Critical Pipe Research Articles

Optimization of software-controlled machining of critical pipe fittings

The quality requirements for pipeline fittings for NPPs and oil and gas facilities have become more stringent recently, which is related to ensuring their safe operation life. When manufacturing parts using subtractive machining technologies, special importance is attached to accuracy indicators of linear-angular dimensions and surface shapes. This study examines ways to optimize dimensional turning using the example of a “separator” part on a multifunctional CNC turning and milling center MULTICUT 630/2000S. Operations of designing and optimizing the production of parts are increasingly determined by the results of simulation modelling, virtual models, which, in fact, are an integral part of technological processes. In this work, simulation modelling is performed on simulators with CNC Sinumerik 810/840D/Operate Turn. This procedure is a simplified version of the Weiler-Atherton clipping algorithm as applied to stock removal turning. In addition to the algorithm, additional modules for dynamic corrections of control programs are proposed in order to guarantee the requirements of design documentation for accuracy in the conditions of a dynamic SPID system: machine – fixture – tool – part. The cutting speed, depth of cut and tool feed in turning have the greatest influence on the stock removal process from the technological control parameters. Modules of dynamic corrections of control programmes allow to estimate quite accurately the influence of control factors in turning (cutting speed, depth of cut and feed) on cutting force and machining accuracy.

A graph-based method for identifying critical pipe failure combinations in water distribution networks

ABSTRACT Water distribution networks (WDNs) are critical infrastructures prone to vulnerabilities which lead to failures. Identifying vulnerable components, especially multiple pipe failure combinations, is crucial for effective management and ensuring high reliability. Hydraulic simulations are commonly used for analysing the criticality of WDN, but are time-consuming and highly data-reliant, limiting the number of testable combinations. To address these limitations and constraints, a graph-based method is proposed to quantify the impact magnitude of multiple pipe failure scenarios on performance, enabling the identification of critical combinations. The proposed graph-based approach utilizes structural and topological characteristics of WDNs as well as spatial demand distribution to replicate hydraulic behaviour. The accuracy of the approach is assessed by testing it on three case studies with various pipe failure combinations, and the results are compared with hydraulic analyses. The results demonstrate a strong correlation (Spearman coefficient > 0.75) between graph-based ranking and state-of-the-art hydraulic-based ranking. Additionally, the method exhibits a significant computational gain factor of greater than 30 compared with the hydraulic-based method, rendering it valuable for actively exploring a wide range of critical pipe failure combinations and devising countermeasures. Furthermore, a hybrid-based method that integrates both the graph and hydraulic-based methods is proposed for enhanced accuracy and robust assessments.

Dynamics of inclined simply supported piping system subjected to slug flow

In this paper, the linear and nonlinear dynamics of a simply supported inclined piping system conveying slug flow are investigated, by using a dimensionless approach. A method is proposed for constructing equivalent flow parameters in order to achieve a dimensionless model equation. The validity of this method has been verified through the literature data. The effects of superficial velocities and inclined angle on the stability of the system, as well as post-instability nonlinear dynamical behaviors, are investigated. The linear analysis results showed that the superficial gas velocity stabilized the system at lower values, but had a destabilizing effect at higher values. The main reason is the reduction in system mass resulting from the increase in superficial gas velocity. The superficial liquid velocity negatively impacted the system's stability, necessitating evaluation through the critical pipe length. The nonlinear analysis results showed that the inclined system, in the absence of modal coupling occurrence, may exhibit chaotic behavior due to its inherent nonlinearity. The system stability could be regained as the superficial gas velocity increased following self-weight instability under low superficial gas velocity conditions. This work is helpful for the design of operating parameters to ensure the safety of the piping system.

Thermal Mixing and Flow Characteristics Study in a T-Junction

The objective of the current paper is to investigate the turbulent flow characteristics, thermal mixing behavior, and backflow features of coolant fluid in a T-junction using three-dimensional numerical simulations. The impact of critical flow parameters and different branch pipe axial and transverse incident angles on thermal mixing performance are explored as a function of momentum ratio. The investigation identifies the impact of jet flow, deflection flow, and wall jet flow patterns. The results reveal that the upside backflow of T-junction is more significant for a lower momentum ratio (<0.32) and decreases with higher momentum ratio (0.32 < momentum ratio < 2.7). The efficiency of thermal mixing is considerably improved by changing the incident angle and momentum ratio. Thermal mixing length decreases by ∼39%, 28%, and 21% as compared to the reference case. The current findings will help researchers to understand flow behavior and thermal mixing in a T-junction. It is also useful in high-temperature engineering applications for the evaluation of thermal cracking and safety management.

Study on the motion patterns of shallow-embedded pipelines in sand

Pipe-soil interactions are a crucial consideration in the realization of shallow-embedded pipelines’ in situ stability, and the choice of pipe-soil interaction model is correlated with the distinction between “light” and “heavy” pipe motion patterns. Based on the difference in the motion pattern of a shallow-embedded pipeline in sandy soil after a breakout, a numerical model of pipe-soil interaction is constructed. The influencing factors of different motion patterns are studied, while taking into account the shear expansion or shrinkage characteristics of sand. Accordingly, a method of discriminating pipeline motion patterns is proposed. The results show that the motion pattern of a shallow-embedded pipeline in sandy soil depends on the relative weight of the pipe and soil bearing capacity, that the smaller the embedment, the easier the “heavy pipe” motion pattern appears, and that the critical pipe weight required for “heavy pipe” motion increases with initial sand density and pipeline embedment depth.

Machine learning‐based prediction of the seismic response of fault‐crossing natural gas pipelines

AbstractHerein, we utilized machine‐learning (ML) and data‐driven (regression) techniques to tackle a critical infrastructure engineering problem—namely, predicting the seismic response of natural gas pipelines crossing earthquake faults. Such a 3D nonlinear problem can take up to 10 h to solve by performing finite element analysis (FEA), considering the length of the pipeline and a large number of pipe and soil elements. However, the ML and data‐driven techniques can learn the projection rule of input‐output and predict the pipeline response instantaneously given a set of input features. In addition, the well‐trained ML model can be implemented for regional‐scale risk and rapid post‐event damage assessments. In this study, the input for ML comprised approximately 217K nonlinear FEAs, which covered a wide range of combinations of soil, structural and fault properties and yielded critical pipe strain responses under fault‐rupture displacements. We adopted various regression models and physics‐constrained neural networks, which can accurately and rapidly predict the tensile and compressive strains for a broad range of probable fault‐rupture displacements. Performances of various ML and conventional statistical models were systematically examined. Not surprisingly, neural networks exhibited the best performance for this multi‐output regression problem, in whichR2 &gt; 0.95 was achieved for a wide range of fault displacement (FD) levels. Further, we used the trained neural network with 14.5 million Monte‐Carlo‐generated input samples to predict the maximum tensile and compressive strain curves of pipelines. This new dataset aimed at filling the missing input‐output points from the 217K FEAs, and improved the accuracy of the prediction of probability of failure for natural gas pipelines under FD hazards.

Graph method for critical pipe analysis of branched and looped drainage networks.

Enhancing resilience of drainage networks is a crucial practice to protect both humans and nature. One way to enhance resilience is to identify critical parts of drainage networks for targeted management and maintenance strategies. While hydrodynamic modelling approaches for identification are computationally intensive, in this study, a novel method based on complex network analysis is used to determine the most critical pipes in a benchmark and a real network of an Alpine municipality. For evaluation, the results of the proposed graph method are compared with hydrodynamic simulations in terms of accuracy and computational time. Results show that the proposed method is very accurate (R2 = 0.98) for branched benchmark network while the accuracy reduces slightly for the more complex real network (R2 = 0.96). Furthermore, the accuracy of the proposed method decreases with increasing loop degree and when the system is pressured with higher return period rainfall. Although the outcomes of the proposed method show slight differences to hydrodynamic modelling, it is still very useful because the computational time and data required are much less than a hydrodynamic model.

Fluid flow and thermal performance of the pulsating heat pipes facilitated with solar collectors: Experiments, theories and GABPNN machine learning

Solar energy could be effectively exploited and transferred by the solar collectors, where thermal transport efficiency was inhibited by actual operations and applications. In present research, solar collector combined with pulsating heat pipes (PHP) was proposed to enhance solar energy conversion and management. Fluid temperature oscillation, flow patterns and motions, heat transfer mechanisms inside present facility were comprehensively investigated, which aimed to suitably determine the flow stability of working fluid for PHPs, such that the whole system performance could be fully optimized. Firstly, an experimental investigation was comprehensively conducted to obtain the flow motions, temperature oscillation, and thermal resistance of PHPs, under multi-parameter conditions. Our results indicated that heat transfer performance was promoted with an increase in thermally driven force, accompanied by which low frequency with “small amplitude” transformed to high frequency with “bulk amplitude”. In addition, filling ratio of 25% even a minimum input power generally results in dry-out phenomena, superior liquid-vapor patterns and heat transfer performance were observed as filling ratio was 60%. Following that, theoretical modeling results confirmed that, within the critical pipe diameter, larger saturated vapor pressure and lower surface tension were significantly beneficial for the application of PHPs-solar collector. Considering dimensionless parameters and experimental data, Genetic Algorithm-Back Propagation Neural Network (GA-BPNN) was further built to predict the heat transfer performance of PHPs, which was in great agreement with the experimental data. Optimal filling ratios were further confirmed depending on the best Ku performance, within average deviation being no more than 10%. Present theoretical and experimental researches could facilitate the optimization and application of PHP- solar collectors, greatly exploiting solar energy for buildings.

Analysis of critical pipe break sizes leading to reactor pressure vessel liquid level collapse and core uncovery with APROS

Collapse of liquid level in reactor pressure vessel (RPV) and uncovery of core in typical pipeline rupture accidents, such as steam generator tube rupture (SGTR), main steam line break (MSLB), and loss of coolant accident (LOCA) for pressurized water reactor (PWR), may occur. This study used APROS to establish a full-scale simulation model of VVER440 reactor and evaluated different break sizes that can lead to RPV liquid level collapse and core uncovery during these accident processes. It is demonstrated that in SGTR accident, the liquid level in RPV collapsed under the condition of four or more heat transfer tube ruptures without the risk of core uncovery in all analyzed cases. In the MSLB accident, RPV liquid level collapse and core uncovery were absent due to the integrity of the primary circuit. In the LOCA accident, the RPV liquid level collapsed under a break size of 0.5% of pipe area (PA) of cold and hot leg. Notably, core uncovery occurred when the break area was 1.8% of PA in the cold leg and 65% of PA in the hot leg. The time required until core uncovery was earlier in the cold leg than that in the hot leg.

Fractality in water distribution networks: application to criticality analysis and optimal rehabilitation

ABSTRACT Fractals have been identified as a common feature in many natural and artificial networks that exhibit self-similarity of the topological patterns, i.e. different parts of the system have similar structures to each other as well as to the whole system. This study investigates the fractality in water distribution networks (WDNs) and the application of the fractal property in WDNs analysis. Specifically, we explore the existence of fractal topological patterns in eight real-world WDNs of different complexities by using the box-covering algorithm. The results demonstrate all of the studied WDNs are fractal. Moreover, the application of the fractal property is demonstrated via critical pipe identification and optimal rehabilitation of benchmark real-world WDNs. All results show that the fractal-based approach can achieve better or equally good solutions compared with conventional methods in a much more efficient way, e.g. via automation of some processes or significant reduction in the search space/components to consider.

Modeling of mechano-electrochemical interaction at a corrosion defect on a suspended gas pipeline and the failure pressure prediction

Suspension effect poses a big threat to the integrity and safety of corroded pipelines. In this work, a finite element (FE) based multi-physics field coupling model was developed to determine the mechano-electrochemical (M-E) interaction at an external corrosion defect on a suspended X100 steel pipe and predict its failure pressure. Theoretical calculations were used for model validation. Parameter effects including the defect location on the pipe, geometry of the defect, suspension length and pipe burial depth were determined. Results demonstared that, generally, the M-E effect at corrosion defect caused an increased stress concentration and anodic current density (i.e., corrosion rate), decreasing the failure pressure of the pipeline. The effect became more apparent when the pipe was in suspension. Both the stress and the anodic current density at the corrosion defect were dependent on the defect geometry, especially the defect depth. When the depth was up to 40% of pipe wall thickness, the von Mises stress exceeded the yield stress of the steel, causing local plastic deformation. A critical defect length of 20Dt (D is the outer diameter of the pipe and t is pipe wall thickness) existed, below which the von Mises stress and the anodic current density at the corrosion defect increased with increased defect length. When the defect length exceeded the critical value, the effect was not obvious. An increased suspension length of the pipe would elevate the local stress and anodic current density at the corrosion defect, reducing the failure pressure of the pipe. A critical pipe burial depth of 2.5 m was identified, exceeding which the failure pressure of the pipe decreased rapidly with the increased burial depth. When the burial depth was smaller than 2.5 m, the effect was marginal. The location of the corrosion defect on the pipe did not affect the local stress, anodic current density and failure pressure at an appreciable level, and could be ignored in defect assessment on suspended pipelines.

Analysis and numerical modeling of subcooled boiling in energy systems in vertical porous channel

Boiling phenomena are interested in many fields of engineering such as piping and cooling electronic systems. Usually, the phase change through the heat transfer process is avoided as it makes the fluid flow unstable and complex. In the current study, the effect of using porous media in the channel to control the thermo-hydraulic characteristics of the system is studied. To do this aim a steady-state one-dimensional system of equations is solved by numerical method. The gas and liquid Navier–Stokes equations coupled with energy equations are solved simultaneously. The developed method validated with a well-known benchmark problem and the comparison shows a good agreement. The results show that Sauter bubble diameter, forces on the cross-sectional area of fluid, Froude number, fluid wall forces, velocity of mixture, Reynolds number of vapor, fluid velocity, square root of Froude number divided by Weber number, base volume fraction, vapor volume portion, maximum vapor volume portion, critical vapor volume fraction decrease by an increase in Darcy forces, while mean root square of the applied force over the cross section of fluid and heat transported by thermal radiation increased by an increase in Darcy friction up to 1000. The porous media parameters have negligible effects on Eotvos number, speed of sound, liquid Reynolds number, bubble departure frequency, convection heat transfer coefficient, and critical pipe diameter.

Significant variables for leakage and collapse of buried concrete sewer pipes: a global sensitivity analysis via Bayesian additive regression trees and Sobol’ indices

Identifying key variables that influence crack formation in buried concrete sewer pipes and impact their structural integrity is crucial for evaluating the leakage and collapse vulnerability of these underground structures. The present study performs a comprehensive global sensitivity analysis for these critical pipe responses considering various uncertainties associated with material properties and loading. A high-fidelity three-dimensional nonlinear Finite Element (FE) model of a typical pipe is developed and used to capture pipe behavior. Considering the significantly high computational demand of the generated FE model, a surrogate model using Bayesian Additive Regression Trees (BART) is developed to accurately approximate input-output relationships in this high-dimensional problem. Significant variables are subsequently determined via a global sensitivity analysis based on Sobol’s theorem through the application of Markov Chain Monte Carlo simulation to the trained BART model. Results indicate that concrete and backfill soil properties and variables associated with truckloads contribute significantly to the variation of key pipe responses, thereby affecting the likelihood of leakage and collapse. Findings of this study can benefit the design and management of sewer pipes in large wastewater networks and significantly reduce the complexity of assessing the reliability of sewer pipes.

Stress and strain analysis of buried PE pipelines subjected to mechanical excavation

With the rapidly development of urbanization progress, various pavement constructions tend to be the primary threat to the structural integrity of buried pressurized polythene material pipes. Moreover, the excavation damage of the third-party interference is the main cause of buried pipe's failure. Thus, in the presented study, a validated finite element model was established to characterize the failure behavior of buried PE80 pipes under excavation by the hydraulic excavators, influence of various factors, such as the pipe diameter, pipe thickness, internal pressure, tooth size, excavation position, on pipeline failure behavior were elaborated in detail. Results show that the excavation load could induce large plastic deformation on PE pipes, which suggested that strain-based criterion is more suitable comparing with the stress based criterion for the failure assessment of PE pipes. It also indicated that the excavation load generally give rise to certain strain in the contact area between pipes and bucket teeth, which locates exactly at two sides of the end of the contact area. Besides, relative small deformation would also be induced on both sides of pipes. Results indicate that the increase of internal pressure could enhance the ability of pipes to resist the excavation load. Pipe thickness had a significant effect on the critical resistance, the increase of pipe thickness can dramatically improve the ability of pipeline to resist deformation. Decreasing the pipe diameter or increasing tooth length, tooth width can also effectively increase pipe's critical resistance. As for the excavate position, the simulation revealed that the critical load reached the minimum value when the excavate angle was 30° or the excavation offset distance was 0.3D. In addition, a prediction equation for the critical pipe resistance force of PE80 pipelines under the excavate load was derived based on numerical results and regression analysis. Good agreement was achieved between the proposed method and the numerical results.

Influence of the vent pipe diameter on the discharge capacity of a circuit vent building drainage system

Experiments on different vent pipe diameters (nominal diameters of 100, 75 and 50 mm; DN100, DN75 and DN50, respectively) in a full-scale circuit vent building drainage system were conducted in a 60 -m high structure, and the wastewater discharge capacities as a function of vent pipe diameter were measured. Critical pipe pressures, water seal losses of sanitary fixtures and air flow rates were measured. The ultimate pressure values in pipes on lower floors were larger than those in pipes on higher floors using DN100 and DN75, which was opposite to the results with DN50. A positive correlation between the ultimate pressure values and floor heights, as well as between ultimate pressure values and water seal losses, was found for DN100 and DN75. The maximum discharge flow of the three systems using DN100, DN75 and DN50 vent pipes was 17.0 L/s, 14.0 L/s and 7.5 L/s, respectively. Nevertheless, in China, the maximum wastewater discharge capacity in a circuit vent system adopting a DN100 vent pipe connected to a DN100 drainage stack in tall residential buildings is 11.5 L/s according to the Code for Design of Building Water Supply and Drainage. Thus, the vent pipe diameter DN75 can fully meet the design requirements of drainage systems for high rise buildings in China. The engineering cost associated with material expenses for building drainage systems can be minimised by optimising the size of vent pipe based on required capacity rather than using a single size universally. Practical application: The engineering cost associated with material expenses for building drainage systems can be minimised by optimising the size of vent pipe based on required capacity rather than using a single size universally.

Reconsideration of the friction factor data and equations for smooth, rough and transition pipe flow

The key element in design of pipelines is the friction factor estimation. After the brief review of the experimental data and friction factor correlations for isothermal single phase flow, we have checked the validity of well-known correlations through statistical criteria. During this process it was statistically proved that some of the well-known and permanently cited friction factor equations can be improved. Moreover we have prepared, for practical engineering purposes, equations that cover the entire range of laminar, critical and turbulent pipe flow.

Laminar-turbulent transition in the near field of the jet at the instability regime of the jet source

The paper presents the results of an experimental study of the hydrodynamics of jets flowing from long tubes at low Reynolds numbers. The main attention in the research is given to the mechanism of interaction between pipe and jet instability, which results in a vortical motion in several spatial regions. In the experiments we used Hilbert-visualization, high-speed visualization, and measurements with a hot-wire anemometer. The subsonic gas jet flows into the air space from a long tube with a diameter of 2, 3.2, and 5 mm within the Reynolds number range of 200-6700. Air and Freon-22 were used as the working gases. The critical pipe Reynolds numbers are characterized by the mechanism of a two-stage instability caused by the formation of turbulent spots (puff) inside the tube and generation of vortex structures in the jet mixing layer. These organized structures (puff) exert a strong influence on the free jet flow destroying the laminar flow part. The obtained data make it possible to consider in detail the evolution of turbulent spots along the distance downstream, while the spots are generated in a cylindrical tube due to the laminar-turbulent transition.

New Approach for Critical Pipe Prioritization in Wastewater Asset Management Planning

AbstractThis study proposes a new methodology that enables utilities to focus on the most critical pipes in the network while maximizing the network performance. Two hybrid algorithms were proposed...

Structure optimization for horizontal ground heat exchanger

With the advantages of lower installation cost and lower drilling technology requirement, the horizontal ground heat exchanger (HGHE) has attracted much attention. In this paper, the pipe arrangements with in-line and staggered are evaluated comparatively and the effects of the relative displacement of staggered pipes are investigated. Meanwhile, the comprehensive effects of bending number, pipe spacing and buried depth on thermal performance of HGHE are studied. The results show that the thermal performance of staggered arrangement outperformed that of in-line arrangement when the relative offset displacement is greater than 1/3. The thermal interference between adjacent buried pipes is the significant factors causing thermal resistance. For double-layered HGHE, the critical pipe spacing of first layer and second layer is 40d and 100d respectively. The buried depth has little effect on the thermal performance of HGHE.

Pulsed Eddy Current Sensing for Critical Pipe Condition Assessment.

Pulsed Eddy Current (PEC) sensing is used for Non-Destructive Evaluation (NDE) of the structural integrity of metallic structures in the aircraft, railway, oil and gas sectors. Urban water utilities also have extensive large ferromagnetic structures in the form of critical pressure pipe systems made of grey cast iron, ductile cast iron and mild steel. The associated material properties render NDE of these pipes by means of electromagnetic sensing a necessity. In recent years PEC sensing has established itself as a state-of-the-art NDE technique in the critical water pipe sector. This paper presents advancements to PEC inspection in view of the specific information demanded from water utilities along with the challenges encountered in this sector. Operating principles of the sensor architecture suitable for application on critical pipes are presented with the associated sensor design and calibration strategy. A Gaussian process-based approach is applied to model a functional relationship between a PEC signal feature and critical pipe wall thickness. A case study demonstrates the sensor’s behaviour on a grey cast iron pipe and discusses the implications of the observed results and challenges relating to this application.