Drilling and workover rigs on Floating Production Systems (FPS’s) are fastened to the decks of offshore structures sea fastenings to prevent movement during hurricanes. Tie-down systems include bolted clamps, weldments, or other mechanical means. During Hurricane Ivan, a number of drilling or workover rigs shifted. These movements were studied and assessed relative to current design philosophy and installation practices, and onboard storm operational practices to ready FPS’s for a hurricane. Results will provide information that can be used to assess any needs to revise tiedown criteria or practices to avoid future damage.
Information was gathered for the FPS’s with rig movement during Ivan. Information was obtained for Horn Mountain (BP), Medusa (Murphy), and Ram Powell (Shell). No information was obtained for Devils Tower (Dominion). An interim report to MMS and an OTC paper summarized the observations and learnings from these rig movements. We were also able to work with the API’s Hurricane Evaluation & Assessment Team (HEAT) and provide input to API Bulletin 2TD, Guidelines for Tie-Downs on Offshore Production Facilities for Hurricane Season, First Edition that was issued in June 2006.
This report describes the analyses for a hypothetical TLP and Spar to further study the loads and failure modes for rig tie-down clamps for drilling rigs during hurricanes. Results tended to confirm the observation from hurricane Ivan, and illustrate that tie-down clamps should be purpose-designed for the functional requirements and motion characteristics the specific FPS.