There are many areas of Gas Engineering Operations, these can be broadly categorised into 2 sections, above ground (pressure control equipment) and below ground (pipe systems) you can further break these down into various pressure tiers, but for today I am going to focus on the most significant asset in terms of quantity – low pressure pipes!
The low pressure (LP) system generates by far and away the most work for a Gas Distribution Network, work such as escapes, repairs, connections, and replacement. It also provides the largest impact on customers for a Network as the vast majority of customer connections are to the LP system.
When I looked at this as a topic, my first thought was that it really hasn’t changed much over the last 40 odd years that I have been involved in the Gas Industry. After all, a pipe in the ground now is the same as a pipe on the ground back in the 1970’s, right?
Well almost, but not quite. It’s true that today the pipes are different, but what else is? So, settle down for a brief history lesson and an answer to the question.
When I started in the gas industry it was on the back of the “King Report” which was written because of some notable and serious explosions in the mid 1970’s. The primary cause of these explosions was the material of the low-pressure gas distribution system – Cast Iron, a material used widely since the 1800’s
Cast iron had itself been through an evolution, it started off as pipes being “pit-cast” with one end of the pipe being a socket and the other being a spigot. The socket end was sealed into the spigot end by stuffing the space with yarn and sealing it with molten lead hence the term you may have heard, “lead yarn joints”.
In the mid 1900’s the pipe manufacturing technology was upgraded to centrifugally spun cast iron, a process that ensured that the wall thickness of the pipe was more even and hence the strength of the material was improved. This was known as “spun cast iron”. The joining method remained the same, albeit the lead yarn joints were later replaced by a mechanical jointing system.
The cast iron system was in place for the low-pressure gas distribution system for a very long time. It was mostly very good at doing its job – apart from when there was ground movement, the lead joints would crack and cause joint leakage. Then, when natural gas was introduced to replace the manufactured gas, it was a very dry gas and this caused the yarn to dry out and cause further leakage.
And then there was the big problem with the cast iron pipes, the showstopper if you like – It had the propensity to break, especially but not exclusively, the smaller diameters (3” and 4”). It would literally crack into two pieces under stress. This would occur due to ground movement, which could be from traffic or weather conditions or even the filling placed around the pipe when it was laid.
So herein lies the problem, this infrastructure had been in place for years and had done a decent job, but it had a major inherent danger. When it broke (fractured) the gas could then migrate to buildings and once it reached its explosive range (5 – 15% Gas in Air) a catastrophic explosion could occur. After a series of such high-profile incidents had taken place in 1977 the Government commissioned Dr Philip King to chair an inquiry and make recommendations. Several recommendations were made, including the setting up of a National Gas Emergency Service. The main recommendation though was that the most at-risk cast-iron pipes were replaced with plastic pipes.
Virtually overnight, the gas industry went through its most significant change since the conversion from towns gas to natural gas in the 1960’s and 1970’s. This proved to be an evolution of epic proportions for the gas industry and coincided with the use of Polyethylene (PE) pipes and systems.
(It is worth mentioning at this point that post the King Report work programme further programmes were introduced for medium pressure ductile iron and certain types of valves, however the major replacement programme commenced in 2002 with the introduction of the 30/30 programme. In essence getting rid of all cast iron pipes within 30 metres of a building within 30 years. This programme continues today, with the industry regulator (Ofgem) continuously demanding efficiency and driving down costs.)
Despite some forays into alternative metallic systems (most notably Ductile Iron) PE pipe systems became an absolute game changer for the gas industry and enabled a whole plethora of innovative approaches to be deployed when installing them.
In the early days PE networks were not well received by the Gas Engineers of the day, it was mistrusted, and it had to be kept a certain distance from properties. For many years after introduction, PE services were not allowed to be taken directly to the property. Instead, they had to terminate at least 1 metre away from the building line and from there to the house, be laid in steel, this is known as a “steel tail” in the industry. There are still many in existence, but many more have had to be replaced and guess which bit failed? Yes, the steel bit!
So why am I telling you all this? It’s important to recognise this period of time as the breeding ground for evolution and innovation within gas distribution networks. The innovation in networks has been continuous and not just with PE systems.
PE systems allowed for quicker installation times and the jointing process was done via fusion – literally welding (melting) one pipe to the next by a variety of techniques. Excavations could become smaller and didn’t need to be straight to accommodate the new PE pipes. Then someone had the absolute brainwave of ‘inserting’ the new flexible PE pipe into the old cast iron main which was being abandoned. Another example of game changing innovation as it would save a significant amount of the excavation required as you would only need to excavate where a joint or connection was required.
But there was a problem, the maximum length of smaller diameter PE was 12 metres. Cue the PE manufacturing companies getting their brains working – then out came coils of PE pipe, literally like a cable. It was a bit unwieldly at first, and actually quite dangerous if not handled correctly due to the stored energy – I recall as a young engineer, someone letting go of the end of a coil with a cap end attached which then flew into the mouth of a colleague and physically lifted him off the floor, needless to say some dental work was required.
Further innovation saw the introduction of coil trailers which bore the weight of the plastic coil and enabled it to be dispensed safely. The lengths available on coils also increased, a more recent innovation saw coils of 500m in length in certain diameters in regular use.
Insertion took off in a big way and is now the most used technique when replacing mains and services. Dead insertion, where the parent main is isolated before the insertion begins is a good technique, but requires a significant effort at the end of the working day to make the connections at either end of the “push” and to reconnect all the affected customers with the new PE services. This also requires much preparation work in advance of the operation. A technique which is not new but certainly an evolution of dead insertion is “live insertion” where the new PE pipe is pushed through the parent main whilst it is still alive. This means that customers can be connected in a more planned way, minimising disruption and improving customer satisfaction.
Let’s now fast forward to the present day. The LP distribution network is now circa 75% PE, the remaining Cast Iron is mainly larger diameter pipes that are less likely (although not impossible) to fracture. So, are there less leaks? Yes of course. Do network operations still need to continue? Absolutely.
The evolution these days is still focussed heavily on how things are done with today’s challenges mainly on the cost of replacement. Ofgem are challenging allowances for the completion of this work and the safety Regulator – the Health & Safety Executive (HSE) also having an influence on how things are done.
The innovation in recent years to meet the cost challenges has focussed on the planning of the works and designing larger projects that can be designed to drive efficiencies and economies of scale. There is no doubt that innovative designs will give the best chance of efficient projects with c80% of the opportunity saving being in the design. It is common practice these days to complete a camera surveys of insertion schemes ahead of work commencing. The specialist team will head to a job and will ensure the existing mains are as per plans and identify any internal issues and highlight all the required service connections. This will enable the most efficient delivery on site. Another potential benefit of an all-PE network is that depending on whether it is discrete or integrated it may be able to run at higher pressure (the top end of an LP network is 75mb) and hence need smaller pipes that are more likely to be insertable.
The way projects have been delivered has also evolved over time with some Networks operating in-house models with others electing to hand over the whole process (design and deliver) to contract partners, the delivery usually being by smaller sub contactors. The name of the game is to innovate to find the best model to meet the Ofgem allowances and changing customer expectations.
Data collection on projects is another area where innovation has taken significant steps forward in recent years, Networks have an absolute duty under their licenses to provide Ofgem with accurate data and have invested in systems that are able to accurately capture data from the field and ensure that it is efficiently and accurately recorded in the Networks primary repository.
There are numerous innovative techniques under trial or test at the current time. Anything that minimises time spent on the job, or the amount of excavation required to complete the job will be actively pursued. Robots that can work inside the larger diameter mains are now deployed and may defer the replacement by extending the life of that asset. One thing is for certain, as the end of the 30/30 programme nears, the remaining work will have to be delivered at a more efficient price.
A problem amplified by the fact that the remaining work is probably in the less efficient category given the way in which networks have managed their programmes over the last 20 years. Looking further forward to GD3, the next 5-year price control to commence in April 2026, it is not beyond the realms of possibility that Ofgem could severely curtail the need for the remaining 6 years of the programme given network incidents are now thankfully extremely rare. This though would also need agreement from the HSE as well as engagement from network customers.
The HSE are also currently influential in the way that work on the networks is carried out. They have always been a key part of the process and indeed must sign off each Networks plan in respect of the mains replacement programme. In recent years though several areas have come to the fore in terms of Network compliance, these have also necessitated networks to innovate to ensure compliance and avoid HSE enforcement, these include Hand Arm Vibration Syndrome (time spent on vibratory equipment) Networks have progressively mechanised their processes and mitigated much of this risk, however, it is still a key consideration. Fatigue, the amount of time spent “on duty” has necessitated devising innovative work patterns, especially where operatives also cover out of hours standby duty. The HSE are also currently focussed very much on Human Factors and Safety Critical Task Analysis. This will also ensure that Networks are considering all aspects of the jobs that are being undertaken, the procedures in use and the training and competence of operatives.
In conclusion, while the job today looks fairly like how it looked half a century ago, it is in fact very different and has been continuously innovating throughout that period. Whilst these changes are happening, they aren’t all immediately obvious but if I look back on my 16-year-old self it is staggering to see the changes that have occurred, and the performance of the Networks compared to how things used to be.
I could go on and on, and I haven’t even mentioned greening the gas and potential hydrogen systems as the race to net zero continues, but this is the slimmed down version. If anyone has any questions on this, or wants me to cover any other area of the gas Network Operations, please get in touch.
By Andrew Hopkins
Andrew Hopkins is a Strategic Advisor at Skewb. To speak with him about this topic in more detail, you can connect with him on LinkedIn.
