Materials Performance

MAR 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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32 MARCH 2018 W W W.MATERIALSPERFORMANCE.COM FEATURE ARTICLE To test the system reconfiguration, a trial application was carried out using a small number of junction boxes in Section 12, a 24-m length of the wharf. "We replaced junction boxes and did full testing of the trial area, including external mapping of potential measurements using the embed- ded and portable reference electrodes, to get a better understanding of the current distribution within the area," Cheaitani says. "Basically, this verified that the new ICCP design—the combination of zoning— wouldn't affect the system's performance." Evidence gathered during the trial dem- onstrated the CP system performance for Section 12 was not negatively impacted when CP circuits with similar exposure and geometry were combined and the cabling was simplified. The conclusion, he com- ments, was that fewer large CP zones pro- vided the same level of corrosion protec- tion as many smaller zones. Impressed Current Anodes vs. Sacrificial Anodes After 15 years of system operation, the current requirement for the original ICCP to achieve corrosion protection of the wharves, based on the applicable Austra- lian and global standards for CP, was ~11.25 mA/m 2 . Cheaitani comments that a sacrificial anode-based CP system would not, under any circumstances, have the capacity to deliver this level of CP current and provide the required corrosion protec- tion of the wharves. The typical size of a galvanic zinc anode for concrete (18-mm diameter by 113-m long) will deliver between 0.4 and 0.8 mA. Even if that amount of current could be delivered con- tinuously for a sustained period of time, it would require between 14 to 28 anodes per square meter of concrete to obtain the required level of current using sacrificial anodes, he says. This is practically impossi- ble to achieve based on cost, practicality, and engineering considerations. "We believe sacrificial anodes have their own applications in certain areas. For wharf structures that are always subjected to a very harsh marine environment, an impressed current system is really the only practical and cost-effective CP application to stop corrosion," he adds. The new system design eliminated the installation of electronics underneath the wharf, and required less cabling. The over- all number of circuits was reduced from 14 to 8 in each typical section, and the number of sections was decreased from a total of 13 localized control units underneath the wharves to six control units all located in a central climate-controlled room above the wharves. This resulted in a total reduction in the number of circuits—from 172 to 48. Cable design and voltage drop calculations were performed for all cables between the structure and the new location of the con- troller units, and different sized cables, from 4 to 16 mm, were used between the junction boxes at the wharves and the new locations of the control units to ensure proper current delivery to all system zones. The repair work and CP trial took about a year to complete, and the redesigned sys- tem has been performing very well since it was brought online about two years ago. "The whole idea is to build CP systems that require minimal maintenance—that is the key lesson we've learned over the years," Cheaitani says. "The less maintenance you need to keep the technology viable, the more cost-effective the system is for the client. We believe future ICCP systems will have a simple design with larger zones, and use heavy-duty equipment that will not be negatively affected by the environment. If we can build a system like this, it will cost less, deliver the same CP protection, and will be extremely low maintenance, which is very important for the client." References 1 "Brisbane Wins Port of the Year 2017," Port of Brisbane, News & Media, November 17, 2017, https://www.portbris.com.au/news-media/ item/?release=/News-and-Media/Brisbane- wins-Port-of-the-Year-2017 (February 13, 2018). 2 NACE RP0290-90, "Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures" (Houston, TX: NACE International, 1990). 3 AS 2832.5-2008, "Cathodic Protection of Metals—Steel in Concrete Structures" (Syd- ney, Australia: Standards Australia, 2008). Bibliography Cheaitani, A. "Cathodic Protection to the Port of Brisbane Structure, Australia." CORROSION 1999, paper no. 545. Houston, TX: NACE International, 1999. Cheaitani, A. "Review of Cathodic Protection Sys- tems for Concrete Structures in Australia." CORROSION 2017, paper no. 9024. Houston, TX: NACE International, 2017. The approximate concrete area underneath Wharves 4 and 5 that is protected by the ICCP system is 8,000 m 2 . Photo courtesy of Atef Cheaitani.

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