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A new corrosion sensor which takes advantage of the features of pipeline coatings to perform electrochemical corrosion rate measurements offers exciting potential as an effective way to detect and prevent dangerous corrosion in underground pipelines.
High pressure underground pipelines are typically protected against corrosion with a combination of barrier coatings and cathodic protection systems. When their coatings become ‘disbonded’ pipelines become susceptible to corrosion that can eventually lead to leaks or catastrophic failure. In November 2013, in Qingdao, China, for example, undetected oil leaking from a corroded pipeline caused a major explosion which killed 55 people. At Varanus Island in Western Australia, in 2008 a major gas explosion caused an energy crisis in the state. This explosion was also due to unidentified localised corrosion.
Maintaining the vast network of pipelines that carry oil and gas across Australia is a massive task, which involves millions of dollars a year spent in regular assessment to detect corrosion issues and target sections that need to be replaced or repaired. Safe operation of pipelines relies on this inspection to detect and repair disbonded areas but digging up pipelines is expensive. So, pipeline managers use sophisticated indirect assessment techniques to locate and prioritise defective areas. Even so, the tools available do not always detect localised corrosion.
An effective and commonly used method to detect corrosion is ‘smart pigging’ where a non-destructive testing device (known as a pig) is inserted in the pipe and carried along by the fluid flow. However, this method is expensive and is usually only carried out at intervals of at least five years. Smart pigging is capable of locating pipeline defects through metal loss evaluation but usually only detects corrosion once the damage is greater than 30 per cent of the original pipe wall thickness.
A new corrosion sensor which enables continuous and real-time monitoring of the efficiency of cathodic protection and the initiation and spread of localised corrosion could complement smart pigging as an effective way to detect and prevent dangerous corrosion. This new sensor is being developed by a research team led by Professors Mike Tan and Maria Forsyth at Deakin University, supported by the Energy Pipeline Cooperative Research Centre. The sensor simulates the conditions occurring at typical corrosion defects and measures corrosion rates electrochemically. The sensor can check remotely every day and identify localised corrosion in its early stages. In the case of Qingdao, for example, the sensor would have shown the extent of the problem.
The advantages of sensors over other methods include their low operational costs, their flexibility for use with different pipeline designs and their high inspection frequency. Deakin University PhD student, Mr Facundo Varela is the driving force behind the development of this new sensor. He says it is an exciting new technology that could help us to see an essentially invisible process that occurs underground and to inexpensively evaluate the associated risks in minutes. Testing in the laboratory has given good results and this year the probe will be tested on pipelines in the field.