Recent completion of the marine pipeline linking Algeria and Spain across the Mediterranean Sea, with a 24-inch pipeline, aspart of the Medgaz Gas Transmission project, successfully overcame the challenges of 2,155 metres water depths, deep watercable crossings and sea bed post trenching activities. This paper summarizes the various key design considerations addressedto meet the demanding requirements of the ultra deep Medgazpipeline together with the engineering challenges met by Saipem inplanning and executing the laying of the 24-in. gas pipeline in theMediterranean Sea ultra deep water.Design issues discussed include route optimization, efforts inrelation to mitigating geohazards and challenging seabed topographycharacterising both Algerian and Spanish continental slopes. Theintrinsic difficulties in performing intervention works in ultradeepwater, stimulated the application of advanced analysismethodologies for the assessment of in-service buckling and longterm freespan fatigue. The installation of the Medgaz marinepipeline presented numerous difficulties which were of morecomplex nature than for the normal laying of a trunk line. Crossing of the Alboran Sea (the particular area of theMediterranean Sea), (see Fig. 1) with a 24-inch pipeline that reached a depth of 2,155 metres was, without doubt, the mostcomplex 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 depthsand outlines the many engineering challenges faced as well as the solutions adopted that contributed to an effectivedevelopment in pipelay technology. The presentation reviews also the post-lay intervention work using the Belugadeepwater trencher, the Innovator Remotely Operated Vehicle guiding ultra deep water laying and crossing of five existingseabed cable. Resolution of the many technical problems faced during the execution of the Medgaz Marine Pipeline projecthas proven the soundness of the engineering solutions adopted for the implementation of this ultra deep water pipelay project.
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