Monitoring the impact of corrosion on the thousands of kilometres of buried pipelines in Australia is important for ensuring pipeline integrity. This infrastructure represents many millions of dollars of investment by governments and companies and the cost implications of ignoring the effects of corrosion are large, make the management of risks important.
The advantages of planning for corrosion control and mitigation, include extending the life of the asset while reducing maintenance time and costs.
Jim Galanos, NSW Engineering Manager at Corrosion Control Engineering (CCE), said there are two aspects to protecting pipelines that traverse urban environments. The first is ensuring that there is no physical damage done to the pipelines by third parties who carelessly dig or drill near the buried pipes. “It happens far more often than we’d like. The most common is another utility company excavating and then boring or directional drilling where they haven’t checked the plans and applicable procedures.”
The second is preventing coating damage and disruption of the cathodic protection (CP) systems. “It’s not just digging into the ground,” said Galanos. “Certain types of backfilling and compaction methods can affect the flow of CP current through the soil from the anodes to a pipeline.” Once disrupted, the protection offered is greatly diminished and can be costly to restore.
Mark Dragar, Asset Manager – Pipelines for Jemena, agreed that it is often third-party construction crews that cause damage but then neglect to report it. “We’ve had a contractor digging a trench to install a water pipe that damaged large sections of the coating on a steel pipe and then thought it would be OK to simply place back the damaged coating and secured it with gaffer tape,” he said.
To support industry, the Australasian Corrosion Association (ACA) works with academia and companies such as CCE and asset owners like Jemena to research all aspects of corrosion in order to provide an extensive knowledge base that supports best practice in corrosion management, thus ensuring all impacts of corrosion are responsibly managed, the environment is protected, public safety enhanced and economies improved.
Galanos indicated that the pipelines for which his company is responsible are the high pressure, high volume supply lines that traverse both country and urban areas carrying petroleum, gas, water and other products. “Beneath Sydney there are hundreds of kilometres of steel pipes in a range of diameters,” he said. “Some of these have been safely in place for decades but urban sprawl is now threatening them.” Most pipes lie beneath public spaces such as roads and parklands, but some do cross private property.
Dragar added that the coating on the buried pipelines was the primary way his company mitigates corrosion thereby maintaining the structural integrity of its assets. The weakest points in the network, however, are the field joints where lengths of pipe are laid and welded together on site and then recoated. “We could have the best design and materials being used for a project, but the effectiveness of the coating over a joint comes down to the abilities of the applicators applying it,” he said. “As a consequence, quality control is a paramount.”
An example of this is where the instructions for applying a heat-shrink sleeve to a pipe joint say that the pipe surface has to be heated to more than 80 degrees Celsius. However, some applicators may heat the metal to an even higher temperature but then take too long putting the sleeve in place during which the temperature has dropped to around 70 degrees which means the sleeves do not adhere properly. “As a result, we have mandated that all construction is to be carried out to a higher level than that required by the relevant Standard,” Dragar said.
Another corrosion control method used on pipelines is cathodic protection (CP). This is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded “sacrificial metal” to act as the anode. The sacrificial metal then corrodes instead of the protected metal.
“Where current is applied to a pipeline, it provides protection, but where the current leaves a pipe it causes corrosion,” Brian Martin, a consulting engineer specialising in CP systems, said. “The shortest time I’ve seen for a hole to appear in a steel pipeline because of stray current interference, is six weeks.”
According to Martin, the effectiveness of a CP system of a pipeline is dependent on the quality of the coating applied to a pipe, the age of the pipe and to some extent the pipe diameter. “Up until the 1980s it was very difficult to get a good coating on a pipe large than 20 inches.” In Sydney, many pipelines are quite old and have poor coatings, whereas most modern (post-1980) non-urban, large diameter pipes have very good coatings.
The thousands of kilometres of buried steel pipelines across Australia mostly have some form of cathodic protection associated with them. Older Impressed Current Cathodic Protection systems used to consist of a small number of high-capacity anode groundbeds spaced along the pipeline. Galanos said that the design of newer cathodic protection systems now incorporate larger numbers of smaller capacity systems located much closer to the pipeline. The main reason for this revolves around urban development and interference effects of foreign buried metallic structures.
“The designs incorporate a great deal of redundancy because it has been found that adding lots of extra connections and test points when a pipeline is constructed is far cheaper than having to dig up sections of pipeline to add them at a later date,” Dragar said.
Town planners in the 1950s and ‘60s did not expect the rapid and extensive growth of the major Australian cities. “It is not just in the capital cities either,” Galanos said. “The construction costs associated with effectively isolating the rail lines of new DC-powered light rail systems or installing stray current mitigation devices post construction can be in the order of millions of dollars. These costs include ongoing monitoring to ensure the stay current effects on nearby foreign buried metallic structures remain within acceptable limits.”
“There is a wealth of experience with the effects of current flow and railways in Melbourne and Sydney because all the trains are DC,” Martin added. “In Queensland, the trains run on AC power which doesn’t interfere with pipelines in the same manner.” Electricity flows from the catenary wires to the train motors then back along the rails. However, some current strays from the rails into the earth which can flow onto a buried pipeline, or some other structure, near the track and then out again, overriding the CP system. Modern controls for the CP are constantly monitored and adjust the output to mitigate the effect of fluctuations caused by stray traction current. “The latest telemetry and data logging equipment is now integral to our projects,” said Dragar.
Dragar said that Jemena has worked closely with train and tram operators for many years to ensure there is minimal disruption to its CP systems from new light rail lines being built in Sydney. All asset owners must ensure their systems do not interfere with other organisations metallic infrastructure. The CP systems being installed by Jemena near train and tram lines are Transformer Rectifier Assisted Drainage units, which monitor the voltage on the pipeline and return stray current back to the railway line.
CCE is a leading company developing and implementing innovative solutions to support pipeline integrity, surveillance and corrosion mitigation activities. “An essential part of any work involving cathodic protection and quantifying the effects of activities around buried pipelines is to ensure that accurate and timely baseline data is recorded,” said Galanos. While there may be a lot of historical data associated with the installation and operation of an existing pipeline, the most recent data and information is critical. “The above recordings and reports must all be produced during the time that any new projects are proposed or announced, as they will provide the most up to date information and data which can be used as a baseline,” he added.
The latest CP systems used to replace those on ageing pipelines have substantial improvements on earlier systems. “There have been a number of advances that allow significant improvement in the monitoring and control of CP systems,” Martin said.