High Density Polyethylene Pipe Research Articles

Evaluation of Time Evolution of Mechanical Parameters of Polymeric Pipes by Unsteady Flow Runs

The paper presents the results of the calibration, by means of a microgenetic algorithm, of the mechanical parameters of high-density polyethylene pipes, to reproduce experimental unsteady flow runs in an installation consisting primarily of a steel pipe and of an additional polyethylene pipe. The mechanical parameters of viscoelastic models are estimated using both one-dimensional and quasi-two-dimensional models. Two sets of runs carried out at a distance of about 12 years are considered. The calibration of a three-parameter Kelvin-Voigt model provides evidence of the impossibility of obtaining general results. The use of a model with a single Kelvin-Voigt element (two-parameter model) gives good results in terms of comparison between numerical and experimental results for both pressure head and velocity. The calibration for the second series of tests shows increased deformability of the material (the reduction of the elastic modulus is more than 30%). The calibrated values of the retardation time result linearly correlated to the oscillations period, increasing with time due to the reduction of the elastic modulus. The obtained results allow evaluation of the viscoelastic parameters starting only with the knowledge of the equivalent elastic modulus.

Development of Innovating Materials for Distributing Mixtures of Hydrogen and Natural Gas. Study of the Barrier Properties and Durability of Polymer Pipes

With the growing place taken by hydrogen, a question still remains about its delivery and transport from the production site to the end user by employing the existing extensive natural gas pipelines. Indeed, the key challenge is the significant H 2 permeation through polymer infrastructures (PolyEthylene (PE) pipes, components such as connecting parts). This high flow rate of H 2 through PE has to be taken into account for safety and economic requirements. A 3-year project was launched, the aim of which was to develop and assess material solutions to cope with present problems for hydrogen gas distribution and to sustain higher pressure compared to classical high density polyethylene pipe. This project investigated pure hydrogen gas and mixtures with natural gas (20% of CH 4 and 80% of H 2) in pipelines with the aim to select engineering polymers which are more innovative than polyethylene and show outstanding properties, in terms of perme-ation, basic mechanical tests but also more specific characterizations such as long term ageing and behaviour. The adequate benches, equipments and scientific approach for materials testing had been developed and validated. In this context, the paper will focus on the evaluation of the barrier properties of 3 polymers (PE, PA11 and PAHM). Experiments were performed for pure H 2 and CH 4 and also in the presence of mixtures of hydrogen and natural gas in order to study the possible mixing effects of gases. It will report some round-robin tests that have been carried out. Secondly, by comparing data obtained on film, polymer membrane and on pipe section, the influence of the polymer processing will be studied. Innovative multilayers systems will be proposed and compared on the basis of the results obtained on monolayer systems. Finally, the evolution of the transport properties of the studied polymers with an ageing under representative service conditions will be discussed.

Morphology of high-density polyethylene pipes stored under hydrostatic pressure at elevated temperature

The morphology of unimodal and bimodal high-density polyethylene (HDPE) pipes during a hydrostatic pressure test was studied in detail using 1H solid-state NMR. Characterizing the changes of the molecular network during such a test is of key importance for understanding the long-term properties of different HDPE pipe grades. The changes in amount, thickness, and molecular mobility of the crystalline phase, the interface, and the amorphous phase of the two pipe grades with the storage time have been quantified for the first time. The most sensitive microscopic parameter to storage is the molecular mobility of the amorphous phase, with the strongest changes shown by the unimodal HDPE. The density of the tie-molecules is not the main factor controlling the very different behavior of the two pipe grades, but rather it is the density of the entanglements. The NMR results offer unprecedented insights into the changes in the molecular network and support existing deformation models.

Uniaxial Fatigue of HDPE-100 Pipe. Experimental Analysis

In this paper, an experimental analysis for determining the fatigue strength of PE-100, one of the most used High Density Polyethylene (HDPE) materials for pipes, under cyclic axial loadings is presented. HDPE is a thermoplastic material used for piping systems, such as natural gas distribution systems, sewer systems and cold water systems, which provides a good alternative to metals such as cast iron or carbon steel. One of the causes for failures of HDPE pipes is fatigue which is the result of pipes being subjected to cyclic loading, such as internal pressure, weight loads or external loadings on buried pipes, which generate stress in different directions: circumferential, longitudinal and radial. HDPE pipes are fabricated using an extrusion process, which generates anisotropic properties. By testing in the Laboratory a series of identical specimens obtained directly from PE-100 HDPE pipes in longitudinal directions, the relationships between amplitude stress and number of cycles (S-N curve) test frequency 2 Hz and stress ratio R = 0.0 are established.

Laboratory Study on Geosynthetic Protection of Buried Steel-Reinforced HDPE Pipes from Static Loading

AbstractGeosynthetic layers above a pipe can potentially reduce the deflection and strain in the pipe attributable to static loads. This paper discusses the laboratory results of shallowly buried steel-reinforced high-density polyethylene (HDPE) pipes subjected to static loads with or without geogrid. In the testing, static loads were applied to a steel plate seated on the ground with a 0.61-m-diameter steel-reinforced HDPE pipe buried in a compacted-sand trench. Four static loading tests were run with two different base courses and geogrids inside and above the trench. The test section was instrumented to record pipe deflections, earth pressures, and strains in the pipe wall and geogrid. Installation deflections were monitored and compared with a theoretical model. The measured earth pressures were compared with those estimated by the current AASHTO live-load distribution method. Reduced deflections and strains of the pipe were recorded as a result of the geogrid reinforcement. The type of base course al...

Environmental Assessment of Sewer Construction in Small to Medium Sized Cities Using Life Cycle Assessment

In a world with an increasing urban population, analysing the construction impacts of sanitation infrastructures through Life Cycle Assessment (LCA) is necessary for defining the best environmental management strategies. In this study, the environmental impacts of one linear meter of sewer constructive solution were analysed for different pipe materials and diameters used in Southern Europe; a unit of different sewer appurtenances (pump, manhole and inspection chamber) was also considered. The impacts of the pipe materials were compared considering different lifespan periods and high-density polyethylene (HDPE) turned out to be the worst option, being polyvinyl chloride (PVC) and concrete the most favourable ones. Few data are available on the material and energy flows in the installation stage; therefore, a comparative analysis of trenches with sand and concrete bedding was conducted. The results show that the installation stage represents up to 80 % of the total life-cycle impact of the constructive solutions. Concrete pipes with half-concrete/half-sand bedding are the best option and produce 20–30 % of the impact of HDPE pipes with concrete bedding. Hence, designers should focus not only on the pipe but also on the trench model. A methodology was presented to enable the impact aggregation of the different sewer elements, and Betanzos (Spain) was selected to conduct a pilot study in small cities. In the future, studies will need to incorporate the use and maintenance stage, as it is not standard and varies according to the physical features of the cities. Finally, this study provides basic concepts for developing eco-efficiency indicators.

Data Mining of the Thermal Performance of Cool-Pipes in Massive Concrete via In Situ Monitoring

Embedded cool-pipes are very important for massive concrete because their cooling effect can effectively avoid thermal cracks. In this study, a data mining approach to analyzing the thermal performance of cool-pipes via in situ monitoring is proposed. Delicate monitoring program is applied in a high arch dam project that provides a good and mass data source. The factors and relations related to the thermal performance of cool-pipes are obtained in a built theory thermal model. The supporting vector machine (SVM) technology is applied to mine the data. The thermal performances of iron pipes and high-density polyethylene (HDPE) pipes are compared. The data mining result shows that iron pipe has a better heat removal performance when flow rate is lower than 50 L/min. It has revealed that a turning flow rate exists for iron pipe which is 80 L/min. The prediction and classification results obtained from the data mining model agree well with the monitored data, which illustrates the validness of the approach.

A Stochastic Tool for Determining the Presence of Partial Blockages in Viscoelastic Pipelines: First Experimental Results

Partial blockages in water pipe networks may contribute to large energy dissipation throughout the system and reduce the service effectiveness for the customers. In this paper, a recently developed stochastic model using transient head measurements for detecting partial blockages in water pipelines is tested with two experimental case studies. The model is a stochastic Successive Linear Estimator (SLE, Yeh et al., 1996) previously used in groundwater hydrology for detecting the heterogeneity pattern of the subsurface. The model provides statistically the best unbiased estimate of diameter distribution due to partial blockages and quantifies the uncertainty associated with these estimates. Tests were carried out at the Water Engineering Laboratory of the University of Perugia (WEL) on two high density polyethylene pipe systems. In the experiments the partial blockages were simulated by placing a smaller diameter pipe of two different lengths between the main pipe. Results show that a first good estimate of the length and the size of the blockage can be obtained by a single short duration transient test executed by maneuvering a ball valve located far away from the blockage position.

Fracture Mechanics of Creeping Solids Applied to Pre-cracked NOL Ring Specimens to Predict Residual Lifetime of High Density Polyethylene Pipes

High Density Polyethylene (HDPE) is widely used for the distribution of drinking water and are exposed to an internal pressure due to water flow. Furthermore, when they are in contact with disinfectants, oxidation of HDPE occurs at the immediate surface of the inner wall. This leads to a decrease in the HDPE molar mass and consequently, to a hardening as well as an embrittlement of the material. The oxidised layer thickness seems to stabilize at 200μm whatever the initial pipe thickness due to the diffusion of reactive species in the inner wall. Inspections with a scanning electron microscope (SEM) of the inner wall of pipes collected on site, after several years of service, showed a network of cracks. The most noxious (deepest) longitudinal crack propagates under the steady internal pressure until the complete failure of the pipe. The experimental investigations consisted of creep crack growth tests, carried out on an original geometry for this type of test using NOL ring. These specimens were cut from the pipes and an internal longitudinal crack implanted. Creep crack growth tests were performed at various net stresses and at various crack depth ratios. At the end of each test, the time to failure was recorded. Before applying the theory of fracture mechanics of creeping solids, 3D finite element simulations were carried out to assess the suitability of assuming plane strain conditions. To this end, a porous viscoplastic model was implemented into an in-house finite element code. A fracture criterion based on critical porosity allowed for the simulation of creep crack growth. The localization of the maximum damage at mid-thickness and the thickness reduction were well captured. In these conditions, the crack front curvature is located near the surface so that a 2D calculation with plane strain conditions can then be justified to determine the C* load parameter. The residual lifetime of a real pipe containing a longitudinal defect, under in-service loading was estimated by using the correlation between the time to failure and the C*-integral.

폴리에틸렌 소재의 대구경 배관 설계 고찰

고강도/연성소재이면서 화학적으로 안정된 폴리에틸렌 소재가 배관으로 양산되면서 수도용 및 산업용으로 그 사용이 확산되고 있다. 최근에는 국내 플랜트에서도 기존 주철배관의 부식 누설 해소방안으로 고밀도 폴리에틸렌 배관이 사용되고 있는데, 각각의 플랜트 설계조건 및 운전조건을 적절히 고려하지 않을 경우 고밀도 폴리에틸렌 배관은 물리적인 손상이 유발될 수 있다. 폴리에틸렌 소재의 대구경 배관을 플랜트에 적용함에 있어 관련기준 및 설치 경험사례를 고찰한 결과, 수충격이 발생되는 환경에서 균열손상 가능성이 있어 폴리에틸렌 배관을 대구경 배관으로 사용시주의가 필요하다고 판단된다. As the polyethylene of high strength and ductility stabilized chemically has been mass-produced, it is spreading widely as material of industrial piping and water service piping. Recently, High density polyethylene (HDPE) pipe has been used even in water supply system of plant as buried pipe instead of cast iron pipe in domestic, but HDPE pipe has a probability of occurrence of damage if plant design and operating conditions are not considered. As a result of reviewing with respect of system design engineering based on operating conditions and verification test results, the specific design criteria for the use of HDPE piping in fire water supply system need to be established because of the possibility of crack damage due to water hammer.

원자력발전소 적용 고밀도 폴리에틸렌 배관의 맞대기 융착절차 및 검증절차 분석

In nuclear power plants, lined carbon steel pipes or PCCPs (pre-stressed concrete cylinder pipes) have been widely used for sea water transport systems. However, de-bonding of linings and oxidation of PCCP could make problems in aged NPPs (nuclear power plants). Recently at several NPPs in the United States, the PCCPs or lined carbon steel pipes of the sea water or raw water system have been replaced with HDPE (high density polyethylene) pipes, which have outstanding resistance to oxidation and seismic loading. ASME B&PV Code committee developed Code Case N-755, which describes rules for the construction of buried Safety Class 3 polyethylene pressure piping systems. Although US NRC permitted HDPE materials for Class 3 buried piping, their permission was limited to only 10-year operation because of several concerns including the quality of fusion zone of HDPE. In this study, various requirements for fusion qualification test of HDPE and some regulatory issues raised during HDPE application review in foreign NPPs are introduced.

Laboratory Tests to Evaluate Mechanical Properties and Performance of Various Flexible Pipes

AbstractThis study presents the experimental results for seven different tests carried out on high-density polyethylene (HDPE), PVC, and metal pipes with medium-size diameters. The main objective of the experimental program is to evaluate and characterize, under laboratory conditions, the performance and mechanical properties of the various flexible pipes considered in the study. The diameters of the pipes studied are 36 in. (914 mm) and 48 in. (1,219 mm). The laboratory tests conducted are the simple-beam test, parallel-plate test, flattening test, curved-beam test, joint-integrity test, and tensile test, as well as an environmental stress-cracking test. The results of the tests are presented in terms of load-deflection relations, load versus longitudinal and transverse strains, failure modes, and pipe stiffness. The test results indicate that HDPE and PVC pipes show good performance compared with metal pipes. In addition, the experimental results for flexible pipes meet AASHTO specifications. The HDPE a...

Experimental Study on Microwave Test of Cold Weld Defects in HDPE Piping Thermal Fusion Welds

In this paper, an effective method for detecting the cold weld defects in the thermal fusion weld of high-density polyethylene (HDPE) pipeline based on microwave technique is proposed. Using a microwave testing system, HDPE piping welds were examined in a proper position by frequency sweep within the range of 9.3-9.9 GHz. At a frequency that was most sensitive to the cold weld defects, the measured reflection coefficient S11 exhibited significantly different values between the good weld and those containing cold weld defects. The readily detectable differences in S11 value make identification of the cold weld defects possible. This work provides a basis for inspection of defects in HDPE piping welds.

Fracture characterization of high-density polyethylene pipe materials using the $$J$$ J -integral and the essential work of fracture

In this paper, fracture mechanics concepts are reviewed and their relevance to examine the toughness of highly deformable materials such as high-density polyethylene (HDPE) pipe materials is discussed. Using two different specimen configurations (single edge notched bending and compact tension), it was found that the \(J-R\) approach is unable to give pertinent indications on fracture toughness of HDPE. Alternatively, applying the essential work of fracture approach to double edge notched tension specimen, seems a more appropriate way to measure the fracture strength of HDPE and therefore to analyze the fracture process of such materials. Nevertheless, the severe necking occurring at the crack tip and in the plastic zone makes difficult the crack growth measurement, which clearly depends on the strain state and on the stress triaxiality level.

English

The effect of passive aeration on substrate quality, composting period and yield was studied using different perforated high-density polyethylene (HDPE) pipes arrangements, as a composting method for substrate preparation to Agaricus bisporus cultivation. The ingredients are, mixture of wheat straw (60%), wheat bran (5.5%), chicken manure (31%), urea (0.5%) and gypsum (3%) with initial moisture (75%) used for composting. It was demonstrated that passive aeration is the key parameter controlling composting process, shortened the compost period, enhance the substrate quality and Agaricus yield as of pile composting. The substrate physico-chemical characteristics that is, moisture content, temperature pattern, bulk density, pH, electric conductivity, C: N ratio and thermophilic fungi activity varied significantly with composting period. The parallel arrangement (10% perforations) was found best among all the passive aeration treatments for achieving the quality substrate in shortest composting period of 16 day and enhance the A. bisporus yield up to 27.6%. This study also opens possibility to cultivate A. bisporus on a lingo-cellulosic, non-pasteurized, non-conditioned, aerated substrate and that composting for 16 days improve the mushroom yield with minimum energy, labor and infrastructure.

Detecting Cold Weld Defects in HDPE Piping Thermal Fusion Welds Based on Microwave Technique

In the present paper, an effective method for detecting the cold weld defects in the thermal fusion weld of high-density polyethylene (HDPE) pipelines based on microwave technique is proposed. Using a microwave testing system, HDPE piping welds containing cold weld defects caused by insufficient heating time were examined by frequency sweep within the range of 9.2-9.9 GHz. At the frequencies that were most sensitive to the cold weld defects, the measured reflection coefficient S11 showed greatly different values between the good weld and those containing cold weld defects. The readily detectable differences in S11 value make the detection of the cold weld defects possible and feasible. This work provides insights for non-destructive testing of technical defects in HDPE piping welds.

Buried high-density polyethylene pipe deflections at elevated temperatures

The impact of elevated temperatures on high-density polyethylene (HDPE) pipe deflections when deeply buried is examined. Measurements of pipe deflection from full-scale physical tests are reported where 100-mm-diameter, DR 11, HDPE pipes backfilled with sand were subjected to a vertical pressure of 500 kPa for 1000 h while at temperatures of 22, 55 and 80 °C. Short-term vertical deflections were found to increase by a factor of 1.3 when the temperature was increased from 22 to 80 °C as increased temperatures resulted in greater circumferential compression of the pipe. Vertical pipe deflections continued to increase at a slow rate when the pressure was sustained for 1000 h, to values that were 1.4 to 1.2 times larger than the short-term deflections at temperatures of 22–80 °C, respectively. Even under elevated temperatures, it appears that ultimately HDPE pipe deflections are governed by the soil as, when extrapolated to 50 years, vertical deflections of −3.2% of the original mean pipe diameter were predicted at 22, 55 and 80 °C.

Microwave Scan Inspection of HDPE Piping Thermal Fusion Welds for Lack of Fusion Defect

In this paper, microwave scan inspection was employed to detect the lack of fusion defect existing in the thermal fusion welds of high-density polyethylene (HDPE) piping. The thermal fusion welds without defects were firstly inspected by microwave scan technique. The obtained microwave interference pattern and the scan image produced were taken as the evaluation standard. Then the thermal fusion welds containing lack of fusion defects obtained under different welding conditions were inspected, and the corresponding scan images were recorded. The problems occurring in the welding processes that lead to lack of fusion defects in thermal fusion welds can be distinguished by analyzing the scan images. Mechanical tests were performed to confirm the effectiveness and reliability of the microwave scan method in detecting the lack of fusion defects in thermal fusion welds of HDPE piping.

Simplified Design Equations for Joints in Buried Flexible Pipes Based on Hetényi Solutions

AbstractLaboratory experiments conducted on corrugated steel, PVC, and high-density polyethylene pipes have demonstrated that deformations in flexible pipes resulting, say, from surface live loads, attenuate rapidly away from the location of load application. As a result, while surface loads in the vicinity of a joint connecting two shallow buried pipe segments influence that joint, the deformations become negligible at the other ends of the two pipe segments. Therefore, solutions for shear, moment, and rotation have been developed assuming that the two pipes are very long, and that the response is not affected by the location or the characteristics of those other joints. This paper presents the formulations of the simplified design equations for flexible pipes, for both moment-transfer and moment-release joints. The design equations are developed using various closed-form solutions for beams on elastic foundations. A parametric study is then presented to examine the factors controlling the structural res...

Effect of Greenhouse Environment on Organics Migrating from Agricultural High-Density Polyethylene (HDPE) Pipes

Effect of Greenhouse Environment on Organics Migrating from Agricultural High-Density Polyethylene (HDPE) Pipes