Mechanical behaviour of machined polyethylene filaments subjected to aggressive chemical environments/ Agresyvios chemines aplinkos veikiamo polietileninio vamzdzio mechaniniu savybiu kitimas

During the construction process of fluid handling structures, material selection for pipe applications is an important step. Both natural gas and drinkable water are mainly transported in underground polyethylene (PE) pipe networks. It is known that the interaction between materials like HDPE (high density PE) and its service environment represents critical factors of the influence on the structure behaviour for short and long terms. The goal of this study is to establish the effect of some chemical agents on the mechanical properties of PE tubes for underground use. The results are discussed basing on the stress strain curves and according to the mechanical resistance to aggressive environments. It was found that the environments consisting of solvents show degradation of mechanical properties of the tubes and a structural weakening of the rigidity of the system is observed. Organic solvents have significant oxidizing capacity which weakens polyethylene chains, whereas acids such as [H.sub.2][SO.sub.4] have less influences on the mechanical properties compared to organic solvents. In the case of crude oil, the results show moderate effect although it is known to attack many polymers. In the case of solvents, the elasticity modulus is reduced up to 64% for crude oil which represents a serious problem for the underground polyethylene networks. Design equations of such structure should take into account serious adjustments of long term loads when polyethylene is exposed to aggressive environment.