New progress in studying alternating current corrosion on metal pipelines

A damage caused by alternating current (AC) corrosion on buried metal pipelines can not be ignored because alternating current may not only result in corrosion on metal pipelines through stray current but also generate an alternating electric current within metal pipelines by induction, which creates alternating current interference. Moreover, risks of AC corrosion or overprotection on buried metal pipelines are increasing with the increase of laying coated pipelines in proximity to AC powered rail transit systems or high voltage AC power transmission lines. Here we made a systematic review on AC corrosion researches of recent years in terms of the experimental study, theoretical analysis and corrosion mechanism, respectively. It is generally believed that a higher alternating current could lead to a higher risk of AC corrosion. The results of laboratory experiments on the influence of AC interference show that an alternating electric current can not only accelerate metal corrosion, destroy the passive film and induce pitting corrosion, but also interfere with the normal operation of a cathodic protection system due to a sharp increase of the cathodic protection current, a severe disturbance of the protection potential and even an anodic polarity reversal. Mechanisms of AC corrosion are very complex and people have made great attempts to explain these complicated processes through theoretical analyses and experimental simulations. There are only a few typical hypotheses on mechanisms of AC corrosion proposed so far and many difficult problems remain to be unsolved though studies on AC corrosion may date back to the late 19th century. In addition, we discussed some key problems of AC corrosion in details, predicted the research prospect and development trend of this frontier, which may be a help to researchers involved in the related domains.