Ultra Deep offshore oil exploitation (down to 3000 meters depth) presents new challenges to offshore engineering and operating companies. Flow assurance and particularly the selection of insulation materials to be applied to pipe lines are of primary importance, and are the focus of much industry interest for deepwater applications.

In this field, particular attention is now focussed on the long term behaviour of the assembly between coated field joints and parent coating material which appears to be critical for in-service durability. A field joint is the uncoated area that results when two pipe sections with coating cutbacks are assembled by welding.

The in-service environmental conditions of the structure are severe and include high hydrostatic pressure up to 30 MPa and large thermal gradients through the thickness of the material (inner temperature up to 100°C and external temperature 4°C). This study aims to establish a model allowing the thermo-mechanical behaviour of the assembly to be evaluated and to describe the experimental protocol required in order to identify the model parameters.

First, the mechanical behaviour of the parent coating (usually glass syntactic polypropylene material) and coated field joint material are determined using hydrostatic compression tests (static and creep) at different temperatures and Dynamic Mechanical Analysis (DMA).

Then, a thermo-mechanical model of the parent material allowing hydrostatic creep deformation is developed and implemented in Comsol Multiphysic ™ software. A global model of the structure under service conditions, from the manufacturing process to the in service conditions, is then proposed and allows the strain distribution in the structure to be predicted. This distribution highlights the critical area of the assembly which is the bond between the parent coating material and the field joint coating.

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