Full-Scale Testing of Prototype Composite Drilling Riser Joints-Interim Report

Abstract

Abstract As exploration for hydrocarbons moves into progressively deeper offshore waters worldwide, life cycle costs are becoming an increasingly more significant consideration in the economics of deepwater projects. The high strength-to-weight ratio, corrosion resistance, fatigue tolerance and design flexibility of advanced composite structures can reduce deepwater project life cycle costs. An industry/university team, which includes ABB Vetco Gray, Deepstar, Reading & Bates/Falcon, Northrop Grumman Marine Systems, Hexcel Carbon Fibers, and Offshore Technology Research Center, with cooperation from the National Institute of Standards and Technology(N1ST) Advanced Technology Program(ATP), has designed, developed and fabricated advanced composite deepwater drilling riser prototype joints and choke and kill line prototypes for full scale testing and evaluation. This paper describes the project plan, the development and fabrication of the full scale prototypes, and focuses on the results of recently completed testing of the full scale prototypes. In addition, the plans for the remainder of the project are presented. Background The benefits of advanced composite structures have been acknowledged by the offshore industry for a long time, however the recent emphasis on deep water tracts worldwide has magnified the potential benefits. Stationary seabed supported jacket type structures have been used in shallow water projects, but in deeper water projects, floating structures anchored to the sea bed are the preferred platform. Steel is the common material for the riser and mooring systems, but the weight, fatigue characteristics and corrosion properties are becoming more significant life cycle cost drivers. In addition, steel drilling riser systems tend to limit the depth capability of mobile drilling platforms as a result of their variable deck weight capability. Figure 1 shows a mobile offshore drilling unit with a deployed drilling riser and the details of an advanced composite individual drilling riser joint conceptual design. Development work on lightweight advanced composite drilling riser systems was started in April 1995 by an industry/university team. References 1 and 2 describe the project and review the initial results achieved. Key aspects of the work included a definition of the requirements for a 6000 ft. water depth Gulf of Mexico system with input by DeepStar as shown in Figure 2. Using these requirements, individual from riser joint performance requirements were developed. Advanced composite drilling riser joints were designed and fabricated at Northrop Grumman Marine Systems as shown in Figure 3. In addition, choke and kill line prototypes were fabricated, Figure 4. The first full scale prototype test to be conducted was an external pressure test which was designed to assess the collapse pressure capability of the riser main body structure. The University of Texas part of the team designed and built a specially configured test fixture which eliminated the end loads on the specimen during test and thus just applied acircumferential compressive load. The test specimen and the installed fixture are shown in Figure 5. The assembly was installed into the hyperbaric test chamber at H. 0. Mohr in Houston, Texas as shown in Figure 6. The collapse pressure test was conducted and the prototype collapsed at 3 120 psi. The post test result is shown in Figure 7.