PPIM Contra – call for papers
PPIM Contra – call for papers

Connecting Italy: the Zimella – Cervignano pipeline project

The largest pipeline in Italy, the Zimella – Cervignano Pipeline Project, is currently under construction by Max Streicher S.p.A.

The project involves the construction of a natural gas pipeline across the Po Valley River in northern Italy, which aims to strengthen the national transport network as part of the Snam Rete Gas Network Programme.

Streicher is constructing pipeline spreads 2 and 3 of the four spreads being contracted by Snam Rete Gas. The project is split into a series of operations; the new pipeline that is being constructed will replace the existing pipeline and have a larger diameter than its predecessor, and the adaptation of the lines of various diameters will guarantee connection to new energy users.

Streicher began construction of spread 3 in November 2012, while spread 2 began in November 2013. The company expects to complete both pipeline spreads by the end of 2015.

Project scope

The 56 inch Zimella – Cervignano pipeline has a total length of 170 km, with a steel grade of EN-L450/MB, equivalent to API 5L grade X-65. The pipes are spirally welded, and have internal and external coatings. The external coating is polyethylene-based, with a thickness of 3.0 mm.

Streicher’s contracts comprise construction of the pipelines in the table on the next page.

Po Valley: the new energy centre

The Zimella – Cervignano project will strengthen the existing facilities from east to west along the Po Valley by increasing pipeline transport capacity. This infrastructure will connect the sources of supply located in the NE and central north regions of Italy, with the natural gas consumption centres and storages in the NW regions. The project will provide an increased supply of gas to enhance the local supply sources of the NW region.

Energy consumption in the NW of Italy amounts to more than 40 per cent of the annual national consumption, while supply sources located in the region do not exceed 20 per cent of the country’s total.

Energy operators are turning their focus to the NE and central north regions of Italy to ensure future demand coverage, so the transport of natural gas across the Po Valley is expected to increase in the coming years.

With this in mind, the increase in transport capacity along the Po Valley will ensure flexibility of supply in the NW. For technical reasons, and due to the progressive urbanisation of the Emilia, Veneto, and Lombardy areas, the gas pipeline will also replace the existing 34 inch Tarvisio – Sergnano pipeline and the 30 inch Sergnano – Mortara pipeline, both of which are located in the area.

A unique pipeline project

The Po Valley is one of the most urbanised and populated regions in Italy; the majority of the Italian industrial production takes place in the area, in addition to agricultural production which includes vineyards, orchards, vegetables, corn and wheat. This has affected the design and construction of the pipeline project.

The agricultural activities require substantial irrigation. This presents challenges when establishing the pipeline right-of-way and trenching for pipeline construction, as many farmers still use the ancient field-flooding technique to irrigate, which means the area is characterised by damp soil.

Damp soil represents a big challenge: Streicher chose to use drainage where soil conditions allowed, and wells for the remaining sections of the pipeline route. This technique required deployment of a large number of dewatering pumps.

In addition, a large number of archaeological sites of interest from prehistoric, Roman, and medieval times have since been discovered within the right-of-way.

Ensuring safety on the line

Due to the highly populated area through which the pipeline route passes, considerable importance has been placed on taking health, safety, and environment (HSE) measures to mitigate the impact of the project on the population and the environment. To manage this, Snam Rete Gas has contracted a specialist company to monitor the environmental impact of the project.

Some of the safety techniques put in place by Streicher in the construction of spreads 2 and 3 are based on the subsoil features. The subsoil consists of a simple structure, composed of continuous layers of sand, gravel, silts, and clays, all with variable thicknesses which contribute to the formation of the region’s aquifers. For this reason, Streicher decided to use sheet-piling for all trenches deeper than 3.5 m, where it is not possible to provide a trench with sloping sides.

To ensure hazard prevention during the welding process (both semi-automatic and manual welding are being used) Streicher is also using welding helmets with powered air-purifying respiratory systems to protect welders during welding, cutting, and grinding, as well as providing clean, filtered air for long work shifts.

Obstacles overcome

More than 100 crossings in less than 95 km of the main 56 inch pipeline required alternative installation methods, as the pipeline construction route crossed existing infrastructure such as pipelines, streets, highways, and railways, and natural obstacles, such as rivers and protected areas. All of these crossings required trenchless techniques in order to preserve the subsurface and minimise the impact of the project on the surrounding environment.

The trenchless crossings on spreads 2 and 3 include the following:

  • 90 thrust borings
  • 4 stainless steel micro-tunnels
  • 7 concrete micro-tunnels
  • 2 direct-pipe drills

The direct-pipe drilling project is considered the most challenging phase of the Zimella-Cervignano Pipeline. This technique was implemented after the refusal by the park authority to allow laying of approximately 1,500 m of pipe across an environmentally-protected area. Streicher proposed the innovative trenchless solution using two direct-pipe drills of 750 m each and a junction point inside the protected area.

Direct-pipe drilling is a unique technique developed by Herrenknecht, combining the advantages of microtunnelling and HDD technologies. The prefabricated pipeline is installed and the required borehole excavated at the same time, which allows an efficient and economic installation of the pipeline.

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