ABSTRACT

The effects of solvents and temperature on thermoplastic hose for umbilical service are reported in this paper. Accelerated ageing tests were undertaken and analysed by gravimetric, mechanical and calorimetric measurements. Water and methanol were found to cause physical degradation of the polymer, mainly at high temperatures, whereas xylene caused chemical degradation, which increased with increasing temperature. The activation energy for the a-process within polyethylene (PE) was found to be 96.3 kJ mol-1 for un-aged PE and increased to 106.2 kJ mol- 1 after 64 days of ageing in water at 100°C. The changes in activation energy will be used to make a life-time prediction of umbilical lines.

INTRODUCTION

Thermoplastic hoses have been used in umbilicals for over 25 years for control applications and to carry production service fluids from a control or service centre to sub-sea wellheads or subsea production centres. Umbilicals have an expected service life of around 20 years and it is vital that they withstand the harsh environmental conditions to which they are subjected, as well as sometimes carrying, highly aggressive, well service fluids. As oil and gas recovery moves into deeper waters, the installation of umbilicals becomes increasingly expensive. The aim of this study is to improve the existing method of predicting the service life of thermoplastic hose fluid conduits by accelerated ageing studies. Accelerated ageing studies usually involve heat-ageing tests, in which the material is tested at temperatures much higher than the actual service temperature. This will give results in a much shorter time and by extrapolating the data, the material's conditions at lower temperatures can be derived. This method is widely used to predict polymer properties [Braginskii, Dashevskaya and Peshkov, 1982; Bruggeman, Yang, Zaoutsos, Boulpaep, Dumortier and Cardon, 1998], but as Bright [1993] pointed out, many problems are connected with it.

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