Finding the gas leaks under our streets…

gas leak excavation

Introduction

Our gas networks are aging: as a result, gas utility companies are waging an ongoing battle to ensure that our gas infrastructure remains safe and continues to provide us with an uninterrupted supply to meet our demands for heating our homes and cooking our food. Similar to our electricity supply, we tend to take for granted the vast network that connects these supplies to our houses and providing that our lights go on when we flick a switch and the blue flame appears when we operate our cooker, we don’t give much thought to the work that’s required to deliver this service on demand.

In countries with mature networks like the UK, EU and the USA, we’ve been connected to the ‘grid’ for so long that some of the pipework running under our streets is approaching 150 years in service. While these pipes have provided an excellent service through the years, they are experiencing continuing degradation due to age. In most cases, these aged cast iron pipes are the source of the gas leaks that impact our supplies, present a safety risk and contribute to global warming.

The aging gas network

The UK gas network has grown from its early beginnings in the late 1800’s delivering town gas to properties in urban areas to the fully interconnected system that supplies our needs today. The makeup of the network has also evolved through the years and now consists of a mixture of cast iron, steel and plastic pipes with a total length of some 275,000km. In addition, there are some 23million connections from buildings and residential properties to the main distribution network.

Cast Iron Gas Main

Although there is an ongoing works programme to replace the older parts of the network, due to the scale of the task, the replacement programme is expected to continue for decades. Until the entire grid has been upgraded to the modern polyethylene pipes, the network operators will continue to be plagued by leaking pipe joints and corroded iron and steel pipes resulting in lost gas, increased risk and higher costs, all of which impact the prices we, as consumers, pay for our gas supplies.

Based on the recent average rate of replacement of iron and steel pipes, the HSE estimates that it could take in excess of 50 years to replace all at risk metal mains suggesting that reactive leak location and repair operations will be required for the foreseeable future.

Environmental Impact

In recent years, reduction of carbon dioxide emissions has been the focus of environmental campaigners and governments across the globe. While major steps have been taken to limit CO2 emissions, there is significant evidence that greenhouse gases in the atmosphere are impacting our climate now, highlighting the need to minimise future emissions and mitigate future environmental damage.

As methane is a potent greenhouse gas with over 80 times the damaging potential of CO2, there is now a growing focus on reducing these emissions alongside CO2 reduction. Methane is the main constituent of natural gas and leakage from the gas networks worldwide make a potentially significant contribution to future climate change. Recent legislation from California attempts to focus methane emitters on reducing gas releases by treating all escapes as potentially hazardous and penalising the companies involved accordingly. Whether this approach is adopted in other states or countries remains to be seen but it has certainly raised the profile of this often overlooked problem.

Finding the Leaks

From an economic and environmental perspective, it’s difficult to see why the gas networks are not repairing and replacing gas mains at a higher rate. After all, the lost gas, environmental penalties and increased risks should ensure that this task should be one of the main priorities for the people maintaining the networks. Unfortunately, things are never that simple. The process of identifying a possible gas leak is complex and time consuming with a number of factors influencing the investigation.

– The miles of gas main and associated connections mean there are a large number of potential leak points including joints and branches feeding individual properties.
– Any gas escaping from a main will find the easiest pathway to the surface and in some cases can travel a significant distance from the escape point before venting to the atmosphere.
– Our underground utility infrastructure (cable TV, telephone, electricity cables etc), particularly in urban areas, is becoming more congested and associated service ducts can provide a range of pathways to the surface, again, not necessarily in close proximity to the leak point.
– The large number of underground services in place also increase the amount of excavations required to maintain them, providing more opportunities to damage the integrity of pipes, joints and ducts thereby creating more leaks and pathways to the surface.
– Current gas leak detectors can only pinpoint gas at or near access points such as manholes and due to the distances that gas can travel before reaching the surface, these detectors have limited use in identifying the actual leak location.

All of the above difficulties have to be considered when responding to a gas leak report and current procedures are designed to find the leak and reduce the risk as quickly as possible while working round these limitations.

Gas barhole

As such, the main method of locating leaks involves exploratory excavations and drilling of barholes to take gas readings along the line of any buried gas mains. The process is labour intensive and time consuming and can have a significant impact on road users and members of the public. Obviously, the cost of such exercises can be significant when considering the time on site and reinstatement costs once the leak has been located and repaired.

Repairing & Replacing the Pipes

Once the leak point has been identified, the repairs are usually completed quickly using procedures specific to the pipe material. Similarly, any broken ducts identified during the investigation are reinstated to close off the gas escape path to surface.

Providing repairs can be made with minimal impact, the pipes are not generally replaced at this stage, although any pipes with significant degradation will be highlighted for future replacement.

Therefore, the bulk of the cost associated with gas leaks is the operational costs related to locating the leak rather than the physical repairs of the damaged pipe work.

Improving Safety & Maintaining Gas Supply.

The key to improving the leak repair process is reducing the time to locate the leak and also reducing the amount of investigative excavation required. Current gas detection systems are not ideally suited for leak detection as these rely on gas readings taken at the limited access points available. To deploy these systems along the line of a buried gas main involves road drilling to create access to ducts and gas pipes for the insertion of the gas detector extraction tube.

Gas Distribution Network (GDN) operators have been researching the gas detection market for a more suitable solution that could be deployed without the need for extensive earthworks and to provide a more detailed profile of the underground gas conditions.

As a result, a collaborative project was initiated between the GDNs and a UK gas detection specialist to develop a new tool for gas leak detection and investigation. The initial design brief is summarised below:

– Gas detection tool that can be inserted into cable / service ducts to profile gas concentrations.
– Substantially improve the gas leak identification process and hence the integrity, safety and reliability of the gas network.
– Faster leak location to reduce fugitive methane emissions to the atmosphere.
– Provide reductions in excavation and street works.
– Deployment over 30m-50m.
– No spark gas detection solution.
– Minimal training required.
Working to this design brief, a new instrument was developed in collaboration with the UK energy industry and is currently undergoing extensive field trials with UK gas network operators. On completion of the field trials, the instrument is expected to be deployed initially across all UK GDNs prior to its introduction to the worldwide gas markets.

The system is designed to be deployed on arrival at a newly reported gas leak and is intended to quickly guide the operators to the gas in duct ingress points and, by inference, the general location of the gas leak. This approach will allow the operators to significantly reduce the area for investigation and in some cases, guide them directly to the gas main leakage point. The system uses a novel laser and fibre optic based detection technique that allows the operator to obtain real-time gas profiles within the service / utility duct with the detected gas peaks indicating gas ingress / leakage points. As gas readings are taken in real time, the operators are able to instantly monitor the distribution and speed of gas build up within the ducts which again provides a clear indication of the proximity of the actual gas leak. As operator and public safety are key factors when dealing with gas leaks, the inherently safe, all optical sensing system was particularly well received by the GDNs.

As this system can be used with minimal impact above ground, the GDNs are interested in deploying it retroactively rather than in response to a reported leak. As most leaks are reported during the winter months due to higher pressure within the gas network, this would enable GDNs to identify and resolve problems during quieter periods, smoothing out their operational requirements and reducing the pressure on gas escape teams during the busier winter months. A programme of planned preventative maintenance trials will be undertaken in 2015 to verify the use of the system for this application.

Conclusion

As discussed, a combination of factors have encouraged GDNs to consider their leak detection & repair process and the adoption of this system will help them meet a number of their key objectives. Reducing the time taken to find reported gas leaks will minimise the potential explosion risks while also making a significant impact on the maintenance costs that the networks incur. Faster repairs will also reduce the amount of greenhouse gas emissions caused by the leaking methane, helping to mitigate any environmental penalties and potentially reducing energy costs to end users.

Although initially focussed on the UK gas network, the system will no doubt attract interest from other aging gas networks around the world. The US is particularly interesting as they are currently engaged in a programme of mapping and quantifying the environmental emissions from their networks in urban areas and forthcoming legislation is likely to increase the pressure on the network operators to remedy the leaks in their network. Recent high profile gas explosions in New York have also helped focus the operators, legislators and the public on addressing this particular problem.

The OptoMole mobile leak detection system is expected to be in commercial use across the UK early in 2016.