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Ageing of thermoplastic umbilical hose materials used in a marine environment I : Polyethylene

Pethrick, Richard and Banks, William and Brodesser, Monika (2014) Ageing of thermoplastic umbilical hose materials used in a marine environment I : Polyethylene. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 228. pp. 45-62. ISSN 1464-4207

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Abstract

This study of the behaviour of high density polyethylene umbilical hoses subjected to constant and cyclic variation of pressure and temperatures attempts to simulate the effects of experience in off shore operations. Measurements are reported for exposure between 400C and 1000C in water, methanol and xylene and using an applied pressure of 200 bar (3000psi). The changes in the physical properties of the hose were monitored by measurement of the tensile properties, dynamic mechanical thermal analysis, differential scanning calorimetry and gravimetric uptake of the fluids. Significant changes occur immediately on application of pressure and reflect changes in crystallinity. The rates and extent of the modifications depend primarily on the ageing temperature but is also influenced by the fluid. Water has little effect on the rate at which ageing occurs, whereas xylene, which is a potential solvent for HDPE, exhibits characteristics of plasticization. Methanol behaves as a weak solvent and shows characteristics intermediate between xylene and water. Burst tests carried out on the aged material show that significant loss in strength is only observed with the highest temperatures and most aggressive solvent systems. The study indicates that engineers should use pressure aged rather than initial materials data when designing umbilical hose systems.