en گروه سرامیک Ceramic Materials and Engineering Research Paper Research Paper <p align="justify"><font style="BACKGROUND-COLOR: #f4f4ff">Abstract: The risks of alternating current (AC) corrosion and overprotection increasingly demand new criteria for<br>cathodically protected pipelines. To assess the risk of AC corrosion, new cathodic protection (CP) criteria have been<br>proposed based on DC/AC current densities measurements using coupons. The monitoring system designed for this<br>project was based on the instant-off method, with steel coupons simulating coating defects on a buried pipeline. The<br>problems associated with the instantaneous off-potential measurements have been attributed to a non-sufficient time<br>resolution. In present study, it has been possible to determine the de-polarisation of steel coupon within a few<br>milliseconds after disconnecting the coupon from the DC/AC power source, by increasing data acquisition rate. For<br>this, a monitoring system was developed in order to measure the IR-free potential together with the DC/AC current<br>densities. The monitoring system was utilized for both laboratory experiments and site survey to study the mechanism<br>and the condition of AC corrosion, its mitigation and more importantly to define new CP criteria.</font></p> AC Corrosion, Cathodic Protection, Monitoring, IR-Free Potential, Pipeline. 18 23 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-167-5&slc_lang=en&sid=1 S.R. AllahKaram akaram@ut.ac.ir 180031947532846001849 180031947532846001849 Yes R. Shamani 180031947532846001850 180031947532846001850 No