Electrochemical behavior of various micro-areas on the welded joint of Q235 steel

The electrochemical behavior of welded joints of used Q235 pipeline steel was investigated in soil simulation solution. Polarization curves of various micro-areas were measured and related electrochemical parameters were acquired. The results show that the sequence of free corrosion potential from lower to higher or the sequence of free corrosion current density from higher to lower is melt run, incomplete normalized zone, overheated zone, normalized zone, tempered zone, base metal, and weld metal. These micro-areas of a welded joint compose a multiple electrode system when exposed to the same electrolyte. Melt run and incomplete normalized zone suffer corrosion dissolution firstly as the anode of a galvanic cell composed of a complex multiple electrode system, while weld area and base metal are subjected to cathodic protection as the cathode of the galvanic cell.