?-Flex®: A New Material for High Temperature Flexible Pipes
Authors: Marion A. , Rigaud J. , Werth M. , Martin J. 
Published: October 2008

A new resin designed for use as a pressure barrier in high temperature / high pressure flexible pipes is introduced. The resin finally selected is a modified PVdF homopolymer. Material characterisation has been conducted in full compliance with the applicable API standard requirements. This has confirmed an excellent blistering resistance, chemical ageing resistance, low creep and dimensional stability compatible with the final product long term performance requirements.

With a plasticizer content limited to 3% in mass, this new product is ensuring an optimum mechanical behaviour, not only at high temperature but also when low temperature conditions are a specific project requirement.

Particular attention has also been paid to end fittings of the finished product in order to guarantee their suitability for high temperature thermal cycling conditions. Based on a specifically designed testing facility, short length pipe samples have been submitted to such thermal cycling tests as required by the latest API specifications.

Having passed satisfactorily all characterisation and qualification testing required, Technip-Coflexip and Atofina are now in a position to introduce this new material, called ?- Flex£, which will provide the oil and gas industry with an even higher performance flexible product whilst reducing delivery lead times.

Introduction

Unbonded flexible pipes have been in operations since the early seventies and are available from a number of manufacturers around the world. This technology has proved its worth in a number of offshore developments worldwide, whether used in ultra deep water applications such as in Brazil [1] or used for high temperature / high pressure conditions in the North Sea.

Flexible pipes are composed of a succession of extruded thermoplastics and spiraled/armoured steel layers, each layer being designed to resist a specific loading. Figure 1 below displays the basic build-up for a typical dynamic riser structure.

Figure 1: Standard flexible riser construction(Available in full paper)

Extensive work took place in the industry a few years ago to qualify new end fitting constructions compatible with severe thermal cycling associated with regular shut down conditions. This new termination assembly, certified by Bureau Veritas, has proved since then its total reliability in such service conditions.

The methodology used in this process was, in particular, relying on pre-deplasticization of the Coflon£ material prior to end fitting mounting in case of high severity applications. Although technically sound and fully effective, this approach introduced additional delays in the end fitting mounting process which could be as high as several weeks, depending on the PVdF grade used and the anticipated operating conditions. This also made offshore repairs more cumbersome in case remedial work had to be undertaken under the form of inserting an additional end termination.

A new thermoplastic product has therefore been developed which aimed at suppressing the need for such predeplasticization, enabling therefore shorter delivery lead times and reducing risks during the manufacturing process.