High-density Polyethylene Pipelines Research Articles

Reliability Analysis of Slow Crack Growth in HDPE Pipes: Impact of Buried Pipeline Design and Soil Characteristics

This study delves into one of the most common fracture mechanisms in polyethylene pipes and the primary cause of their long-term failure, the slow crack growth (SCG) phenomenon. This failure mode in high-density polyethylene (HDPE) pipelines can potentially lead to brittle-like fractures without any localized yielding or plastic deformation. Leveraging the ISO 9080 standard for estimating pipe service life under SCG, we employ a reliability-based assessment incorporating Monte Carlo simulations to explore the impact of geometric burial design and soil characteristics on pipeline integrity.Variables including pipe diameter, depth of cover, bedding angle, trench width, soil type, and compaction level were analyzed to determine their impact on the progression toward medium and high SCG-mediated probability of failure levels. In addition to a thorough examination of these variables, a machine learning analysis was employed as a supplementary tool to contrast and quantify their significance in influencing the time of entry into medium and high probability of failure states. This layered approach, combining detailed variable analysis with machine learning insights, underscores the complex interplay of design and environmental factors in mitigating SCG probability of failure.Our research underscores that bedding angles under 90° substantially increase the likelihood of SCG-induced failures in HDPE pipelines. Although additional factors studied also affect failure probabilities, their impact is less critical in comparison to that of the bedding angle. By optimizing these lesser factors, minimal failure probabilities can be sustained across the standard 50-year service life of HDPE pipelines, thus bolstering their durability and reliability across diverse operating environments.

Multi-objective frequency–time domain transient-based creep identification of leaky polymer pipes

Determining the creep function of polymer pipes is crucial to accurately predicting hydraulic behaviour during transient events. This research presents a novel multi-objective framework that uses transient frequency and time domain pressure data to determine the creep function parameters for a viscoelastic pipeline, accounting for the potential presence of leaks. The innovation of this approach is attributed to employing two pressure signal indicators unaffected by leakage: the resonance frequencies and the zero crossing times, which refer to the moments when the transient pressure signal crosses the steady-state pressure signal. To ensure the efficiency and uniqueness of using these determinants to estimate the accurate creep function parameters, a multi-objective optimization problem is defined and applied to identify the creep function parameters inversely. The developed approach has undergone validation and analysis through different intact and leaky experimental tests and numerical simulations on a high-density polyethylene pipeline. The results and findings confirm that the proposed method could precisely determine the creep function of polymer pipes.

Automatic defect detection for electrofusion joints of high-density polyethylene via spatial sequence to sequence attention neural network

High-density polyethylene pipelines have been widely used in various industries owing to their inherent advantages, such as resistance to harsh environments. However, a variety of defects are caused by welding process such as electrofusion technology. Therefore, detecting defects is necessary to guarantee welding quality and safety. The existing methods of detecting defects mainly neglect the internal spatial characteristics and depend on many rules. In this paper, detecting defect is regarded as a sequence labelling problem, and a novel spatial sequence to sequence attentive neural network is proposed to automatically identification defects via the natural spatial features of electrofusion joint. The proposed network utilizes the relative position between the neighbour resistance wire and possible defect to generate the vector representation, and expands the vectors through multivariate Gaussian probability distribution to highlight the vital sequence features related to defect. Self-attention is employed to capture the prominent distinguishing information between normal resistance wire and possible defect. The experimental results on the actual dataset collecting from electrofusion joints of high-density polyethylene illustrate that expanded vector is useful to focus on crucial features and self-attention promotes the identification ability of the proposed network, achieving the F1-score of 92.28 %.

Evaluation of the seismic performance of butt-fusion joint in large diameter polyethylene pipelines by full-scale shaking table test

High-density polyethylene (HDPE) pipelines in nuclear power plants (NPPs) have to meet high requirements for seismic performance. HDPE pipes have been proved to have good seismic performance, but joints are the weak links in the pipelines, and pipeline failures usually initiate from the defects inside the joints. Limited data are available on the seismic performance of butt-fusion joints of HDPE pipelines in NPPs, especially in terms of defects changes inside the joints after earthquakes. In this paper, full-scale shaking table tests were performed on a test section of suspended HDPE pipelines in an NPP, which included straight pipes, elbows, and 10 butt-fusion joints. During the tests, the seismic load-induced strain of the joints was analyzed by strain gauges, and it was much smaller than the internal pressure and self-weight-induced strain. Before and after the shaking table tests, phased array ultrasonic testing (PA-UT) was conducted to detect defects inside the joints. The locations, numbers, and dimensions of the defects were analyzed. It was found that defects were more likely to occur in elbows joints. No new defect was observed after the shaking table tests, and the defects showed no significant growth, indicating the satisfactory seismic performance of the butt-fusion joints.

Ultrasonic phased array detection method for butt fusion welding defects of HDPE pipes

The welding joint is the weak link of the high-density polyethylene pipeline. The continuous development of ultrasonic phased array technology is expected to replace traditional non-destructive testing methods. In this paper, ultrasonic phased array technology is used to detect the defects of butt fusion welding. The results show that the ultrasonic phased array can distinguish between metallic and non-metallic inclusions, and the inclusion size can be displayed. Besides, insufficient fusion defects have no obvious defect features in the sector scan results. The types of insufficient fusion defects can be judged from the end-face line scan results.

Experimental and numerical study of shallow‐buried high‐density polyethylene pipeline under collapse touchdown impact

AbstractThe debris from structures produced during the blasting demolition of engineered buildings (structures) may fall near buried pipelines, which threaten the integrity of the buried gas pipeline. In this paper, the dynamic response of nearby shallow‐buried high‐density polyethylene (HDPE) gas pipelines under collapse impact loads was investigated. The stress‐strain curve and material parameters of the HDPE pipe were obtained through uniaxial tensile tests. The strain distribution of buried pipelines under collapse loading was obtained. Subsequently, a 3D nonlinear finite element (FE) model of a buried HDPE pipeline impacted by a collapsed body was established. Finally, the effects of the impact velocity, touchdown angle, touchdown mode, offset distance, and pavement structure on the mechanical behavior of buried HDPE pipelines were analyzed in detail. The results show that, as the touchdown velocity and angle of the collapsed body increase, the von Mises stress of the pipeline is significantly affected. The pipe section close to the center of the impact zone tends to be damaged due to the von Mises stress reaching the maximum tensile strength. The maximum von Mises stress of the pipeline that is impacted by the edge of the collapsed body is the smallest, but the buried pipeline undergoes the largest displacement. The rigidity of the overlying pavement structure has a significant impact on the reliability of the buried HDPE gas pipeline. The stress concentration areas of buried pipelines mainly appear on the top, bottom, and the arches of the pipeline.

Experimental and numerical investigations on damage assessment of high-density polyethylene pipe subjected to blast loads

Buried high-density polyethylene (HDPE) pipelines have been extremely vulnerable to terrorist attacks and third-party damage in recent years, so it is important to study the vibration response and safety criterion of buried HDPE pipelines under the action of surface blast loads. In this paper, based on the full-scale field tests, the damage characteristics of HDPE pipes under the action of surface blast loads are studied. Next, a 3D numerical calculation model was established to analyze the response characteristics of the buried pipes subjected to surface blast loads and its reliability was verified using the field monitoring data. Then, the safety of the pipes under different blast load conditions was studied in combination with numerical simulation software, and different damage models of the pipe were established based on damage theory. The results show that the peak particle velocity (PPV) of both the pipe and the surface increases as the distance from the explosive decreases, and the vibration velocity of all measurement points is dominated by the vertical direction (Y). Meanwhile, as the surface explosive is triggered, the pipe is prone to overall bending deformation in the axial direction, resulting in the destruction of the pipe. Finally, based on the comprehensive numerical calculations, numerical simulation results were obtained for different damage levels of the pipes under surface blast loading. What’s more, the damage prediction model of the pipes is also proposed, and the critical curves corresponding to different damage levels are derived.

An Accurate and Efficient Fitness-For-Service Assessment Method of Pipes with Defects under Surface Load

With continued urbanization in China, the construction of urban gas pipelines is increasing, and the safety of gas pipelines are also increasingly affected by urban development and the increased scope of buildings and roads. Pipes with defects are more likely to fail under the surface loads. In this study, uniaxial tensile tests of high-density polyethylene (HDPE) pipes were carried out to obtain the real material parameters of pipe. A pipeline-soil interaction finite element model of HDPE pipeline with defects under surface load was established. The failure mechanism of the urban gas pipeline was studied and the influence of parameters such as internal pressure, defect position, defect depth on the mechanical behavior, and failure of pipelines were analyzed. A failure criterion for HDPE pipes with defects under surface load was proposed based on the limit-state curves obtained under different working conditions. Furthermore, an accurate and efficient fitness-for-service assessment procedure of pipes with defects under surface load was proposed. The results showed that maximum Mises stress of the pipeline gradually increased with increasing surface load and the position of maximum stress changed from the top and bottom of the pipe to the defect position and both sides of the pipe. Finally, when Mises stress of the HDPE pipe exceeds the yield limit, failure will occur. Internal pressure, defect location, and defect depth were found to influence the failure process and critical surface load of the pipeline. Safety evaluation curves of the gas pipeline with defects under surface load were obtained by calculating the critical failure load of the pipeline under various working conditions. Finally, a nonlinear fitting method was used to derive a formula for calculating the critical surface load under different defect parameters. The proposed method provides a useful reference for urban gas pipeline safety management.

Hydraulic Transients in Viscoelastic Pipeline System with Sudden Cross-Section Changes

It is well known that the water hammer phenomenon can lead to pipeline system failures. For this reason, there is an increased need for simulation of hydraulic transients. High-density polyethylene (HDPE) pipes are commonly used in various pressurised pipeline systems. Most studies have only focused on water hammer events in a single pipe. However, typical fluid distribution networks are composed of serially connected pipes with various inner diameters. The present paper aims to investigate the influence of sudden cross-section changes in an HDPE pipeline system on pressure oscillations during the water hammer phenomenon. Numerical and experimental studies have been conducted. In order to include the viscoelastic behaviour of the HDPE pipe wall, the generalised Kelvin–Voigt model was introduced into the continuity equation. Transient equations were numerically solved using the explicit MacCormack method. A numerical model that involves assigning two values of flow velocity to the connection node was used. The aim of the conducted experiments was to record pressure changes downstream of the pipeline system during valve-induced water hammer. In order to validate the numerical model, the simulation results were compared with experimental data. A satisfactory compliance between the results of the numerical calculations and laboratory data was obtained.

Field Measurements and Numerical Modeling of Hydraulic Transients in HDPE Pipeline with PRV Interaction

Pressure reducing valves (PRVs) and high-density polyethylene (HDPE) pipes are commonly used in urban water supply systems (UWSS). To study the joint effect of PRV and viscoelasticity on transient wave propagation, extensive experiments have been conducted in a field-scale reservoir-PRV-viscoelastic pipeline system covering a wide range of internal pressure heads (∼10 to 60 m) and air temperatures (12°C–33°C). In addition, a one-dimensional method of characteristics (MOC) based model that incorporates a PRV model and the generalized Kelvin-Voigt (K-V) model for pipe viscoelasticity is developed and validated against field data for the first time. The simulated transient pressures are in good agreement with field measurements. The K-V parameters exhibit a clustered distribution and the mean value for each element can provide a satisfactory simulation. The PRV in hydraulic transients can be interpreted as a quasi-dead-end with a self-adjusting opening, and causes additional positive pressure wave reflections that are gradually damped due to viscoelasticity. The dynamic changes in PRV opening, head loss, pressure wave reflection, and transmission induced by an incident pressure surge are predicted. Due to the joint action of PRV and pipeline viscoelasticity, the pressure oscillations in an intact pipe settle to a value that is considerably higher than the initial PRV set pressure. In a leaking pipe, the downstream pressure reverts to the original set pressure within a few wave cycles. Leaks can be detected by wave reflections in the time domain signals. The existence of leaks is also found to be associated with the the amplification and damping of the frequency response function (FRF) of the system at certain resonance peaks. This study provides new insights into wave propagation in HDPE pipeline with PRV interaction and an original data set for validation of leakage detection methods.

Effect of biological degradation by termites on the abnormal leakage of buried HDPE pipes

Buried high-density polyethylene (HDPE) pipes are widely utilized to transport gas and water due to its great shape flexibility, light weight and cost effectiveness. Because of the concentration of population and wealth, leakage accidents of buried HDPE pipelines would lead to catastrophic loss of life and property. Therefore, the comprehensive investigation and understanding of the mechanisms behind the unexpected failure of buried HDPE pipes is of great significance. In this paper, abnormal leakage occurred on the buried HDPE pipes in China. Multiple of holes and cracks were observed on the buried HDPE pipes during visual examination. Considering that no obvious third-party interference existed during the service period, systematic analyses on both mechanical properties and chemical structure were conducted to figure out the root cause of the failure. The results indicated that the abnormal leakage of the buried HDPE pipes resulted from the biological degradation by termites. Some countermeasures were also proposed to avoid the similar failure occurred again.

Estimating acoustic wave dispersion in water pipelines using a single spatial measurement.

Estimating acoustic wave dispersion in pipelines filled with water is studied using theoretical analysis and laboratory experiments. Previous methods for experimentally estimating the dispersion of the propagating modes require multiple spatial measurements, making it difficult to measure. In this work the authors propose a method that utilizes only one spatial measurement using a singular value decomposition based approach. Experimental results of a cylindrical high-density polyethylene pipeline are used to demonstrate the usefulness of the approach. The approach could be useful in estimating the size and material properties of pipelines.

Automatic detection of burst in water distribution systems by Lipschitz exponent and Wavelet correlation criterion

Bursts on water distribution systems are a major problem, since they cause great loss of water, interrupt the supply and damage the streets and buildings. It is a challenge for water distribution systems to detect bursts as soon as they happen, reducing the probability of false positives and the size of the burst that can be detected. This paper solves this problem presenting a new equation that uses the Wavelet correlation criterion to estimate Lipschitz exponent and the theory of decisions to calculate the threshold used for burst detection. The algorithm was validated experimentally using 120 signals acquired from a high-density polyethylene pipeline. This paper shows that the algorithm and proposed equation obtain better results in burst detection than those reported by the scientific community.

Heat transfer approximate modeling, parameter estimation and thermography of thermal pulsing in electrofusion joints of gas pipelines

Today significantly long distribution pipelines are employed to ensure the availability of natural gas as a clean energy even in the most rural areas. High Density Polyethylene (HDPE) Electrofusion joint has been emerging as the primary means of connection in such HDPE pipelines. Heat transfer has a leading role in the integrity of these joints and clearly a thorough but quick thermal understanding of these joints can be a critical step for effective maintenance and reduction of the associated uncertainties. Therefore, in this study two separate (a primary and a modified) approximate transient heat transfer models are developed to simulate the thermal pulsing of those joints. This pulsing is initiated by converting the electrical into thermal energy within the joint. The modified model is prepared by introducing novel geometric coefficients into the heat source terms by borrowing the idea of skin factors and sphericity coefficients from the petroleum and food engineering domains respectively. Moreover, experimental thermography and TGA are used for validation and design purposes. The results are used to calculate the thermal efficiency of the joint and it was found to be 87.04%.

Effect of carbon black distribution on the properties of polyethylene pipes part 2: Degradation of butt fusion joint integrity

As a continuation of the previous work (Deveci, Antony, & Eryigit, 2018), we investigated the effect of carbon black distribution on the degradation of mechanical properties of butt-fusion joints and overall mechanical integrity of high-density polyethylene pipelines. Polyethylene pipes with similar carbon black concentrations but different distributions were produced with industrial scale compounding and extrusion equipment. Waisted tensile specimens were milled directly from the butt-fused pipe samples and elongated to fracture. Carbon black distributions at the butt fusion interphase, both in axial and radial directions, were investigated using stereo and scanning electron microscopy. A significant decrease in joint integrity, measured as work of fracture, was observed for the welds made with high-density polyethylene pipes with inhomogeneous carbon black distributions. It was found that the width of areas that do not contain carbon black (windows) can significantly enlarge at the butt fusion interphase due to shearing, resulting in brittle failures at the butt fusion interphase with a magnitude related to the level of inhomogeneity.

Nondestructive Testing of Nonmetallic Pipelines Using Microwave Reflectometry on an In-Line Inspection Robot

Microwave and millimeter-wave reflectometry, a form of continuous-wave surface penetrating radar, is an emerging nondestructive inspection technique that is suitable for nonmetallic pipelines. This paper shows a $K$ -band microwave reflectometry instrument implemented onto an in-line pipe-crawling robot, which raster-scanned cracks and external wall loss on a high-density polyethylene (HDPE) pipe of diameter 150 mm and wall thickness 9.8 mm. The pipe was scanned with three environments surrounding the pipe that approximated the use cases of overground HDPE pipelines, plastic-lined metal pipes, and undersea HDPE pipelines. The instrument was most sensitive when cracks were oriented parallel to its magnetic (H) plane. Any small variation in the standoff distance between the instrument’s probe antenna and the pipe wall, which was not easy to avoid, was found to obscure the image. To mitigate this problem, a sensitivity analysis showed that an optimal frequency can be chosen at which standoff distance can vary by up to ±0.75 mm within a certain range without distorting the indications of defects on the image.

A new hybrid model for rigorous analysis of buried pipelines under general faulting accounting for material and geometrical non-linearities with focusing on corrugated HDPE pipelines

Earthquake-induced Permanent Ground Deformations (PGD) can be occurred due to fault movements, land sliding or liquefaction-induced soil displacements. This kind of deformation could significantly affect underground lifelines, such as buried pipelines. To assess the integrity of the pipelines against fault deformations, it is important to quantitatively evaluate the interaction between the pipelines and the surrounding soil. The simplified analysis procedures for buried pipelines crossing active faults given in the major seismic design guidelines for pipelines consider some bilinear force-displacement relationship curves to represent the soil-pipeline interaction. In a case of fault's large movement or existing relatively soft soil, the soil adjacent to the pipe could behave more in a nonlinear fashion and then affects the pipe's response and also changes the pipeline-soil interface behavior significantly. In this study, the effect of soil non-linearity as well as pipe's geometric and material non-linearities due to large ground deformations on seismic performance of buried pipelines were investigated. A new hybrid approach was developed to reduce the number of degrees of freedom of the soil-pipeline system accounting for rigorous soil-pipeline interaction. The approach combines the finite-element method (FEM) which models the pipe itself as well as the near-field soil around the pipe and the scaled boundary finite element method representing the far-field soil beyond the soil near-field. The behavior of pipeline embedded in the near field soil is modeled using large deformation shell elements, while the segment located far away from the fault, is considered as elastic beam elements. The proposed method was used to evaluate the maximum strains for the fault-crossing steel and High Density Polyethylene (HDPE) plane and corrugated pipes subjected to various fault movements. Parametric responses for different fault crossing angles, fault displacements and pipe diameters have been presented.

Detection and Isolation of Interior Defects Based on Image Processing and Neural Networks: HDPE Pipeline Case Study

AbstractThis paper investigates the condition of polyethylene (PE) pipelines as a case study. This study introduces a novel method to detect and diagnose defects of high-density polyethylene (HDPE)...

Advanced high-density polyethylene used in pipelines networks

This paper presents the most important results obtained during tensile tests carried out on high-density polyethylene (HDPE) for pipelines used for water supply networks. Various specimens have been cut from HDPE 20 x 2 mm, 63 x 4 mm and 90 x 6 mm pipelines and subjected to tensile and four-point bending loads to determine their mechanical properties including stiffness and Young’s modulus. Load-extension distributions have also been determined. Two special cases of composite pipelines have been taken into consideration in theoretical approach: the cross-ply composite pipeline and the balanced angle-ply composite one, both subjected to internal pressure. In tensile tests, the stiffness evaluation of high-density polyethylene pipelines used for water supply networks put into evidence that the Young’s modulus and stiffness increase with the increase of pipelines’ diameter.

Propagation of monopole source excited acoustic waves in a cylindrical high-density polyethylene pipeline.

Acoustic wave propagation (up to 50 kHz) within a water-filled high-density polyethylene (HDPE) pipeline is studied using laboratory experiments and theoretical analysis. Experiments were carried out in a 15 m length of cylindrical HDPE pipeline using acoustic transducers to acquire signals uniformly spaced along the axis of the pipe. By proposing the use of the iterative quadratic maximum likelihood algorithm to this experimental configuration, wavenumbers, attenuations, and mode amplitudes could be accurately extracted from the measurement data. To allow comparisons with theoretical analysis, dispersion curves of the wavenumbers, attenuations, and acoustic power characteristics of the axisymmetric and nonaxisymmetric modes are predicted by extending an existing waveguide model. The model extensions included the introduction of a monopole acoustic source into the water medium so that amplitude variations with respect to individual modes and frequencies could be investigated in detail. In addition, stiffness coefficients of HDPE material are carefully used to account for viscoelastic effects. The comparisons between the theoretical predictions and experimental results demonstrate a very good match and are a validation of the theoretical model.