Experimental study on stray current corrosion of coated pipeline steel

The experimental investigation on the coated pipeline steel was performed with respect to induced stray current including the alternating current (AC), direct current (DC), and the superimposed AC + DC sources in the soil-simulating conditions. The results showed that the corrosion potential and rate increased with the increases of stray current density. The extent of corrosion was found to be less in AC when compared to the DC sources. When an alternating current was superimposed on a direct current, the corrosion rate was larger than their respective corrosion. AC corrosion on the X70 pipeline steel represented three classic patterns, including the uniform corrosion, ring-like corrosion and pitting corrosion according to the geometrical shape of the corrosion images. The corrosion pattern would transfer to the local corrosion from the uniform corrosion, when the AC density increased. The quantity, area and depth of the corrosion pits arose with the increase of the AC current density. The relationship between the pit number or pit area and AC current density followed the power function, y = aib.