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              The First 1500m Deep-in-water Steel Catenary Riser in China Tied Back and Put in Place


              A few days ago, good news that CNOOC has independently tied back the first 1500m deep-in-water steel catenary riser (SCR) came from the operation waters of the large gas field Deep Sea No. 1 in the South China Sea. So far, China has mastered all deep-water technologies such as laying of horizontal pipes, laying and tie-back of steel catenary risers in 1500-meter deep waters, construction and installation of subsea pipeline terminal structures, and comprehensively improved the deep-water exploration and development capabilities. 

              The SCR installed is the chemical delivery pipeline for the Deep Sea No. 1 energy station, and was successfully laid by the vessel Haiyang Shiyou 201 in August, 2020. Seven months later, Haiyang Shiyou 201 in close cooperation with the Deep Sea No. 1 energy station again seized the rare good weather window and completed tie-back of risers simply in 20 hours after the 7 major steps, e.g. recovery of side system, underwater crossing, crane lifting and towing in place by the platform hoisting system, thus gaining valuable time for subsequent riser tie-backs. 

              SCR is widely used in deep-water oil and gas development projects and serves as a transport channel for critical production media between subsea production facilities and floating systems. Its design, manufacturing and installation technologies were monopolized by well-known foreign oil companies before. Being confronted with abundant challenges like lack of experience, long design fatigue life, complicated sea conditions and platform motions, CNOOC has been sparing no efforts for technological breakthrough. For risers of different diameters, different limiting systems are configured to lower the risk of risers moving irreversibly towards the platform. To address the fatigue sensitivity, a new type of pipeline end structure is adopted, and a VIV (vortex-induced vibration) suppression device is added in the laying of subsea pipelines, which increases the fatigue life by 2.5 times. 

              After completing the tie-back of the first riser, the builders of the Deep Sea No. 1 energy station will proceed with tie-back of the remaining five risers and system commissioning as planned, so as to lay the foundation for the platform to be put into service on schedule. 

              Figure 1: Work site in aerial photo 

              Figure 2: Tie-back site of the Deep Sea No. 1 energy station