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 u Fig. 1 -Route map of Medgaz Pipeline ltra deep water pipelay project.

The exploitation of subsea hydrocarbons fields as well as large subsea gas to market infrastructures often requires pipelines to route across sharp slope transitions. Site conditions are sometime so critical to represent a severe design concern and to require costly seabed preparation works, extremely challenging and environmentally impacting. This paper presents an innovative solution that allows avoiding any preparation work as well as a novel installation method for its effective and safe implementation. Specifically, the paper presents a design case study for a gas export pipeline crossing a severe escarpment at the intersection between the Continental Shelf and the Continental Slope (Shelf Break). The rigid pipeline installed by normal continuous pipelay across such sharp slope transition would be subject to excessive bending due to localized imposed curvature that requires mitigation. Two alternative design solutions have been developed and compared: one based on excavation (trenching) to shape the escarpment edge and one introducing vertical bends on the pipeline string. The design solution based on trenching results in large excavation volume with associated environmental impact in term seawater turbidity and damaged seabed surface (biocenosis). The analysis results also show that the solution is very sensitive to trenching profile accuracy and profile long term stability. Constructability is discussed in terms of availability of technology vs water depth, soil uncertainties, excavation volume, excavation tolerances. The alternative design based on bends allows avoiding any seabed preparation works and all the associated issues. The analysis results demonstrate much higher performances in terms of pipeline integrity and safety throughout the pipeline life. However, its implementation requires special installation solutions as bends are not installable with the normal continuous pipelay method. The paper presents a new installation method (Saipem patented) that allows realizing vertical cold bends safely and effectively on the pipeline profile with no interruption of the continuous pipelay process. The novel idea is to realize the bends underwater, when the pipe is landing or close to landing on the seabed, by means of a remotely operated Underwater Bending Machine purposedly designed. The paper describes the new Underwater Cold Bending technology, presenting the engineering work done to support the demonstration of its robustness and reliability. The paper also presents a case study for escarpment crossing design developed according to two alternative design concepts, the standard and the novel one. The two solutions are compared, listing pros and cons of each one, highlighting relevant design issues as well as construction criticalities and risks.

Offshore pipelay is a complex activity that is subject to some risks due to the challenging operating scenario. The risks may concern the workers during pipes handling, the subsea environment that may be subject to huge seabed rectification works and the integrity of the pipeline. This paper will present the technological roadmap developed by Saipem to implement a more sustainable pipelay operation, focusing on the safety and integrity of the environment, personnel and pipeline. Four innovative tools will be described. The Hands Free Lifting Beam (HFLB) is a system for automatic offshore lifting of pipes, removing human intervention and keeping the workers away from the line of fire. The AFT (Anti Flooding Tool) is a remotely operated tool for pipeline protection from flooding in case of a wet buckle occurrence during lay. The I.A.U (Integrated Acoustic Unit) can perform a safe and non-intrusive, continuous piggability monitoring of the pipeline catenary during lay. The UCB (Underwater Cold Bending) is a solution for crossing sharp slope transition avoiding seabed preparation work and associated environmental impacts. The HFLB grabs and lifts the pipes from cargo barge to pipelay vessel under the control of the operator located in a safe area. The AFT runs inside the laid pipeline during the entire lay, remaining in the safe section already laid (free from possible buckling running effects); it automatically plugs the pipe in case of an accidental flooding event, keeping safe the portion of the pipeline already laid. The I.A.U exploits the acoustic reflectometry and can be integrated with the ILUC (Internal Line Up Clamp) on firing line. It is an alternative to Mechanical Buckle Detector (MBD) which is an intrusive system with associated risks for the pipeline like wire break and loss of the device inside the pipeline, device stacking and possible damage of internal coating during pulling. The UCB is a combination of a new installation method and new subsea bending machine ROV operated, to realize cold bends safely and effectively on the pipeline profile without interrupting the continuous pipelay operation. The UCB can realize the bends underwater, directly on the pipeline catenary when the pipe joint to be bent is landing or close to landing on the seabed, reducing the operational cost while increasing the sustainability. The presented tools can pave the way for safer worker operations during pipe handling (with HFLB); for de-risking the flooding of laid pipeline in case of wet buckle event avoiding the use of a dewatering spread and chemicals for seawater treating, reducing costs and environmental impact (with AFT); for de-risking the monitoring of pipeline during lay (with I.A.U) and for a sustainable crossing of steep escarpment without excavation works (with UCB).