When NSW Ports in Australia embarked on a two-year programme to rehabilitate the structures and combat corrosion levels at its Bulk Liquid Berth 1 (BLB1), it commissioned Melbourne-based consultancy Infracorr to deliver a bespoke cathodic protection (CP) system. Designing the system presented several challenges because BLB1 houses hazardous gas, petroleum and chemical pipelines that could be at risk of ignition if exposed to unsafe levels of voltage and current. To deliver the system safely, the consulting firm engaged cathodic protection specialist Omniflex to support the hazardous area and remote monitoring aspects of the CP system design.
The system had to allow for tight control of the currents and voltages used across the site for two key reasons. Firstly, Port Botany is NSW’s main bulk liquid and gas port, and BLB1 is a key part of this facility, playing an active role in loading and unloading volatile liquids and gases. With these hazardous materials, any stray sparks caused by excess voltages and currents could become an ignition source for a major fire or explosion. Secondly, because many of the structures present are constructed using pre-stressed concrete, it was extremely important that all electrical currents applied were carefully controlled to avoid structural damage caused by overprotection.
To control corrosion in steel it is necessary to give it a more negative electric potential than its environment by 800 mV. However, if the charge applied results in the steel being 1 V more negative than its environment, hydrogen embrittlement can occur, leading to failure of the steel and long-term structural damage that is not easily repaired.
“One of the big technical challenges for the project was that there was no off-the-shelf CP system available that had certification for use in zone 1 classified hazardous areas,” explained Ashley Rangott, asset manager at NSW Ports. “We had to design a bespoke system that met the cathodic protection objectives, including dealing with the challenge of prestressed concrete. It also had to be certified to meet the requirements under AS60079 regulations.”
The system designed was a hybrid CP system that combined the properties of both passive galvanic and impressed current cathodic protection (ICCP). It worked by inserting specially designed anodes directly into the structure in a matrix. A voltage was applied to force salt migration from the steel to the anode and passivate the zone. When the zone was sufficiently charged, the power source was disconnected and the sacrificial anodes were left to operate galvanically, providing passive protection to the structure. The hybrid system reduced the ongoing risk of hydrogen embrittlement on prestressed concrete elements.
The system used remote monitoring technology to provide asset managers with ongoing reassurance that corrosion levels were under control. To deliver this, Godson requested the assistance of Omniflex to advise on the hazardous area and remote monitoring issues. “Because of the low currents required to meet the prestressed steel and hazardous area limitations, the hybrid CP system required an initial power-up phase of four months before the external power source was disconnected and the system left to operate galvanically,” explained David Celine, managing director of Omniflex.
The system had nearly 35 000 embedded hybrid anodes that were installed in the structures at BLB1 to control corrosion for up to 50 years. Because of BLB1’s ongoing operational nature, extra controls were put in place to manage activities across the site during the system installation phase.
“Because this was the first large-scale implementation of hybrid CP used in a working hazardous area anywhere in the world, some components needed certification for the design to meet the requirements of AS60079 as an intrinsically safe certified system,” added Celine. “The hybrid anodes were sourced from CP Technologies in the UK, Omniflex’s technology was manufactured in South Africa, and the project was in Australia, so navigating certifying bodies was challenging. However, the design was eventually approved and certified as being intrinsically safe for use in areas classified as zone 1 hazardous for gas group IIB.”
System performance and corrosion levels are now continuously monitored 24/7 using 24 remote monitoring units situated throughout the site, each with the capacity to monitor 16 structures. These ensure that the integrity of BLB1 is maintained, and that the berth remains reliable and available to handle NSW’s growing bulk liquid trade volumes for the next 50 years. “Omniflex’s systems are high quality, and are suited to our unique harsh marine environment. The knowledge that Omniflex brought to the project ensured that the monitoring and control system was procured and operated to a high level,” concluded Rangott.
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