Evaluation of Corrosion Risk and Cathodic Protection Effect for Weld of Buried Bimetal Composite Pipe

The electrochemical behavior of the base pipe (L360QS steel) and the weld (625 alloy) of L360QS/N08825 bimetallic composite pipe was studied in simulated soil solution in field. The effect of cathodic protection on the risk of galvanic corrosion in weld area was discussed. The risk of hydrogen induced cracking caused by galvanic corrosion in the weld area was further analyzed under excessive cathodic protection. The effect of exposed area ratios of base pipe to weld on the effectiveness of cathodic protection was analyzed using full-size pipe sections. The results show that in the absence of cathodic protection, the base pipe had a high risk of galvanic corrosion in simulated soil solution. Forced current cathodic protection could effectively slow down the corrosion of base pipe, and there was no risk of hydrogen induced cracking in weld area under excessive cathodic protection condition. Under cathodic protection, as the exposed area of base pipe gradually decreased, the free corrosion potential and off-potential of base pipe shifted positively under the influence of weld, and the cathodic protection effect decreased.