Medium Density Polyethylene Pipes Research Articles

Finite Element Analysis of Polyethylene Pipe with Elliptical Hole Supported by Saddle Fusion Patch with Fin

Underground pipe installation is one of the crucial components in supporting industrial activities. Damage to the underground pipe is typical and usually done by patching repair. Analysis of the stress distribution on pipe with patch has been done previously. An analysis needs to be done to determine the effectiveness of the patches and the effect of the growth of the damage. The purpose of this paper is to know the effect of the application of fins on the saddle fusion patch with variations in the number of fins, fin angle orientation, and fin height on the stress distribution on the PE 80 pipe. The research was carried out on a polyethylene pipe with elliptical defects that have been repaired with a saddle fusion patch with a fin as a stiffener. The pipe is a medium-density polyethylene pipe (MDPE80), and the patched is high-density polyethylene (HDPE100). The variation in the research is the fin’s height, the fin’s number and orientation of the fin, and the variation of defect dimension as representative of crack growth. The study was carried out using a finite element analysis tool, ANSYS 2020. The simulation results showed that the addition of fins and the difference in given height on the saddle fusion patch could reduce the stress acting on the cracked pipe. The stress drop that occurs in the addition of the number of fins is not only influenced by the number of fins but also influenced by the orientation of the added fins. The results of this study will provide an overview of the optimal patch thickness after being given reinforcement by fins added to the patch. The hole variations carried out aim to simulate so that the damage that occurs does not repeat itself after being given a patch. Information regarding the optimal and efficient patch thickness becomes an input that is used as a consideration in determining effective and economical repair steps.

Novel communication system for buried water pipe monitoring using acoustic signal propagation along the pipe

PurposeWireless sensor networks (WSN), as a solution for buried water pipe monitoring, face a new set of challenges compared to traditional application for above-ground infrastructure monitoring. One of the main challenges for underground WSN deployment is the limited range (less than 3 m) at which reliable wireless underground communication can be achieved using radio signal propagation through the soil. To overcome this challenge, the purpose of this paper is to investigate a new approach for wireless underground communication using acoustic signal propagation along a buried water pipe.Design/methodology/approachAn acoustic communication system was developed based on the requirements of low cost (tens of pounds at most), low power supply capacity (in the order of 1 W-h) and miniature (centimetre scale) size for a wireless communication node. The developed system was further tested along a buried steel pipe in poorly graded SAND and a buried medium density polyethylene (MDPE) pipe in well graded SAND.FindingsWith predicted acoustic attenuation of 1.3 dB/m and 2.1 dB/m along the buried steel and MDPE pipes, respectively, reliable acoustic communication is possible up to 17 m for the buried steel pipe and 11 m for the buried MDPE pipe.Research limitations/implicationsAlthough an important first step, more research is needed to validate the acoustic communication system along a wider water distribution pipe network.Originality/valueThis paper shows the possibility of achieving reliable wireless underground communication along a buried water pipe (especially non-metallic material ones) using low-frequency acoustic propagation along the pipe wall.

Analysis of Acoustic Signal Propagation for Reliable Digital Communication along Exposed and Buried Water Pipes

Wireless sensor networks (WSN) have emerged as a robust and cost-effective solution for buried pipeline monitoring due to the low cost (a maximum of a few tens of UK pounds (GBP)), low power supply capacity (in the order of 1 watt/hour) and small size (centimetre scale) requirements of the wireless sensor nodes. One of the main challenges for WSN deployment, however, is the limited range of underground data communication between the wireless sensor nodes of less than 3 m, which subsequently increases deployment costs for a utility owner for buried pipeline monitoring. A promising alternative to overcome this limitation is using low-frequency (<1 kHz) acoustic signal propagation along the pipe. This paper examines the feasibility of using low-frequency acoustic signal propagation along exposed and buried medium-density polyethylene (MDPE) pipes and makes predictions of the potential distances at which reliable data communication can be achieved. Quantification of the acoustic attenuation was performed using both analytical and numerical models in addition to laboratory and field experiments. The predicted acoustic data communication distance ranged between approximately 18 m for an exposed and approximately 11 m for a buried MDPE pipe. These results demonstrate the feasibility of using low-frequency acoustic signal propagation for achieving reliable wireless underground communication.

Beam-on-spring modeling of buried MDPE pipes in sand subjected to lateral loads at a pipe junction

Buried pipelines in landslide areas may experience excessive stresses or strains that depend on a complex soil-pipe interaction. The simplified beam-on-spring analysis is recommended in current pipe design guidelines to assess buried pipes subjected to ground movements. The recommended method was developed based on observations of buried steel pipes. The applicability of the methods was not evaluated for Medium-Density Polyethylene (MDPE) pipes that are widely used in gas distribution systems. This paper evaluates the applicability of the beam-on-spring modeling technique for MDPE pipes experiencing relative ground movements observed in laboratory tests. Finite element analysis was performed, modeling the pipes as beams and the soil reactions using the pipe-soil-interaction (PSI) elements in Abaqus, representing springs. The study reveals that while the beam-on-spring analysis can simulate the pipe responses, the spring parameters recommended in the design guidelines are not applicable to buried MDPE pipes. The required magnitudes of peak axial and lateral spring forces and the yield displacements for MDPE pipes are larger than those recommended in the design guidelines. Based on the simulation of experimentally measured pipe responses, modifications to the recommendations of existing design guidelines for estimating the spring parameters are proposed for application to the MDPE pipe assessment.

Effects of Axial Relative Ground Movement on Small Diameter Polyethylene Piping in Loose Sand

Small diameter (42 mm) medium density polyethylene (MDPE) pipes are widely used in the gas distribution system in Canada and other countries. They are sometimes exposed to ground movements resulting from landslides or earthquakes. The current design guidelines for evaluating the pipes subjected to ground movement were developed for steel pipes of larger diameters and may not apply to flexible MDPE pipes. This paper evaluates 42 mm diameter MDPE pipes buried in loose sand under axial relative ground movement for developing a design method for the pipes. MDPE is a viscoelastic material; therefore, the behaviour of MDPE pipes exposed to landslides would depend on the rate of ground movements. In this research, full-scale laboratory tests were conducted to investigate the responses of buried pipes under various rates of relative axial displacement. Finite element modelling of the tests was used to interpret the observed behaviour using the continuum mechanics framework. The study revealed that the pulling force on the pipe depends on the rate of relative ground displacement (pulling rate). The nondimensional pulling force possessed a nonlinear relationship with the pulling rate. A rate-dependent interface friction angle could be used to calculate the maximum pulling forces using the conventional design guidelines for the pipes in loose sand. Based on the pulling force, the pipe wall strains can be estimated using the methods available for larger diameter pipes.

Modeling Time-Dependent Behavior of Medium-Density Polyethylene Pipes

AbstractMedium-density polyethylene (MDPE) pipes are widely used for gas transmission and distribution systems. The behavior of the pipes buried in the ground is governed by soil–pipe interaction. ...

On the Response of Polyethylene Pipes to Lateral Ground Movements: Insights from Finite-Discrete Element Analysis

The current knowledge of the behaviour of polyethylene pipes subjected to lateral soil movement is limited and the commonly used design equations were initially developed for steel pipes. In this study, an attempt has been made to understand the soil–structure interaction using a three-dimensional finite-discrete (FE-DE) element model of a medium density polyethylene (MDPE) pipe buried in dense sand and subjected to lateral soil movement. The soil particles are modelled using discrete elements, while the pipe is modelled using finite elements and interface elements are introduced to transfer the forces between the two domains. Validation is performed using experimental data. This study shows that, when a pipe section experiences lateral movement induced by two symmetrically applied loads, the pipe will resist the imposed lateral forces by bending. Particle displacement patterns show that passive wedges develop locally close to the applied loads and the remaining pipe sections experience negligible deformation. Furthermore, it is found that the current expressions used to estimate the ultimate lateral soil force on buried pipes in granular soil, which is generally developed for rigid steel pipes, should be used with caution as they may overestimate the soil load on flexible MDPE pipes.

Damage evaluation and protection method of resin pipe for gas conduit subjected to impact load

Medium-density polyethylene pipe has been widely introduced to low-pressure gas pipes because of its high flexibility and corrosion resistance. However, many third-party damages due to the impact of heavy equipment have been reported during the construction every year, thus, to prevent the third-party damage, materials such as high-density polyethylene and polyamide have been considered as the new gas pipe candidates. However, their impact resistance capacity under the third-party attack has not been clarified. In this study, static and impact loading experiments were conducted to compare load resistance capacities. As a result, it was revealed that the high-density polyethylene pipe and the polyamide pipe had higher static load capacity and impact resistance than the medium-density polyethylene pipe. By comparing the absorbed energy of the static test and the impact test and calculating the pseudo absorbed energy of the impact test, the evaluation formula judging the safer side of whether the penetration occurred was proposed. Furthermore, as one of the methods to protect the gas pipe, the protective effect of winding a sheet made of reinforced fiber and non-woven fabric was clarified.

A finite-discrete element approach for modelling polyethylene pipes subjected to axial ground movement

ABSTRACT The response of medium-density polyethylene (MDPE) pipes subjected to ground movement is often investigated using soil-pipe interaction models that were originally developed for steel pipes. In this study, the behaviour of MDPE pipes buried in dense sand under pull-out force is investigated using a coupled finite-discrete element framework. The pipe is modelled using finite elements whereas the granular soil is modelled using discrete elements. The model is validated using experimental data and then used to investigate the response of the pipe and the surrounding soil. The response of the MDPE pipe-soil system to axial loading is found to differ significantly from that of steel pipes due to the elongation and distortion that develop in the MDPE pipes, which affect the mobilized friction forces along the pipe. This study demonstrates that caution must be exercised when using current methods in the analysis of MDPE pipes.

Prediction of leak flow rate in plastic water distribution pipes using vibro-acoustic measurements

Leakage from water distribution systems is a worldwide issue with consequences including loss of revenue, health and environmental concerns. Leaks have typically been found through leak noise correlation by placing sensors either side of the leak and recording and analysing its vibro-acoustic emission. While this method is widely used to identify the location of the leak, the sensors also record data that could be related to the leak’s flow rate, yet no reliable method exists to predict leak flow rate in water distribution pipes using vibro-acoustic emission. The aim of this research is to predict leak flow rate in medium-density polyethylene pipe using vibro-acoustic emission signals. A novel experimental methodology is presented whereby circular holes of four sizes are tested at several leak flow rates. Following the derivation of a number of features, least squares support vector machines are used in order to predict leak flow rate. The results show a strong correlation highlighting the potential of this technique as a rapid and practical tool for water companies to assess and prioritise leak repair.

The effect of sunlight on medium density polyethylene Water pipes

The suitability of medium density polyethylene (MDPE) water pipes beyond (2 years) being stored outdoors was studied. The resistance of MDPE pipes to ultraviolet (UV) radiation was evaluated by measuring changes in tensile strength at break. MDPE pipes under study have two formulations: the first without carbon black (virgin) and the anther with carbon black, the samples were exposed to UV radiation using an accelerated weatherometer for (200 h) to simulate the effect of (2 years) of exposure to sunlight. The values of tensile strength at break of MDPE with C.B have higher values (160.7Kg/cm2) than virgin MDPE(137Kg/cm2) after exposure MDPE with C.B cutoff at 25% of strain with tensile strength about (161Kg/cm2) before exposure to UV radiation, but it is cut off at 50% of strain with the same value of tensile strength after exposure. The percentage of carbon black and the degree of its dispersion have been determined by employing thermogravimetry (TGA) technique and reflected light microscopy respectively

Effect of defects on the burst failure of butt fusion welded polyethylene pipes

With the increasing demand of Medium density polyethylene (MDPE) pipes for gas transmission, the safety concern related with welding defects is becoming a serious matter. In this paper, experimental burst tests and finite element analyses were employed to study butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes. These defects were used to simulate lack of bonding during the welding. Test results showed that in all pipe test cases, the failure location originated from pipe substrates, even though the defect size was increased to 45% of the pipe’s wall thickness. The burst pressure could be estimated by the expression employed in the ASME BPVC, and in the burst pressure, the hoop stress was 20.28 MPa. Simulation results showed that the failure position was not only affected by the defect size, but also by the welding bead. It can be argued that a single welding defect whose maximum size is smaller than 15% of the thickness can be used without failure during short-term usage, even when there is no welding bead in the welded joint.

Effects of defects on failure of butt fusion welded polyethylene pipe

Medium density polyethylene (MDPE) pipes are usually welded together by butt fusion welding. The quality of butt fusion welded MDPE pipe joints is seriously affected by welding defects sometimes. This paper presented the results of tension test, burst test, three-point bending test, crush test, and fatigue test to show the effect of a single welding defect on the failure of butt fusion welded MDPE pipe joints. The fracture resistance of the joints without welding defects was studied by a fracture test too. The results showed that under the tension, pressure, bend, and crush loadings, the failure of the joints was not affected by the single welding defect if the defect size was smaller than 15% of the pipe's wall thickness regardless of the defect geometry, but the defect accelerated the failure even though the defect size was only 15% of the pipe's wall thickness under the fatigue loading.

Effects of Defect Size on Crush Test Load of Butt Fusion Welded MDPE Pipes

It is expected that the size of welding defect affects the mechanical performance of welded medium density polyethylene (MDPE) pipe joints. In this study, butt fusion welded MDPE pipe joints with a single spherical or planar defect of various sizes were studied using experimental crush testing and also by finite element method. The crush test showed that the mechanical performance of crush was not affected by the size and geometry of a single welding defect when the defect size was increased to 45% of the pipe's wall thickness. The simulation results indicated that the effect of the single welding defect on the Von Mises stress distribution near the defect explained the reason of the test results.

Study on Viscoelastic Behavior During Slow Crack Growth of Medium Density Polyethylene Pipes

The viscoelastic behavior of a medium density polyethylene (MDPE) pipe is investigated by using samples cut out from thick-walled MDPE pipe. Preliminary experimental work has been performed to characterize the nonlinear time-dependent response of such semi-crystalline thermoplastic material. Tests have been carried out at 80 °C, on smooth tensile, full notched creep tensile (FNCT) and pennsylvania notched tensile (PENT) specimens. Research on the resistance to slow crack growth (SCG) of MDPE pipes and prediction of pipe lifetime is also presented. The primary aim of this investigation is focused on the simulation and analysis of the stress and strain distribution of the crack tip using finite element method, which is helpful to understand the mechanism of crack propagation. The results demonstrate that the resistance to SCG of welding joint is worse than the pipe, and it can be concluded that FNCT not only describes the SCG behavior, but also it has less fracture time than PENT.

Effects of defect size on failure of butt fusion welded MDPE pipe under tension

Since medium density polyethylene (MDPE) pipes are increasingly used in the gas industry, welding defects are becoming a safety concern. In this study, butt fusion welded MDPE pipe joints with spherical and planar defects of various sizes were studied by experimental tensile tests and finite element analysis. These defects were considered for simulating lack of bonding during the welding. The tensile test results showed that pipe strength was not reduced by defects that were up to 15% of the pipe’s thickness in size. On the other hand, when the size of the defect was increased to 30% and 45% of the thickness, the failure strain decreased considerably. Finite element analysis verified that the effects of steel defects inserted intentionally before welding are comparable to those of air defects, which are close to actual weld defect conditions. Hence, the experimental results obtained in this study can represent the actual situation. It is argued that a single welding defect with a maximum size smaller than 15% of the pipe’s thickness can be accepted without compromising the structural integrity of the pipe during short term of usage not considering long term creep or slow crack growth.

A Study on Proper Location of Welding Defect in Three Point Bend Testing with MDPE Pipe

Welding defects affect the performance of welded pipe joints. In this study, a three point bend test of welded steel and medium density polyethylene (MDPE) pipe joints with defects of various defect locations and defect materials was studied using the finite element method. The defect was assumed to be located at 12 oclock, 3 oclock or 6 oclock direction. The results showed that pipes failed more easily on the compression side due to stress or local buckling. The air defect was more dangerous than the steel defect if the defect was located in the compression side; otherwise, the defect material effect on the integrity of pipes was ignorable. It is argued that the integrity of pipes with defects in the compression side is weaker than that in other regions, and the defect should be located in the compression side or the 12 oclock position in the three point bend test to maximize the effect of defect existence on the pipe structural integrity.

Effects of Defects on Failure of Butt Fusion Welded Polyethylene Pipe

Medium density polyethylene (MDPE) pipes are usually welded together by butt fusion welding. The quality of butt fusion welded MDPE pipe joints is seriously affected by welding defects sometimes. This paper presented the test results of an experimental tension test, burst test, three-point bend test, crush test, and fatigue test to show the effect of a single welding defect on the failure of butt fusion welded MDPE pipe joints. The fracture resistance of the joints without welding defects was studied by a fracture test too. The results showed that, under the tension, pressure, bend, and crush loadings, the defect could not increase the failure of the joints if the defect size was smaller than 15% of the pipe's wall thickness regardless of the defect geometry, but the defect increased the failure even though the defect size was only 15% of the pipe's wall thickness under the fatigue loading.

Erosive Failure of Natural Gas Pipes

This paper presents the study of the sequential failures of a nominal pipe size 8 (API 5L X42) carbon steel and SDR 17 medium density polyethylene (MDPE) pipes near a high-pressure water pipe. The study was conducted by reviewing the background information and visual inspection on failed specimens. The investigation revealed that a jet issuing from a water pipe joined with surrounding soil to form a slurry with highly erosive properties. The impact of this slurry upon the pipe caused the loss of pipe coating material and thinning of the pipe surface, which eventually led to its failure. Subsequently weaker ground support caused the MDPE pipe to sink into the high-speed gas jet from the failed API 5L X42 pipe. The high impact of the gas jet physically hit the MDPE pipe, causing its rapid erosion.

Failure Investigation of Natural Gas Pipeline

A study was carried out to investigate the probable cause or events that might have led to the failure of two parallel natural gas pipes, API 5L X42 carbon steel (NPS 8) and the SDR 17, 125 mm medium density polyethylene pipes. These two pipes were laid side by side in the same trench with a water pipe. The investigation was performed by analyzing the existing design and construction data, visual inspection of failed pipes, and pipe material analysis. Investigation from the relevant pipes data suggests that the leaked water pipe was the first to fail. The leaked water pipe created high pressure water jetting that mixed with the backfilling soil to form water–sand–soil slurry with high erosive properties. The impact of this erosive slurry upon the NPS 8 pipe had caused serious losses of pipe coating materials. This phenomenon explains the rapid thinning of the steel pipe body which later led to its failure. Evidence from the metallurgical study using photomicrograph showed that the morphology of the steel material was consistent and did not show any evidence of micro fractures.