Mechanical Performance of Composite Production Risers
Authors: Johnson Douglas B. , Baldwin Donald D. , Long J. Randy 
Published: October 2008

In 1995, a joint effort was begun, under the auspices of the NIST ATP, to design, develop and test a composite production riser (CPR) suitable for deep water (3000 to 5000 feet) applications. The objective of the effort is to arrive at a costeffective design for a composite production riser that meets reliability performance of current metal systems.

An integrated CPR design meeting the project cost, weight and performance goals was developed. A test program was defined to derive statistically sufficient data on mechanical properties and to identify failure modes and locations to achieve the required confidence in design, fabrication, and short and long term performance of the CPR. A total of 80 prototypes were fabricated and tested for ultimate strength determination, static and cyclic fatigue performance, and characterization of damage tolerance. A primary purpose of this testing was to correlate and analyze riser joint actual performance with predicted values, in the interest of verifying static and cyclic performance and manufacture variability. The final results of this testing and analysis are presented in this paper.

Introduction

As competition for oil increases, oil companies are drilling in deeper waters. Current deepwater oil completion and production technology utilizes steel riser systems that are heavy, require expensive tensioning and buoyancy systems, and whose designs are often governed by fatigue considerations. Composite risers would provide advantages over conventional steel risers because composite materials are (1) lighter weight, (2) more fatigue resistant, (3) more corrosion resistant, (4) can be designed for improved structural and mechanical response, and (5) are better thermal insulators. Overall, production platform cost reductions are possible as a result of the lower weight and greater compliance of composite risers, along with improvements in system reliability.

A CPR has the potential of reducing capital expenditure, 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 tensioning system, resulting in further cost benefits to the riser system and platform construction.

Background

CPR's are one of the most characterized structural composite applications for offshore platforms because they have been the subject of several major studies within the last several years. The Institut Français du Pétrole (IFP), Aerospatiale, and several major oil companies sponsored a development and evaluation study of a 9 5/8-inch diameter CPR to prove the concept. The study was conducted between 1985 and 1990 (see Refs. 1, 2, and 3). The CPR was fabricated of a hybrid of carbon and S-glass fibers. The CPR was designed to withstand a combined internal pressure of 105 MPa (15,000 psi) and axial tension of 450 metric tons (1,012,500 lbs). The CPR was also designed for a maximum external pressure (differential) of 10 MPa (1430 psi). The study included several static, fatigue, multi-axial loading and damage assessment tests.