Swagelining makes welcome return to Edinburgh

Swagelining advantages were rediscovered for a number of key rehabilitation projects National Grid Transco (NGT) has undertaken in Edinburgh, Leamington Spa and Sutton Coldfield.

Swagelining is a safe, effective rehabilitation technique developed by British Gas in the 1980s.

However, it has not been so widely used in the last few years - until recently, when its advantages were rediscovered for a number of key rehabilitation projects National Grid Transco (NGT) has undertaken in Edinburgh, Leamington Spa and Sutton Coldfield.

In all these schemes, 469mm Uponor PE gas pipe made the ideal insertion into old Imperial sized 18" gas pipe.

The advantages of this well-proven technique include a significant reduction in the number of excavations required, and time, cost and disruption saved compared to open cut work.

At its simplest, the procedure entails using a winch to draw the PE gas pipe through a diameter-reducing die to temporarily reduce its outside diameter - to 'stretch' it.

To obtain the appropriate length of pipe for the individual project, typically 12-metre sticks of PE pipe are first butt-welded and the outer weld bead that forms removed to ensure a smooth outer surface throughout the single pipe length (up to 400 metres is common).

The new pipe is then pulled through the 'host pipe' by the winch.

Once installed, and secured at the opposite end, the pulling pressure on the pipe is released, when it will try to revert to its normal diameter, forming a tight fit against the inside of the host pipe.

Prior to this procedure, the host pipe is thoroughly checked for debris or scale build-up and any potential blockages, obtrusions or bends removed.

Two recent swagelining projects in Edinburgh effectively minimised traffic disruption and saved considerable time as well.

The first, at Dalry Road, in the centre of Edinburgh, entailed around 1km of new pipe, incorporating about 500 metres of swage in two pushes.

Around 800 metres of swage was also successfully installed at Abercorn Crescent.

The start saw around 600 metres of open cut pipe installation, in diameters of 250mm, 315mm and 400mm, on one of the world's most famous streets, Princes Street, and great care was taken by NGT and its contractors to notify residents and businesses of the essential work.

The three phases, completed in Spring 2005, began at South St David Street, continued through Princes Street, and finished with South St Andrew's Street to Carlton Road - including everything coming to a stop between November and January for the Christmas shoppers in Princes Street.

NGT network operations manager Stuart Pender described the extensive operation: "We have had a major task in renovating these gas mains in the centre of Edinburgh whilst causing minimal disruption to local residents and businesses.

Everything's gone well and this project benefited from swaging due to there being no surges and our teams being able to isolate the gas at either end, plus the network being fed from different parts of the city.".

NGT network operations officer Hywel Williams also confirmed that swagelining would be considered wherever feasible for this type of work.

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