How to Provide Relevant Data for the Prediction of Long Term Behavior of Insulation Materials Under Hot/Wet Conditions ?
Authors: Choqueuse Dominique , Chomard Angèle , Chauchot Pierre 
Published: October 2008

The thermal behaviour of fluid transport pipelines must be increasingly taken into account in new field developments, in order to prevent production of waxes or hydrates. The deepest developments (water depth&gt; 1500m) are particularly sensitive to these problems and solutions are needed for such depths.

The currents solutions, coated pipe, pipe-in-pipe, syntactic foam, have to be adapted to ultra deep sea, as there are limitations in terms of thermal conductivity, hydrostatic pressure, and installation possibilities. One of these solutions considers the insulation material to be in contact with the surrounding environment, which means high pressure, sea water and, in the case of modules, high temperatures (up to 130°C).

In the framework of a national project a solid experience has been developed in the evaluation of insulation materials applicable to ultra deep sea flow lines. Given the long service life of these structures (20-30 years) particular attention has been focussed on the long term evaluation of the properties.

This paper will present a methodology for the definition of a proper ageing test programme in order to provide relevant data for the prediction of the insulation material long term properties. Ageing test conditions must couple the pressure with the temperature in natural sea water. Accelerating ageing factors such as the temperature and the sample dimensions are also considered.

This method is now applied in an on-going JIP. Tests on samples under representative conditions provide relevant data on different types of insulation materials. These will be used as input data in a model to estimate the long term behaviour of the materials under service conditions, in terms of both thermal and mechanical properties.

Presentation

This paper presents a test methodology for predicting the long term behaviour of insulation materials under hot/wet conditions. It is a one of the results from a three year program carried out in France which involved the main actors of the offshore industry (ref 1-3) and which mainly addressed syntactic foams. The characterisation of such materials is discussed here and results led to a recommended practice and a specification which have recently been proposed for the materials concerned (ref 4-5)

The first part consists of a brief reminder and discussion of the tests performed to evaluate the essential initial properties of such materials.

In the second part, taking into account the long lifetime requested (20-30 years) special interest is focussed on the long term evolution of properties. Considering a significant thickness of an insulation material and the temperature gradient through the insulation layers, the way to access the variation of properties of the materials in relation to temperature is highlighted. The basis of a model is proposed in order to estimate the long term behaviour of an actual insulation system.

Based on the lessons learnt in the previous program, a JIP has been proposed to the major actors of the offshore industry and is now underway. The program of the JIP is described in the third part of the paper.