessed employing the Debye-Callaway model, accounting for three distinct phonon processes. Our findings highlight the remarkable attributes of the solid solution (Y1/4Gd1/4Er1/4Yb1/4)3Al5O12, 1 / 4 Gd 1 / 4 Er 1 / 4 Yb 1 / 4 ) 3 Al 5 O 12 , which displays a noticeable reduction in lattice thermal conductivity compared to its individual constituents while maintaining a favorable range of CTE values. The T/EBC materials, distinguished by their multifaceted functionalities, are promising next-generation T/EBCs for protecting nickel-based superalloys in gas turbine engines. Furthermore, this work serves as a testament to the efficacy and reliability of our computational framework, which holds the potential to expedite the design of next-generation T/EBC materials.

Advancing thermal/environmental barrier coating (TEBC) materials with integrated thermal-mechanical functions is paramount for safeguarding SiC-based ceramic matrix composites (CMCs) in high-efficiency gas turbines. Herein, we employ a synergistic approach, combining density functional theory (DFT) methods and combinatorial chemistry techniques, to design high-performance and low-cost RE2Si2O7 (RE = rare earth elements) TEBC materials tailored for enhanced compatibility with SiC-based CMCs. Expanding on phase stability of alloying pure RE2Si2O7, the investigation extends to the mechanical and thermal properties of solid solution systems, including Er1/2Y3/4Yb3/4Si2O7, Gd1/4Er1/4Y3/4Yb3/4Si2O7, and Eu1/4Er1/4Y3/4Yb3/4Si2O7. The solid solution systems exhibit a major reduction in lattice thermal conductivity relative to their pure counterparts, achieving ultralow values of 0.25 to 0.39 W m(-1) K-1 at 1500 K. Furthermore, the coefficients of thermal expansion (CTE) of these solid solutions are precisely tuned within the desired range for SiC (4.4 to 5.5 x 10(-6 )K(-1)), while maintaining good mechanical properties. In particular, the addition of Eu(2)Si(2)O(7 )demonstrates to be an important variable to the tuning of CTE and lattice thermal conductivity by leveraging its strong anharmonicity, presenting a pioneering avenue for fine-tuning material properties. In summary, this research not only identifies promising TEBC materials with superior thermal properties, but also introduces a valuable computational material design methodology for the rapid discovery of complex materials for harsh environments.

Minor additions of rare earth elements (REEs) have been shown to improve various steel properties. In particular, Cerium (Ce), as a relatively abundant and inexpensive element, has received attention as a potentially beneficial minor alloying addition for a variety of steel applications, including pipeline materials. The objective of this work is to investigate the effect of Ce on corrosion performance of experimental pipeline steel. Electrochemical corrosion experiments were carried out on steel without and with 0.0057, 0.0164, and 0.0263 wt.% of Ce in 3.5 wt.% NaCl saturated with CO2 at 20 °C. For comparison purposes, X100 carbon steel specimens machined from an experimental pipe with a yield strength of 731 MPa were tested under the same conditions. The electrochemical techniques employed included: potentiodynamic polarization (PDP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). In addition, post-corrosion surface characterization was performed using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The corrosion of base metal without Ce was significantly lower (0.15 mm/y) compared to carbon steel X100 (0.9 mm/yr). The electrochemical results showed that adding Ce accelerates corrosion rates compared to base metal without Ce. No pitting corrosion of tested steel was detected.

Abstract The aging pipeline infrastructure in the United States raises concerns about potential greenhouse gas leaks, corrosion damage, and catastrophic failures. Many pipelines are 30 to 60 plus years in service with an average age of over 40 years. The three main causes of pipeline gas interruption are material or weld failure, corrosion, and excavation damage. As pipelines age, these risks increase. In addition, there is increased interest in repurposing the existing pipeline networks for hydrogen and hydrogen-methane blends. Refurbishment of existing pipelines to prevent corrosion damage, and subsequent gas leaks and preparation for hydrogen transport will significantly accelerate decarbonization efforts. Traditional approaches to refurbishing existing pipelines utilize coatings such as fusion bond epoxy or polymer-based liner. These materials provide corrosion protection but are difficult to install on active natural gas networks without significant service interruption. Often sections of pipe need to be removed for offsite repair and refurbishment. In this paper, the authors present a novel smart liner technology that is designed for on-site installation in existing natural gas pipelines. The goal of the liner is to be installed without pipe removal, avoiding major interruptions to gas service. This paper presents an in-depth investigation into the development of an advanced liner technology with thorough characterization of the various layers of material involved and the performance against corrosion and hydrogen. The liner material, with various topcoats for corrosion prevention, was evaluated using linear polarization and electrochemical impedance spectroscopy under a CO2-saturated 3.5wt% NaCl solution. Corrosion studies demonstrated an advanced nanocomposite omniphobic surface treatment with a corrosion rate of 0.5x10−6mm/year at a thickness of ~20µm. In addition, the omniphobic treated liner showed strong adhesion strength and resistance against folding/bending. Refurbishment, repair, and transformation of natural gas pipeline networks require new technologies that enable modification with limited interruption to the gas transport at a fraction of the cost of new metal pipelines. The advanced composite liner technology presented here offers a unique solution aimed at overcoming existing installation challenges for corrosion prevention, H2 transport, and leak mitigation.

Abstract Steels have a proven track record of safe operation in steam power plants for decades. Interest in developing supercritical CO2 power cycles as a more efficient and sustainable alternative to steam cycles has driven a need to understand steel performance in these new environments. In particular, the potential of the high temperature CO2 environment to influence the creep behavior of the steel must be determined. Prior research on this topic between the 1960s and 1980s found conflicting conclusions, but nevertheless raised the possibility that carburization during CO2 exposure may strongly affect the creep behavior. This raises concerns particularly for thin-sectioned components such as compact heat exchangers, where even small rates of carburization can become problematic over long operating lifetimes. To shed light on this issue, this research investigates the creep behavior of austenitic stainless steel 347H and 309H (a higher Cr alternative) at 650°C. Specimens of 0.5, 1.0, and 2.0 mm thickness were tested to further assess the effect of steel thickness. Both steels show a reduction in creep life in CO2 relative to air, with 309H showing slightly better performance than 374H. Analysis is ongoing to determine the reason for degraded creep properties.

Internal corrosion is a problem for steel pipelines transporting natural gas or CO 2 containing water and partial pressures of H 2 S higher than 0.3 kPa (0.05 psi). This work aims to mitigate internal corrosion in steel pipelines transporting natural gas containing H 2 S using cold spray coatings. Two types of the cold spray binary metallic coatings (zinc chromium (ZnCr]. zinc niobium (ZnNb]) were studied using electrochemical techniques: potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy. The corrosion resistance of cold spray coatings (ZnCr, ZnNb) was evaluated in an environment containing 4 bar CO 2 pressure, simulating the partial pressures found in gas transmission lines over a solution of 3.5 wt% NaCl heated to 40 degrees C. A concentration of 0.003 M Na 2 S 2 O 3 5H 2 O, corresponding to H 2 S partial pressures around 0.079 bar (1.146 psi), was used to simulate sour conditions. Postcorrosion surface characterization was performed using a scanning electron microscope (SEM) equipped with an energy -dispersive x-ray spectroscope (EDS) and x-ray diffraction analysis. The data showed that the presence of 0.003 M Na 2 S 2 O 3 5H 2 O shifted the corrosion potential to more anodic values and decreased the corrosion current density. Both coatings showed similar behavior after 1 h of exposure in the CO 2 /H 2 S environment, indicating that similar electrochemical reactions were occurring on ZnNb and ZnCr. SEM images and EDS surface analyses for specimens showed a significant change in the surface chemical composition of carbon steel coated with ZnNb and ZnCr after 24 h of immersion. In the presence of thiosulfate (under sour conditions), the formation of corrosion product layers (ZnCO 3 and ZnS) on top of ZnNb and ZnCr coatings increased their corrosion resistance, which helped to reduce their corrosion by a factor of 2. Under a sweet environment, the corrosion rates for steel coated with cold spray coatings after 14 d of exposure are lower than that for galvanized steel by a factor of 5 due to the ZnCO 3 layer formed on top of the coatings. The ZnCO 3 layer formed on the steel surface acts as a physical barrier against corrosion by blocking the diffusion of corrosive species to the surface. No localized attack was observed. ZnCr Cold spray coating with defect showed promising corrosion protection against CO 2 corrosion (sweet corrosion) after 14 d of exposure to a CO 2 environment. The scratch on the coating simulated damage created in service, and it was deep enough to expose the substrate material (steel). The formation of zinc oxide (ZnO) and zinc carbonate (ZnCO 3 ) on the scratch confirmed the cathodic protection of the steel by ZnCr and ZnNb coatings.

The thermal characterization of a micro-pin solar thermal receiver (MSTR) for supercritical carbon dioxide (sCO2) gaseous working fluid is presented. In a companion paper of this two-part study [1], the design and fabrication methodologies employed in the development of the MSTR were presented. As described in Fronk et al. [1], the MSTR is formed by a microlamination process with brazed headers to form multiple unit cell flow paths with fluid inlet/outlet ports. In this part of the study, on-sun tests to estimate the thermo-fluidic performance of the MSTRs using a parabolic dish concentrator are described for a 15 cm x 15 cm design with 6 unit cells. The MSTR is installed in a closed-loop sCO2 test facility coupled to a seven-meter diameter parabolic dish. On-sun tests were performed at a receiver inlet pressure of up to 15.5 MPa and a receiver inlet temperature ranging between 31 to 398 degrees C. Receiver thermal efficiencies were calculated using an indirect estimation of the absorbed flux, by summing the convective and radiative losses and absorbed energy to the fluid. Thermal efficiency greater than 0.98 were obtained for estimated incident heat flux of 34-40 W/cm2 at average surface temperatures ranging from 113 to 332 degrees C and peak surface temperatures of up to 550 degrees C. A sensitivity analysis, performed on the convective and radiative losses, indicates the lower limit of efficiency to be within 1.5 % of the estimated value. After a few hours of testing, the receiver failed due to an internal flow blockage that led to overheating. Optical and microstructure analysis is performed on the 15 cm x 15 cm and a failed 8 cm x 8 cm MSTR from prior work to identify possible reasons for failure.

Ensuring the management of gas transportation infrastructure requires the monitoring of internal corrosion within pipelines. The utilization of membrane-based electrochemical sensors is a promising advancement in corrosion risk monitoring. These sensors demonstrate an ability to operate within humidified gas environments, previously inaccessible to conventional electrochemical monitoring methods. Simultaneously, ongoing research is delving into novel sacrificial coatings and application methods to prolong the lifespan of existing pipeline structures and minimize associated repair costs. In this context, we broaden the application of membrane-based electrochemical sensors to investigate the response of electrodes equipped with cold-spray coatings. This examination encompasses a range of fluids exhibiting varying levels of corrosivity pertinent to natural gas pipelines. Multiple sensors with 316 stainless steel working electrodes were coated with cold spray sacrificial coating then exposed to humidified gases with differing relative humidities (RH) (5 %, 50 %, and 95 %) and condensed phases with differing salt content (deionized water and 0.1 mol kg-1 NaCl solution). Three electrochemical techniques (potentiometry, impedance spectroscopy and potentiodynamic scans) were used to monitor the corrosive environment and probe the extent of coating coverage. For the conditions studied, impedance values were extremely sensitive to changes in water content through changes in the membrane resistance (from ~1 kΩ in deionized water to ~5 MΩ with 5 % RH). Polarization resistances (Rp) consistently decreased with increasing corrosivity (~3 kΩ in deionized water to 15 GΩ with 5 % RH). Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to identify the extent to which corrosion products permeated the membrane after major corrosion events.

Development of gas-based solar receivers that can withstand the extreme temperatures (>700 degrees C) and high pressures required in next generation concentrating solar plants remains a significant challenge. This study presents an investigation of the design and fabrication methods of a prototype modular, micro-pin solar receiver for directly heating supercritical carbon dioxide from temperatures of 550 degrees C to 720 degrees C at a pressure of 20 MPa and an incident flux > 100 W cm(-2). The receiver is fabricated from high nickel content Haynes 230 alloy. Multiple failure modes related to design and fabrication methods were identified in a first-generation prototype. Here, these failure modes are mitigated by the introduction of improved diffusion bonding, brazing, design of the receiver header and micro-pin array. The efficacy of each improvement was evaluated separately using a combination of simulations and lab-scale experiments. The design improvements were then integrated into sub-scale (5 cm x 5 cm) and prototype scale (15 cm x 15 cm) test devices. The study resulted in the successful fabrication and proof and cyclic pressure testing of a prototype receiver that was tested in a concentrating solar dish. The results of this study can guide the development process of other high temperature receiver technologies that must operate at extreme pressures and incident fluxes.

Internal corrosion and sulfide stress cracking (SSC) are problems for steel pipelines transporting natural gas or CO2 containing partial pressures of H2S higher than 0.3 kPa (0.05 psi). The objective of this work is to mitigate internal corrosion and SSC in steel pipelines transporting natural gas containing H2S using cold spray coatings. Two types of the cold spray binary metallic coatings (zinc chromium (ZnCr), zinc niobium (ZnNb)) were studied using electrochemical techniques: potentiodynamic polarization (PDP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The evaluation of the corrosion resistance of cold spray coatings (ZnCr, ZnNb) was carried out in an environment containing 4 bar CO2 pressure, simulating the partial pressures that are found in gas transmission lines over a solution of 3.5 wt.% NaCl heated to 40 °C. To simulate sour conditions, a concentration of 0.003 M Na2S2O3.5H2O, which corresponds to H2S partial pressures around 0.079 bar (1.146 psi), was used. Post-corrosion surface characterization was performed using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscope (EDS) and X-ray diffraction analysis (XRD). The data showed that the presence of 0.003 M Na2S2O3.5H2O shifted the corrosion potential to more anodic values and decreased the corrosion current density. Bothcoatings showed similar behavior after 1 hour of exposure in CO2/H2S environment, which indicated that similar electrochemical reactions were taking place on ZnNb and ZnCr. SEM images and EDS surface analyses for specimens showed a significant change in surface chemical composition of carbon steel coated with ZnNb and ZnCr, after 24 hours of immersion. No localized attack was observed. The EDS analysis and XRD results revealed the presence of zinc sulfide (ZnS).

Abstract Future technologies require structural materials resistant to environmental degradation in high temperature CO2-rich environments. Herein we exposed several commercially available Ni-based alloys (230, 263, 282, 617, 625, 740H) to atmospheric pressures gases intended to simulate the compositions expected in future direct-fired supercritical CO2 power cycles. The alloys were exposed to 95% CO2 + 4% H2O + 1% O2 and the same gas containing 0.1% SO2 at temperatures of 600, 650, 700, 750, and 800°C for 2500 h. With minor exceptions, chromia scales formed on all alloys at all temperatures in the SO2-free gas, yielding parabolic growth rates that followed a clear Arrhenius temperature-dependence. Behavior in the SO2-containing gas was more complex. Generally, the alloys performed well at temperatures of 650, 750, and 800°C. While some alloys further performed relatively well across the whole temperature range, several of the alloys experienced chromia failure and higher oxidation rates at temperatures of 600 and 700°C. Deviation from protective behavior was associated with internal sulfide formation and, additionally for the case of 600°C, external sulfate formation. The thermodynamic and kinetic factors influencing the accelerated corrosion in the presence of sulfur are discussed. The results suggest that caution is required when assessing compatibility of Ni-based alloys for CO2-based systems when sulfur-based impurities are expected.