TEMPERATURE AND AGEING SENSITIVITY ANALYSIS OF A POLYAMIDE USED AS PRESSURE SHEATH MATERIAL IN OFFSHORE FLEXIBLE PIPES
Thaís de Sant'anna1; Pablo Parize Coutinho1; João Reis1; Heraldo da Costa Mattos1; Antonio Henrique Monteiro2; Sylvia Corrêa dos Santos Teixeira2; Érica Gervasoni Chaves2
1 Universidade Federal Fluminense; 2 Petrobras
doi:10.20906/CPS/COB-2015-2743
Resumo
In the construction of a flexible pipe, an inner polymeric pressure sheath is the only layer which seals the conveyed fluid within the pipe structure. Therefore, understanding the mechanical behaviour of this polymer material is crucial to safe and reliable operation. Polyamide is a commonly used pressure sheath material, other options being polyvinylidene fluoride and polyethylene. One major aging mode of polyamide is the decrease in molecular weight due to the hydrolysis of the macromolecular chain. The molecular weight can be measured by the solution viscosity (CIV - The Corrected Inherent Viscosity value is an index of the molecular weight of the polyamide matrix) and this gives a very simple way to monitor the material ageing. The present work is concerned with the thermo-mechanical analysis of a particular Polyamide. The main focus is to analyse the influence of temperature and ageing in its mechanical behaviour and fracture. Fracture and tensile tests were performed over a wide range of temperatures (from -5ºC to 90°C) and corrected inherent viscosity (1.0 to 1.8 dl/g). For higher values of the CIV, the material presents a superplastic behaviour, but the behaviour tends to be brittle for lower values of the inherent viscosity and temperatures. It is proposed a general model for the uniaxial behaviour (valid for a wide range of temperatures and inherent viscosities) and also for the fracture behaviour Experiments are compared with the model predictions and show a good agreement.
Palavras-chave: Polyamide 12; Ageing; Temperature; Mechanical properties; Modelling