埋地双金属复合管焊缝区域腐蚀风险及阴保效果评价

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

在模拟现场土壤溶液中,对L360QS/N08825双金属复合管基管(L360QS钢)与焊缝(625合金)的电化学行为进行了研究,探讨了阴保条件对焊缝区域电偶腐蚀风险的影响,并在过保护阴保条件下分析了焊缝区域电偶腐蚀致氢致开裂的风险。利用全尺寸管段探析了基管与焊缝暴露面积比对阴保效果的影响。结果表明:在无阴保条件下,基管在模拟土壤溶液中存在较高电偶腐蚀风险;强制电流阴极保护可以有效减缓管道腐蚀,且过保护阴保条件下焊缝无氢致开裂风险;在阴极保护下,随着基管暴露面积逐渐减小,基管的自腐蚀电位及断电电位受焊缝影响发生正移,阴保效果降低。

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.