Internal Pressure Research Articles

Nonlinear Slippage of Tensile Armor Layers of Unbonded Flexible Riser Subjected to Irregular Loads

The unbonded flexible riser has been increasingly applied in the ocean engineering industry to transport oil and gas resources from the seabed to offshore platforms. The slippage of helical layers, especially the tensile armor layers of unbonded flexible risers, contribute to the nonlinear hysteresis phenomenon, which is a research hotspot and difficulty. In this paper, on the basis of a typical eight-layer unbonded flexible riser model, the nonlinear slippage of a tensile armor layer and the corresponding nonlinear behavior of an unbonded flexible riser subjected to irregular external loads are studied by numerical modeling with detailed cross-sectional properties of the helical layers, and are verified through a theoretical method considering the coupled effect of the external loads on the unbonded flexible riser. Firstly, the balance equation of each layer considering the effect of external loads is established based on functional principles, and the overall theoretical model of the unbonded flexible riser is set up in consideration of the contact between adjacent layers. Secondly, the numerical modeling of each separate layer within the unbonded flexible riser, including the actual geometry of the carcass and pressure armor layer, is established, and solid elements are applied to all the interlayers, thus simulating the nonlinear contact and friction between and within interlayers. Finally, after verification through test data, the behavior of the unbonded flexible riser under the cyclic axial force, torsion, bending moment, and irregular external and internal pressure is studied. The results show that the tensile armor layer can slip under irregular loads. Additionally, some suggestions related to the analysis of unbonded flexible risers under irregular loads are drawn in the end.

Public-Private Powerplays in Generative AI Era: Balancing Big Tech Regulation Amidst Global AI Race

Public-Private Powerplays in Generative AI Era: Balancing Big Tech Regulation Amidst Global AI Race

Adjustable Friction Force of Elastic Post via Regulating Internal Cavity Pressure

The objective of this study is to investigate and obtain an adjustable friction force between an elastic polymeric post with cavity and a rigid, smooth, flat surface. Elastic cylindrical posts made of polymers are generally used as surface texturing components. In this study, the friction force of the elastic cylindrical posts with a flat tip in contact with a smooth and rigid surface was adjusted by a pneumatic-based actuation system. Finite-element based simulation was performed to adjust the friction force of the cylindrical posts by pressurizing the inner cavity of the posts. The frictional contact between the elastic posts and the counter rigid surface was modeled using the Amontons-Coulomb friction law, neglecting the adhesive contribution. The friction force amplitude was calculated with different cavity dimensions of the elastic posts and different cavity pressure values. The results show that the presence of an internal cavity reduces the friction force, and the cavity diameter has more influence on the reduction of the friction force than the cavity height. In conclusion, regulating the cavity pressure was shown to be an effective method of adjusting the friction force.

Experimental and Simulation Studies on Stable Polarity Reversal in Aged HVDC Mass-Impregnated Cables

Mass-impregnated (MI) cables have been used for many years as cables in high-voltage direct current (HVDC) systems. In line commutated converter (LCC) HVDC systems, polarity reversal for power flow control can induce significant electrical stress on MI cables. Furthermore, the mass oil and kraft paper comprising the impregnated insulation have significantly different coefficients of thermal expansion. Load fluctuations in the cable lead to expansion and contraction of the mass, creating pressure within the insulation and causing redistribution of the impregnant. During this process, shrinkage cavities can form within the butt gaps. Since the dielectric strength of the cavities is lower than that of the surrounding impregnation, cavitation phenomena in impregnated paper insulation are considered a factor in degrading insulation performance. Consequently, this study analyzes the electrical conductivity of thermally aged materials and investigates the transient electric field characteristics within the cable. Additionally, it closely analyzes the formation and dissolution of cavities in MI cables during polarity reversal based on a numerical model of pressure behavior in porous media. The conductivity of the impregnated paper indicates that it has excellent resistance to thermal degradation. Simulation results for various load conditions highlight that the interval of load-off time and the magnitude of internal pressure significantly influence the cavitation phenomenon. Lastly, the study proposes stable system operation methods to prevent cavitation in MI cables.

Profilometry‐Based Indentation Plastometry and Uniaxial Testing of Pipelines: Detection of In‐Plane Anisotropy and Potential for Simplification of Test Procedures

This article concerns anisotropy in stress–strain relationships exhibited by steel pipelines. Since the stress from internal pressurization is highest in the hoop direction, standard industrial practice to measure these properties has focussed on tensile testing in this direction, requiring a prior flattening operation. The associated plastic deformation may affect properties, typically causing a (poorly‐defined) degree of hardening and the creation of inhomogeneity. Field testing of such pipelines, requiring in situ measurement of tensile properties (yield stress (YS) and ultimate tensile stress (UTS)), is based on indentation testing of the outer surface. One such test (profilometry‐based indentation plastometry (PIP)), not only gives the stress–strain curve, but also allows detection of any (in‐plane) anisotropy, with a high sensitivity. Both PIP testing and compression testing (with and without prior flattening) have confirmed that none of the eight pipes examined in the current work exhibited any such anisotropy, although the effects of flattening did tend to generate apparent anisotropy in the tensile test outcomes. It may therefore be appropriate to switch the focus of tensile testing to the axial direction, such that no flattening would be required.

Flow Field Analysis and Performance Study of a Hydrogen Circulation Pump for Proten Exchange Membrane Fuel Cell Vehicles with Different Working Clearances

This study investigates the impact of working clearances on the internal flow field, pressure pulsations, flow pulsations, and radial forces experienced by a hydrogen circulation pump. Numerical calculations are conducted on seven sets of distinct working clearances for the pump. The research findings demonstrate that an increase in meshing clearance and radial clearance results in higher leakage flow rate during the compression exhaust process, leading to a decrease in hydrogen circulation pump's exhaust flow rate. When the meshing clearance increases from 0.15 to 0.21 mm, the actual exhaust flow rate of the pump decreases from 37.46 to 32.73 m3 h−1. Similarly, when the radial clearance increases from 0.18 to 0.24 mm, the actual exhaust flow rate of the pump decreases from 42.46 to 29.71 m3 h−1. Additionally, with an increase in meshing clearance, both the radial forces Fx and Fy of the active rotor exhibit a downward trend. Yet, as radial clearance grows, the radial force Fx slightly descends, while the change trend of radial force Fy is first positive decrease and then reverse increase.

Fragility assessment for process pipelines in flood events through physically-based hazard response analysis

Natech events triggered by floods have occurred frequently, resulting in physical damage to process equipment and subsequent releases of hazardous substances, threatening the operational safety of the process industry. Therefore, it is necessary to conduct flood fragility assessments on typical process equipment, such as storage tanks and process pipelines. Compared to storage tank, there are relatively few flood risk analysis methods applicable to process pipelines, and there is a lack of dedicated fragility models to quantify the probability of pipeline damage in flood hazard scenarios. Thus, this paper develops a process pipeline fragility model to support the quantitative risk assessment (QRA) of flood-induced Natech events more comprehensively. This model simultaneously considers the structural physical damage caused by internal pressure and external load in the pipeline and establishes the limit state equation (LSE) corresponding to the failure mode. On this basis, parametric fragility functions are trained using Monte Carlo simulations and logistic regression. A pipeline case is used to test the proposed fragility functions, and the results show that the fitted parameterized fragility model can sensitively capture changes in the failure probability curve caused by hazard intensity and pipeline characteristics changes. The proposed pipeline fragility model is applied to a composite area of pipelines and storage tanks, accurately assessing the failure probability of different types of pipelines in flood scenarios.

Unsteady behaviour and plane blade angle configurations' effects on pressure fluctuations and internal flow analysis in axial flow pumps

Pumps play a crucial role in various applications, and this study employs the CFD method to simulate the internal flow of an axial pump. Utilizing a three-dimensional model with real clearances, our investigation focuses on the pump's internal flow and pressure pulsation under diverse operating conditions. Specifically, we operated an axial pump at varying blade angles (30°, 45°, 60°, and 75°) to determine transient flow fields, aiming to identify both qualitative and quantitative characteristics. In line with current research practices, we present a comparison between numerical calculations and experimental results, revealing reasonable agreement. The simulation results highlight the influence of flow rate and plane blade angle on key parameters such as static pressure, dynamic pressure, total pressure, velocity magnitude fluctuations, and shear stress. Notably, pressure increases near or at the blade tip, and hydraulic flow becomes more evident under different blade angles and conditions. The highest pressure and velocity are observed on the blade with a 45-degree plane angle. These findings provide valuable insights for enhancing the hydraulic performance of axial pumps. To ascertain the model's accuracy and reliability, our research establishes a side-by-side comparison between numerical predictions and experimental data, demonstrating a satisfactory level of agreement. The CFD simulations yield critical insights into the pump's performance, emphasizing the profound sensitivity of parameters to variations in flow rate and blade angle, crucial for understanding and optimizing the pump's behavior.

Study on the Interaction Propagation Mechanism of Inter-Cluster Fractures under Different Fracturing Sequences

Horizontal-well multi-cluster fracturing is one of the most important techniques for increasing the recovery rate in unconventional oil and gas reservoir development. However, under the influence of complex induced stress fields, the mechanism of interaction and propagation of fractures within each segment remains unclear. In this study, based on rock fracture criteria, combined with the boundary element displacement discontinuity method, a two-dimensional numerical simulation model of hydraulic fracturing crack propagation in a planar plane was established. Using this model, the interaction and propagation process of inter-cluster fractures under different fracturing sequences within horizontal well segments and the mechanism of induced stress field effects were analyzed. The influence mechanism of cluster spacing, fracture design length, and fracture internal pressure on the propagation morphology of inter-cluster fractures was also investigated. The research results indicate that, when using the alternating fracturing method, it is advisable to appropriately increase the cluster spacing to weaken the inhibitory effect of induced stress around the fractures created by prior fracturing on subsequent fracturing. Compared to the alternating fracturing method, the propagation morphology of fractures under the symmetrical fracturing method is more complex. At smaller cluster spacing, fractures created by prior fracturing are more susceptible to being captured by fractures from subsequent fracturing. The findings of this study provide reliable theoretical support for the optimization design of fracturing sequences and fracturing processes in horizontal well segments.

Influence of input variables on the unitary deformation experienced in pipes subjected to the action of lateral loads

The hydrocarbon transportation industry uses extensive pipeline networks subject to complex loading conditions. The finite element analysis (FEA) has proven to be effective in simulating the deformation behavior in these pipelines, which assists in the assessment of their integrity and risks. In this work, a model developed using finite elements is proposed to analyze the behavior of API 5L Gr B carbon steel pipes, subject to internal pressure and lateral loads. The model is validated through uniaxial tensile and four-point bending tests. In addition, parametric analysis is carried out considering variables such as diameter, lateral load, and distance between supports. The objective is to identify which one of these variables has the most influence in the unit strain. The results indicate that the unit strain obtained from the numerical model agrees with the experimental tests. Furthermore, it is concluded that the diameter is the influential parameter.

Effect of sodium citrate on compressive strength and microstructure of NaOH-activated slag pastes/mortars exposed to high temperatures

Fire resistance is a critical consideration in the performance of concrete. This study investigated the impact of sodium citrate on the compressive strength and microstructure of NaOH-activated slag cement at temperatures ranging from 200 to 1000 °C. The findings indicated that the addition of sodium citrate led to an increase in matrix density and a decrease in porosity, ultimately resulting in a notable enhancement compressive strength for both AAS paste and mortar samples. Nevertheless, this condition was not conducive to the high temperature resistance of AAS paste due to the elevated internal pressure resulting from the vaporized water within the matrix pores. The incorporation of fine aggregates could notably enhance this capability, particularly in sodium citrate-activated specimens. This enhancement can be attributed to the optimization of the pore structure of the sand, facilitating the elimination of free water without compromising the integrity of the structure and minimizing the occurrence of micro-cracks. Furthermore, the elevated temperature of 200 °C facilitated the AAS reaction, resulting in an increased formation of gel phases.

Multi-factor corrosion model of TP110TS steel in H2S/CO2 coexistence and life prediction of petroleum casings

The failure of petroleum casings due to the combined effects of CO2/H2S corrosion and internal pressure has become a main concern during the exploitation of high-temperature, high-pressure, and high-corrosion gas fields. Therefore, establishing a corrosion evolution model is crucial for accurately predicting the service life of casings. In this study, an analytical model describing the corrosion rate of casing steel TP110TS under different CO2/H2S partial pressures and applied stresses was established, combined with the mechanical-chemical effect. The weightlessness method was used to determine the model parameters from the experimental results using a multiple regression. Based on the elasticity, a service life prediction model considering mechanical property attenuation and casing stress fluctuation was established from the assumption of uniform thickness thinning. The effects of internal pressure and CO2/H2S partial pressures on the service life were analyzed. The corrosion rate initially decreased with time. However, the stress increased as the wall thickness decreases from corrosion. The stress-promoting corrosion effect gradually manifested, and the corrosion rate rapidly increased. The higher the internal pressure and H2S/CO2 partial pressure, the shorter was the service life of the casing. In the H2S/CO2 coexistence environment, the influence of H2S partial pressure was more significant than that of CO2.

EXPERIMENTAL STUDY OF THERMODYNAMIC PROPERTIES OF BIOFUEL COMPONENTS

The density () and speed of sound (u) of two main components of biofuels, methyl laurate and methyl stearate, were measured at temperatures from (283 to 353) K and from (313 to 353) K at atmospheric pressure, respectively. An Anton Paar DSA 5000 М sound-speed analyzer, has been used to simultaneously measurements of the density and speed of sound of the methyl laurate and methyl stearate as the primary components of biodiesel fuel. The measured values of density and speed of sound were used to calculate other derived thermodynamic properties such as adiabatic coefficient of bulk compressibility, coefficient of thermal expansion, isothermal coefficient of bulk compressibility, isochoric and isobaric heat capacities, enthalpy and entropy difference, partial temperature derivative of enthalpy, entropy, and the partial specific volume derivatives of internal energy (internal pressure), of the methyl laurate and methyl stearate as a function of temperature. The overall uncertainties (at the 95 % confidence level) of the reference correlations of the density and speed of sound of methyl laurate and methyl stearate are 0.025 % and 0.045 %, respectively.

The analytical solutions of squeezing flow and heat transfer in an horizontal filtering channel

Flow and heat transfer dynamics inside different industrial chambers play a vital role in understanding momentum and heat transfer during industrial operations. Analysis of such flow and heat transfer helps operators to know how the system works. To better understand the filtration process, the current study analytically investigated the internal flow and heat transfer through a porous horizontal filter channel under the influence of a uniform magnetic field while removing unwanted contaminations from the fluid inside the filter chamber. Thus, the novelty of the current study is to advance the filtration process by investigating how the top moving wall, which aims to minimise filter cake formation, affects permeates outflow (the current design). The partial differential equations (PDEs) model representing the internal flow and heat transfer during filtration is transformed into a system of ordinary differential equations (ODEs) using Lie point symmetry reduction without changing the dynamics under investigation. After that, the transformed equations are solved analytically using the perturbation approximation technique. The comparative analysis between the obtained semi-analytical and NDSolve numerical solutions was used to show the correlation of internal flow, temperature, and pressure profiles. The obtained solutions are used to find the best combination of dimensionless parameters that arise from flow and heat transfer dynamics that lead to optimum outflow. Graphical analysis of flow and heat transfer dynamics are used to indicate the combination of parameters that leads to maximum outflow based on scientific evidence. It is observed that, on average, the velocity increases significantly by 122.55% across all cases of Re ranging from 0 to 3.2 at the top permeable wall y=1. This significant increase is due to the motion of the moving wall and fluid injection happening at y=1. The results show that more chamber volume, small pores size, weak injection, weak magnetic force, and less Joule heating are crucial to increase internal temperature and permeate outflow velocity during filtration.

A Simplified Design Method for the Mechanical Stability of Slit-Shaped Additively Manufactured Reactor Modules

Equipment integrity is an essential aspect of process engineering. Design guidelines facilitate the design and production of safe-to-operate and economic devices. Thin-walled, slit-shaped modules form a subgroup of process engineering devices made via additive manufacturing (AM). Being subject to internal pressure, they have lacked design guidelines until now. We derived a user-centered calculation model for such modules with regular internal structures. It was validated with Finite Element Analysis (FEA) and practical pressure tests for which the modules were manufactured additively. The performance of the calculation could be confirmed, and a design graph was derived. Slit-shaped modules with appropriate internal structures can withstand high pressure at a minimum wall thickness, and they are efficiently fabricated. These structures, being pins, fins, lattice, or heat transfer enhancing fluid-guiding elements (FGEs), occupied approximately 10% of the modules’ internal volume.

Thermal creep properties of virgin and irradiated cladding tubes made of Ti-stabilised DIN 1.4970 (15-15Ti) austenitic stainless steel

ABSTRACT This paper presents assessments performed on a large database of virgin material and irradiated material thermal creep data from uniaxial and pressurised DIN 1.4970 Ti-stabilised austenitic stainless steel i.e. EN X10NiCrMoTiB15–15 or ‘15-15Ti’ cladding tubes. The data base incorporates multi-heat data from uniaxial and bi-axial (internal pressure) creep tests conducted during the fast reactor R&D program of the DeBeNe (Deutschland-Belgium-Netherlands) consortium between the 1960s to the late 1980s together with more recent data, for example, from the European projects MATTER and PATRICIA and the EERA JPNM pilot project TASTE. The data comprises of a virgin material data base and a data base with irradiated creep data. The virgin material data comprises of time-to-rupture and time-to-0.2% creep strain in a temperature range of 600–800°C and covers a large range of stresses. The irradiated data base has less data and does not cover all material heats tested for the virgin material properties. The irradiation conditions are also different depending on the test reactor specifics and the irradiation campaign targets. The attained ‘irradiation damage’ in displacements per atom (DPA) for the irradiated materials range from 0.1 up to 38.1. Un-irradiated ‘reference material’ models for tensile strength and creep strength are constructed from the current-state of the art literature data and more recent results from the Sandvik 24% cold worked 1515–Ti cladding tube currently used as the main material batch studied at SCK CEN. The tensile strength model is used throughout the paper for normalizing creep strengths by the tensile properties, needed when applying the Wilshire (WE) creep model. Time factors (TF), stress factors (SF) and temperature ratio factors (TRF) are calculated for different material states for describing the impact of heat treatments, (virgin and irradiated) and irradiation conditions. This initial study targets to give estimates for the thermal creep properties of cladding tubes with a cold work range of 16–24% in a non-annealed state, as it is the preferred option for future designs according to the state-of-the art knowledge base. However, the main bulk of the available data on irradiated material is on claddings with a cold work range of 0-16% with and without annealing and at various levels of irradiation damage, thus leading to the need for estimation by interpolation and extrapolation assuming that irradiation damage levels and trends, e.g. time reduction factors found on a lower cold worked material can also be applied on materials with higher cold work levels. The results of the assessments clearly show relative strength differences between chosen material heats and heat treatments and has enabled constructing simple multilinear models for estimating the life of irradiated material. The models show that low creep test temperatures (and irradiation temperatures), low stress levels, low levels of cold work and high irradiation doses are increasing the detrimental difference between the specific material condition and the reference material. Also, it was found that the general level of life reduction (time factor TF and stress factor SF) for irradiation damaged material failure, in relation to the reference material failure, roughly coincides the corresponding values of time to 0.2% creep strain for virgin material. The estimated ‘failure creep temperature limits’ for 30 000 hours of service are studied and compared for both virgin and irradiated materials at a reference stress level of 1/3 of the tensile strength (at temperature).

Effect of the impeller blade outlet setting angle on the performance of the helical axial-flow multiphase pump

Effect of the impeller blade outlet setting angle on the performance of the helical axial-flow multiphase pump

Building blocks of good governance: Fostering an ethical work climate in public sector organizations

AbstractPromoting an ethical work environment in public‐sector organizations is crucial for good governance, particularly in developing countries that face internal and external pressures to modernize their public service and combat corruption. This study examined the mechanisms by which an ethical environment in public‐sector organizations is enhanced by investigating the role that employee public service motivation (PSM) as well as ethical leadership plays in the workplace. Utilizing first‐hand data collected in 2022 through a survey of public employees working at the Jordanian ministries and public sector agencies, the study showed that public employees in Jordan enjoy a high level of PSM, which was positively correlated with an ethical work environment. This relationship was, however, improved when mediated by ethical leadership, indicating the importance of ethical leadership as an organizational intervention to promote a more ethical workplace. The implications, contributions, and limitations of the study were further discussed.

CFD modelling of Close-Coupled Gas Atomisation (CCGA) process by employing the Euler-Lagrange approach to understand melt flow instabilities

This paper presents a CFD analysis of the melt and flow-field instabilities in a close-coupled gas atomisation process (CCGA) caused by the gas–melt interactions. The melt mass flow is coupled to the atomiser internal pressure, which varies over time due to the unsteady flow field. A two-phase flow of Argon gas and melt particles is modelled using a coupled Euler-Lagrange framework. Three different initial gas-to-melt ratios (GMRs) of 5.5, 2.6 and 1.32 are considered to study the gas–melt interaction. The results show that in the case GMR = 1.32, sustained instability both in the melt and in the flow-field are distinctly observed, resembling physical atomisation process. This melt fluctuation corresponded to an alternating flow-field fluctuation; alternating between open- to closed-wake condition, where the local maxima of the melt corresponded to an open-wake condition, and the local minima of the melt corresponded to a closed-wake condition.

Understanding post-irradiation creep behavior of M5Framatome zirconium alloy

After in reactor use, the nuclear fuel assembly of pressurized water reactors is stored in water and is eventually transported, in a dry cask, to a long-term storage facility or to a reprocessing plant. During transportation in dry environment the fuel rod temperature and internal pressure both increase. This leads to simultaneous creep deformation and annealing of the cladding tubes made of M5Framatome11M5 and M5Framatome are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries. zirconium alloy. This study shows that post-irradiation creep, or heat treatment, leads to the recovery of the radiation induced hardening and also to the recovery of the uniform elongation because of <a>-loop annealing. On the other hand, it is shown that cladding tubes made of M5Framatome alloy exhibit low post-irradiation creep rates, especially at low applied stress. This strain rate is significantly lower than for the unirradiated material and similar to the as-irradiated material, despite the significant <a> loop annealing. The low creep rates are mainly attributed to the Nb-rich nano-precipitates that act as dispersed strengthening particles. These nano-precipitates appear under irradiation and are stable at temperatures up to 450 °C explaining their strengthening effect even after significant annealing.