The Jemena Gas Network (JGN) was originally constructed using cast iron pipe, with polyethylene (PE) and steel mains added later.
During the 1980s and 1990s a major rehabilitation program, known as the Goldline Project, was undertaken based on inserting smaller diameter PE mains into the existing pipe.
At the start of the project, the network was losing over 20 PJ/a of unaccounted-for gas – almost more than the amount of gas being sold at the time. After a capital investment of approximately $A450 million, Jemena has now reduced leakage to less than 2 per cent of the system’s annual throughput.
A high proportion – approximately two thirds – of network operation and maintenance costs relate to highvolume activities with low-repeatable costs that include:Article continues below…
• Maintenance works, including programmed and corrective maintenance, and response and surveillance activities; and,
• Routine capital works, including mains extensions, service connections, and meter installations and replacements.
The remaining portion of operating costs relate to non-routine capital projects.
Second, gas networks are generally located within densely populated urban areas. As a consequence there is a high risk of third-party interference to the network.
Third, gas networks are subject to constant additions and modifications, which in turn present a challenge in terms of creating and maintaining accurate records such as maps showing the location of mains.
The importance of safety
Safety is an overarching issue.Network operators are fundamentally in the business of ensuring the safety of the public and of their own employees.
From a risk perspective, a key objective of network operators is to achieve an optimal balance between technical, operational, commercial and safety issues. This requires skilled and motivated staff, good management systems, prudent and efficient investment decisions, and an appreciation of emerging challenges.
One emerging challenge relates to a public that has, thanks to the internet, more access to all manner of information and with it a general trend of lower risk tolerance – with respect to issues affecting public safety.
For gas networks this manifests itself in higher compliance costs, particularly in relation to health, safety and environmental requirements.
For example, complying with traffic control legislation has been one of the most significant increases to the JGN’s cost base in recent times.
Another challenge relates to worsening traffic congestion, which often slows the response times of crews involved in emergency repair work.
From a technical perspective, the main challenge for the JGN relates to its demand profile – in particular, the growth of instantaneous hot water systems.
This has led to an increase in capacity development and facility upgrade projects as part of JGN’s networks capital program.
An associated challenge is recruiting and retaining the resources required to deliver the capital program in an industry that is experiencing a skills shortage.
Another technical challenge for gas networks is integrity assessments for nonpiggable,high-pressure mains. This issue is addressed by conducting a program of ‘integrity digs’ to check the condition of the primary main at sites selected based on the consequence of a major breach, for example, the impact on surrounding built and natural environment, and the potential for damage.
The latter is significantly affected by the type of ground in which the pipe is buried.
For example, where a gas pipeline runs under or close to salt water, there is a greater likelihood of external corrosion. Jemena was faced with this very challenge when it had to investigate a section of pipeline located in the bank of the Parramatta River at Majors Bay.
The pipeline is approximately 2.5 m below the surface of the water and is on the edge of a mangrove forest.
By implementing strict controls in accordance with an environmental management plan, Jemena was able to safely expose the pipe and check it for corrosion and any other potential defects.
A carbon-constrained future
A final challenge for gas networks is the future design of energy networks as society adapts to a carbon-constrained future.
One possible model envisages smallscale gas turbine generators distributed throughout urban centres. All but major commercial and industrial users would be linked to these generators by electricity networks. This model would mean significant changes to the design of future networks.
The City of Sydney has commissioned Jemena to conduct a feasibility study into powering the Sydney CBD with more than 100 gas-fired tri-generation engines to help it meet 70 per cent of its electricity needs by 2030. These gas-fired engines can do three things – generate electricity for buildings, supply heat by using waste heat produced to heat water for office use, and cooling.
By producing energy locally instead of obtaining it from the electricity grid, costs could be cut by $A200 million by 2020 and up to $A1 billion by 2030.
These gas-fired tri-generation engines can produce electricity for as little as 8 cents an hour. Their real attraction is that they are three times more energyefficient than coal-fired power so they have the potential to reduce the city’s greenhouse gas emissions by up to 40 per cent.
If the City of Sydney were to proceed with their plans, Jemena would have to install approximately 10 km of new high-pressure primary gas mains, significantly upgrade the secondary mains system, and install new primary regulating stations.
Such a project would have the potential to increase the total volume of gas transported through the JGN by about 15 per cent.
Another model envisages the universal use of hydrogen fuel cells enabling households to generate their own electricity requirements. This scenario would also require significant enhancement of gas distribution networks.
The challenge for gas networks is to make the correct investment decisions today given significantly different future scenarios.