Pipe Wall Research Articles

Research on Safety of Aero-Engine Oil Pipe Under Heating Conditions Based on Fluid–Solid Thermal Coupling

This paper examines the safety of aero-engine pipelines under different heating conditions. Based on the fire test standard documents, a model of an aero-engine oil pipe was constructed, and its safety under heating conditions that meet the standard was analyzed using fluid–solid thermal coupling. The pipe material was stainless steel 1Cr18Ni9Ti, and the oil inside the pipeline was China RP-3 kerosene. To simulate the different working conditions or pump failure scenarios, various kerosene inlet flow rates were used for the calculations. The results indicate that the pipe wall exhibits an uneven temperature distribution under standard heating conditions. As the kerosene flow rate decreases, the pipe wall temperature rises, and heat transfer deterioration occurs. The increase in the pipe wall temperature reduces the material’s strength, while the uneven temperature distribution generates thermal stress, further increasing the safety risk. When the kerosene flow rate is reduced to a certain level, the equivalent stress in the pipe wall exceeds the material’s yield strength, leading to a high risk of rupture.

Analysis of hydrodynamics and thermal–hydraulic performance of twisted angle fins within an annular conduit

AbstractThis paper investigated the influence of various twisted angles of fin inserts integrated on the inner heated pipe wall of a double-pipe heat exchanger by analysing the thermal–hydraulic performance through numerical simulations. Results showed twisted angle fin (TAF) induced turbulent fluid flow phenomena, generating transverse and longitudinal vortices, along with swirling flow. This collaboration between the vortices and swirling flow effectively prevents heat trapping and enhances heat transfer from the inner pipe wall through the intensive fluid mixing. Despite longitudinal swirling vortices and turbulence significantly enhance local and global heat transfer performance, they led to increased pressure drop. However, TAF twisting reduces pressure drop by streamlining flow. The performance evaluation criterion (PEC) value is a dimensionless quantity that facilitates the comprehensive evaluation of optimal configurations by comparing the increment in Nusselt number and the increment in friction factor. PEC values greater than 1 indicate that the increase in Nusselt number exceeded the increase in friction factor. Among tested configurations, the twisted fin angles of 60° (TAF60) exhibited the highest improvement in Nusselt number and friction factor, also achieving the highest PEC of 1.59712 at Reynolds number of 1194.71. TAF40 and TAF50 were identified as optimal configurations for enhancing the thermal–hydraulic efficiency, with average PEC values of 1.26893 and 1.27030, respectively. Overall, the study indicated a consistent enhancement trend with increasing twisted angles and emphasizes the significant thermal performance improvement of TAF configurations compared to the smooth conduit. Furthermore, the results showed a converging tendency across all TAF configurations in the percentage improvement in Nusselt number and friction factor, as well as PEC compared to the baseline No fin configuration with increasing Reynolds number, suggesting that future improvements in thermal–hydraulic performance are more dependent on geometric angles than fluid flow velocity.

Effect of Pipe Materials and Interspecific Interactions on Biofilm Formation and Chlorine Resistance: Turn Enemies into Friends

Drinking water distribution systems (DWDSs) may be contaminated to various degrees when different microorganisms attach to the pipe walls. Understanding the characteristics of biofilms on pipe walls can help prevent and control microbial contamination in DWDSs. The biofilm formation, interspecific interactions, and chlorine resistance of 10 dual-species biofilms in polyethylene (PE) and cast iron (CI) pipes were investigated in this paper. The biofilm biomass (heterotrophic bacterial plate count and crystal violet) of dual species in CI pipes is significantly higher than that in PE pipes, but the biofilm activity in CI pipes is significantly lower than that in PE pipes. The interspecific interaction of Sphingomonas-containing group presented synergistic or neutral relationship in PE pipes, whereas the interspecific interaction of the Acidovorax-containing group showed a competitive relationship in CI pipes. Although interspecific relationships may help bacteria resist chlorine, the chlorine resistance was more reliant on dual-species groups and pipe materials. In CI pipes, the Microbacterium containing biofilm groups showed better chlorine resistance, whereas in PE pipes, most biofilm groups with Bacillus exhibited better chlorine resistance. The biofilm groups with more extracellular polymeric substance (EPS) secretion showed stronger chlorine resistance. The biofilm in the PE pipe is mainly protected by EPS, while both EPS and corrosion products shield the biofilms within CI pipe. These results supported that dual-species biofilms are affected by pipe materials and interspecific interactions and provided some ideas for microbial control in two typical pipe materials.

Enhanced elastic stress solutions for junctions in various pipe bends under internal pressure and combined loading ([formula omitted] pipe bend, U-bend, double-bend pipe)

Piping systems in nuclear power plants normally operate under high pressure and high temperature. To efficiently manage space within these systems, pipe bends are extensively used. However, the welded joints connecting these pipes may be susceptible to flaws due to weld residual stress, transient loads, and operating environments. When flaws are present in such areas, analytical evaluation of flaws is to be carried out based on fracture mechanics parameters such as stress intensity factor. To calculate the stress intensity factor, distributions of the elastic stress are required. Therefore, this paper presents closed-form approximations of elastic stress in the junction between a pipe bend and a straight pipe under internal pressure. Review of the existing elastic stress solutions for estimating the stresses in pipe bends was carried out analyzing their limitations. Based on those limitations elastic stress solutions for thick to thin wall pipe bends were proposed and were validated against finite element (FE) analysis for thick-wall to thin-wall pipe bends under internal pressure and combined loading (i.e. internal pressure, in-plane bending, out-of-plane bending inflicted simultaneously). 90° pipe bend, U-bend and double-bend pipe configurations were considered and showed good agreement with the FE results exhibiting less than 5.8 % discrepancies. The accuracy of the elastic stress solutions for pipe bends provided in the existing code are summarized and validated in the appendix as well.

Entropy generation analysis of unsteady MHD nanofluid flow in a porous pipe

This article presents a numerical investigation into the entropy production of nanofluids flowing through a porous medium in a permeable conduit, focusing on water-based solutions containing Titanium Carbide (TiC) and Silicon Carbide (SiC) nanoparticles. These nanoparticles are selected for their heat transfer properties. The flow system's governing equations are developed and solved using the Runge-Kutta-Fehlberg method. The study examines the influence of key nondimensional parameters, including the solid volume fraction of nanoparticles, radiation parameters, and Reynolds number, on temperature, velocity profiles, and entropy generation. The results show that Silicon Carbide-water nanofluids perform efficiently in terms of heat transfer and entropy minimization. Additionally, Silicon Carbide exhibits low skin friction at the pipe wall, with this effect increasing as the solid volume percentage of nanoparticles rises. The study also indicates that irreversibility due to heat transfer becomes more significant near the pipe wall as the solid volume fraction decreases and increases with higher radiation parameters and Reynolds number. These findings are presented graphically and in tabular form to illustrate the physical significance of the problem.

Detection of Two-Phase Slug Flow Film Thickness by Ultrasonic Reflection

Slug flow is a common phenomenon in closed pipes, occurring in two-phase flow where liquid and gas phases mix, impacting the custody transfer or the efficiency of chemical reactions. This study aims to detect and analyze slug flow film thickness in two-phase flow, providing detailed structural flow information. The ultrasonic or Doppler reflection method is employed to identify slug flow and detect detailed thickness. Additionally, electrical resistance tomography (ERT) is used to image and confirm the presence of slug flow. A high-speed camera records the slug flow's shape in real time, validating its existence. The ultrasonic reflection method offers high accuracy, with a measurement error rate of less than 1% based on experimental results. The study uses a homogeneous block calibration method to measure slug flow thickness. Graphical results reveal clear differences between the slug flow regime, inner pipe wall, and outer pipe wall, with the first echo of slug flow being easily observable. The accuracy of results is attributed to the combination of FPGA (Field-Programmable-Gate-Array) instruments and measurement methods, showcasing the study's novel approach. This research introduces a new perspective or novelty on slug flow in multiphase flow studies, highlighting an innovative method for detecting film thickness.

Backward motion suppression in space-constrained piezoelectric pipeline robots

In response to the current challenges of detecting micro pipelines, a micro pipeline robot based on the principle of piezoelectric inertia stick-slip drive was proposed in this paper, which can be effectively applied to the detection and maintenance of micro pipelines. However, during the analysis of the robot's displacement trajectory, it was observed that using inertial drive could cause the backward motion of the robot. This may adversely affect the accuracy and stability of the robot's operation within the micro pipelines. Therefore, a novel control method is derived from the original pipeline robot structure. By affixing piezoelectric sheets to the driving feet of the robot to adjust their deformation and subsequently employing collaborative control of piezoelectric sheets and piezoelectric stacks to regulate friction between the driving feet and the pipe wall, the backward motion of the robot was effectively mitigated. Compared to existing backward motion suppression methods, the approach proposed in this paper has a minimal impact on the actuator's size, allowing for flexible adaptation to various space-constrained applications, while also offering the advantage of a simple control strategy. After determining the structure and working principle, deformation analysis of the driving foot and dynamic simulation analysis of the driving system were conducted. These analyses provide insights into the relationship between mechanical and electrical parameters and output performance within the driving system, thereby validating the feasibility of the control method. Subsequently, a prototype was fabricated, and its output performance was tested. Results demonstrate that this control method can effectively suppress inertial backward motion, achieving a suppression rate close to 100 %. This research presents a novel idea and methodology for mitigating the backward motion of piezoelectric inertial stick-slip actuators with driving foot structures.

Asymptotic solutions for heat transfer and stresses in functionally graded porous sandwich pipes subjected to nonuniform pressures and thermal loads

In this work, thermomechanical behaviors of temperature-dependent (TD) functionally graded porous (FGP) sandwich pipes subjected to nonuniform pressures and thermal loads are studied. Because the material properties are variable across the wall of the pipe, seeking exact solutions for the pipe is almost impossible. We use a slice model where the pipe is partitioned into plenty of annular slices and each slice is assumed to have uniform material properties. First, the nonlinear heat transfer along the pipe wall thickness is obtained by introducing an iterative procedure. Then, by using the Fourier series, the mechanical problem is decomposed into axisymmetric and nonaxisymmetric parts. Both the parts can be treated by the state space method and transfer matrix method, and then the superposition principle is used to obtain the displacement and stress distributions. The model results are in good consistency with those obtained from the numerical simulation and those reported in the literature. Finally, an FGP sandwich pipe is considered to discuss the effects of the temperature dependence of material properties (TDMP), power-law index, porosity, and pressure distribution on its thermomechanical behaviors.

Research on digital vibration model of typical components in pipe system

The spatial distribution of pipe system is complex, long span and multi-point elastic support, so vibration analysis of pipe system is required in the pipeline design. This paper takes the pipe system as a typical component, based on the Timoshenko beam model, establishes a dynamic procedure for straight pipe elements that considers the axial flow rate of fluid, the pressure on the pipe wall, the Poisson coupling effect of fluid and pipeline structure, and the axial, transverse and torsional vibration. Through Laplace transform, the frequency simplified dynamic model is established. And the frequency transfer matrix model of straight pipe elements and the boundary constraint matrix of common boundary (such as fixed support) is established. Finally, the frequency domain transfer matrix model of different pipeline elements are set to the overall transfer matrix of the flow pipe system, providing a convenient means for rapid optimization of pipe system vibration.

Study of the acoustic transmission characteristics of a pipe opening with a baffle considering structural elasticity

Noise can radiate to the external environment through pipe openings. The acoustic transmission characteristics of the pipe openings greatly affect the efficiency of sound radiation. In fluid-filled elastic pipelines, the sound radiation is significantly influenced by the coupling between the fluid and the elastic structure. The elastic structure studied in this paper includes the pipe wall, as well as the baffle attached to it. Waveguide analysis of fluid-filled elastic pipelines shows that the coupling results in the presence of several types of propagating waves within the pipeline, even bellow the cut-on frequency. To evaluate the acoustic transmission characteristics of the pipe opening, it is necessary to separate the components of the lowest-order fluid type wave from these waves. A multi-case approach is developed to separate the target waves successfully, thereby obtaining the characteristics of the pipe opening. The accuracy of the proposed method is verified, and the impact of structural elasticity is analyzed. Subsequently, the effects of the dimensions of the baffle are discussed.

Analysis of the gas pipeline defects formation mechanism as a result of arc discharge impact on the pipe wall

The article presents an analysis of the formation possibility through defects in a gas pipeline as a result of short-term exposure to an arc discharge. The results of metallography, electron microscopy, elemental analysis, as well as the modeling results, confirming the formation possibility through defects in a 7 mm thick gas pipeline wall during an exposure to an arc discharge of less than 2 seconds are presented.

A Mesh Convergence Study for 2D Axisymmetric Pipe Wall Thickness

A meshing size study is essential for any simulation, as it affects the accuracy of the results by approximating the real-world geometry. This paper presents a detailed mesh convergence study for a 2D axisymmetric pipe model. The model incorporates a one-quarter cross-section due to the axisymmetric nature of the pipe. Four pipe wall thicknesses were investigated: 3.40 mm, 7.11 mm, 10.97 mm, and 18.26 mm. The results revealed a significant advantage for simulations involving thin pipes. They achieved convergence, a state with stable solution values, by utilizing a less dense mesh, leading to reduced computational time. This trend was exemplified by the fact that a thinner pipe with thickness, t = 3.40 mm has converged with only 8 mesh elements, whereas a significantly thicker pipe, t = 18.26 mm necessitated 14 elements for convergence. This suggests that more complex geometries, with intricate details, may require a larger and denser mesh for convergence, leading to increased computational time. In conclusion, the mesh convergence study confirms that the finite element analysis (FEA) model has achieved a converged solution.

Prediction of the Strength of the Concrete-Filled Tubular Steel Columns Using the Artificial Intelligence

Introduction. The machine learning algorithms are highly promising for predicting the load-bearing capacity of the building structures. The paper aims at building the predictive models for calculating the strength of the concrete-filled steel tubular (CFST) columns to enable a highly accurate prediction of the ultimate loads for the entire possible range of parameters affecting the load-bearing capacity of the eccentrically compressed columns.Materials and Methods. The article studies the eccentrically compressed short concrete-filled steel tubular (CFST) columns of circular cross-section. Model input parameters: column outer diameter, pipe wall thickness, yield strength of steel, compressive strength of concrete, relative eccentricity. Output parameters: the ultimate loads without taking into account and taking into account the random eccentricities. The models were trained on synthetic data generated based on the theoretical principles of the limit equilibrium method. Two machine learning models were built. When training the first model, the ultimate loads were determined at a given eccentricity of the longitudinal force without taking into account the additional random eccentricity. When training the second model, the additional random eccentricity was taken into account. The effect of the features on the model predictions was assessed using the Feature Importance function. The Optuna method was used to select the hyperparameters. The machine learning models were implemented in the Jupiter Notebook environment using the Gradient Boosting learning method. The total volume of the training sample was 179 025 samples.Results. The importance of the features most affecting the predictive values of the model have been determined. For both models, the outer diameter of the column and the relative eccentricity have proved to be the most important features, which is consistent with the existing experience of designing and calculating such structures. Optimisation of the hyperparameters using the Grid Search method enabled getting the improved results. The high accuracy of prediction has been ascertained by the low values of the regression metrics: MSE = 9.024; MAE = 9.250; MAPE = 0.004 — for the model built without taking into account the additional random eccentricity; MSE = 8.673; MAE = 8.673; MAPE = 0.004 — for the model built taking into account the additional random eccentricity.Discussion and Conclusion. The developed Gradient Boosting models for predicting the ultimate loads of the eccentrically compressed short concrete-filled steel tubular (CFST) columns of circular cross-section, both without taking into account and taking into account the additional random eccentricities, have demonstrated high accuracy and stability of prediction, they can be applied for assessing the strength of the columns during design and construction, which will reduce the time and resources involved in physical testing. In the future, it is planned to expand the data range by including other materials, different cross-section geometries of the columns and a slenderness parameter, which may improve the generalization ability of the model.

One-dimensional model for vertical hydraulic transport of high-concentration mineral particles

A novel model is proposed for analyzing high-concentration granular flow systems comprising equally sized spherical particles within vertical, long straight pipelines. This model is specifically tailored for simulating the vertical hydraulic transport of ore particles in marine mining projects. The proposed model treats the granular system akin to a pseudo-fluid and operates through three mechanisms. First, fluid characteristics of the granular system are derived from particle–particle collisions. Second, the resistance exerted by the pipe wall on the granular system is calculated based on the momentum loss of particles during particle–wall collisions. Third, the interaction between individual particles and the surrounding fluid is transformed into an interaction between the carrier fluid and the pseudo-fluid. Additionally, the present work develops a dedicated numerical format and iterative method for solving the one-dimensional two-fluid governing equations. The one-dimensional (1D) model notably enhances computational efficiency and facilitates accurate tracking of high-concentration particles over extended distances within straight pipelines. Notably, the proposed 1D model demonstrates a high degree of predictive accuracy when compared against experimental data as well as results from computational fluid dynamics and discrete element method simulations.

Numerical study of swirl core-annular flow and factors influencing pressure drop in vertical pipelines for oil-water two-phase flow

As oil field production progresses, the water content of the produced fluid increases and wax deposits form on the pipe wall as the crude oil is transported vertically through the pipeline. This causes the cross-sectional area of the pipeline to decrease, the flow resistance to increase and the pipeline pressure to decrease. As a result, production from oil wells declines and extraction costs rise. Therefore, in the current study, a vortex structure is utilized to generate a vertical core-annular flow for oil production and transportation in high-water-content oil wells. This study uses computational fluid dynamics (CFD) software to investigate the influence of various oil properties on the oil phase distribution and pressure drop in core-annular flow in vertical pipes. The findings demonstrate that the ring-forming effect of the core-annular flow increases with larger oil droplet sizes and lower oil phase densities, while it becomes weaker with higher inlet oil phase volume fraction and lower inlet velocities. As the size and density of the oil droplets grow and decrease, respectively, the pressure drop reduces. On the other hand, the pressure drop increases with higher inlet oil phase volume fraction and viscosity. When the oil droplet size is greater than 0.2 mm, the density is less than 850 kg/m3, the oil phase volume fraction is less than 30% and the inlet velocity is greater than 1 m/s, the annular flow works better. When the inlet oil phase volume fraction is above 30%, and the ring formation effect decreases significantly. The utilization of swirl core-annular fluid significantly mitigates the pressure drop in pipelines compared to pure oil transport downhole, rendering it highly suitable for conveying crude oil in high-water-content oil wells.

Study on the inlet backflow characteristics and particle deposition of screw mixed-flow deep-sea mining pump under small flow conditions

Abstract When a screw mixed-flow deep-sea mining pump operates under small flow conditions, significant backflow occurs at the impeller inlet and in the inlet pipe, which seriously affects the pump performance. To investigate this backflow characteristic, this paper presents a numerical study of the internal flow field of the mining pump based on the CFD-DEM coupling method. The flow state at the impeller inlet, the velocity distribution law in the inlet pipe, and the particle motion state under the flow rate condition of 0.52Qd are obtained. The results show that, when the pump operates under small flow conditions, the leakage from the tip gap of the impeller head causes a screw high-speed backflow with the same rotation direction as the impeller on the wall of the inlet pipe. The backflow intensity attenuates as it propagates towards the pump inlet. The backflow mixes with the main flow in the middle of the pipe and reaches a balanced state, which causes the particles to deposit here. The deposition process can be divided into a formation stage and a stable stage. When the particles in the middle of the pipe reach the stable stage, their shape and position become stable. The velocity pulsation of the monitoring points near the wall is periodic, and its pulsation frequency is the same as the impeller rotation frequency.

METHODS OF MINIMIZING THE RISKS OF CAVITATION IN UNDERWATER PIPELINES

In the article, the classification of various loads that affect underwater pipelines during construction and operation is given. Offshore pipelines are subject to bending moment, hydrostatic pressure, tension, waves, and currents. In addition, the issues of determining the load that the pipeline can withstand or, conversely, the thickness of the pipe wall corresponding to the given load were also considered. At great depths, where the external pressure (hydrostatic pressure) is greater than what can be released, the pipeline is crushed, and the accident propagates along the length at a high speed. Therefore, it is recommended to protect pipelines in deepwater basins from possible crushing. Also, an overview of cavitation is given, and the conditions and consequences of its occurrence, currently known as a hydraulic phenomenon, are listed. It is noted that despite the negative effect of the cavitation factor, it is possible to use it for useful purposes. It is also shown that such effects can be applied in perspectival technologies by preserving them in new nanoobjects at meso and microscales.

Development of geopolymer and cement-based shotcrete mortar: Impact of mix design parameters and spraying process

Shotcrete mortar is used in various construction works, including repair, tunneling, mining, and slope stabilization, among others. Traditionally, cement is used to produce shotcrete mortars with high viscosity, flowability, and early strength. Geopolymers (GP) have the potential to replace cement in shotcrete mortars, owing to their ability to reduce the material’s environmental footprint without compromising performance. This investigation assesses the feasibility of utilizing fly ash and blast furnace slag-based GP mortars produced with dune sand in shotcrete applications while comparing them to cement-based mixtures. The GP and cement-based shotcrete mortars were designed to have similar yield stress values. The evaluated properties included the initial flow, thickness layer, rebound material, rheological properties, setting time, compressive strength, ultrasonic pulse velocity, and pull-off bonding strength. Test results showed direct relationships between the yield stress and initial flow values, as well as between the buildup thickness and plastic viscosity, revealing that GP mortars were suitable for shotcrete applications, specifically those produced with flow values of 18.5 cm or less. GP mixtures produced with higher slag content than fly ash, higher sand content compared to binder, higher SH molarity, and lower solution content achieved higher buildup thickness owing to their higher viscosity. In the second phase, the performance of four mixes with different initial flows was assessed at various pumping flow rates and distances between the wall and machine pipe nozzle. The findings confirmed that these spraying parameters are crucial to improve the shotcrete performance of GP mortar with varying fresh behaviors.

Experimental study on high temperature gaseous hydrogen fluoride corrosion of boiler water-cooled wall pipes

ABSTRACT Hydrogen fluoride (HF) corrosion of boiler water-cooled wall pipes at high temperature hinders the co-disposal of fluorinated hazardous wastes and coal by combustion. In this paper, common water-cooled wall pipes (15CrMoG and 20G) were utilized to perform gaseous HF corrosion experiments at high temperature on a horizontal tube furnace. The effects of temperature on HF corrosion of different water-cooled wall pipes in 0.2% HF were investigated. Corrosion kinetics curve was obtained by calculating the mass increase due to corrosion. The microscopic morphology and physical phase composition of water-cooled wall pipes after HF corrosion were analyzed. The corrosion resistances of the two water-cooled wall pipes decrease with increasing the temperature. The corrosion weight gain curves of 15CrMoG and 20G at 550 ℃ are ΔW 1.9144 = 0.2100t and ΔW 1.8356 = 0.1344t, respectively. The average corrosion rates of 15CrMoG and 20G are 0.0177 and 0.0125 mg/(cm2·h), respectively. The corrosion resistance of 15CrMoG is superior compared to 20G. The HF corrosion at high temperature consists of non-alternating fluorination and oxidation of the metal matrix. This study is of great significance for the protection of boilers with HF corrosion at high temperature.

Study on the influence of slit pipe wall thickness on the rock breaking effect of slit charge explosion

Study on the influence of slit pipe wall thickness on the rock breaking effect of slit charge explosion