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Polyethylene (PE) materials bring added value to the utility and industrial pipe sectors

Borealis A/S : 06 August, 2004  (New Product)
Since its introduction, polyethylene (PE) from Borealis
To the pipe producer Borstar PE has improved process efficiency, reduced production costs and increased the effective plant capacity, as well as extending the range of pipe sizes that can be produced from PE. Through its superior balance of properties, Borstar PE enables engineers and system designers to utilise PE where they would previously have had to specify more costly steel or iron pipes. The advantages and benefits they bring to system managers include lower installation costs, simplified installation with reduced disruption to residential communities and, importantly, they provide reliable long-term performance.

Borstar medium density PE80

Borstar PE has proven it can meet the needs of a wide range of pipeline projects using many different installation technologies including insertion, pipe bursting and directional drilling. Borstar bimodal medium density (MD) PE80’s special properties produce tough flexible pipes for challenging projects such as renovating gas pipe systems in congested urban environments. The bimodal process provides a higher resistance to crack growth than previously possible, which enables pipes produced from Borstar MDPE PE80 to be used for difficult insertion projects and operated at a higher pressure than other MDPE pipes.

In Milan, Italy, AEM Gas had used bitumen coated steel pipes for its medium pressure gas distribution system but the highly corrosive conditions meant that a number of these mains needed to be renovated by inserting a smaller diameter PE pipe. To carry out the work in the centre of Milan it was essential to minimise disruption to normal street activity and this was best achieved with a flexible MDPE pipe. Borstar ME3441 was specified for its high flexibility and its high resistance to slow crack growth and rapid crack propagation.

In the first project, which was undertaken in 2003, a 400mm SDR11 pipe was inserted into the 500mm, 160m long steel main in just four days with a minimum of disruption to Milan’s busy Via Stresa. Moreover, AEM Gas was able to use their own equipment and workforce to replace the main and made an overall saving of 20% compared to replacing the mains by other means.

Transco, the major gas distribution company in the United Kingdom, is conducting a major renovation of the gas system in response to demands from the UK Health & Safety Executive to replace all metal pipes within 30 metres of buildings. One such pipeline was a 24 inch cast iron main in Bethnal Green, London. While renovation by insertion of a PE pipe was an option, a close fit method was necessary to retain the maximum flow capacity of the pipeline and therefore the “Subline” renovation technique was chosen.

In order to reduce the risk of failure from surface damage induced in the inserted pipe, a PE material with a high resistance to crack growth was required and Borstar ME3441 specified.

The 595mm SDR33 pipe was welded on site into continuous lengths and fed through the Subline forming unit to form a “C” shape (see photograph). As the pipe exited the machine, an automatic strapping unit located and friction welded the polyester straps at regular intervals to keep the pipe in shape.

A winch cable was connected to the front end of the liner pipe and the pipe pulled into position. Because the cross sectional area was reduced by approximately 40%, the winch load was low and an insertion rate of one metre per minute was achieved. Once the liner pipe was in place the winch cable was de-coupled and the pipe reverted to circular form using cold water at a pressure of 2 bar. As the pipe reformed the restraining straps broke and remain trapped between the liner pipe and the cast iron host pipe.

The whole renovation process was completed in a remarkably short time with minimal disruption, providing Transco with a very cost-effective method for the renovation of large old cast iron mains.

Borstar high density polyethylene PE100

Borstar low sag (LS) polymers have extended the range of pipe diameters and wall thicknesses achievable, enabling PE pipe solutions to be offered for many more large projects.

At the BP Sullom Voe Oil Terminal, Shetland, UK, a 1400mm diameter pipe was needed to protect undersea oil flowlines. The PE pipe was required to have a wall thickness of 100mm which until recently would not have been possible in PE materials. However, the pipe was produced from Borstar HE3940–LS, a material that is specially designed to produce large diameter thick-walled pipes. The material’s high viscosity at low shear rates means that it resists gravity flow, thereby producing a pipe with a very even wall thickness. The pipe produced by Pipelife Norge AS, was extruded directly into the adjacent fjord and then towed the 1000km to Sullom Voe behind a barge.

In a separate exercise a section of the1400x100mm pipe was fully evaluated as if it were a pressure pipe. It was pressurised at 8MPa and a transducer was used to monitor the hoop strain in the pipe over a 2000 hour test period (approximately 3 months). The measured strain was then extrapolated to 100 years and this value compared to the recommended limiting strain of 5%. In fact the 100 year extrapolated strain value was just 3%, indicating that as a pressure pipe operating at its maximum design pressure, the pipe would have a long-maintenance free life even with its extreme dimensions.

When the Municipality of Montpellier, France, needed a long sea outfall pipe to dispose of sewage from a new treatment plant they considered a number of alternatives. Ultimately they chose a PE solution rather than steel, glass reinforced plastic (GRP) or concrete materials for what was to be Europe’s largest-ever plastic pipeline project.

Taking full advantage of the special low sag properties required to efficiently produce large diameter pipes, Pipelife Norge manufactured the 11kms of 1600mm diameter PE pipes from Borstar HE3490-LS in lengths of 550m. Once the pipe lengths were capped they were coupled to a barge and towed from Norway to the French port of Séte on the Mediterranean.

At Séte the sea outfall pipeline was prepared for installation into a pre-cut 2m deep trench in the seabed. Preparation involved the fitting of concrete rings which would provide the necessary ballast to keep the pipeline submerged and to physically protect the PE pipe against damage from anchors and trawler nets.
The 550m lengths of pipe were joined using specially designed end-load resistant GRP couplings, and the resulting pipe strings were pulled into position and installed.

The success of this and other large diameter PE pipeline projects has encouraged Pipelife Norge to install a 2m diameter PE pipe production line at their plant in Norway. This will enable PE solutions to be offered for even more pipeline projects - thanks also to the special features of the Borstar process.
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