Mechanical behaviour of machined polyethylene filaments subjected to aggressive chemical environments

Abstract

During the construction process of fluid handlingstructures, material selection for pipe applications is animportant step. Both natural gas and drinkable water aremainly transported in underground polyethylene (PE) pipenetworks. It is known that the interaction between materialslike HDPE (high density PE) and its service environmentrepresents critical factors of the influence on thestructure behaviour for short and long terms. The goal ofthis study is to establish the effect of some chemical agentson the mechanical properties of PE tubes for undergrounduse. The results are discussed basing on the stress straincurves and according to the mechanical resistance to aggressiveenvironments. It was found that the environmentsconsisting of solvents show degradation of mechanicalproperties of the tubes and a structural weakening of therigidity of the system is observed. Organic solvents havesignificant oxidizing capacity which weakens polyethylenechains, whereas acids such as H2SO4 have less influenceson the mechanical properties compared to organic solvents.In the case of crude oil, the results show moderate effectalthough it is known to attack many polymers. In the caseof solvents, the elasticity modulus is reduced up to 64% forcrude oil which represents a serious problem for the undergroundpolyethylene networks. Design equations of suchstructure should take into account serious adjustments oflong term loads when polyethylene is exposed to aggressiveenvironment.