December 2017, Vol. 244, No. 12


Britain Moves Forward on Gas Mains Replacement Program

By Nicholas Newman, Contributing Editor

Britain is halfway through replacing the regional gas distribution network which serves 23 million businesses and homes. A pipeline system of about 155,000 miles (250,000 km) in total length – it is also rather old.

“Much of the original U.K. network is over a hundred years old,” said Jonathan Callighan, Construction and Procurement director of Cadent Gas, which operates half of the regional gas distribution network.

Preconstruction surveys of the network have identified and prioritized what needs to be done and where. To minimize disruption to the public, the replacement of all cast-iron and ductile mains will be restricted to within 100 feet (30 meters) of buildings. This work is progressing at the rate of about 2,175 miles (3,500 km) a year, said Callighan, who added it will ultimately be charged to customers.

Natural gas is important since it accounts for 30% of Britain’s energy mix and provides heating and electricity to households and businesses. The country consumes about 250 million tons of oil equivalent of gas a year, of which 45% comes from the North Sea and East Irish Sea. About 38% of the gas supply is imported by pipelines from Europe and Norway, while the remaining 17% is imported as LNG by tanker, mostly from Algeria, Nigeria and Qatar. This year marked the first imports of U.S. LNG.

As to onshore supplies, Britain has encouraged biomethane or green gas, produced in anaerobic digesters from food waste, sewage or energy crops. Production is small at 617 MW – or enough to power about 800,000 homes.

Reasons for Replacing Pipelines

The replacement of gas mains was initiated by Britain’s national safety regulator, the Health and Safety Executive (HSE). Under its auspices, The Iron Mains Risk Reduction Programme (IMRRP) addresses the potential risk of failure of iron gas mains and the potential consequences of injuries, fatalities and damage to buildings.

It is designed to secure public safety while allowing for efficiency, environmental, strategic and customer service factors to contribute to driving the program and allowing sufficient flexibility to enable Ofgem (the Office of Gas and Electricity Markets) to encourage innovation in risk management. A significant benefit of the decommissioning of all at-risk iron pipes, based on a risk prioritization model, is to reduce the possibility of gas explosions by a significant 60% on pre-2005 levels.

The Stakeholders 

About 80% of British homes are served by the gas pipeline network which consists of two parts. There is the national transmission network, which is owned and operated by National Grid which transmits gas to eight regional gas distribution networks (GDN). Cadent, in which National Grid owns a minority stake, distributes gas in four regions – the West Midlands, North West England, East of England  and North London. The 5.9 million homes and businesses in Scotland and the south of England are supplied with gas by SGN.

The Northern Gas Network delivers gas to 2.7 million homes and businesses in the North East, Northern Cumbria and much of Yorkshire. Finally, Wales and the West of England’s 7.5 million gas customers are supplied by the Welsh and the West of England distribution networks. The regional gas distribution networks are natural monopolies and are regulated at the national level by Ofgem.

The current phase of the nationwide gas pipeline replacement program, ending in March 2021, is being delivered by the eight GDN operators, contractors, suppliers and councils under agreements between Ofgem and the safety regulat  or — the HSE.

Informing People

The GDNs are engaged in a wide-ranging public  awareness campaign to provide information on work schedules to the public and businesses in their areas. This has included local media campaigns, onsite posting and short videos about what people should expect from the work. GDN staff have increased their public profile by participating in local community events and campaigns.

For example, Cadent’s 5,000-strong workforce  has pledged to bake, cycle, run, climb and even skydive in an effort to generate funds for the estimated 850,000 people affected by dementia in the U.K. There have been local community meetings where project managers have addressed the public and answered questions about specific details on local work.

Overview Program

The replacement program (REPEX) began in 2002 and is scheduled for completion in 2032. To complete the program in 25 years would have meant replacing about 2,675 miles (4,300 km) of pipe a year but this was not seen as practical on Britain’s densely populated island. At the same time, it was recognized that a 35-year program would be impossibly slow.

The choice of a 30-year program requires a rate of replacement of 2,225 miles (3,580 km) of pipe a year. After consultation with the industry, the HSE decided that during the current phase, between April 2013 and 2021, the pipelines would be replaced with polyurethane at the rate of 3,185 km a year in the low-pressure parts of the network.

Each regional distribution network is working at targets set by the HSE for replacement of  their Tier 1 pipes ( less than 8 inches in diameter) and Tiers 2 and 3 pipes ( over 8 inches in diameter). The annual targets are as follows: Cadent Gas, operator of four regional distribution networks (12,742 km), Northern Gas Networks (1,760 km), Scotland Gas Networks (1,736 km), Southern Gas Networks, (4,944 km) and Wales and West (2,537 km).

GDNs make quarterly progress reports to the HSE, and in case of failure, must explain how they intend to recover their schedule. Interestingly, the HSE’s decision was based on practicality rather than value for money, and GDNs are investing heavily in the program. For example, according to the Northern Gas Networks Business Plan 2017, their total Tier 1 mains REPEX program is costing some $748 million (£564 million) a year.

Onsite Day to Day

“The onsite staff are trained to communicate with the public and to maintain good relationships,” said Callighan. “Staff safety training and operational safety is regarded as paramount, as seen by the fact that every time a section is being upgraded, it is isolated first for both workplace and public safety reasons.”

Much of the technology being used is low-tech including the basic breaking up of services and live insertions rather than dead insertions. However, the next phase could be accomplished with hi-tech equipment.

“We are looking for game-changing technologies such as using robots that could either pull plastic pipeline or spray a plastic coating to the inside of existing old pipelines,” he said. “There is a long horizon ahead of us, so we have opportunities to change and revise the program in all aspects of the replacement chain.”


Natural gas and LNG supplies are augmented by small amounts of biogas, a renewable resource that can be expected to grow in importance as Britain prepares for a low-carbon future. Over 250,000 cubic meters of biogas enters Cadent’s distribution network in a single day. By 2050, renewable gas could produce between 68-183 TW hours a year, sufficient to heat 7-15 million homes, or enough gas to meet the needs of southeast England, London and East Anglia.

For the not-too-distant future, gas pipeline operators are studying other options, including removing the carbon dioxide from gas before distribution, and the transmission of hydrogen, Callighan added.

When all is said and done, it is clear that Britain’s gas pipeline network operators are preparing their networks to carry new forms of energy with a high degree of safety.

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