Design Robustness Saves Marco Polo Oil SCR During Its Installation

The Marco Polo TLP, located in Green Canyon Block 608 in 4300 ft water depth exports oil and gas through 12-inch oil and 18-inch gas export SCRs that are connected to Marco Polo 14-inch oil and 18inch/20-inch gas export pipelines. Following completion of the installation of the 14-inch oil export pipeline and during the installation of the 12-inch oil export SCR on the seabed (with about 3,000 ft or 77 SCR pipe joints still to go), the operation had to be abandoned due to bad weather and the SCR pipe lowered to the seabed. During the abandonment operation, a high tension event occurred, causing the transition joint between the 14-inch and 12-inch pipes to slide by about 820 ft toward the TLP. This would have the effect of changing the touchdown position along the SCR and consequently the Three Layer Polyethylene abrasion coating would not be located at the at the touchdown to perform its function. In order to move the SCR touchdown area at least partially to the TLPE region, it was decided that four extra joints would be welded to the SCR resulting in the SCR departure angle to changing from 12 degrees to 10 degrees. This paper presents the methodology used for the original design of the oil export SCR and the design robustness, flexibility and margins that allowed for the design to be modified in the last minutes without compromising the integrity of the SCR. The paper also discuss the steps taken to ensure that the modified design is acceptable and within the code requirements. Some strength and fatigue results are presented.