Insights into the intergranular corrosion of overlay welded joints of X65-Inconel 625 clad pipe and its relationship to damage penetration

•IGC resistance of the welded joint decreased as the position of the specimen approached to the X65 side.•Corrosion in the HAZ penetrated along the grain boundaries.•Nb and Mo affected the penetration of inter-dendritic corrosion in BM.•Pitting in the BM became deeper and evolved into inter-dendritic corrosion. Intergranular corrosion (IGC) behaviors of X65-Inconel 625 clad pipe welded joints of different thickness (1.5, 2.0, 2.5 mm) were investigated. Corrosion tests showed that as the position of the specimen approached to the X65 side, the resistance of IGC decreased. The increased susceptibility of the welded joint to IGC was due to the small grain size and high Fe content. Different corrosion morphologies were observed in the base metal (BM) and heat-affected zone (HAZ), while corrosion penetrated differently into the interior of material. Pitting in the BM became deeper and evolved into inter-dendritic corrosion as the corrosion immersion test progressed.