Most utilities use a combination of metallic and non-metallic pipe materials in their network and often the biggest challenge for pipe integrity is related to the corrosion of metallic pipelines. The recent introduction of relining systems for pressure mains has provided a unique opportunity for Queensland Urban Utilities to trial the new technology to extend the life of pipes in its network.
With vast kilometres of pipeline networks in Australia, utilities are all faced with a common challenge to understand the condition of pipes and when they need to be replaced.
Many of Queensland Urban Utilities’ larger trunk pipelines are mild steel, which utilise cathodic protection systems and reliable coating systems to mitigate the potential for corrosion.
Cast iron and ductile iron systems used in the network rely on protective bitumen coatings and polyethylene sleeving systems, depending on the age of the asset.
These pipelines are susceptible to external corrosion and as such condition assessment is required periodically.
While pipe integrity tools continue to improve and are crucial in maintaining critical pipeline infrastructure, they are not always practical to employ in the greater reticulation network.
Queensland Urban Utilities Principal Civil Engineer, Scott Stevens, said the utility uses a variety of methods to undertake condition assessments that are tailored to the material type, pipe accessibility and expected corrosion levels.
“In some circumstances we undertake external inspections at discrete locations using ultrasonic testing, broadband electro-magnetic scanning or magnetic flux leakage. This provides a snapshot of the pipe condition at nominated locations. We target the investigations to locations where environmental factors are conducive to corrosion,” Mr Stevens said.
“Most of these methods can be employed in the field while the main is still online, including acoustic and transient sensory methods and tethered-in-pipe leak detection which don’t require the pipeline to be exhumed.
“We have also used in-pipe scanning tools for large rising mains to understand the extent of internal corrosion from hydrogen sulphide gas, however, this requires the pipeline to be taken offline, drained and cleaned to permit access.”
Mr Stevens said Queensland Urban Utilities has previously undertaken physical testing of aged cast iron pipes after they have been removed from the field. The pipes are blasted to remove graphitisation and fully mapped to understand the variance in wall thickness and corrosion pit depths.
The pipes then undergo a suite of mechanical testing to understand the characteristic strength of the material and corrosion rates, to input into structural and predictive failure models.
Relining offering an alternative to replacement
Pipe relining technologies have been available for rehabilitation of gravity pipelines for some time and are proven means to enhance the structural integrity and extend the life of an asset.
Using this technology, kilometres of cast iron and bonded asbestos cement water pipelines can be relined instead of using traditional replacement methods that require excavation.
Queensland Urban Utilities has been trialling various products in the market to gain a better understanding of their application in the field, installation process, advantages and constraints.
“Where applicable, we are looking to use these technologies as an alternative to traditional replacement. As with any trenchless technology, relining is ideal for certain circumstances and we will always need to use a variety of different technologies,” Mr Stevens said.
In a recent trial, Queensland Urban Utilities used new Primus Line technology to reline 1.8km of water mains at Redbank Plains in Ipswich, making it the longest and largest stretch of pipe to be relined using this method in Australia.
Queensland Urban Utilities Water Network Program Director, Gavin Flood, said he believed relining technology was an important tool in the trenchless toolbox.
“Relining has been used in the sewerage industry for years, but it’s only been in the past 12 months that Australian water utilities have begun implementing this technology for potable water pipes,” Mr Flood said.
“Relining is quicker and can be more cost effective than traditional alternatives and importantly, it minimises disruption to the community and the environment.
“Depending on the technology, it’s possible to reline up to 650m of pipe per day compared with 40m using excavation. Plus, we’ve found it has potential savings of up to 40 per cent in capital costs.
“Instead of our crew spending six months digging up the existing main and replacing it with a new one, we were able to complete the project at Redbank Plains in a matter of weeks.”
Keep on trialling
Queensland Urban Utilities has undertaken trials with both structural and non-structural relining solutions.
Typically the trial applications have been on trunk water mains, which are susceptible to leaking joints rather than structural barrel failure. These systems have proven to be quick, efficient and cost-effective alternatives.
Where the condition of the host pipe is structurally sound for external loading and frequency of pipeline appurtenances is lower, the utility used non-structural lining systems capable of taking internal pressure.
“Where the pipeline condition is largely unknown or not practical to assess, we’ve trialled structural lining systems. These systems have been targeted at reticulation size mains and we’ve found them to be an effective alternative to traditional replacement,” Mr Stevens said.
“We are undertaking further trials with various materials to gain better insight into how we can use these lining techniques in our capital works program in the future.”
The industry is constantly developing new and innovative ways to solve known problems, however, not all innovations are suitable for every application.
“It is vital to have a good understanding of the technology, its intended application and the asset condition, balanced with robust engineering judgement,” Mr Stevens said.
As accurate field data collection improves, it will provide better insight for predictive modelling and data assessment, and help asset owners better understand the health of their network and inform their investment strategy.
“I expect to see advancements in condition asset methods and tools, or the application of existing technologies to specific industry needs,” Mr Stevens said.