ABSTRACT

This paper describes some of the problems which have been met during the laying, with SAIPEM 's semisubmersible lay vessel Castoro Sei, of multiple gaslines across the Strait of Messina in 1979 and across the Channel of Sicily, the latter project being still under way.

A description is given of the mathematical models which have been utilized since the early project design stages and later for control of actual laying. The presentation includes description of specific techniques and solutions adopted for overcoming particular difficulties met during the performance of the work. The following items are presented:

  • Description of of Sicily.

  • Problems related to very deep water pipe laying. Tri-dimensional mathematical model; design and monitoring of stress status.

  • Abandonment and recovery in very deep water.

  • Description of problems caused by irregular seabed in deep water; use of a manned submarine for guided pipelaying along corridors cleared by means of explosives.

  • Problems related to currents.

A) Description of the Project

Crossing of the Channel of Sicily (for the Messina Strait Crossing please revert to OTC-80 paper No 3739) :

  • number of lines: 3

  • 2 Routes, the Northern and the Southern.

Two lines are laid on the Southern route - over a length of 156 km for eachline. The Pipe is 20" in diameter, X65, longitudinal welded with wall thicknesses of 19.05 mm and 20.62 mm. Concrete coating 50 mm thick resulting in a negative buoyancy of 137 kg/m and 156 kg/m for the 19.05 mm and 20.S2 mm thick pipes respectively. In the deepest section, the 20.62 mm pipe was laid bare with a negative buoyancy of 46 kg/m. The maximum water depth has been reached on the southern route with 608 mt (2,000 ft).

The seabed profile is extremely uneven on both routes with sections where slopes reach inclinations of up to 23 ° in the southern route and as much as 33 °on the northern route. On both routes the ruggedness of the sea bed has imposed on certain sections the use of explosives to clear a negotiable corridor, in water depths averaging 500 mt, providing a 50 mt wide path free from rocky outcrops preventing therefore the risk of excessive free spans in the pipeline which could induce stresses in the pipeline itself exceeding the allowable limits.

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