Polyethylene Pipe Research Articles

POLYETHYLENE GAS PIPELINES: PROBLEMS AND EXPERIENCE OF TECHNICAL DIAGNOSTICS

More and more often in various industries, polymer materials are replacing metal structures. The gas industry is no exception, one of the areas of development of which was the introduction of polyethylene pipes to replace traditional steel pipes. This process began more than half a century ago, and according to data at the beginning of 2023, polyethylene pipes account for about 49.5 % of the length of all underground gas pipelines of gas distribution networks.
 The main obvious advantage of polyethylene pipes over steel pipes is corrosion resistance, which allows them to be operated without the use of protective anticorrosive coatings and electrochemical protection means. The strength properties of polyethylene pipes allow their operation at gas pressure up to 1.2 MPa, which makes it possible to almost fully meet the needs of the gas distribution sphere. The welding technologies of polyethylene pipes are well developed, standardized and automated.
 An important problem for long-term operating polyethylene gas pipelines is the assessment of their technical condition and determination of the residual life. Despite the existing need for work of this kind (for example, in 2022 only in the territory of the Saratov region it was required to carry out technical diagnostics of 8 gas pipelines with a total length of 39.86 km), expert organizations do not have the necessary tool for implementing this task today. Although the mechanism of aging of polyethylene is well known, there are no generally accepted standards for assessing the performance of polyethylene gas pipelines based on a comprehensive accounting of the influence of aging factors that determine their technical condition.
 The purpose of this article is to highlight the experience of Giproniigaz JSC in technical diagnostics of polyethylene gas pipelines, as well as to draw the attention of specialists from both the gas industry and academic science to the problem of developing a methodology for technical diagnostics of polyethylene gas pipelines.

Detection of defects in polyethylene pipes using open microwave coaxial line resonator sensor

A new method using a microwave coaxial line resonator sensor for the non-destructive evaluation of defects in polyethylene pipes is presented. The sensor consists of a coaxial line section and an extended section of circular waveguide. One end is short-circuited and the other end is open to free space. The sensor aperture is designed to conform to the curvature of the pipe outer surface, so that the common problem of the standoff distance effect by open-ended waveguide scanning is well circumvented. The presence of defects causes local permittivity and volume changes, leading to variations of the resonance frequency and quality factor due to material perturbation. The detection principle is confirmed by electromagnetic simulation. From the experiments, it is shown that the proposed sensor can perform both detection and classification of flat-bottom holes. The minimum diameter of the hole that can be detected is 1 mm, which is lower than that of a hole required in the standard practice. This method can also effectively detect axial defects and determine the lengths. In addition, an open-ended waveguide is used to detect axial holes, and the results were compared with those of coaxial line resonator. The sensor system presented here has the advantages of low cost, convenience for on-site detection and quantitative analysis.

A risk-based soft sensor for failure rate monitoring in water distribution network via adaptive neuro-fuzzy interference systems

Water Distribution Networks (WDNs) are considered one of the most important water infrastructures, and their study is of great importance. In the meantime, it seems necessary to investigate the factors involved in the failure of the urban water distribution network to optimally manage water resources and the environment. This study investigated the impact of influential factors on the failure rate of the water distribution network in Birjand, Iran. The outcomes can be considered a case study, with the possibility of extending to any similar city worldwide. The soft sensor based on the Adaptive Neuro-Fuzzy Inference System (ANFIS) was implemented to predict the failure rate based on effective features. Finally, the WDN was assessed using the Failure Modes and Effects Analysis (FMEA) technique. The results showed that pipe diameter, pipe material, and water pressure are the most influential factors. Besides, polyethylene pipes have failure rates four times higher than asbestos-cement pipes. Moreover, the failure rate is directly proportional to water pressure but inversely related to the pipe diameter. Finally, the FMEA analysis based on the knowledge management technique demonstrated that pressure management in WDNs is the main policy for risk reduction of leakage and failure.

On the experimental research of long-term hydrostatic performance and lifespan of polyethylene pipe

ABSTRACT Long-term hydrostatic (LTH) capacity test up to 10,000 h of polyethylene pipe (PE pipe) was successfully conducted according to Arrhenius theory. It was revealed that in some cases the pipe damage points initiate within the marker line on pipe body, indicating that the addictive of marker line could somehow weaken the mechanical property of pipe base materials. Test pressure test time data was fitted using dual-parameter model under the guidance of ISO9080: 2012, and its serving life was calculated as 28.9 years, ductile-brittle transition point was found at 8456 h. Conclusions drawn from this paper could contribute to understanding the long-term mechanical behaviour of PE pipe.

Application of Terahertz Nondestructive Testing Technology in the Detection of Polyethylene Pipe Defects.

At present, polyethylene pipeline is widely used in urban gas projects, but a relatively mature and reliable nondestructive testing technology has not been formed. Therefore, it is urgent to develop a new nondestructive testing technology to meet the increasing demand for inspection of non-metallic pipes. The terahertz testing technology and related equipment have played an increasingly important role in the nondestructive testing of many nonmetallic structures, but they have not been applied to polyethylene (PE) pipes. In this work, terahertz time-domain spectroscopy was used to detect prefabricated defects inside the PE pipe specimens. The results show that the terahertz nondestructive testing technology can be used to detect common defects in nonblack PE pipes with a detection error of less than 10%. Higher-power terahertz devices can detect defects in black PE pipe, while lower-power terahertz devices cannot. Because the black PE pipe contains carbon and has a strong absorption of terahertz waves. The penetration of lower-power terahertz devices to the black PE pipe is not enough, resulting in a low resolution of the imaging. The results of this work may promote the progress of the nondestructive testing technology of nonmetallic pipelines.

Determination of Blast Vibration Safety Criteria for Buried Polyethylene Pipelines Adjacent to Blast Areas, Using Vibration Velocity and Strain Data.

In order to ensure the safe operation of buried polyethylene pipelines adjacent to blasting excavations, controlling the effects of blasting vibration loads on the pipelines is a key concern. Model tests on buried polyethylene pipelines under blasting loads were designed and implemented, the vibration velocity and dynamic strain response of the pipelines were obtained using a TC-4850 blast vibrometer and a UT-3408 dynamic strain tester, and the distribution characteristics of blast vibration velocity and dynamic strain were analyzed based on the experimental data. The results show that the blast load has the greatest effect on the circumferential strain of the polyethylene pipe, and the dynamic strain response is greatest at the section of the pipe nearest to the blast source. Pipe peak vibration velocity (PPVV), ground peak particle velocity (GPPV), and the peak dynamic strain of the pipe were highly positively correlated, which verifies the feasibility of using GPPV to characterize pipeline vibration and strain level. According to the failure criteria and relevant codes, combined with the analysis of experimental results, the safety threshold of additional circumferential stress on the pipeline is 1.52 MPa, and the safety control vibration speed of the ground surface is 21.6 cm/s.

A Lifetime Prediction Method of Pressured Gas Polyethylene Pipes by Strain-Hardening Modulus and Tensile Test

In recent years, polyethylene (PE) pipes have been widely utilized for urban natural gas transmission. However, as the use of high-density polyethylene (HDPE) pipes increases, their service life and long-term performance assessment have become one of the most significant issues to be addressed. There has been a ton of studies on PE pipe life prediction techniques both domestically and internationally, but very little has been carried out on PE pipe life prediction in actual gas working environments with varying acid and alkaline levels. This experiment accelerates the aging of PE pipes using acid and alkaline corrosion immersion experiments to determine the lifespan of PE pipes. This study aims to investigate the performance changes of HDPE under strong, weak, and neutral corrosion conditions using corrosion solutions with PH values of 1, 5, and 8, to propose the impact of corrosion caused by various acids and alkalies on the HDPE aging life for natural gas, and to develop a mathematical model between the aging life of polyethylene and the PH values of acid and alkali corrosion solutions. The studies involved soaking and corroding HDPE pipes with various acidity and alkalinity chemicals to speed up the aging process, and then the tensile test was used to determine the mechanical characteristics of the aged PE pipes. Based on our findings, the empirical equation between acidity and service life of PE pipes is obtained by the mathematical fitting method, and a life prediction model of buried city gas HDPE pipes is proposed. The actual life of the aged pipes is determined by the relationship between strain-hardening (SH) modulus and aging time. The findings demonstrate that the service life of PE pipes changes with different levels of acidity and alkalinity: 1.872 days, 1060.507 days, and 1128.58 days following corrosive solution-accelerated aging with solution acidities of PH1, PH5, and PH8, respectively. The life prediction method applies to various plastic pipes in comparable environments as well as HDPE city gas pipes that are subject to acid and alkali corrosion forces.

Ultrasonic defect detection of high-density polyethylene pipe materials using FIR filtering and block-wise singular value decomposition

Condition monitoring of high-density polyethylene (HDPE) pipes used for fluid and gas transfer is important for the safety of energy conservation and the environment. Ultrasonic phased array imaging methods provide a solution to detect and assess defects in HDPE pipes. However, ultrasonic bulk waves propagating in these viscoelastic media are strongly attenuated, resulting in reduced signal amplitude. In this study, a linear-phase Finite Impulse Response (FIR) filter is used to remove unwanted frequency components from the measured ultrasonic signals to improve the signal-to-noise ratio before applying the imaging algorithm of the total focusing method (TFM). Building upon this, a block-wise singular value decomposition (SVD) technique, which can adaptively determine the singular value cutoff threshold based on each block in the whole TFM image, is used to enhance the obtained TFM image quality. The performance of the combination of FIR filtering and block-wise SVD technique is validated by experimental data of HDPE pipe materials. Results demonstrate that the proposed approach generates good images to provide the detection and characterization of side-drilled holes in HDPE pipe materials.

Influence of hydrogen-methane gas mixtures on the physical and chemical structure of polyethylene pipes of the operating gasdistribution networks of Ukraine

Influence of hydrogen-methane gas mixtures on the physical and chemical structure of polyethylene pipes of the operating gasdistribution networks of Ukraine

INFLUENCE OF GAS MIXTURES OF HYDROGEN WITH METHANE ON THE OPERATIONAL AND THERMOPHYSICAL CHARACTERISTICS OF POLYETHYLENE PIPES OF OPERATING GAS DISTRIBUTION NETWORKS OF UKRAINE

The paper presents the results of complex studies of the influence of mixtures of hydrogen gas with natural gas in the ratios of 10%Н2/90%СН4 and 20%Н2/80%СН4 on the operational and thermophysical characteristics of PE-80 polyethylene pipes and their material Research was conducted on an experimental stand, the diagram of which is attached. The results of comprehensive strength and thermophysical studies of the material of PE-80 polyethylene pipes, which were previously operated in the current gas distribution networks of Ukraine for 15 years, after 6 months of hydrogen exposure, are presented. In order to indicate possible changes in the properties of the material, the same complex of studies was carried out before hydrogen exposure of the samples. The influence of gas mixtures on the thermophysical properties of polyethylene pipes has been established, which is manifested in the reduction of the size of polyethylene crystallites and their orderliness in the volume of pipe walls under the influence of gas mixtures. At the same time, the appearance of crystallites of a new shape was found on the surface of the inner wall of the pipes. It is assumed that this may be caused by the competing action of methane and hydrogen molecules. In the course of conducting hydraulic tests on the resistance of pipes to internal pressure and mechanical studies on uniaxial tension, it was determined that all pipe samples, according to their strength characteristics, meet the requirements of regulatory documents issued for polyethylene pipes used for natural gas transportation. The relationship between the concentration of hydrogen in the mixture and the degree of its influence on the strength characteristics of the samples was established. No changes in the chemical structure of the material of polyethylene pipes were detected. It should be noted that the given results are only the beginning of a more detailed study, during which it is also planned to investigate the effect of hydrogen mixtures on technical polyethylenes after 12 and 24 months of hydrogen exposure. Bibl. 17, Fig. 11, Tab. 2.

Effect of recycled material on failure by slow crack growth in multi-layer polyethylene pipes

Among polymer materials, high-density polyethylene (HDPE) is one of the most demanded polymers for packaging as well as in sectors with higher material requirements, such as the plastic pipe industry. The extensive use of HDPE means it is often present in municipal waste. Therefore, there is a high potential for reprocessing and exploring new applications for recycled HDPE, aiming for a circular economy. In the plastic pipe industry, recyclates have found practical use in non-pressure applications. However, the high structural and loading requirements do not allow using it for pressurized pipes yet. The presented study is focused on the possible utilization of recycled HDPE in pressurized pipes in the form of a layer in a multi-layer pipe with two protective layers made of virgin HDPE. The performance of the pipes is assessed based on numerical simulations, coupled with lifetime estimations. The lifetime assessment is based on linear elastic fracture mechanics using experimentally measured slow crack growth (SCG) rates in the virgin and recycled HDPE grades. Thanks to the numerical models, it was possible to describe damage by SCG of the multi-layer pipe as well as to find the dependency of the pipe performance on the thickness ratio and material properties of the layers.

A novel strategy for construction of multiple dynamic hybrid crosslinking network for polyethylene pipes and self-healing behavior via thermal stimulation

Polyethylene (PE) pipes with excellent comprehensive performances have been most widely applied, while endowing PE pipes with self-healing property was conducive to prolong their service life. Due to nonpolar nature of PE molecules, its self-healing functionalization remains extremely challenging. In this work, by introducing amide and carboxyl groups into PE/natural rubber (NR) chains to construct reactive sites and compositing with zinc acrylate (ZDA)/ferric chloride (FeCl3), the hybrid crosslinking network composed of covalent bonds and multiple dynamic bonds, including hydrogen bonds, Fe3+-carboxyl/amide coordination bonds and Zn2+-carboxylate ionic bonds was successfully constructed in PE/NR blend via reactive processing and in-situ vulcanization crosslinking. Upon stretching, the dynamic crosslinking network was first broken, resulting in large energy dissipation, apparent hysteresis loss and stress relaxation, while when removing stress, its residual strain decreased remarkably with increasing waiting time, displaying reversible dynamic characteristic. As a result, the hybrid crosslinking network was reconstructed via thermal stimulation, facilitating diffusion and entanglement of PE/NR chains across interface, and the width/depth of the scratch obviously decreased. The tensile strength and fracture toughness recovered obviously, and the self-healing efficiency of the blends and pipes reached 65–70 %, showing a significantly enhanced self-healing ability with promising application potential.

Guided Wave Ultrasonic Testing for Crack Detection in Polyethylene Pipes: Laboratory Experiments and Numerical Modeling.

The use of guided wave-based Ultrasonic Testing (UT) for monitoring Polyethylene (PE) pipes is mostly restricted to detecting defects in welded zones, despite its diversified success in monitoring metallic pipes. PE's viscoelastic behavior and semi-crystalline structure make it prone to crack formation under extreme loads and environmental factors, which is a leading cause of pipeline failure. This state-of-the-art study aims to demonstrate the potential of UT for detecting cracks in non-welded regions of natural gas PE pipes. Laboratory experiments were conducted using a UT system consisting of low-cost piezoceramic transducers assembled in a pitch-catch configuration. The amplitude of the transmitted wave was analyzed to study wave interaction with cracks of different geometries. The frequency of the inspecting signal was optimized through wave dispersion and attenuation analysis, guiding the selection of third- and fourth- order longitudinal modes for the study. The findings revealed that cracks with lengths equal to or greater than the wavelength of the interacting mode were more easily detectable, while smaller crack lengths required greater crack depths for detection. However, there were potential limitations in the proposed technique related to crack orientation. These insights were validated using a finite element-based numerical model, confirming the potential of UT for detecting cracks in PE pipes.

POLYETHYLENE GAS PIPELINES: PRACTICAL POSSIBILITIES TECHNICAL DIAGNOSTICS

Technical diagnostics of in-service polyethylene-exhaust gas pipelines face a number of difficulties, since the existing methods of destructive control are not applicable for determining the mechanical and physical characteristics-stick of polyethylene pipes. The search for effective control methods that can most fully characterize the quality of pipe material and the interpretation of the results obtained are of scientific and practical interest. The article on the example of technical diagnostics of the polyethylene gas pipeline built in 1985 considers possible criteria for assessing the condition of pipes and their ranking by significance. It was found that polyethylene pipes produced during the development of their production did not always meet mandatory quality requirements and could have hidden defects in the form of inhomogeneities, cavities and cracks throughout the volume of pipe material. Based on the experimental studies carried out, it was shown that the pipe material during underground operation does not undergo significant changes in its initial characteristics. At the same time, it was noted that the pipe grades of polyethylene raw materials of the first generation had low resistance to slow crack growth, therefore, the presence of internal defects in the pipe material in owning value with the effect of concentrated loads can lead to premature loss of containment. The work carried out confirmed the possibility of a quantitative design assessment of the technical condition of the gas pipeline based on the results of destructive tests of pipes for long-term hydrostatic strength. The experimental data presented in the article are of interest to specialists who are faced with the need for expert assessment of the state of the pipes of the operated polyethylene gas wires and forecasting their service life.

Strain assessment of polyethylene pipes in dense sand subjected to axial displacement

Buried polyethylene pipes used in gas distribution systems can experience excessive wall strain when exposed to ground movement that can affect the performance of the pipes in service. This paper presents full-scale laboratory tests performed to investigate the responses of medium-density polyethylene (MDPE) gas-distribution pipes in dense sand when subjected to axial ground movement. Pipes buried in sand in a large test box were pulled at the rates of 0.5 mm/min, 1 mm/min, and 2 mm/min to simulate relative ground movement in the longitudinal direction. The test facility was instrumented to measure pulling force, pipe wall strain, and soil stress. The measured pullout force was significantly higher than predicted using the equations recommended in current design guidelines, which is attributed to the increase of normal stress on the pipe wall by shear-induced dilation of interface soil. The cavity expansion theory was successfully applied to calculate the normal stress increase. The distribution of measured strains was nonlinear along the pipe length. Assuming a parabolic distribution of the strains, simplified equations were developed to calculate pullout resistance and pipe wall strain from the relative ground displacement. The developed method reasonably predicted the pipe strain measured during the tests.

Terahertz Spectroscopy Characterization and Prediction of the Aging Degree of Polyethylene Pipes Based on PLS.

Polyethylene (PE) is widely used in pipeline transportation owing to its excellent corrosion resistance, good stability, and ease of processing. As organic polymer materials, PE pipes inevitably undergo different degrees of aging during long-term use. In this study, terahertz time-domain spectroscopy was used to study the spectral characteristics of PE pipes with different degrees of photothermal aging, and the variation in the absorption coefficient with aging time was obtained. The absorption coefficient spectrum was extracted using uninformative variable elimination (UVE), successive projections algorithm (SPA), competitive adaptive reweighted sampling (CARS), and random frog RF spectral screening algorithms, and the spectral slope characteristics of the aging-sensitive band were selected as the evaluation indices of the degree of PE aging. Based on this, a partial least squares aging characterization model was established to predict white PE80, white PE100 and black PE100 pipes with different aging degrees. The results showed that the prediction accuracy of the absorption coefficient spectral slope feature prediction model for the aging degree of different types of pipes was greater than 93.16% and the verification set error was within 13.5 h.

Benzene Diffusion and Partitioning in Contaminated Drinking Water Pipes under Stagnant Conditions.

Benzene contamination in drinking water systems affected by wildfires is a problem of emerging concern. Polyethylene pipes used in service lines and premise plumbing are vulnerable to permeation by benzene and can potentially cause challenges in sampling and remediation of contaminated systems. However, the kinetics and equilibria of the uptake of benzene by and release of benzene from pipes of differing polyethylene types and manufacturers are not well studied, leading to additional uncertainty when interpreting sampling data and selecting remediation options. This work addresses this data gap by providing diffusion and partitioning data for benzene and several varieties of polyethylene pipes, including field samples from water distribution systems. All polyethylene pipes that were studied exhibited similar partitioning behavior during benzene uptake and release, but some differences in kinetics were observed among pipes. However, these differences were of minor practical importance in the pipe contamination scenario examined in this work. The results of this study can be used in conjunction with diffusion modeling to inform remediation decisions for benzene-contaminated, polyethylene service lines, and premise plumbing.

Near-Surface Defects Identification of Polyethylene Pipes Based on Synchro-Squeezing Transform and Deep Learning

To conduct the ultrasonic weld inspection of polyethylene pipes, it is necessary to use low-frequency transducers due to the high sound energy attenuation of polyethylene. However, one of the challenges in this process is that the blind zone of the ultrasonic transducer may cover a part of the workpiece being tested. This leads to a situation where if a defect appears near the surface of the workpiece, its signal will be buried by the blind zone signal. This hinders the early identification of defects, which is not favorable in such a scenario. To address this issue, we propose a new approach to detect and locate the near-surface defects. We begin by performing a synchro-squeezing transform on the original A-scan signal to obtain an accurate time-frequency distribution. While successful in detecting and localizing near-surface defects, the method alone fails to identify the specific type of defect directly: a limitation shared with other signal processing methods. Thus, an effective and lightweight defect identification model was established that combines depth-wise separable convolution and an attention mechanism. Finally, the performance of the proposed model was compared and visually analyzed with other models. This paper successfully achieves the detection, localization, and identification of near-surface defects through the synchro-squeezing transform and the defect identification model. The results show that our model can identify both general and near-surface defects with an accuracy of 99.50% while having a model size of only 1.14 MB.

Interface heat transfer for hydronic heating: heating tests of concrete blocks and numerical simulations

ABSTRACT A comprehensive understanding of the heat transfer mechanism of hydronically-heated structures is crucial to predicting their heating performance. However, few studies considered the heat transfer at the interface of heating pipe and host material. In this paper, heat transfer at two critical interfaces for hydronically-heated concrete structures, e.g. pipe-concrete interface and concrete-air interface, has been tested and analyzed. Two concrete blocks, one with an embedded cross-linked polyethylene (PEX) pipe and one with an attached PEX pipe, were fabricated to represent heated bridge decks for the heat transfer study. The two blocks were tested inside a freezer box in a series of heating response tests at varied room and fluid temperatures. Measured temperatures at different depths were used to find the convection heat transfer coefficient and the thermal contact conductance between the concrete and PEX pipe through equations developed via finite difference method (FDM). Finite element models (FEM) of the two blocks were developed to verify the thermal contact values derived from a 1-D thermal resistance model. A comprehensive analysis of the temperature response of the models was performed, especially at the two interfaces, and the FEM models were able to predict the lab measurements accurately. The obtained contact heat transfer coefficient and the FEM models can be used for all hydronically-heated structures.

Effect of outdoor pipe materials and community-intrinsic properties on biofilm formation and chlorine resistance: Black sheep or team leader

Community-intrinsic properties affect the function and composition of microbial community, and understanding of the microbial community-intrinsic properties in different pipe materials of drinking water distribution systems can help to prevent microbial pollution more reasonably and efficiently. This study investigated the biofilm formation and chlorine resistance of multi-species biofilms in two representative outdoor pipe materials (polyethylene (PE) and cast iron pipe). The results showed that cast iron pipes have higher biofilm biomass but lower biofilm activity than PE pipes. The different growth environments of the two pipe materials resulted in diverse microbial community-intrinsic properties and affected multi-species biofilm formation. The microbial communities without Sphingomonas or Acidovorax in cast iron pipe exhibited higher biofilm biomass, when compared with those in PE pipe. In contrast, the microbial community without Bacillus in PE pipe presented higher biofilm biomass, when compared with those in cast iron pipe. Extracellular polymeric substance (EPS) and corrosion products protected bacteria from chlorination. Although community-intrinsic properties helped bacteria resist chlorination, the same microbial community exhibited diverse chlorine resistance in different pipe materials owing to different community-intrinsic properties. While the chlorine resistance of microbial community without Bacillus was low in PE pipe, that in cast iron pipe was better owing to high corrosion degree. Multi-species biofilm without Sphingomonas or Acidovorax presented higher biofilm biomass, but lower EPS content and corrosion products in cast iron pipe, resulting in low chlorine resistance. In summary, this study revealed that outdoor pipe materials could affect microbial community-intrinsic properties, which in turn could influence biofilm characteristics, and provided unique insights for ensuring drinking water safety.