Journal of Pipeline Systems Engineering and Practice

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This paper presents an analytical solution for thrust restraint analysis of buried pipelines subjected to internal pressures and thermal and earthquake loads. The proposed analytical solution is modified from the current approach, which does not include the effect of temperature or earthquake loads or the complexities of pipe–soil friction nonlinearities resulting from change in the direction of relative pipe-to-soil motions. The proposed analytical solution is validated using a finite-element model that accounts for longitudinal pipe-to-soil friction and soil stiffness against transverse movement of the pipe. This paper also includes two case studies using the approach presented in this paper: one is a steel pipeline with a 5.4-in. (0.137-m) diameter and a 45° bend in a nuclear facility subjected to high internal pressure and high temperature loading, and the other is a prestressed concrete cylinder pipe with a 72-in. (1.83-m) diameter and a 45° bend subjected to internal pressure and temperature and earthquake loads. Both case studies suggest that the demands on the pipe segments adjacent to the pipe bends are greater when we include temperature and earthquake loads. In addition, this paper also shows that the sequence of load application of temperature and earthquake loads may result in changes in the direction of friction along the length of the pipeline, which affect the internal forces in the pipeline. This paper presents a procedure for analysis of pipelines where a change of direction of friction is likely.

In the field of sewage pipeline inspection, the Pipeline Assessment Certification Program (PACP) requires encoding pipe cracks at the subcategory level in practical applications. This study seeks to address the need to improve the accuracy of the crack pixel-level segmentation and subcategory classification problem based on sewer pipe inspection video images. The proposed framework consists of a feature extraction module, a multiscale feature fusion module, a mask-guided attention module, and a subcategory classification module. First, the multiscale feature fusion mechanism is used to integrate the convolution features of different scales to obtain the convolution features rich in both semantic and detailed information, which can improve the characterization ability of cracks and achieve accurate crack detection. Then, mask-guided attention is used to refine features and eliminate background noise, enhancing the feature representation for crack pixels and reducing the ambiguity of the fine-grained crack classification task as well. Finally, the subcategory classification result is obtained based on the feature maps with erased background clutter. The experimental results show that the proposed method achieved F1-scores of 97%, 94%, and 95% for longitudinal, circumferential, and multiple cracks, respectively. The main contribution of the study is the formulation of a multitask collaborative learning framework, which combines pixel-level segmentation and global image-level classification annotation to achieve a desirable performance of sewer crack detection and classification at a subcategory level.

A commissioning test of the deep-burial simulator at Queen’s University, Canada, was conducted on a 3.05-m-diameter steel-reinforced polyethylene pipe to evaluate the behavior and design of this pipe class under deep burial. The diameter change measurements indicated that friction on the side walls was mitigated ensuring that the surface load was transferred to the pipe. Measurements of the displacement and rotation of the surface loading plates and strain in the steel reinforcing strips combined with visual observations after exhumation indicated that the pipe failed due to yielding of the steel reinforcing ribs. The surface pressure that the pipe was able to withstand exceeded the maximum burial depth specified by the manufacturer. Comparisons are also made between the experimental thrust forces at the springline and estimates from two design codes and a finite-element estimate; all were similar, with the rate of thrust increase with overburden pressure from the computer analysis approximately 8% larger than the measurement. Thus, the experimental results confirm that use of finite-element and code-equation analyses to design this pipe class for deep-burial conditions appear to be appropriate.

Nonpiggable multiproduct pipelines lack effective methods for detecting the pipe’s external defects (PEDs). Therefore, a pipeline remote magnetic detection (PRMD) technology for buried small-diameter pipelines was developed, which can achieve trenchless detection of PEDs. In this paper, an external pipe defect remote detection model is established to reveal the features of the three-dimensional magnetic gradient signal of PEDs. The quantitative relationship between the magnetic gradient modulus and defect depth was analyzed, and the influence of some factors was obtained. Furthermore, a PRMD method was established to detect a 3.56-km buried small-diameter multiproduct pipeline. The diagnostic indicator $F_d$ based on the magnetic gradient modulus is proposed to determine damage levels of defective pipes, which was validated by the excavation inspection results. The results show that the magnetic gradient modulus $G$ reaches a peak at PEDs. The maximum magnetic gradient modulus $G_{\max }$ has an exponential relationship with the defect depth. Finally, 10 Level II defects and 19 Level III defects were found in the 3.57-km buried pipeline.

Pipeline transportation is one of the major methods of transportation, widely used in various industries. Water hammer, a common vibration phenomenon in pipeline transport, has shown promising results in detecting leaks, blockages, and defects in pipelines. This study focuses on several aspects: (1) the vibration characteristics of pipeline water-hammer waves in air, water, and soil environments; (2) the vibration characteristics of pipeline water hammer in soil (sand and clay) with different collapse lengths; and (3) the use of wavelet transforms to analyze vibration signals under engineering conditions, assuming that the transmission characteristics of pipeline water-hammer waves are sensitive to the surrounding environment. The simulated water-hammer model was found to be approximately 90% accurate compared to the classical water-hammer formula, and was combined with the COMSOL simulation model and experimental verification. The experiment found that the attenuation rate of pipeline water-hammer waves in clay and water environments was 24% and 29%, respectively. Furthermore, under engineering conditions, the collapse length of pipelines in clay environments was more sensitive than in sand environments, which was consistent with the theoretical analysis and simulation results. These findings were further studied and summarized using wavelet analysis, highlighting their accuracy and applicability in the field of water-hammer detection.

Abstract

The performance of double-pipe culverts remains unclear due to insufficient research on double culverts. This study made use of polyvinyl chloride pipe to simulate culverts. The effect of culvert spacing and fill height on the mechanical properties of double-pipe culverts before and after expanded polystyrene (EPS) plate load reduction was investigated through a series of model tests, and the results were compared with those obtained from single-pipe culverts. It was found that the earth pressure at the top of the culvert was the smallest when the culvert spacing was $1D$ (where $D$ is the diameter of the double-pipe culvert). When compared with the single-pipe culvert, the earth pressure at the top of the culvert was smaller than that of the single-pipe culverts; only when the culvert spacing was $1D$, the earth pressure on the right side of the culvert was slightly larger than that of the single-pipe culvert. The earth pressure at the top of the culvert could be reduced by 20% before load reduction and by 42% after load reduction. The effect of fill height on earth pressure was small, but it could reduce the circumferential strain of the culvert pipe.

Practical Applications

With the widespread use of double-pipe culverts, the study of double-pipe culverts is crucial. However, the current research on double-pipe culverts is insufficient. In order to understand the mechanical characteristics of double-pipe culverts, this study simulated double-pipe culverts through model tests. The influence of culvert spacing and filling height on the mechanical properties of double-pipe culverts with EPS plate before and after load reduction was studied and compared with single-pipe culverts with the same drainage capacity. The results showed that the replacement of single-pipe culverts with double-pipe culverts can effectively reduce the earth pressure at the culvert top and lateral. The earth pressure at the top of the culvert will be reduced by 20% before and 42% after EPS load reduction. The earth pressure on the top of double-pipe culvert decreases with the decrease of culvert spacing, and the circumferential strain of the pipe culvert can be effectively reduced with the increase of filling height.

In this paper, numerical simulations were conducted to investigate the detection of blockages and leaks in piping systems, and the method’s applicability was confirmed by comparing it with data from previous studies. The study explores the effects of using pressure waves generated by different valve closing times, closing methods, and openings to detect blockage and leakage locations. The results demonstrate that extending the valve closing time reduces the maximum pressure in the piping system, but it also makes it harder to identify information about blockages and leaks, thus hindering their location. However, a two-stage valve closure can effectively suppress the amplitude of pressure in the pipeline. The wavelet transform method is capable of accurately detecting the location of sudden pressure changes caused by blockages and leaks in the pipeline using various valve regulation methods. Furthermore, when the valve is partially closed, the pressure wave generated will be reflected as it propagates toward the blockage and leakage location, resulting in a significant sudden pressure change at the valve. Finally, this paper confirms the feasibility of using pressure waves generated by partially closed valves and the combined adjustment of two valves to locate blockage and leakage in the piping system.

Pipelines serve as a crucial infrastructure for long-distance and cost-efficient transportation of oil and gas resources. The safety and reliability of oil and gas pipelines crossing mountainous areas, however, are susceptible to rainfall-induced landslides. Landslide-induced pipeline leakage or fracture may result in the release of oil and gas, causing resource waste and environmental contamination as well as casualties. To date, user-friendly and comprehensive methods for early warning about pipeline safety issues under landslides are scarce. The present study develops a novel early warning degree (EWD)-based safety early warning framework for oil and gas pipelines subjected to landslides, including three monitoring indexes of disaster-inducing bodies, disaster-causing bodies, and disaster-bearing bodies. The use of an improved fuzzy decision-making trial and evaluation laboratory (DEMATEL) method determines the weight of each index. The hybrid application of fuzzy comprehensive evaluation approach and three-dimensional (3D) space method is used to develop the 3D early warning matrix. The matrix finally integrates an improved radar chart technique to estimate EWD-based early warning intervals. The proposed framework has been implemented through a case study on an in-service pipeline, demonstrating its capability to improve the safety of oil and gas pipelines traversing landslide-prone areas, and enhance the resilience of pipelines against landslides.

To improve failure predictions and replacement decisions for cast iron pipes, a better understanding of their capacity and failure mechanisms is required. A series of ring bearing and four-point bending tests was conducted on exhumed small-diameter cast iron pipe specimens instrumented with distributed fiber optic sensors (DFOS). Dynamic DFOS enabled the measurement of longitudinal and circumferential strains around and along each specimen, including at the critical location, which, due to the material variability of cast iron, could not be determined prior to testing. The ring bearing tests were used to estimate the modulus of rupture, initial elastic modulus, and secant modulus for each pipe. Additionally, variation within the same pipe and between pipes was characterized. The four-point bending tests illustrated the value of DFOS, which captured the nonlinear development of strain at different locations as a function of load as well as the ratio of longitudinal and circumferential strains (the Poisson’s ratio). The location of failure along the pipe did not correlate with the location of the peak strain, which further highlights the value of DFOS and the need to account for material variability in assessments of cast iron pipe strength.

Natural gas transmission pipelines are at risk of failure when they traverse potential landslide regions, leading to significant service disruptions and environmental impacts. This paper presents the results of an analytical study on the vulnerability of typical natural gas transmission pipelines when they are subjected to landslide-induced ground displacements. Pipeline vulnerability was evaluated for four pipe diameters under different internal pressures and various ground displacement profiles. The effects of pipe wall thickness and steel grade on vulnerability were also evaluated. The finite-element method was used to model the pipelines and the surrounding soils. Nonlinear static analyses were carried out to evaluate the response of the pipelines under landslide-induced ground displacements. Based on results of the analyses, landslide fragility functions were developed for the pipelines at the pressure integrity (PI) limit state. The results of this study indicate that pipeline vulnerability decreases with increasing pipe diameter but increases with increasing landslide width up to a threshold width where the effect becomes negligible. Additionally, internal pressure is found to have no significant effect on the vulnerability of various pipelines at the PI limit state. The results also show that the risk of pipeline failure can be reduced significantly by increasing pipe wall thickness and using a higher grade of steel material in landslide regions.

As an important part of the energy transportation system, oil and gas pipelines are developing toward intelligence and digitalization. Vigorously developing and constructing pipeline networks based on intelligent methods such as big data and neural networks will help improve the efficiency of operation and management. This work provides an overview of recent developments of intelligent methods, including machine learning approaches, heuristic algorithms, and mathematical programming, used in the pipeline industry that can provide beneficial support for various applications enhancing operation and maintenance. Several aspects such as operating condition recognition, safety monitoring, pipeline remaining life prediction, and fault detection are reviewed and discussed. The study shows the need to focus on improving management level and ensuring pipeline safety.

Abstract

This paper presents an approach for probabilistic analysis of pipelines buried through geohazard-prone areas that induce permanent ground movements potentially. In this approach, an easy-to-implement response prediction tool based on the finite-difference method is integrated with simple but robust Monte Carlo simulation methods. The probability of strain capacity exceedance is calculated when a pipeline is subjected to the ground movement of different magnitudes. In the strain-based limit state function, the strain capacity is determined using existing equations in the literature, and the strain demand is calculated using an accurate and efficient tool based on the finite-difference method. After obtaining the conditional probabilities of failure of pipes at given magnitudes of ground movement, the probability of failure of pipes as a function of time is also calculated considering the probability of ground movement initiation. The proposed approach is demonstrated through a case study of pipelines subjected to landslides.

Practical Applications

Pipelines are crucial components of lifeline infrastructure systems that facilitate the transportation of diverse gas and fluid substances. The vulnerability of pipelines buried in geohazard-prone areas necessitates a proactive approach to risk mitigation. This study introduces a methodology for assessing pipeline safety through probabilistic analysis. The methodology considers the probability of the pipeline’s resistance to ground movements, as well as the likelihood of potential geohazards like slope creep and landslides. An innovative approach is employed to calculate the probability of the pipeline’s resistance to ground movement, providing relatively accurate results while minimizing time requirements. The probability of slope creep and landslide events is derived from relevant guidelines and engineering reports. The final result, represented by the probability of failure, serves as a quantifiable measure to determine the safety level of the pipeline. This study can be referenced during decision-making processes related to pipeline design and maintenance, ultimately enhancing pipeline system safety.

Corrugated metal pipes (CMPs) buried in the ground for decades may get corroded and lose their structural capacities supporting surface loading, leading to the end of their service life. Three maintenance options are commonly adopted in the practice for these corroded CMPs: repair, rehabilitate, and replace. The maintenance option of replacement of CMPs buried under roadways through excavation often disrupts traffic and requires considerable time and budget. Therefore, trenchless rehabilitation methods, such as cement mortar (spray-on) lining, sliplining, cured-in-place pipe, fold-and-reformed pipe, spot repair, and spiral wound, have been increasingly used to rehabilitate corroded CMPs under roadways. Nevertheless, limited studies have been conducted to assess the behavior of the rehabilitated CMPs using the spray-on lining method. In this study, a numerical analysis using the FLAC3D software was conducted to evaluate the behavior of buried corroded CMPs rehabilitated with the spray-on lining method. The numerical model was first verified using the available field test results of a corroded CMP. Then a parametric study was carried out to examine the effects of the CMP diameter, embedment depth, compressive strength and thickness of spray-on lining, and type of the pavement on the changes of the horizontal and vertical diameter, and the pavement surface settlement under five cycles of truck loading. The numerical results show that an increase of the lining thickness in the rehabilitated CMPs by 50% and 100% (i.e., from 20 to 30 and 40 mm) reduced the vertical and horizontal diameter changes by 41% and 65%, respectively. When the unconfined compressive strength of cement lining decreased to half, the vertical and horizontal diameter changes increased by approximately 16%.

Buried natural gas pipeline leakage is hidden and persistent, and easily can cause environmental pollution, property loss, and casualties, especially in cities. The main objective of this study was to establish a three-dimensional numerical model to restore the real environmental conditions. Taking the small-hole leakage of a buried medium-pressure natural gas pipeline as the accident scenario, the change law of the pressure, flow rate, and velocity of the pipeline and the leakage hole after the occurrence of single-hole and double-hole leakage was studied using the computational fluid dynamics method. The variation rule of natural gas concentration in the soil environment was analyzed, the warning area and hazardous area were delimited, and then the explosion hazard radius of the leaking gas was calculated using the trinitrotoluene (TNT) equivalent method. The results showed that the natural gas leakage diffusion in front of the orifice is similar to a jet phenomenon, and the pressure and velocity gradient decrease sharply with the increase of distance. The mass flow rate and flow velocity of single-hole and double-hole leakage fluctuated within 0–0.4 s after the leakage. The mass flow rate of single-hole leakage was greater than that of the double-hole’s single leakage source, but the mass flow rate of double-hole leakage was 1.98 times that of single-hole leakage. Regardless of the leakage, the orifice velocity and pressure of single-hole and double-hole leakage can reach a stable state after 2 s of leakage, and remained the same. At the same buried depth, it took twice as long for the early warning area and hazardous area to reach the surface with single-hole leakage than with double-hole leakage. The explosion hazard radius of both single-hole and double-hole leakage increased with the increase of pressure, and the explosion hazard radius of double-hole leakage was 1.3 times that of single-hole leakage.

Rerounding is a technique for remediating excess deflection in thermoplastic pipe. A pneumatic device vibrates along the vertical axis and pushes against the inside crown and invert to restore the original pipe shape and redistribute the surrounding backfill. A systematic evaluation of the method was justified because rerounding is routinely used by contractors to remediate deflected thermoplastic pipes, and it has not been investigated outside of a few previous reports. Three 900-mm and two 450-mm corrugated high-density polyethylene (HDPE) pipes were installed in various bedding and backfill materials. Test pipes were intentionally installed with substantial deflection (10% or more) and then rerounded. The pipe conditions were measured and monitored by collecting profiles, measuring vertical deflections, and monitoring soil pressure, soil stiffness, backfill characteristics, and pipe corrugation depth before and after rerounding. The data from the deflection, soil stiffness, corrugation, and soil pressure monitoring confirmed the following: (1) during rerounding, soil particles migrated and soil pressure was redistributed; fine material from the crown and springline moved down toward the haunch area, at least in the well-graded aggregate backfill; (2) it is difficult to successfully reduce deflection in corrugated HDPE pipes in well-graded aggregate backfill; (3) installing the pipes with excess deflection proved a significant challenge, as all the pipes required much effort to reach sufficient deflection. It proved necessary to create a device to hold the pipe in a deflected state during backfilling; (4) rerounding successfully reduces deflections for pipes in sand backfill; and (5) test pipes backfilled with Ohio Department of Transportation (ODOT) Type-3 backfill were easy to reround, but a change in environmental conditions and/or dynamic loading may create a change in the stress path leading to excessive deflection and reversal of the effects of rerounding.

Excessive lateral movements of buried pipes in geohazard-prone areas frequently jeopardize the structural integrity and serviceability of pipelines, as well as the safety of the surrounding geoenvironments. Based on the material point method (MPM), this paper investigates the pipe–soil interactions under lateral pipe movements, with a focus on the failure mechanisms of the surrounding soil during postfailure stages. The accuracy of the numerical model is validated by comparison with the results of large-scale model tests in the literature. There is a strong correlation between the experimental and numerical results in terms of force–displacement relationships and soil failure patterns. The impacts of burial depths, pipe diameters, and soil densities on the failure mechanism are analyzed in detail. The results showed that general shear failure tends to occur in shallow pipe conditions, resulting in significant ground heave. As the pipe burial depth increases, the peak soil resistance increases accordingly, and a transition from general shear failure to a localized flow-around mechanism gradually evolves. Furthermore, the softening effect after the peak resistance is reduced under the smaller pipe diameter and greater buried depth conditions. Comparisons of failure patterns illustrate that the embedment ratio is the main determinant of pipe–soil interaction modes as compared with the soil density. Transition failure often occurs when the embedment ratio ranges from 4.5 to 9.5, with slight influences from pipe diameters and soil properties. Finally, the prediction of the soil peak lateral resistance is explored to assist in underground pipeline design.

Abstract

Liquid impact forming (LIF) is a new composite forming technology based on tube hydroforming (THF) technology, which changes the volume of die cavity through impact load and rapidly generates internal pressure to realize tube forming. It does not need external pressure supply source, and it is low cost and high efficiency. In order to study the forming characteristics of the natural bulging area of thin-walled metal tube under different model side lengths and different closing velocities, the change of the cavity volume of thin-walled metal tube under impact hydraulic bulging was first analyzed theoretically, and a mathematical model of internal pressure was established. Then the effects of different loading parameters on the internal pressure, bulging height and wall thickness distribution in the natural bulging area of thin-walled metal tube were studied. Finally, through the comparison of finite element simulation analysis and experiment, it was found that the deviation between the experimental results and the numerical simulation was within 6%, which verified the accuracy and reliability of LIF. It also provides a certain theoretical research and application basis for the development of LIF of metal thin-walled tube.

Practical Applications

Tube hydroforming technology based on structural lightweight and integration is now widely used in the production of parts and components in aviation, automobile, household appliances and other industries. The technology takes the tube as the blank, bulges the tube into the desired shape under the combined action of liquid pressure and axial load. But it must rely on the high pressure hydraulic power source and the corresponding control system, which has the disadvantages of high manufacturing cost and low forming efficiency. Liquid impact forming is a new tube forming technology developed on the basis of stamping and hydraulic bulging. By changing the volume of tube cavity by impact load, the liquid pressure can be rapidly increased. This process does not require a high-pressure hydraulic power source, has high forming efficiency, and one-time forming, which has great research value. This technology has many applications in aerospace and mechanical engineering, such as automotive subframes and rear axles, etc. And the technique can also be applied to pipeline engineering, especially metal shaped tubes such as tees and special-shaped tubes, etc.

Abstract

The accuracy of the current buried pipeline management geographic information system (GIS) is not adequate to serve as base information for road digging control and permit in Taiwan. The existing positioning system for buried pipelines does not offer satisfactorily accurate surveying results for all the scenarios because the positioning accurateness decreases with an increase in the pipeline depth. The costly excavation and direct survey of the exposed pipeline method can provide precise measurement at the designed arbitrary interval and then the discrete point is interpolated into the continuous track. The required traffic controls and excavation permits for roads are the most critical drawback of this technology. The method of in-pipe inertial navigation system (INS) can record the complete, continuous pipe tracks, but such measurement drifts with an increase in the survey length. We proposed a pipeline positioning system by radiating an extremely low-frequency (ELF) magnetic field from the electrical coil placed on the ground to constrain the locating measurement of in-pipe INS. The proposed system could easily expand the diameters or increasing turns of a ground-based coil device to enhance the magnetic field intensity for accurately positioning the deeper buried pipes. The field tests were performed using a ductile cast iron pipe (DIP), and the corresponding results revealed that for the overburden depth of 3.4–4.2 m, the average positioning errors were 0.12 and 1.6 m in the horizontal and vertical directions, respectively. This approach is only plausible for an empty pipeline, and access to both ends of the pipe is required. A four-person crew handled the proposed system to locate the track of a 5-km-long buried pipeline in an 8-h-long working day when the pipeline was unfilled.

Practical Applications

Any pipeline with diameter larger than 10 cm (4 in.) could apply this system to locate the continuous track with the requirement of accessibility at both ends of the empty pipe. With 1.45-m coil, the maximum detectable buried depth is 15 m, and locating error is less than 20 cm at both directions for the cases with buried depth less than 5 m. Two people need to move and operate the magnetic coil at the ground and another two people must hoist the in-pipe unit at each end of the pipe simultaneously. With this arrangement, the continuous track of buried empty pipe could surveyed for 5 km in length within an 8-h working day.

The construction disturbance mechanism of rectangular pipe-jacking tunnels is more intricate than that of circular tunnels, leading to potential issues such as excessive accumulation and deformation of the surrounding formation, which can result in engineering disasters. However, there is currently a lack of reliable methods for predicting these disturbances. Machine-learning techniques have the capability to analyze the influence of multiple independent variables on a dependent variable, offering a new approach for predicting surface settlement in the construction of rectangular pipe-jacking tunnels. To address the sensitivity of existing machine-learning models to initial parameters, an improved particle swarm optimization (IPSO) method is employed. This method incorporates an adaptive mutation technique, adaptive inertia weight, and postoptimization method for mutant particles to enhance the particle size and determine the probability of obtaining the optimal value. By leveraging the strong mapping and nonlinear fitting abilities of the backpropagation (BP) algorithm, the IPSO-BP algorithm model is developed and compared with the BP, support vector machine, and random forest (RF) models using actual monitoring data. The findings indicate that in the presence of specific noise in the surface settlement data, the IPSO-BP prediction model demonstrates an enhanced accuracy of 26%, 25%, and 10% for the left amplitude. This approach can serve as a valuable reference for settlement prediction in similar projects.

An air pocket is very likely to be trapped in a downward-sloping pipe (DSP) when water fills an undulating pipeline consisting of a series of inclined U-shaped pipes. To investigate the entrainment and evolution behavior of the entrapped air pocket, a series of experiments was carried out using a self-built inclined U-shaped device. The results show that at the junction between the DSP and the upward-sloping pipe (USP), the water phase forms a liquid accumulation. In addition to the agreed mechanism of liquid film jet shear and turbulent pulsation, the initiation of air entrainment is promoted further by the unique entraining effect of the reverse upward movement of the liquid accumulation in the DSP. Based on this, the flow patterns in the DSP are classified into four categories, namely single long slug flow (SLSF), unsteady transitional flow (UTF), quasi-slug flow (QSF), and plug flow (PF). Among them, UTF identified in this paper is a new and unique flow pattern for U-shaped pipe. Due to the development of UTF, the additional head loss of the air pocket and the critical Froude number required to completely remove the air pocket are increased. The effects of pipe inflow Froude number, liquid film Reynolds number, and upward-inclination angle on flow pattern transition, bubble movement, and air removal are explained and discussed.

Water hammer caused by the closing or opening of valves during pipeline operation and the condensation-induced water hammer phenomenon will occur during steam-water direct condensation in the pipeline system of a power station. The existence of this effect seriously threatens the safe operation of pipelines. In this study, a theoretical and numerical analysis of the ultimate bearing capacity of pipelines under water hammer was carried out. First, a mechanical model of X80 pipelines under water hammer was established. Then, based on the stress function method, an analytical solution of the pipeline under water hammer was derived. Next, the ultimate bearing capacity of pipelines under water hammer was explored based on the Zhu-Leis criterion. Finally, to verify the accuracy of the proposed method, we performed finite-element analysis for the radial, hoop, and axial stresses of the pipe under the action of water hammer, and found that the hoop stress is the main cause of failure under the action of water hammer. The results show that compared with the finite-element method, the prediction error is less than 3%, which can meet the requirements of calculation accuracy. This study provides a reference for the evaluation of pipeline integrity and a novel idea for the ultimate bearing capacity of pipelines under water hammer.

To explore the leakage mechanism of waterstops in deformation joints in utility tunnels, this paper carried out indoor model tests. By testing the apparent resistivity around a deformation joint, the waterproofing performance of a waterstop under different water pressures was obtained. Based on the coupled Eulerian–Lagrangian (CEL) method, a numerical model was established to simulate the dynamic leakage process of the gap between the waterstop and the concrete. The interaction between the water flowing into the gap and the waterstop was analyzed. The influence of different water pressures and different waterstop materials on the waterproofing performance of the waterstop was studied. Based on the fluid flow model of the sealing gap of the rough surface, the leakage rate of the gap flow between the waterstop and the concrete structure was calculated quantitatively. The results of the study show that the leakage mechanism of the waterstop is divided into extrusion deformation, opening flow, and gap leakage, and that the softer the material or the higher the roughness, the higher is the leakage rate of the waterstop. Comparing the results of indoor tests, numerical simulations, and theoretical calculations showed that the roughness of the rubber surface has a significant influence on the waterproofing performance of the waterstop. The calculated results followed the same trend as the test results, verifying the applicability and accuracy of the method described in this paper in predicting the leakage rate of waterstops in utility tunnels and providing an evaluation method for the study of the long-term waterproofing performance of waterstops.

Abstract

When the water supply network leaks, the state of the pipe network changes, which is primarily reflected in the variation of hydraulic characteristic parameters during pipeline operation. Consequently, the monitored pressure fluctuation data can be used to predict and analyze pipe network leakage information. This research combines location analysis and accident simulation with a city’s actual water distribution system. Using EPANET software, a hydraulic simulation model was established, and then a pipeline leakage simulation was conducted to evaluate the pressure changes at nearby points caused by pipeline leakage. To make it easier to observe the simulation results, the maximum pressure change rate of the monitoring point was compared under various leakage levels. The results indicate that the most significant pressure drop occurs at the monitoring point closest to the leak node. Consequently, based on the pressure change at the monitoring site during a leak, the area of the pipe network where the leak occurs can be quickly identified. These findings may provide technical support for future pipe network applications.

Practical Applications

The leakage localization model of the water supply pipe network involved in this study was applied to a development zone in City S, China. By simulating leakage at different locations, degrees, and pipes, the model can approximate the location of the leakage node. The presented leakage loss localization model for the water supply pipe network meets the leakage loss control requirements of the target area, provides better data values for the subsequent real-time leakage point localization model based on a neural network, and provides the theoretical foundation and technical support for future wide application in the actual large-scale pipe network. In addition, the model is practical, feasible, and acceptable for leakage monitoring in low-cost, small to medium-sized drainage networks.