Design of an Optimized Composite Repair System for Offshore Risers Using Integrated Analysis and Testing Techniques
Authors: Alexander Christopher Richard 
Published: April 2012

Composite systems are a generally-accepted method for repairing corroded andmechanically-damaged onshore pipelines. The pipeline industry has arrived atthis point after more than 15 years of research and investigation. Because theprimary method of loading for onshore pipelines is in the circumferentialdirection due to internal pressure, most composite systems have been designedand developed to provide hoop strength reinforcement. On the other hand, offshore pipes (especially risers), unlike onshore pipelines, can experiencesignificant tension and bending loads. As a result, there is a need to evaluatethe current state of the art in terms of assessing the use of compositematerials in repairing offshore pipelines and risers.

The paper presents findings conducted as part of a joint industry effortinvolving the Minerals Management Service, the Offshore Technology ResearchCenter at Texas A&M University, Stress Engineering Services, Inc., and fourcomposite repair manufacturers to evaluate the state of the art usingfull-scale testing methods. Loads typical for offshore risers were used in thetest program that integrated internal pressure, tension, and bending loads. This program is the first of its kind and likely to contribute significantly tothe future of offshore riser repairs. The end result of this study was thedevelopment of a carbon-fiber repair system that can be easily deployed toprovide significant reinforcement for repairing risers. It is anticipated thatthe findings of this program will foster future investigations involvingoperators by integrating their insights regarding the need for composite repairbased on emerging technology.

Introduction

At the core of proving the worthiness of composite repair systems is full-scaletesting, where damage is recreated and loading is generated to simulate actualreal-world loading conditions. These real-world conditions include, but are notlimited to, static and cyclic internal pressure, axial tension and bendingloads, and exposure to environmental conditions. These efforts are essential toestablish the long-term viability of composite repair systems. As the pipelineindustry continues to expand the use of composite materials beyond repairingcorrosion, full-scale validation becomes even more important.

The purpose of this paper is to provide a high-level overview of recent testingand analysis to evaluate the performance of composite repair systems, includingtesting methods, results, and implications. The following assessments arediscussed in this paper:Pressure cycle testing of corroded pipesComposite reinforcement (inter-layer strain distribution), includingdiscussion on long-term design including ASME PCC-2 philosophyWrinkle bend tension testing and composite reinforcementUpcoming research programsGirth weld study (tension and bending)Subsea composite reinforcement of corroded pipes (pressure, tension, andbending)

Also included is a discussion on performing a risk analysis for compositerepair using the elements included in Paragraph 1.3 of ASME PCC-2 Part 4. Finally, a Closing Comments section provides comments for the reader inrelation to how composite materials can and will be used to ensure thelong-term integrity of identified pipeline anomalies.