A 2km long, 6in diameter pipeline in Canada has been shut down due to corrosion issues after a recent inquiry. The pipeline route crosses the land of 5 to 6 landowners, making it particularly difficult to apply for the construction of a new pipeline. Therefore, it was decided to repair the existing pipeline. Wellstream adopted a repair method by inserting a flexible steel pipe into the old pipe. This approach eliminates the need to purchase a new pipe, uses stainless steel composite pipes as internal lining, significantly reducing costs and minimizing environmental damage. The repaired pipeline is used to transport liquid carbon dioxide to injection wells to enhance oil recovery. There are two 90-degree bends and one road crossing near the wellhead. Pre-pipe insertion operations require pigging and cutting of obstacles.
The flexible pipe has four layers: the innermost layer is an extruded thermoplastic pipe that serves a sealing function during fluid transmission; the middle two layers use carbon-filled polyethylene pipes, which have the ability to resist long-term ultraviolet radiation and eliminate external static electricity. The outermost layer is an extruded thick external protective cover used to protect the lower layers of the pipe from external influences. Standard flexible steel pipes are rated according to ANSI classifications, such as Class 300 equivalent to 5.15MPa; Class 400 equivalent to 6.89MPa; Class 600 equivalent to 10.3MPa. The design basis for offshore flexible steel pipes is API 17J, 17K, and RP 17B. The design standard for onshore flexible steel pipes slightly deviates from the requirements of API standards, using API 17J classification methods and materials, such as 316L stainless steel plates, with pressure, tensile strength, and failure limits all within specified ranges. Testing is carried out in accordance with the requirements of API RP 17B.
The design of terminal fittings must meet the requirements to maintain structural integrity, ensure the seal of internal and external extruded layers, and guarantee the transfer of tensile and pressure loads to the pipe structure, such as bimetallic composite pipes. Samples of terminal fittings undergo burst and axial tensile tests.