The Challenges of Data Availability for the Life Extension of Steel Catenary Risers

Many offshore floating production systems including their risers are approaching the end of their original Design Life. Operators are faced with the choice of either decommissioning or demonstrating that the original Design Life can be extended (Life Extension). Life extension requires the Operator to perform detailed engineering analyses to verify that the system can be operated safely over the period of Life Extension. This generally requires detailed fatigue analysis of actual fabrication data to demonstrate that the fatigue damage still within the required design life and the original fabrication flaws or fatigue cracks that may have initiated over the original Design Life will not grow to a critical size resulting in failure. In some cases, the detailed engineering analysis is supplemented by an in-line inspection program. The critical challenge that many operators face nowadays is finding the original design, fabrication and inspection records since they may be more than 20 years old. The use of actual procurement and fabrication data provides more credibility to the life extension engineering. Furthermore, the actual data could support the removal of at least some of the conservatism associated with the design of new risers. This paper will review and discuss specific issues associated with the availability of procurement and fabrication data and how to optimize and use the available knowledge and information in cases where data is not available. Some focus will be placed on the fracture mechanics aspect of the fatigue and the Engineering Criticality Assessment (ECA) approach to determine the riser life extension based on the weld original flaws. Finally, the paper will provide guidance and examples of how to take advantage of in-line inspection to supplement the life extension analysis and provide increased confidence on the predicted life extension.