Going deeper underground

Marc Hobell, Jim Stancliffe

Beneath our feet in the UK lies a vast labyrinth of millions of kilometres of buried pipes and cables, delivering key products and services essential to our social and economic well-being. These networks of buried assets need repair and maintenance, and the growing demands of the UK economy mean that in years to come the networks will continue to grow significantly, as will the amount of traffic on the streets under which many of these assets lie.

There are now more companies involved in digging holes across the UK than ever before. Latest estimates put this figure at around 4 million holes dug by utility companies annually, and this excludes any excavations made as part of construction projects and works away from the street. Every time a hole is dug it impacts on traffic and the local environment. Often, holes turn out to be ‘dry’ – inaccurate information means that assets thought to be there cannot be found.

In addition, with every hole or trench dug or excavation carried out there is a risk of hitting and damaging buried equipment. The estimated cost of third-party damage to utility companies alone is approximately £150 million a year. This figure is dwarfed by the annual £5.5 billion cost to society through delays to road users, disruption to business, environmental damage and safety costs.

Of all the types of underground assets in the UK some buried pipelines are more hazardous than others, due to the contents they carry or the pressure under which those contents are transported. In the UK such pipelines are classified by the Pipelines Safety Regulations as Major Accident Hazard Pipelines (MAHPs). There are nearly 22 000 km of MAHPs in the UK with 20 000 km transporting gas above 7 bar, 1 000 km transporting ethylene and the remainder transporting spiked crude oil and other hydrocarbons.

Whilst these extensive networks are an efficient and low-risk means to transport large quantities of liquids and gases around the country, there is considerable potential for third-party damage to occur if excavation works adjacent to pipelines are not adequately controlled. In particular, where the pipelines enter urban areas or are sited near to communication routes this potential rises sharply. The consequences of damaging an MAHP can be devastating for people and the environment.

In the UK we have thankfully not witnessed the kind of catastrophe that can result from damage to an MAHP. However, on 30 July 2004 just such an incident occurred in Ghislenghien, Belgium. A high-pressure gas pipeline, operated at a pressure of 70 bar, ruptured following recent third-party damage. Twenty-five people died as a result and 150 were hospitalised, mostly with severe burns. It is thought that damage to the pipeline occurred during the final stages of a car park construction project as a mechanical soil stabiliser was driven over it. Two weeks after the completion of the car park the gas pressure was increased in the pipeline, which then ruptured with disastrous results.

Regular maintenance and upgrading of the UK’s MAHPs has revealed instances where damage has occurred to pipelines but has not been reported to the operator. The UK Onshore Pipeline Association believes it is essential for all cases of damage to be reported to the operator immediately. This applies even in cases where only the pipelinecoating or surface appears to be scratched, as this can lead to corrosion and a weakening of pipeline integrity.