Numerical simulation of strength failure of buried polyethylene pipe under foundation settlement

Fragility analysis of continuous pipelines subjected to transverse permanent ground deformation

Polyethylene (PE) pipes are widely used in gas transmission projects due to their excellent performances. Earthquake is destructive and difficult to predicted, which is one of the major disasters caused PE pipe failure. The study was conducted on the mechanical behaviors and failure mechanisms of buried PE pipes under fault movement, and the effects of gas pressure, fault dislocation, soil and pipe size on the mechanical behavior of PE pipes were discussed. The study indicates that gas pressure has a less effect on the mechanical behavior of PE pipe. Under faults, the flatness curve of PE pipe is distributed symmetrically with respect to the fault plane. Deformation rules of PE pipe in different stratums are similar, while the pipe deformation is the largest in clay and it is smallest in sand. The greater the standard pipe size, the greater the diameter flatness coefficient is. The larger the diameter, the smaller the pipe diameter flattening parameter is. PE pipes with a larger standard dimension ratio of a fitting (SDR) and a smaller diameter are prone to failure in fault zone. The results can provide a basis for gas pipe design, laying, testing, and evaluation.

Mechanical behaviors and failure mechanisms of buried polyethylene pipes crossing active strike-slip faults

Mechanical response of buried polyethylene pipelines under excavation load during pavement construction

The serviceability loss of buried high-density polyethylene (HDPE) double-wall corrugated pipes caused by localized ground subsidence has been reported all over the world. Beam-on-nonlinear spring model is widely used to analyze the structural responses of buried pipes to the localized ground subsidence underneath the pipe. However, the pipe–soil separation is not considered by the beam-on-nonlinear spring model which assumes bonded interaction between the pipe and soil. This is because the spring stiffness could not be assigned as zero. The bonded interaction between pipe and soil is not able to capture the pipe behavior and characteristics of load distribution around the pipe when pipe–soil separation occurs. This study presents a series of large-scale model tests aiming to investigate the performance of buried HDPE double-wall corrugated pipes subjected to the localized ground subsidence. Movable plates installed at the bottom of the model test box are lowered down to simulate the localized ground subsidence. Earth pressures, pipe vertical displacements, and settlements at the backfill surface are monitored. For comparison purpose, free field condition (i.e., without pipe) is also tested. The test results demonstrate that soil settlement troughs above buried pipes are shallower and wider than those at the same elevation in the free field condition. Earth pressures at the top of the pipe are found to increase due to the negative soil arching, i.e., earth pressure is greater than the overburden pressure. It is suggested that three-dimensional soil arching, i.e., soil arching effects in both the transverse and longitudinal directions of the tested pipe, should be considered in calculating the earth pressures at the pipe top. The pipe–soil separation is substantiated by the observation that earth pressure measured at the bottom of the pipe is zero. Finally, empirical equations are proposed to correlate the volume of pipe displacement profile with the volume of settlement trough at the backfill surface to facilitate evaluation of the performance of the pipes subjected to the localized land subsidence.

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Laboratory evaluation of buried high-density polyethylene pipes subjected to localized ground subsidence

Polyethylene (PE) pipes are widely used in natural gas transportation systems in urban areas nowadays. As landslide caused by earthquake would cause destructive damage to buried pipes, increasing attention is attracted to the safety of buried PE pipes under seismic load. In this paper, the deformation behavior of PE pipe subjected to seismic landslide was investigated and a related failure criterion due to yielding was proposed. Based on extensive uniaxial tensile tests, a rate-dependent constitutive model of PE was applied to simulate the mechanical behavior of PE pipes. The extended Drucker-Prager model was used for surrounding soil. In our proposed finite element model, a quartic polynomial bending deflection displacement normal to the pipeline was loaded along the axial direction of PE pipe. The numerical simulation results revealed that the main failure mode of buried PE pipe subjected to seismic landslide shifted from bending deformation to ovalization deformation with increasing bending deflection. On the basis of deformation behavior analysis, failure criterion curves were put forward, which depicts the maximum relative deflection of the pipe cross-section, and the maximum displacement of the pipe versus pipe length subjected to seismic landslide. The results may be referable for design and safety assessment of PE pipes due to seismic landslide. [DOI: 10.1115/1.4026148]

Finite Element Analysis of Buried Polyethylene Pipe Subjected to Seismic Landslide

The invention relates to a load testing apparatus for polyolefin and composite pipe and the like thereof and aims to provide an internal pressure-bending load testing apparatus for a polyolefin pipe and a polyolefin composite pipe. The apparatus comprises an internal pressure loading device and a bending loading device; two ends of a to-be-tested pipe are respectively provided with a sealing device, and the internal pressure loading device is connected with the sealing device at one of the two ends; the bending loading device comprises a loading mechanism and a transmission device, and the transmission device is installed on a truss; a clamp of a middle suspended column is connected with the loading mechanism through a rod member and the transmission device; the loading mechanism is further connected with a controller; and the magnitude of a load and a loading rate are adjusted through controlling of the bending loading device, and force born and displacement generated by the middle section of the pipe are recorded in real time in the process of testing. According to the invention, the apparatus can simultaneously provide complex loads consisting of an internal pressure load and a bending static load or bending fatigue load for a pipeline at different temperatures so as to realize testing of mechanical behaviors or safety performance of polyolefin and composite pipes thereof under the action of multi-load coupling.

Internal pressure-bending load testing apparatus for polyolefin pipe and polyolefin composite pipe

Study on the Failure Mode of Cracking Through the Fitting of Electrofusion Joint

The utility model relates to a load testing device for a polyolefin pipe, a polyolefin composite pipe and the like, and aims at providing an internal pressure-bending load testing device for a polyolefin pipe and a polyolefin composite pipe. The device comprises an internal pressure loading device and a bending loading device, wherein sealing devices are arranged at two ends of a pipe to be detected, and the internal pressure loading device is connected to the sealing device at one end; the bending loading device comprises a loading mechanism and a transmission device, and the transmission device is arranged on a truss; a hoop of a middle suspension column is connected with the loading mechanism through a rod piece and the transmission device; the loading mechanism is connected with a controller; the controller is used for regulating a load and a loading velocity through control on the bending loading device, and force and displacement of the middle section of the pipe in a testing pressure are recorded in real time. The load testing device can simultaneously apply a composite load of an internal pressure load and a bending static load or a bending fatigue load to a pipeline at different temperatures so as to perform mechanical behavior or safety performance testing on the polyolefin pipe and the polyolefin composite pipe under a multi-load coupling effect.

Luo Xiangpeng

Papers

Numerical simulation of strength failure of buried polyethylene pipe under foundation settlement

Finite Element Analysis of Buried Polyethylene Pipe Subjected to Seismic Landslide

Internal pressure-bending load testing apparatus for polyolefin pipe and polyolefin composite pipe

Study on the Failure Mode of Cracking Through the Fitting of Electrofusion Joint

Internal pressure-bending load testing device for polyolefin pipe and polyolefin composite pipe