Proposed Methodology for Extending the Lives of Steel Catenary Risers Connected to Floating Production Systems

摘要

Extending the life of steel catenary risers is becoming one of the main subjects of interest nowadays as many steel catenary risers (SCRs) are approaching their design lives. Many of the risers in this situation are export risers, which may require extended design lives due to development of new production fields being tied back to the floating facilities they service. There have been no specific methodologies or defined approaches for dealing with this subject. The conservatism of the design methodology, which is usually adopted for the detailed design of new risers, will have to be adjusted when evaluating existing risers with known environmental and operational history as well as fabrication and installation data. This paper will describe a proposed methodology and potential approach for extending the lives of existing steel catenary risers (SCRs) connected to floating structures in the Gulf of Mexico. It will highlight the essential steps that should be taken to evaluate the risers' current status and to determine their already consumed fatigue lives. The proposed methodology for calculating the riser consumed fatigue damage will be discussed and compared with the typical but conservative approach that is usually taken during the detailed design of new risers. The next step will then be the calculation of the riser remaining life including the treatment of its already consumed fatigue damage. The proposed methodology will also cover the relationship between the safety factors and availability of actual data during the life of the risers. Fracture mechanics assessment for riser welds and their flaws is another step that needs to be performed to support the fatigue analysis calculation. Internal and external inspection of the risers, including pipe welds, pipe corrosion and possible pitting, is a work in progress at this stage and would probably be essential part of any riser life extension program. Some discussion will also be provided for the risers' special components (e.g. strakes, coating, cathodic protection, and top termination units) to ensure all aspects are covered in the evaluation of the riser life extension.