Abstract
This paper presents the investigations performed by TotalEnergies and Saipem on the cost effectiveness potential of internal plastic lining for corrosion protection of offshore production lines. Objective was to better understand for a complete EPCI cost comparison the various parameters that could have a significant impact on the potential savings associated with the use of plastic lining instead of CRAs (Corrosion Resistant Alloys) for very corrosive production fluids such as sour gases.
An extensive cost comparison study between CRA lining and plastic lining for offshore production lines was performed considering sensitivity on several parameters: 3 pipe diameters, S-Lay, Reel-Lay and J-Lay installation, sensitivity to external thermal insulation requirements, mechanical and design requirements, to pipe length and fixed costs (technologies and vessels). A dedicated calculation tool for system design and cost assessment was built on purpose for this sensitivity study. Costs were assessed for the various cases, starting from pipe design, then assessing procurement costs, fabrication costs then installation costs with preliminary cycle time assessment. Project management and engineering costs have been considered to obtain comparative EPCI (as installed) cost assessments for the various study cases.
Plastic lining appears to be a cost-effective solution installed in J-Lay or S-Lay in addition to reeling (up to 45% of potential cost savings on installed line compared to CRA lining). The main driver for the cost savings is associated to the procurement of the pipes and associated lining, including pipe manufacturing. Some smaller savings can also be obtained from the offshore cycle times in J-Lay and S-Lay as the CRA welding add a significant operation time in comparison with standard CS welds. The fixed additional costs associated to the plastic lining (specific tooling for example) can be quickly amortized after a few kilometers thanks to the material cost savings. Integrating them as a company investment allows to unlock costs savings even for shorter lines. The thermal contribution of the plastic liner is also interesting regarding the overall pipe insulation design.
This study completes the works already performed by the industry on the offshore costs of plastic lining as it considers the whole EPCI CAPEX costs from the Contractor and Operator points of view and offshore experience. The study integrates the S-Lay and J-Lay installation methods (while previous studies mainly focused on Reel-Lay) and includes an extensive sensitivity study with various key parameters such as pipe sizes, pipe design requirements, material costs and offshore operation times to get a general overview of potential benefits associated with plastic linings for offshore production lines transporting corrosive fluids such as sour gases.
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