Materials Performance Supplements

Corrosion Management for Pipeline Integrity 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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21 CORROSION MANAGEMENT FOR PIPELINE INTEGRIT Y SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2018 Field joints are lengths of pipe laid and welded together on-site and then recoated. Photo courtesy of Australasian Corrosion Association. porates larger numbers of smaller capacity systems that are located much closer to the pipeline. The main reason for this revolves around urban development and the inter- ference 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 says. Town planners in the 1950s and 1960s did not expect the rapid and extensive growth of the major Australian cities. "It is not just in the capital cities either," Galanos says. " The construction costs associated with effectively isolating the rail lines of new DC [direct current]-powered light rail systems or installing stray current mitiga- tion devices post construction can be in the order of millions of dollars. These costs include ongoing monitoring to ensure the stray current effects on nearby foreign bur- i ed m et al lic str ucture s remain w ithin acceptable limits." Electricity f lows from the rail systems' o v erh ea d cat en ar y w ire s to th e train motors, then back along the rails. However, some current strays from the rails into the earth, which can f low onto a buried pipe- line and then out again and override the CP system. This is known as stray current. Modern controls for the CP are constantly monitored and the CP output is adjusted to mitigate the effects of fluctuations caused by stray current. "Where current is applied to a pipeline, it provides protection; but where the current leaves a pipe it causes corrosion," says Brian Martin, a consulting engineer specializing in CP systems. "The shortest time I've seen for a hole to appear in a steel pipeline because of stray current interference is six weeks." " There is a wealth of experience with the effects of current f low and railways in Melbourne and Sydney because all the trains are DC," Martin adds. "In Queensland, the trains run on AC [alternating current] power, which doesn't interfere with pipe- lines in the same manner." Th e C P sy st ems b ein g instal l ed by Jemena near train and tram lines use trans- former rectifier-assisted drainage units, which monitor the voltage on the pipeline and return stray current back to the railway line. "The latest telemetry and data logging equipment is now integral to our projects," says Dragar. He notes that Jemena has worked closely with train and tram opera- tors for many years to ensure there is mini- mal 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 organizations' metallic infrastructure. "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 base- line data is recorded," says Galanos. While there may be a lot of historical data associ- ated with the installation and operation of an existing pipeline, the most recent data and information are critical. " The above recordings and reports must all be pro- duced during the time that any new proj- ects are proposed or announced, as they will provide the most up-to-date informa- tion and data, which can be used as a base- line," he adds. The latest CP systems used to replace those on aging pipelines are substantially upgraded compared to earlier systems. " There have been a number of advances that allow significant improvement in the monitoring and control of CP systems," Martin says. The effectiveness of a CP sys- tem for a pipeline, he notes, is dependent on the quality of the coating applied to a pipe, the age of the pipe, and to some extent the pipe diameter. In Sydney, many pipe- lines are quite old and have poor coatings. "Up until the 1980s it was very difficult to get a good coating on a pipe larger than 20 inches," he says. However, most modern ( post-1980) non-urban , large-diam et er pipes have very good coatings. To support industry, the Australasian Corrosion Association (Blackburn, Victo- ria, Australia) works with academia and companies such as CCE and asset owners like Jemena to research all aspects of corro- sion to provide an extensive knowledge base that supports best practices in corro- sion management. This ensures all impacts of corrosion are responsibly managed, the environment is protected, public safety is enhanced, and economies are improved. Source: Australasian Corrosion Associa- tion, web site: www.corrosion.com.au.

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