Experimental approach to mechanical property variability through a high‐density polyethylene gas pipe wall

Abstract

An experimental investigation was designed to establish the distribution of mechanical properties throughout a high-density polyethylene (HDPE) gas pipe wall. The proposed approach used a continuous and uniform filament that was automatically machined from the pipe on a precision lathe at a very low cutting speed and an optimal depth of cut to minimize heating and structural disturbances. Typical engineering stress-strain curves, in every layer, were obtained on a testing machine especially designed for polymers, and they were statistically analyzed. The stress-strain behavior of HDPE pipe material could basically be divided into three distinctive zones, the second of which remained important. The average stress level illustrating cold drawing for a given layer was almost constant throughout the pipe wall. The measured stresses and moduli correlated very well with the pipe thickness, and they increased from the outer layers toward the inner layers. This was explained by the crystallinity evolution because the pipe production process was based on a convective watercooling system with a temperature gradient, which generated residual stresses. Computed statistical stress-strain correlations at yielding, the onset of cold drawing, and fracture points revealed acceptable linear relations for an error level of p Յ 0.05. On the other hand, an increasing linear correlation characterized the relationship of the yield stress and elastic modulus. This result was confirmed by literature for standard specimens, prepared by compression molding, that did not represent an actual pipe structure with respect to an extrusion thermomechanical history. Such an approach to mechanical property variability within an HDPE pipe wall highlighted the complexity of the hierarchical structure behavior in terms of stress-strain and long-term brittle failure.

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

“…It is obtained by low-pressure polymerisation. It is harder than polyethylene PE-LD (low density PE), has a higher mechanical strength and higher melting temperature (125 °C) [6], [7]. The most common trade brands of PE-HD are PE80 and PE100.…”

“…However, in case of polyethylene the problems concern: nonlinearity and hysteresis of transferring characteristics, low values of the Young modulus of elasticity resulting in high strain values, long relaxation times, and possibilities of gluing strain gauges (only a few -from the accessible adhesives -are efficiently joining the polyethylene foundation with strain gauges) [6], [10], [17]. The results of the test performed, up to the present, concerning the mechanical properties of polyethylene, can be found in the references: its tightness, strength, relaxation time [6], [7], [9], [11], [18]. However, there is a lack of the results concerning measuring of polyethylene pipeline strains subjected to external loads with the application of the strain gauge measurement technique.…”

Étude des propriétés mécaniques à travers la paroi d’un tube HDPE-80 extrudé destiné à la distribution du gaz naturel

“…où ρ est la masse volumique du matériau, R est la constante des gaz parfaits, T est la température absolue, et le paramètre β est calculé à partir de la formule (4) avec : ∆H f l'enthalpie de fusion et T 0 m la température de fusion à l'équilibre [10]. [12,13].…”

Numerical simulation of ductile fracture in polyethylene pipe with continuum damage mechanics and Gurson-Tvergaard-Needleman damage models

“…The usage of PE pipe has increased rapidly and statistics show that 90% of newly installed natural gas and water pipeline systems are made from PE. 1,2 However, accidents due to pipeline failure which may cause catastrophic results still occurred in Pakistan, 3 Mexico, 4 Kuwait, 5 Brazil, 6 and Malaysia, 7 suggesting that the current approach for characterizing PE pipes has blind spots for the performance evaluation.…”