Transco, the manager and maintenance company for the gas network in the UK, sees horizontal directional drilling (HDD) as a valuable way to speed its mains pipe replacement programme and to deal with a growing shortage of skilled pipelaying labour. A new managers' training course has been set up to help use the tool effectively and safely.
Pressure to increase medium size pipe replacement work has grown recently, largely because of DIMP, or ductile iron mains pipe. These were laid in the 1970s to replace brittle cast iron, but they can suffer point corrosion on the outside which is difficult to inspect and can cause leaks. Two fatal explosions in Scotland, in 1999 and last year, led the Health & Safety Executive to impose an improvement order on Transco requiring all ductile iron pipes within 30m of buildings to be replaced by the end of 2001, usually with less vulnerable medium density polyethylene.
The requirement, on top of programmed or 'policy' work, has meant a much increased workload for most of Transco's twelve Local District Zones (LDZ). In East Anglia £22M must be spent by the year end replacing 160km of mains. It is also likely that the whole DIMP system replacement will be speeded up from a planned 40 year programme to 20 years, keeping workloads high.
'Using HDD means a stretch of pipe laying can be done in one week rather than several using conventional open cut trenching' says Steve Kaminik, network operations manager for the Hitchin hub in Transco's East Anglia district, and the man helping push the technique forwards.
'Obviously there is much less street disruption.'
David Siddals, AMEC project manager for utilities in the Hitchin area, has company approval to spend around £300,000 on two new horizontal directional drilling rigs. He is not sure what they will be, probably Vermeer machines from America.
HDD will initially be used on larger diameter lines, above 180mm and usually 250mm or 305mm, although pipes up to 500mm diameter will be done as experience grows.
Smaller distribution pipes replaced in past years are more suitable for other techniques such as moling, believes Kaminik. 'You have to use what is fit for purpose, ' he says.
Transco, or, pre-privatisation, British Gas, had also been a little wary of directional drilling, even though the company was an early user and developer of trenchless methods.
'If you get one failure, such as heave lifting the road surface, you tend to put things on the back burner, ' Kaminik says.
'You have to feel comfortable with a technique.'
Additionally, he says, subcontractors in the past wanted to cherry pick larger and easier rural jobs. 'That seems to be changing, ' he adds. One reason is that DIMP work involves longer contracts of up to 2km.
Re-examination of trenchless techniques by Kaminik for East Anglia LDZ has shown long term improvements in directional drills, which are now more powerful and easier to guide. The radio emitting sondes carried in the head give a better signal and the hand held detectors are more sensitive. Reamers have also improved, he says.
There are also new data logging systems becoming available to provide critically important evidence about where a pipe has been put.
Things can still go wrong, particularly in urban ground crowded with other pipes and services. An incident last year saw a water pipe damaged by the back reamer, though the method has proved generally successful .
Preparing a job comprehensively is the key, says Kaminik, adding: 'You need a full desk study and physical survey of the course, with detectors and by eye, to know where all the obstacles are, above and below ground.'
With the UK Society for Trenchless Technology he has set up an intensive training course in all aspects of HDD including machine operation, drill technique and safety. Some 40 managers have attended from Transco East Anglia and its term contractors. The first seven have certificates and the course is likely to be taken up nationally.