Materials Performance

JUN 2016

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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JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6 A Novel Technique Studies Water Pipe Corrosion Caused by Microbes C orrosion and the degradation it causes to infrastructure and assets costs the Australian economy many billions of dol- lars annually, and is approximated to be 3 to 5% of the country's annual gross domestic product (GDP). The estimated annual cost of corrosion to the urban water industry alone is $928 million ±30%, according to a report commis- sioned by the Australasian Corrosion Association (ACA) (Kerrimuir, Victoria, Australia), 1 which recorded and mea- sured up to 117 indicators from 73 Aus- tralian water utilities serving ~75% of Australia's population. According to NACE International members Amy Spark, a R MIT doctoral candidate working with the Common- wealth Scientif ic and Industrial Research Organisation (CSIRO) (Clay ton, Victoria, Australia); Ivan Cole with CSIRO; and David Law and Liam Ward with R MIT University (Melbourne, Victoria, Austra- lia), 70% of Australia's potable water pipe- line network, including a large number of critical water transmission mains, is comprised of ferrous metals. These mate- rials are highly susceptible to corrosion, particularly microbiologically inf luenced corrosion (MIC), when buried in soil. Because soil was considered to be a benign environment for many years, pro- tecting these assets from external corro- sion was thought to be unnecessary. Localized corrosion of the external pipe surface, however, has been found to be a leading contributor to water pipe leaks and failures; and one of the primary mechanisms that cause localized pitting corrosion in potable water networks is MIC. This is due to the action of biof ilms that form on the exterior surfaces of pipes. In a paper 2 presented at CORROSION 2016 in Vancouver, British Columbia, Canada, Spark, Cole, Law, and Ward dis- cuss a new technique developed to study MIC of metal in soil. Rather than relying on the aqueous solutions traditionally used, this novel test method utilizes agar (a gel-like substance derived from algae that is used for culturing bacteria) to more closely simulate both the physical structure and chemical components of soil. They explain that the ty pes of nutri- ents present in an environment or in a laboratory grow th medium are important when determining the likelihood and extent of corrosion due to specif ic micro- bial species. Some nutrients have been shown to have an inhibitory effect, although this depends on the ty pe of nutrients and the ratio of aggressive ions (e.g., chlorides) to the inhibitory com- pounds present. Changes in corrosion rate when bacteria are present could be due to the indirect effect of the bacteria consuming nutrients and changing the balance between aggressive and inhibi- tory components of the environment or medium. The authors comment that many different ty pes of bacteria—including sulfur-reducing bacteria, acid-producing bacteria, sulfur-oxidizing bacteria, iron- reducing bacteria, and several other groups of microbes—have been associ- ated with MIC of carbon steel (CS), cop- per, and stainless steel. They note that the number and ty pe of microbial species present, as well as the environment, play a crucial role in localized corrosion. 14 14 JUNE 2016 MATERIALS PERFORMANCE JUNE 2016 MATERIALS PERFORMANCE MATERIAL MATTERS

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