During the 1960s the Trans-Mediterranean Pipeline project was conceived as the most effective way to monetise Algeria’s extensive gas reserves and to enable Italy to expand its natural gas consumption. A preliminary feasibility study was conducted in 1969 and the first route survey completed during 1970.

Italian stated-owned Eni pursued the construction of the subsea pipeline in favour of proposals to ship LNG across the Mediterranean and in 1973, signed a contract with the Algerian Government for the supply of 414 billion cubic feet of gas from the Hassi R’Mel Gas Field for a period of 25 years.

The agreement gave rise to the technical challenge of crossing the Mediterranean with a subsea pipeline at record-breaking depths.

Constructing in deep waters

The 2,340 km pipeline route begins at the Hassi R’Mel field in Algeria and runs 550 km to the Tunisian border. From there it travels 370km through Tunisia to El Haouaria, after which it crosses the 155 km wide Sicilian Channel.

In 1975 Sonatrach and Eni awarded Eni subsidiary Saipem a $US237 million contract to lay three 20 inch gas transmission pipelines across the Sicilian Channel in water depths of up to 610 m and a further four pipelines across the Straits of Messina from Sicily to the Italian mainland.

At the time, worldwide experience in design, construction and maintenance of offshore pipelines was limited to water depths of 150 m. The Trans-Mediterranean Pipeline project necessitated the research and development of new technologies to overcome the engineering and construction hurdles presented by the pipeline’s depth.

Saipem constructed Castoro Sei, a computer-controlled, semi-submersible pipelay vessel, to break the world record and lay pipes in depths up to 610 m. The Castoro Sei was equipped with three tensioners, which provided a maximum tension of 180t in the pipes being laid. The laying system was comprised of three ramps – one fixed and one pivoting ramp, and a ‘stinger’, which was hinged to the internal pivoting ramp.

The severe unevenness of the seabed and steep slopes posed the main difficulties for the project, limiting free spans in the pipeline construction. Saipem developed a model to monitor the stress status of the pipes on the sea floor both during and after laying to minimise the risk of buckling and avoid the associated long delays.

A 45.7 m wide corridor was required to be opened up through rock and coral in water depths of 503 m over a length of 4.8 km in the Sicilian Channel. After obstructing materials were successfully blasted through, a guide cable was laid along the wall of the trench to act as a reference line for surveying the position of the first pipeline, which was laid parallel to it.

The Tunisian crisis

In 1977 Tunisia sought to take advantage of rising oil prices, Eni’s growing commitment to the project, and the fact that the only feasible route for the Trans-Mediterranean Pipeline passed through its territory, to negotiate a transit fee of 12 per cent of the value of the gas that passed through its territory. The demand forced Eni to investigate the option of abandoning the pipeline project in favour of shipping LNG from Algeria instead. This manoeuvre resulted in Tunisia accepting a 5.625 per cent transit fee of transported gas volumes, and the pipeline progressed.

Pipeline progress

Construction began with an official ceremony in Algiers in June 1979 and by the end of 1980, the three pipelines spanning the Sicilian channel had been completed. Pricing disagreements arose once again, this time with the Algerian Government demanding an increase of $US2 per 1 million british thermal unit from the price set in the 1977 agreement. Construction halted when Eni refused to comply with the new demands and the Algerian Government ordered a halt to all Italian industrial contracts and construction projects in Algeria. Construction of the Algerian onshore section of the pipeline did not recommence until a new pricing agreement was reached in 1982.

The first line of the Trans-Mediterranean was finally commissioned in June 1983, while the second phase was completed between 1991 and 1994, which saw the capacity of the pipeline double to 1 trillion cubic feet per annum. Slovenia secured access to the pipeline through the construction of a 35 km spurline, which connects into the Italian end.

Present day

In 2005 Eni and Sonatrach reached an agreement to expand the Trans-Tunisian Pipeline, a section of the Trans-Mediterranean Pipeline that runs through Tunisian territory. Saipem was contracted to carry out the engineering, procurement, construction and commissioning of two new gas compression stations and the upgrading of the existing compression facilities. Work was completed in October 2008 to increase the capacity by 113 Bcf/a and works are planned to increase capacity by a further 116 Bcf/a starting from 2012.