Ghazzoni SpA recently completed an open cut pipeline project on a section of the 72 km Vodnjan-Umag DN 300 methane pipeline that is part of an improvement effort to extend and modernize Croatia’s gas transportation system.
Financed by the European Bank, the pipeline is designed to operate at 50 bar and is owned and operated by Plinacro, Croatia’s gas transmission system operator.
The route of the pipeline parallels the Istrian coastline and required a difficult crossing of the environmentally sensitive Limsky Canal.
The 860-meter canal crossing reached a depth of 36-meters. The crossing profile appears regular with some deformations compatible with the maximum radius of curvature on the pipeline equipment to R = 366 mm. The canal bottom is made up of medium, solid sandy muddy layers.
The pipe selected for the project was API 5L x-50 sp. 12.7 mm steel pipe with a three-layer polyethylene coating and 70 mm thick concrete weight coating.
In preparing for a water crossing, contractors often find that the space required to set up equipment and string the pipe is restricted. This site proved to be no different. The work area width varied between 10 and 18-meters and rollers were set up to support the first section of the pipeline which was constructed in a straight section that was 350-meters long. Three additional parallel pipeline sections, each approximately 300-meters in length, were also constructed.
The pipeline pull-back was carried out using an electric Tesmec CO3543 winch with 40,000 kg pull-back capacity and speeds between 0 and 7 ml/min. The winch was equipped with 38 mm WS Warrington/seale wire rope in order to accommodate the coil winding capability and the length of wire rope required.
Total weight of coated pipe is m 870 x 301.60 kg/m = 262.418 kg.
During the bottom pull-back of the pipeline the residual weight of the submerged pipe in the water was 30 kg/ml. One aim during the pull-back was to reduce the amount of pull-back force needed to move the pipe and prevent it from settling on the muddy bottom. For this, the pulling head was equipped with a special ploughshare to dislodge and displace any calcareous rocks and to carry out pre-trenching operations.
To achieve the required residual weight in water, 40 floats were applied to the pipeline with following characteristics:
The floats were equipped with a special remote-controlled release system which eliminated the need for diver intervention.
To deploy the pipe supported on the rollers into the water, tractors were set up 50 meters apart to apply holding strength during the first part of the pull. Although some difficulties arose with the radio controlled synchronization of the 6 m/min. winch pulling speed, the pipe was successfully deployed and the pull-back was completed in just two days.
Over the course of the project, NDT and hydraulic preliminary tests were carried out along with caliber pig passes to check the integrity of the pipeline.
Once completed, PLINACRO officials expressed satisfaction to all personnel involved in the project.
The project demonstrates Ghizzoni SpA’s capability to tackle technical and environmental problems encountered on projects through the use of advanced technologies and equipments.
Completion of the 45-mile Vodnjan – Umag DN 300 methane pipeline adds to the previous works carried out by Ghizzoni on sections 1, 2 and 3 of the 70-mile Pula – Karlovak DN 500 project along with a new contract for the 175-km Lika – Dalmazia DN 500 project now under construction.