Mat´ eriaux & Techniques 101, 701 (2013) c  EDP Sciences, 2013 DOI: 10.1051/mattech/2013083 www.mattech-journal.org Matériaux & Techniques Short-term HDPE pipe degradation upon exposure to aggressive environments L. Alimi 1,2 , K. Chaoui 2 , W. Ghabeche 1,3 and W. Chaoui 4 Received 2 July 2013, Accepted 13 November 2013 Abstract – Natural gas and drinkable water are regularly transported by underground polyethylene pipe networks in urban and rural areas. The interaction between materials such as high density polyethylene (HDPE) and contact environments is a critical factor which strongly influences pipe behaviour for short and long terms. The aim of this study is to establish separate effects of H2SO4, a mixture of toluene–methanol and distilled water on the mechanical properties of HDPE pipes. Two testing geometries representing the pipe wall are considered: (1) orthogonally machined filaments and (2) ASTM standard specimens. Tensile tests are carried out on both specimen types using a computer controlled Zwick machine. It is observed that chemical environments degrade mechanical properties causing a structural weakening especially those specimens exposed to organic solvent and acid. For instance, filaments show a reduction in elastic modulus of 64% after 7 days of exposure to toluene and methanol. Compared to standard specimens, the obtained properties are much higher indicating that geometry has an effect on the measured values. Fluctuations in mechanical properties are most probably caused by cristallinity gradients all the way through the pipe wall. This type of results allowed establishing the linear relationship between the elastic modulus and the yield stress and is intended to contribute to a better understanding of properties heterogeneity effects when exposed to unfavourable environments. Key words: Polyethylene pipe / environmental stress effect / short-term degradation / yield stress-Young’s modulus correlations / failure strain / OIT 1 Introduction Polyethylene (PE) is mostly distinctive for its lightweight, low production and installation costs, and resistance to corrosion which allowed a wide utilization to in conveying gas, water, sewage and even oily flu- ids [1–5]. In such cases, pipe lifespan is estimated at more than 50 years on the basis of the ISO standard bursting tests used to build a regression curve correlating stress levels and failure times [2]. Lifetime management of un- derground pipelines is mandatory for safety and the use of HDPE pipes subjected to internal pressure, external loading and environmental stress cracking (ESC) agents, requires a reliability study in order to define the ser- vice limits and the optimal operating conditions when creep deformations are significant [4]. In service, the time- dependent phenomena especially creep might lead to sig- nificant strength reduction and brittle failures. Moreover, 1 Welding & NDT Research Centre (CSC), Route D´ ely Brahim, BP 64, Ch´ eraga, 16800 Alger, Algeria latifaalimi@yahoo.fr 2 Laboratoire de recherche en M´ ecanique des Mat´ eriaux & Maintenance Industrielle, LR3MI, D´ epartement de G´ enie M´ ecanique, Facult´ e des Sciences de l’Ing´ eniorat, Universit´ e Badji Mokhtar, BP 12, 23000 Annaba, Algeria 3 LR3MI, D´ epartement de Physique, Facult´ e des Sciences, Universit´ e Badji Mokhtar, BP 12, 23000 Annaba, Algeria 4 LR3MI, D´ epartement de G´ eologie, Facult´ e des Sciences de la Terre, Universit´ e Badji Mokhtar, BP 12, 23000 Annaba, Algeria the temperature and the application mode of the work- ing loads have disastrous consequences on the mechan- ical properties of the plastics especially when combined with environmental effects [5]. The resistance of poly- meric materials to chemical agents depends on the na- ture of polymer as well as additives processed during ex- trusion [6–8]. The strongly oxidizing acids may chemically attack plastics, provoke discolouring and substantially de- grade the mechanical and chemical properties [9–11]. The organic liquids such as fuel oils, mineral oils and various organic solvents cause swelling, softening and eventually the dissolution of the polymer. The possible degradation of plastics can be due to several physical and chemical phenomena such as permeation (solvent access, driven by chemical activity gradient), swelling (interaction be- tween the solvent and the polymer matrix) and plasti- cizer extraction which correspond to a loss of antioxi- dants, fillers, heat stabilizers, or plasticizers because of the solvent permeation [12, 13]. Article published by EDP Sciences