Composite Production Riser Design
Authors: Baldwin D.D. , Newhouse N.L. , Lo K.H. , Burden R.C. 
Published: October 2008

A concentrated effort is underway to design a Composite Production Riser (CPR) and demonstrate its suitability for deep water (3000 to 5000 feet) applications. Functional, operational, and performance requirements have been specified by oil company participants and are representative of current and anticipated projects. Riser responses to platform motions and environmental loads have been provided based on global analysis of a TLP system.

The use of well established advanced composite stuctural design methodologies has resulted in a CPR design with predicted capabilities that exceed the expected loadings. The design of the CPR joint requires three separate efforts: composite tubular design; composite-to-metal interface design; and metal connector design. The composite tubular wall is a hybrid composite structure, with carbon fiber and glass fiber reinforcements in an epoxy matrix. The composite-to-metal interface is a multiple traplock configuration, well-suited for supporting axial and pressure loadings. A premium threaded connection is used for the metal connector design.

The performance of the CPR will be verified through testing of subscale and full-scale specimens. Preliminary results of this testing are discussed. The CPR design effort demonstrates the ability of engineering functions from diverse industries, institutions and companies to work together to obtain a common goal.

Introduction

A joint-industry CPR project, jointly financed by NISTIATP, is currently underway. The goals of the project are to design, develop, manufacture, test and qualify a TLP production riser made with fiber-reinforced polymeric composites. Lincoln Composites is leading the effort in engineering design and fabrication of the CPR. A concentrated effort was conducted in the first part of the project to design a low-cost, light-weight CPR suitable for deep water (3000-5000 feet). Both single casing and dual casing risers are considered.

Figure 1 shows a typical TLP production riser system. Polymeric composites are attractive alternative materials to steel for the production riser mainly because their light weight will give rise to lower riser top tension (and hence lower loads supported by the platform). In addition, the more compliant CPR could help to reduce or eliminate the need for the top tension system, resulting in further cost benefits to the riser system and platform construction. In the current study, several joints of steel riser casing would still be used at the top and bottom of the riser string, in order to avoid the application of significant bending loads to the CPR. Keeping the composite joints below the waterline also avoids exposing the composite material to fire in the case of a calamitous accident. A large variety of tools and equipment may operate in the CPR, including production tubing and possibly an inner casing.

CPR Requirements

The project team has developed a Functional Specification and Performance Criteria document which provides guidance in the production and demonstration of a CPR joint. It is intended that the CPR be fully ready for use by the offshore industry at the completion of the project.

Functionally, the CPR must perform the same duties as a steel riser casing. Generally, these functions are: pressure and fluid containment for well-control purposes;