Offshore pipelines installation: a field-based perspective

This thesis focuses on the installation of a subsea pipeline system as part of the LNG project operated by ENI Congo in West Africa. Six rigid lines are deployed using the S-lay method by means of the DLV Seminole, an anchor-positioned pipelayer supported throughout operations by anchor handling and cargo vessels. The first part is a technical overview of the project, including pipeline geometry, material specifications, external coatings, routing criteria, wall thickness, and cathodic protection to ensure long-term integrity in a marine environment. The following sections describe the S-lay method adopted, the vessels employed with their functions and main features, and the key results of the installation analysis. The simulations are carried out prior to the operation to define the stinger configuration, required lay tension, allowable sea states, and curvature limits along the pipeline. The third part describes the full launch sequence: engineering of the anchor patterns and mooring layout, pipe transport and offshore stacking, firing line operations and deployment through the stinger. These operations include bevelling, mechanized welding, non-destructive testing (NDT), pipe tensioning, surface preparation by sandblasting, and field joint coating. The final part covers the operational phase: vessel mobilization, equipment loading, procedure qualification, and the offshore sequence from start-up to laydown. Pre-commissioning activities, including flooding with chemically treated seawater, internal pigging, bore gauging, and hydrotesting, are covered for completeness. The thesis offers a structured and technically rigorous overview of a real subsea pipeline installation, highlighting the integration of engineering standards, offshore execution, and project quality control measures.