High-density Polyethylene Pipelines Research Articles

Ultrasonic Inspection of Electrofusion Joints of Large Polyethylene Pipes in Nuclear Power Plants

High-density polyethylene (HDPE) pipe has many advantages such as good flexibility, corrosion resistance, and long service life. It has been introduced into nuclear power plants for transportation of cooling water in U.S. and Europe. Recently, four HDPE pipelines (PE4710) were used in essential cooling water system with operating pressure of 0.6 MPa and operating temperature of no more than 60 °C in a newly established AP1000 nuclear power plant in Zhejiang, China. The outside diameter and thickness are 30 in. and 3.3 in., respectively, which are much larger and thicker than traditional HDPE pipe for natural gas. This brought forward a challenge for nondestructive testing (NDT) and safety assessment of such pipes. In this paper, a solution for inspecting electrofusion (EF) joints of thick-walled HDPE pipes is presented, and the results of an on-site inspection of the nuclear power plant are revealed. To expand the thickness up-limit of previously developed ultrasonic-phased array instrument, an optimization method was proposed by calculating weighing effects of different testing parameters and introducing the concept of overall performance according to practical requirement, by comprehensively considering sensitivity, penetration, signal-to-noise ratio (SNR), resolution, and accuracy. Typical defects were found in field inspection. The result shows that the presented technique is capable of inspecting EF joints for connecting large-size HDPE pipes used in nuclear power plants.

Field Inspection of Corrugated HDPE Pipeline Network under Heap Piles at a Copper Mine Site in Chile

AbstractIn-service conditions of a corrugated high density polyethylene (HDPE) pipeline network embedded within a bioleaching pad in the Atacama Desert in Chile were assessed. The pipes provided air for the copper extraction process and were subjected to large overburden stresses generated by the ore heap pile. A pipe crawling device was developed for the study. The field data collected revealed that the pipes were suffering from excessive deflections, circumferential shortening, and flexural bending. Wall buckling was observed in some sections. The flexural bending affected the pipe joint integrity. Field data also revealed localized punctures at some locations because of ore rocks pressing against the pipes. A few sections showed reversed curvature and joint failure. These conditions can generate a loss of functionality for the pipeline system. After a review of the construction record, it was determined the distresses were a result of using inappropriate backfill material and a poor installation procedure.

Mechanical response of buried High-Density Polyethylene pipelines under normal fault motions

Permanent ground deformation is one of the most damaging hazards for continuous buried lifelines. In this paper, numerical models using a Finite Element Method (FEM) were developed to analyze the buried High-Density Polyethylene (HDPE) pipelines subjected to the normal fault motions. The numerical predictions, were compared with those from ASCE Guidelines and with the experimental results obtained from geotechnical centrifuge tests. Moreover, the paper focuses on the effects of the design parameters such as, pipe diameter and thickness, pipeline burial depth, friction angle and density of the soil surrounding the pipe on the maximum bending strain as well as bending strain distribution along the pipeline. The results show that numerical models using a finite element method could produce reasonable predictions. However, the maximum predicted bending strains from the ASCE Guidelines are larger than those from experiments. The pipe deformation mechanisms are also significantly influenced by variation in burial depth, pipe surface characteristics, and backfill type.

Case Study on Failures of Thermoplastics Pipeline Systems

The paper presents some of the most significant situations of tests realised on high density polyethylene pipeline networks from Romania, designed for fluids and gases, which failed during 2008-2014. The inspected objects were assemblies or welded components made of pipes and fittings, as parts of the natural gas and potable water pipeline. The inspections on various assemblies and weldments have identified a number of nonconformities, which have led to failures, generally recorded after welding, during operation. Based on the investigation results, a number of comments and recommendations have emerged, useful for manufacturing companies and for the clients, which could ensue increasing the safety in operation of the high density polyethylene pipeline systems.

Behavior of Bell and Spigot Joints in Buried Thermoplastic Pipelines

Failures in joints are among the most common sources of problems in buried gravity flow pipelines. Poor performance of these elements can cause infiltration and exfiltration, which lead to soil erosion and eventually to serviceability or strength limit states for the system. To prevent poor performance, joints should be designed to adequately accommodate the demands generated under normal loading conditions. Such demands are not clearly understood, however, because joint behavior has received scant attention. The goal of this research was to examine the response of gasketed bell and spigot joints in two, common, thermoplastic pipelines employed in gravity flow applications when subjected to live loading. The specimens examined were a high-density polyethylene pipeline, 1,500 mm in diameter, and a polyvinyl chloride (PVC) pipeline, 900 mm in diameter. Two burial depths and three loading locations were examined for each pipeline buried according to AASHTO guidelines. Moreover, two installations not specified by AASHTO were examined for the PVC specimen, which featured voids in the bedding under the joint. Subsequently, each specimen was loaded directly over the joint up to and beyond fully factored loads under recommended burial conditions to observe the joint performance and the final failure mode of the pipelines. The test measurements provide guidance on the key demands that develop at the joints and how they are influenced by the burial and loading condition. Finally, recommendations are made on the development of structural design procedures.

Geohazards and large, geographically distributed systems

A general classification for scale in geotechnical engineering is used to explore the modelling of large, geographically distributed systems and their response to geohazards. Both component and network performance are reviewed. With respect to components, prototype-scale experiments of underground pipeline response to abrupt ground deformation are described, including control of soil properties, soil–pipeline interaction, and performance of high-density polyethylene pipelines. Direct shear (DS) apparatus size is shown to have a significant effect on DS strength, and the most reliable DS device is identified from comparative tests with different equipment. Mohr–Coulomb strength parameters for partially saturated sand are developed from DS test data and applied in finite element simulations of soil–pipeline interaction that show excellent agreement with prototype-scale experimental results. Apparent cohesion measured during shear failure of partially saturated sand is caused by suction-induced dilatancy. With respect to networks, the modelling of liquefaction effects on the San Francisco water supply is described, and a case history of its successful application during the Loma Prieta earthquake is presented. The systematic analysis of pipeline repair records after the Northridge earthquake is used to identify zones of potential ground failure, and correlate pipeline damage rates with strong ground motion. Hydraulic network analyses are described for the seismic performance of the Los Angeles water supply, with practical applications for emergency response. The effects of Hurricane Katrina are reviewed with respect to the New Orleans hurricane protection system, Gulf of Mexico oil and gas production, and interaction between electric power and liquid fuel delivery systems. The sustainability of the Mississippi delta is discussed with regard to flood control, maintenance of wetlands and barrier islands, and catastrophic change in the course of the Mississippi River.

Structural Deformation Characteristics of Installed HDPE Circular Pipelines

This study presents a survey of deformation characteristics of the installed high-density polyethylene (HDPE) pipelines. Video and laser inspections are carried out on over 15,000 ft (4,572 m) of buried HDPE pipelines installed across the nation. Different types of deformation failure modes observed in the buried HDPE pipelines are identified in this paper. The results show that the majority of buried HDPE pipelines have deformations in excess of the commonly acceptable limits along multiple locations within each pipeline.

Triboelectrostatic Separation for Recycling of Seaweed-Drying Net Frame Plastic Wastes

In this research, on the basis of the control of electrostatic charge, a laboratory-scale triboelectrostatic separation for separating polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS) in seaweed-drying net frame plastic wastes has been carried out. High density polyethylene (HDPE) in a charger material selection tests using a vertical-reciprocation system was found to be the most effective materials for a tribo-charger in the separation of PP, and ABS. In lab-scale triboelectrostatic separation tests using the HDPE pipeline charger, the charge-tomass ratio (nC/g) of the mixed PP and ABS increased when the air velocity was adjusted to over 10 m/s. The optimum splitter position estimated by Newton’s separation efficiency (� n) was a position +4 cm from the central. Furthermore, under the conditions of over 385 kV/m electric field and less than 30% relative humidity, a PP grade of 99.70% and a recovery of 92.30% could be obtained. [doi:10.2320/matertrans.MRA2008268]

Buried high-density polyethylene pipelines subjected to normal and strike-slip faulting — a centrifuge investigation

Permanent ground deformation is arguably the most severe hazard for continuous buried pipelines. This paper presents results from two pairs of centrifuge tests designed to investigate the differences in behavior of buried high-density polyethylene pipelines subjected to normal and strike-slip faulting. The tests results show that, as expected, the pipeline behavior is asymmetric under normal faulting and symmetric under strike-slip faulting. In the case of strike-slip faulting, the soil–pipe interaction pressure distribution is symmetric with respect to the fault. However, in the case of normal faulting, there is a pressure concentration close to the fault trace on the up-thrown side, with much lower soil–pipe interaction pressures at other locations on the pipe. The soil–pipe interaction force versus deformation relationship (i.e., the p–y relationship) was obtained based on the experimental data. The p–y relationships for both the strike-slip and normal faulting cases were also compared with the relationships defined within the American Society of Civil Engineers (ASCE) guidelines. It was found that, for the case of strike-slip faulting, the experimental p–y relationship is generally consistent with the ASCE guidelines. In contrast, the experimental p–y relationship is much softer than that defined by the ASCE guidelines for the normal faulting scenario.

Effect of structural parameters on rapid crack propagation and slow crack growth in high density polyethylene pipeline materials

The influence of molecular structure and microstructure on the fracture of high density polyethylene materials has been studied. By changing the chromium-based catalyst composition and optimising polymerisation conditions, polymers having differing levels of branching, comonomer unit placement and breadth of molecular weight (MW) distribution have been prepared. Structural analyses obtained by gel permeation chromatography (GPC), thermal analysis and elution fractionation were correlated with mechanical characteristics obtained from S4 tests, notch pipe tests and modified plane strain impact Charpy tests. The structural factors underlying this correlation are discussed. Specifically, the ability to place short chain branches into high MW fractions appears to provide good resistance to slow crack growth, whereas the degree of crystallinity and lamellar thickness play a decisive role in the rapid crack propagation process. Polymer grades with improved resistance to both rapid crack propagation and slow crack growth have been successfully produced.