Polyethylene Pipelines Research Articles

Justification of indirect methods of bending stresses polyethylene pipes evaluation

The world and Russian companies have a long experience of the polyethylene pipeline installation and operation. At the same time, the significant attention is paid to the improvement of the relevant machines and the production technology. The polyethylene pipeline installation experience proves that its operation properties (reliability and durability) depend on physical and mechanical characteristics of polyethylene, which should be saved during its installation. Defects can occur, including in cases when the pipe is subjected to the significant bending stresses during installation. To evaluate these stresses, including when exposed to cold weather conditions, an indirect method based on the relationship between strength characteristics and occurred deformations is proposed.

Evaluation of durability of buried polyethylene pipelines and tanks with a cellular wall

Evaluation of durability of buried polyethylene pipelines and tanks with a cellular wall

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

This work studies the lap-shear strength performance of polyethylene pipeline bonded with acrylic adhesive in the temperature range -10 to +20°C. Single lap shear test samples were firstly prepared at 20°C under various clamping pressures and curing times to determine suitable conditions under which to prepare and test further samples at temperatures of -10, -5, 0, +5 and +20°C. It was found that a decrease in curing/testing temperature to zero degrees resulted in a steady reduction in the lap-shear strength performance of the bonded joints from a mean value of 2.72MPa at +20°C to 1.15MPa at 0°C. Below zero degrees the strength of the bonded substrates was significantly reduced; no samples bonded at -5°C had sufficient strength to test and only one sample bonded -10°C was tested, which had very low strength of 0.105MPa.

Multi-directional force–displacement response of underground pipe in sand

A methodology is presented to evaluate multi-directional force–displacement relationships for soil–pipeline interaction analysis and design. Large-scale tests of soil reaction to pipe lateral and uplift movement in dry and partially saturated sand are used to validate plane strain, finite element (FE) soil, and pipe continuum models. The FE models are then used to characterize force versus displacement performance for lateral, vertical upward, vertical downward, and oblique orientations of pipeline movement in soil. Using the force versus displacement relationships, the analytical results for pipeline response to strike-slip fault rupture are shown to compare favorably with the results of large-scale tests in which strike-slip fault movement was imposed on 250 and 400 mm diameter high-density polyethylene pipelines in partially saturated sand. Analytical results normalized with respect to maximum lateral force are provided on 360° plots to predict maximum pipe loads for any movement direction. The resulting methodology and dimensionless plots are applicable for underground pipelines and conduits at any depth, subjected to relative soil movement in any direction in dry or saturated and partially saturated medium to very dense sands.

Design, construction and erection of seawater intake system to establish a biofouling test facility

Large amount of seawater is used in coastal industries, like power generating plants, desalination plants and aquatic culture farms. A similar requirement exists in Department of Atomic Energy campus at Kalpakkam, Tamil Nadu, India. Seawater in large quantities is required for its nuclear power stations and desalination plants erected on the east coast of Bay of Bengal situated in southern part of India. Such seawater systems have biofouling problems. Hence a seawater intake system has been designed, constructed and erected so that virgin seawater will be available for biofouling studies that was proposed to be carried in a once through flow test facility. A major criterion for the test facility was that continuous supply of seawater should be available at the rate of 160m3/h. To meet this requirement, centrifugal pumps were installed at about 150m away from the shoreline and connected to an intake structure using 600m long, 355mm OD, high density polyethylene pipeline laid on the seabed. Details of site selection, options of construction methods, materials selection, pressure drop calculations, sizing of pipes and anchor blocks, stability of intake pipeline, deployment criteria and project cost and planning have been discussed in this paper.

Polyethylene Pipeline Bending Stresses at an Installation

A polyethylene pipeline trenchless installation with special machines is one of methods of gas pipeline constructions between localities. A polyethylene pipeline is exposed to a short term bend and a significant deformation during an installation. The methods and research results of the polyethylene pipeline ability at the short term bending are presented below. The mathematical model has been created. The analytical calculations of the polyethylene pipeline stress state at the bend have been done and experimentally verified. The requirements have been formulated to ensure the necessary installed pipeline operation properties.

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.

Capacity Analysis and Safety Assessment of Polyethylene Pipeline With Local Wall-Thinning Defect

The purpose of this study is to propose a safety assessment procedure for polyethylene (PE) pipe with local wall-thinning defect. A uniaxial tensile test is performed to test the mechanical performance of PE. Then, the constitutive model for PE can be established. The limit load of the PE pipe with local wall-thinning defect can be studied with the method of combining the orthogonal design of experiment and finite element (FE) analysis. Then, the factors of local wall-thinning defect can be analyzed. The results show that the depth of the defect has a great effect on the limit load (internal pressure and bending moment) of PE pipe. The effects that the axial length of the defect and the circumferential length of the defect have on the limit load are not significant. Referring to the safety assessment of metal pipe proposed by GB/T19624-2004, a safety assessment for PE pipe with local wall-thinning defect is revised.

Design and Testing of the Strain Transducer for Measuring Deformations of Pipelines Operating in the Mining-deformable Ground Environment

Abstract Design and laboratory test results of the strain transducer intended for monitoring and assessing stress states of pipelines sited in mining areas are presented in this paper. This transducer allows measuring strains of pipelines subjected to external forces - being the mining operations effect. Pipeline strains can have a direct influence on a tightness loss and penetration of the transported fluid into the environment. The original strain gauge transducer was proposed for performing measurements of strains. It allows measuring circumferential strains and determining the value and direction of the main longitudinal strain. This strain is determined on the basis of measuring component longitudinal strains originating from axial forces and the resultant bending moment. The main purpose of investigations was the experimental verification of the possibility of applying the strain transducer for measuring strains of polyethylene pipelines. The obtained results of the transducer subjected to influences of tensile and compression forces are presented and tests of relaxation properties of polyethylene are performed.

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.

Parametric study of buried steel and high density polyethylene gas pipelines due to oblique-reverse faulting

A numerical study is carried out on buried steel and high density polyethylene (HDPE) pipelines subjected to oblique-reverse faulting. The components of the oblique-reverse offset along the horizontal and normal directions in the fault plane are determined using well-known empirical equations. The numerical model is validated using the experimental results and detailed finite element model of a 114.3 mm (4″) steel gas pipe subjected to a reverse fault offset up to 0.6 m along the faulting direction. Different parameters such as the pipe material, the burial depth to the pipe diameter ratio (H/D), the pipe diameter to wall thickness ratio (D/t), and the fault–pipe crossing angle are considered and their effects on the response parameters are discussed. The maximum and minimum compressive strains are observed at crossing angles of 30° and 90°, respectively. It is found that the dimensionless parameters alone are not sufficient for comparison purposes. Comparing steel and HDPE pipes, it is observed that HDPE pipes show larger compressive strains due to their lower strength and stiffness. For both steel and HDPE pipes, peak strains increase with increasing D/t and H/D ratio for a constant pipe diameter and fault offset. For a given H/D ratio, compressive strains increase with increasing D/t ratio in HDPE pipes, while in steel pipes considered in this study, this effect is negligible. Finally, the peak strains of the pipes are compared to those suggested by Canadian Standard Association for Oil and Gas Pipeline System, CSA Z662.

Reliability-Based Replacement of Polyethylene Gas Pipeline Networks

Lifetime management of underground pipelines is mandatory for safe hydrocarbon transmission and distribution systems. The use of high- density polyethylene tubes under pressure with the presence of external loading requires a reliability study to seek for the ideal operating conditions and the knowledge of the service limits, as reliability analysis is recognized as a powerful decision-making tool for risk-based design and maintenance. During the pipe life, the time-dependent phenomena, especially creep, take place, leading to a reduction of the pipe capacity. The reliability-based assessment of residual stress effects is carried out for underground polyethylene pipelines, under creep deterioration. This work is then applied to define optimal replacement for a gas distribution network, subjected to various operating conditions. The optimization of the total expected cost allows us to define the grouping strategy.

Adhesive technologies in repairing polyethylene pipelines

Adhesive technologies for repairing polyethylene pipelines are considered taking into account the peculiarities of gluing of substrates with a low surface energy. An epoxy composition is suggested based on the modified binder for application in the gluing repair technologies under consideration. It is shown that complex use of preliminary processing of glued surfaces and the composition that was developed allows an increase in the strength parameters of adhesive joints of polyethylene pipelines to be achieved.

Earthquake Response of Underground Pipeline Networks in Christchurch, NZ

This paper explores key aspects of underground pipeline network response to the Canterbury earthquake sequence in Christchurch, New Zealand, including the response of the water and wastewater distribution systems to the MW6.2 22 February 2011 and MW6.0 13 June 2011 earthquakes, and the response of the gas distribution system to the MW7.1 4 September 2010 earthquake, as well as the 22 February and 13 June events. Repair rates, expressed as repairs/km, for different types of pipelines are evaluated relative to (1) the spatial distribution of peak ground velocity outside liquefaction areas and (2) the differential ground surface settlement and lateral ground strain within areas affected by liquefaction, calculated from high-resolution LiDAR survey data acquired before and after each main seismic event. The excellent performance of the gas distribution network is the result of highly ductile polyethylene pipelines. Lessons learned regarding the earthquake performance of underground lifeline systems are summarized.

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.

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.

Creep functions for transients in HDPE pipes

New experimental results obtained from a high density polyethylene (HDPE) pipeline for transient conditions are presented and discussed. Transient pressure data at different pipe sections were collected. Peculiar features were observed, which are typical of viscoelastic pipes, in particular, a significant damping of extreme pressures was observed in comparison to what is typically obtained for metal pipes. Physical constraints of the pipe are important to describe some vibrations observed in the system. The viscoelastic transient solver developed by Covas et al. (2005) was used to carry out numerical simulations of experimental tests. The comparison of numerical results with experimental data has shown that the viscoelastic model accurately predicts observed transient pressures. Additional considerations are carried out about the calibrated creep function for this test case in comparison with the ones obtained in previous researches.

Influence of Polyethylene Pipe on the Quality of Water in a Water Distribution System

In the past two decades economic considerations and very good mechanical parameters of polyethylene pipes contributed to more and more common use of the pipes for construction and repair of water distribution systems all over world. This paper presents the results of research into parameters of water collected from a polyethylene pipeline which was a part of an operational water supply network. We determined Total Organic Carbon (TOC) content and the content of organic compounds in the examined water samples using a multichannel gas chromatograph (Trace Ultra Thermo) coupled with a mass spectrometer (Polaris Q). We identified organic compounds bounded with antioxidants, added to polyethylene in the process of pipe production, in the water samples.

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.