Development of a New, Low Plasticized, PVDF for Monolayer Dynamic Applications in Flexible Pipes
Authors: Chicheportiche Stephanie , Demanze Frederic 
Published: May 2011

Flexible pipes convey petroleum fluids up to 130°C facilitated by sealing layers made of PVDF polymers. The first PVDF grade (Coflon®) which has been qualified and which is still used in flexible pipes is a high molecular weight polymer, supplemented by about 12% of plasticizer to enable process by extrusion. This material has some drawbacks as it requires a time consuming pre-deplasticization operation and the use of a two-layer configuration for dynamic riser applications. In order to eliminate the lengthy and sometimes schedule critical deplasticization process, a second PVDF grade was qualified (Gammaflex®) as a pressure sheath in flexible pipes. This material is a low plasticizer grade with a lower molecular weight. This material still requires a double sheath construction for dynamic riser applications.

This paper will present the work carried out to qualify a new, low plasticized, high molecular weight PVDF material. The primary advantage of this material is that it facilitates monolayer pressure sheath designs for dynamic flexible pipes.

The paper will first present the results of laboratory tests performed to characterize the material properties. Results of these tests clearly demonstrate that the properties of the new material are at least equivalent to, and in many cases superior to those of the previous PVDF grades described above. Then results obtained with severe full scale mechanical tests will be presented, demonstrating an excellent fatigue behavior as well as an improved low temperature behavior. Finally, the results obtained during extrusion trials performed with different carcass sizes, diameters and thicknesses will be discussed.

This new PVDF material optimizes the design, fabrication and operation of flexible pipe. Additionally, it contributes to the optimization of the manufacturing schedule and cost of the pipe.

Introduction

This paper presents a new PVDF polymer qualified for pressure sheath application within flexible pipe structures. This new development is a result of extensive R&D and industrialization and represents a major breakthrough for flexible pipe design. It is the first application of a flexible pipe high temperature polymer grade which does not require multiple layer extrusion for dynamic application and which is not susceptible to significant volume loss through exposure to high temperatures. This allows for significant improvements to the flexible pipe manufacturing cost and schedule in terms of reduced raw material procurement and reduced number of manufacturing and preconditioning processes.

The paper presents the three primary components of the qualification process for the new PVDF grade, namely Laboratory Testing and Characterization of material samples, Full and Mid Scale Tests of flexible pipe prototype samples manufactured using the new material and finally, Extrusion Trials to complete the industrialization process for the new material as a flexible pipe pressure sheath layer.

In a first part, laboratory results are presented showing an equivalent or improved behavior of this PVDF compared to previous grades. In a second part, full scale tests are discussed. And finally, the last part will deal with extrusion trials.

Flexible pipes are composite structures of unbonded layers. Layers are made of steels or polymers and are designed individually since they have their own function within the whole structure.