Recent completion of the marine pipeline linking Algeria and Spain across the Mediterranean Sea, with a 24-inch pipeline, as part of the Medgaz Gas Transmission project, successfully overcame the challenges of 2,155 metres water depths, deep water cable crossings and sea bed post trenching activities. This paper summarizes the various key design considerations addressed to meet the demanding requirements of the ultra deep Medgaz pipeline together with the engineering challenges met by Saipem in planning and executing the laying of the 24-in. gas pipeline in the Mediterranean Sea ultra deep water. Design issues discussed include route optimization, efforts in relation to mitigating geohazards and challenging seabed topography characterising both Algerian and Spanish continental slopes. The intrinsic difficulties in performing intervention works in ultra deepwater, stimulated the application of advanced analysis methodologies for the assessment of in-service buckling and long term freespan fatigue. The installation of the Medgaz marine pipeline presented numerous difficulties which were of more complex nature than for the normal laying of a trunk line. Crossing of the Alboran Sea (the particular area of the Mediterranean Sea), (see Fig. 1) with a 24-inch pipeline that reached a depth of 2,155 metres was, without doubt, the most complex part of the entire works, involving two large semi submersible pipelay vessels: Castoro Sei and the Saipem 7000. The paper presents an overview of the main aspects of pipelay technology facing long trunk lines in ever great water depths and outlines the many engineering challenges faced as well as the solutions adopted that contributed to an effective development in pipelay technology. The presentation reviews also the post-lay intervention work using the Beluga deepwater trencher, the Innovator Remotely Operated Vehicle guiding ultra deep water laying and crossing of five existing seabed cable. Resolution of the many technical problems faced during the execution of the Medgaz Marine Pipeline project has proven the soundness of the engineering solutions adopted for the implementation of this ultra deep water pipelay project.
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